Symposium SB01 : Multifunctional Materials—From Conceptual Design to Application-Motivated Systems

Braids have been used for centuries to enhance the material properties of fibers. However, although nanoscale and microscale braids are expected to show interesting mechanical and electric properties, braiding them remains challenging. Such thin fibers suffer from easy breakage when handled by mechanical braiding machines. Moreover, the complexity of braid topologies makes it extremely difficult to self-assemble braids. Here we demonstrate a gentle yet robust method to programmatically assemble nanoscale and microscale fibers into arbitrary braid topologies. This method relies on repulsive capillary forces to effectively trap and move small floating objects (“floats”) at the air/water interface inside designated channels of our devices. We designed the channels to change shape along the vertical axis. As a result, when a device is moved through the air/water interface, the shape of the meniscus and thus the capillary forces change. This change in force causes lateral motions of floats at the interface. Thus, we can steer the floats around simply by moving the device into or out of water. To braid wires, we attach them to the floats and operate the device such that the floats switch positions in a desired order to drive braid formation. Capillary forces are gentle enough to ensure wires don’t break during braiding. We show that it’s possible to translate, rotate, switch, and separate floats with capillary forces. We also demonstrate methods based on geometry or contact line pinning to repeatedly braid fibers without disassembly. Lastly, we show that any arbitrary braid can be fabricated with our method.

The design of robust wearable technologies (e.g. e-skin) and soft robotics requires a combination of highly conformal mechanical properties and long-term durability to withstand repeated damage from daily use. Self-healing materials offer a promising solution as they continuously and autonomously heal after experiencing damage, however improving self-healing abilities often results in materials with low toughness or large hysteresis. While a range of self-healing materials have been reported in the literature, limited understanding exists on the specific structure-function relationships between molecular design of the polymer and optimizing its resulting macroscopic properties such as toughness, elasticity, and self-healing speed and efficiency.

Here, we present our work to address this gap in knowledge and allow for the more intelligent design of self-healing materials. Using a model system with precise, tunable properties, we simultaneously study the effects of molecular design on the temporal characteristics and spatial morphology of the polymers and relate these changes to their macroscopic properties. Using small-angle x-ray scattering (SAXS), we examine how the molecular design of the polymers affects their resulting microstructure. In addition, through in-situ monitoring via SAXS under dynamic mechanical loading, we investigate how these microstructures evolve via distinct mechanisms after strain and over time as the networks relax. By combining the insights from these analyses and other characterization methods, we propose new rational strategies for the molecular design of self-healing materials, which will be highlighted in this talk. This work aims to provide a better understanding of the underlying molecular mechanisms driving the observed macroscopic properties of self-healing materials and is essential for more efficient design and integration of these materials into advanced multifunctional materials and adaptive structures.

Polymer materials are susceptible to small damages at micron level during service life, which is difficult to detect and further repair, yet can significantly propagate into lager one and subsequently compromise the integrity and functionality of the polymeric materials if left unattended at the early stage. Previously, efforts put on this issue have demonstrated some smart systems, like incorporation of AIEgens, pH indicators, or dyes. However, most of them either needed human intervention, like UV irradiation, or could only tackle the visual detection matter whereas the repairing solution still needed to be dealt with. To develop materials with in-situ autonomous visual indication and simultaneous repair functionalities towards the mechanical damages is a promising yet challenging task, due to difficulties in integrating different functional elements for packaging and lack of suitable vehicles to carry multirole triggers with high reactivity.
Herein, inspired by biomimetic external wound healing and internal bone fracture healing process, a genuinely fully autonomous smart composite material capable of self-reporting and self-healing was designed via simply incorporating the triple microcapsules containing Fe-ion solution, strong basic hardener and isocyanate/epoxy, respectively, as prepared by the versatile interfacial or in-situ polymerization methods. Microcapsule concentration and relative ratios were optimized.
Damage-triggered visualization, magnetization and healing can be accomplished by the delivery of core healants that precipitate magnetic nanoparticles and form new polymer networks upon mixing. Both ‘subcutaneous’ damage and macroscopic surface damage can be warned by the sharp color change from light yellow to conspicuous black, not only rapidly upon occurrence but also permanently even after repaired. Despite of black color visible to naked eyes, the magnetism of the precipitated ferromagnetic particles allows multiple methods for further detecting the damage shape, like magnetic sensor, and thermal imagery. Assisted with the Fe-ion/-OH/isocyanate combinations, the coasting showed superior anti-corrosion and sealing performance. Also, a sharp color contrast occurred exactly where the crack is. Interestingly, by applying an alternating magnetic field, the ferromagnetic particles answered with heating effect, which could be utilized for thermal imagery, or as heat source (up to 60 degrees Celsius) intrinsic self-healing of thermal plastics coatings, while avoiding heating the non-damaged regions. On the other hand, the combination of Fe-ion/-OH/epoxy showed high healing efficiency up to 100% for both fracture toughness and dynamic impact strength. The magnetic detection and thermal imagery here enabled a detailed understanding of the damage shape and scale, which is beneficial for evaluation of the damages and consideration for further solutions.

The design and self-assembly of membrane-bounded cell-like artificial vesicles not only offers new inspiration for technology and applications in many fields, but also has the potential to help uncover the mechanisms for compartmentation that may have occurred in the origin of life. In natural cells, the out-of-equilibrium self-assembly of their membrane is a critical process that eventually results in the control of cell behaviors such as vesicular transport, cell motion or division. An intriguing aspect of the cell membrane in extant living systems is their dynamic permeability. It is selectively permeable to small molecules but blocks the passage of certain macromolecules, and, at the end of their lifetime, it would be disassembled by the degradation of the lipid amphiphiles to lead to burst release of all cellular contents. Despite the advance in the assembly of various vesicular structures (e.g. liposomes, fatty-acid vesicles, colloidosomes, polymersomes), to date, little progress has been made in the construction of biomimetic vesicles with such a similar dynamic membrane and application potential to many areas in chemistry and engineering.
To address this challenge, we designed and synthesized biomimetic vesicles with a photo/chemo programmable synthetic membrane using a one-step polymerization induced self-assembly (PISA) strategy. These polymeric vesicles can realize either release of small molecules only by light-induced selective permeability, or burst release of all contents from their lumen by chemo-induced degradation of the amphiphiles and the vesicular structure. Notably, the cell-like dynamic permeability is realized by installing a single azobenzene to bridge the hydrophilic block and hydrophobic blocks of the amphiphiles. Specifically, light-induced isomerization of the azobenzene module in the membrane enables the full system to direct dissipative energy into functional pathways as a form of dynamic membrane permeability. Our work not only exemplifies a new strategy and easily implementable at the laboratory and industrial scales for the construction of cell-like active vesicular structures, but also opens new avenues to engineer synthetic material structures with spatially controllable functionalities.

Soft solids capable of conducting ions offer promise for the design of entirely new classes of highly deformable and bio-inspired devices. While resistive and capacitive ionic circuit elements are well established, next generation ionotronics will require advanced elements that can control and switch ion flow. Here, we introduce ‘ionoelastomers’—soft polymer networks capable of selectively conducting either anions or cations—to demonstrate liquid-free, elastic, and stretchable ionic diodes and transistors that operate entirely via non-Faradaic processes. We show that the junction of two oppositely charged ionoelastomers yields an ‘ionic double layer’, analogous to the depletion layer in a semiconducting p-n junction. This enables the design of ionic devices for rectifying and switching non-Faradaic ionic currents. Further, soft and stretchable ionoelastomer junctions provide fundamentally new functionalities including: 1) low voltage reversible electro-adhesion and 2) electro-mechanical transduction, i.e., the conversion of mechanical deformation into electrical signals. Our studies provide new fundamental insight on the interface between two oppositely charged ionoelastomers and open opportunities for the application of these soft ion-conducting devices.

Colloidal nanocrystals offer a route toward engineering new classes of materials by acting as discrete units that can be assembled to construct composite solids. The self-assembly of two sizes of spherical nanocrystals has revealed a surprisingly diverse library of structures. To date, at least fifteen distinct binary nanocrystal superlattice (BNSL) structures have been documented. BNSLs naturally represent a powerful platform for practical implementations of multifunctional materials. However, the stability of the observed binary phases cannot be fully explained using the traditional conceptual framework treating the assembly process as entropy-driven crystallization of rigid spherical particles. We evaluate new theoretical models treating the co-crystallization of deformable spheres and to formulate new hypotheses about the factors affecting the nucleation and growth of the binary superlattices. The deviation from hard sphere behavior can be explained by specific topological textures developed within deformable layers of surface ligands. Our results also suggest that the relative abundance of BNSL phases is determined not only by their thermodynamic phase stability but also by a postulated pre-ordering of the binary fluid into local structures with icosahedral or polytetrahedral structures prior to nucleation.
Strong electronic coupling between individual nanocrystals within a superlattice is an important prerequisite for the emergence of non-additive physical properties. However, a simultaneous realization of strong electronic coupling and dense ordered packing of nanocrystal solids has remained elusive. We report a method for growing all-inorganic highly ordered solids of electrostatically-stabilized nanocrystals with the interstitial space filled with a glassy metal chalcogenide matrix which, combined with the short separation between particles leads to very strong electronic coupling. Temperature-dependent conductivity measurements show metallic transport across our supercrystals. The formation of strongly-coupled all-inorganic nanocrystal assemblies represents an important step toward the bottom-up design of functional nanostructured composites.

Magnetoelectric cell sorting offers the potential to sort large numbers of cells quickly. Cells can be tagged with fluorescent markers that identify cell type. They can also be tagged with magnetic micron or smaller magnetic beads. These beads experience a translational force in the presence of a magnetic field gradient. Macro scale cell sorting magnetically tags cells that are to be captured, making it possible to hold those cells and remove the unwanted cells. Magnetoelectric devices offer the ability to control magnetism at the sub-micron scale. There are multiple challenges faced when applying magnetoelectric devices to cell sorting. In an envisioned device, the magnetically tagged cell is in a fluid bath that flows across a nanomagnet. The magnet traps the cell. Ideally, when voltage is applied, the cell is released. Some of the challenges include: the design of nanomagnets to produce the right force to trap and hold a cell in a flow field, and the ability to alter the magnetization in a way that enables releasing the cell. Ideally, an applied voltage would turn the magnetization off completely. The approach taken to developing a voltage-controlled magnet was to produce magnetostrictive structures on a piezoelectric substrate. At small length scales this approach can be used to produce single domain magnets with the magnetization in-plane. In certain systems like a NiCo layered structure, when the layers are thin enough, interface effects dominate and the magnetization shifts to an out-of-plane orientation. The work that will be presented describes the design of the nanomagnets to produce the desired capture force, the fabrication and characterization of an array of nanomagnets under an applied magnetic field to produce M-H curves, and the effect of strain on those M-H curves. Although the ability to switch these magnetic structures from a state of perpendicular magnetic anisotropy to an in-plane magnetic state has not yet been demonstrated, sufficient progress has been made to suggest that the approach may ultimately be successful.

Enabling access to hard-to-reach areas in a remotely controllable manner, small-scale soft continuum robots capable of active steering and navigation through complex and constrained environments hold great promise for medical applications in diverse areas across the human body. Several concepts of continuum robots have been commercialized so far, offering a range of new therapeutic and diagnostic procedures that are safer for patients owing to their minimally invasive nature. However, existing continuum robots are often limited to relatively large scale due to miniaturization challenges inherent in their conventional actuation mechanisms such as pulling mechanical wires. Such miniaturization challenges have rendered even the most advanced form of commercialized continuum robots, mostly used for cardiac interventions, substantially unsuited for neuro-surgical applications due to the considerably small and tortuous vascular structures.

Recently, burgeoning efforts have been made to utilize fully soft-bodied robots in medical applications with great expectations that their inherent compliance would lead to enhanced safety. Despite the purported advantage, the field of soft robots is still faced with a set of key challenges. First, existing soft robots based on pneumatic or hydraulic actuations are mostly heavily tethered, which limits their use in realistic medical applications that typically require tether-free actuation. Second, most soft robots are difficult to accurately control based on quantitative models, largely because their actuation mechanisms often rely on highly nonlinear deformation or instabilities. Third, conventional soft robots are difficult to miniaturize below millimeter scales, because their actuation mechanisms and associated fabrication methods are often unfavorable to such small size.

Here we present a submillimeter-scale, self-lubricating soft continuum robot with omnidirectional steering and navigating capabilities based on magnetic actuation, which are enabled by programming ferromagnetic domains in its soft body while growing hydrogel skin on its surface. The robot’s body composed of soft polymer matrices with embedded ferromagnetic microparticles can be miniaturized below a few hundreds of microns in diameter. To cope with the significant friction experienced by the robot while navigating through highly unstructured environments, we grow hydrogel skin, a thin layer of hydrated crosslinked polymers, onto the robot’s surface. This hydrogel skin substantially decreases the surface friction due to its high water content.

Elaborating on our recent progress in magnetic soft materials towards untethered soft machines and robots, we present novel material systems and fabrication schemes to realize ferromagnetic soft continuum robots at submillimeter scale. We also present our model-based material design strategies to optimize the actuation performance of our soft continuum robots. Combining all these features, we demonstrate the capability of navigating through complex and constrained environments with close relevance to clinical challenges, such as tortuous phantom neurovasculature with cerebral aneurysms, which are difficult to navigate with bulky robotic catheters or manually controlled passive instruments. Incorporating a functional core, such as an optical fiber, in the robot’s body, we further demonstrate additional functionalities such as steerable laser delivery for potential clinical applications in laser atherectomy. Given their compact, self-contained actuation and intuitive manipulation, our ferromagnetic soft continuum robots may open new avenues to minimally invasive robotic surgery for previously inaccessible lesions, thereby addressing challenges and unmet needs in healthcare.

Smart fluids are suspensions of functional particles in which an applied field drastically changes the fluid’s properties. For example, ferromagnetic microparticles in solution form magnetorheological (MR) fluids in which an applied magnetic field causes the liquid to solidify through the formation of rigid columns of particles. This field-driven transition enables the fluid to change reversibly from a viscous state to an elastic state that can be described as a Bingham plastic. As a result of this unique property, MR fluids have been widely used in a variety of systems such as brakes, dampers, and clutches. We propose to leverage MR fluids to realize novel classes of soft robotic systems in which magnetic fields interact with fluid flow to actuate systems in novel ways. However, there are two major barriers to this vision, (1) new architectures of actuation need to be developed and (2) more generally, sedimentation of the magnetic particles is a common issue hindering the use of MR fluids. We address the sedimentation challenge through the detailed exploration of MR fluid performance with different thixotropic agents in novel water-based MR fluid formulations. Controlling the formulation allows us to realize low sedimentation, low off-state viscosity, and high on-state viscosity. By mapping their response to magnetic fields, we ensure a predictable, variable resistance caused by increased thickening of the fluid enabling users to design a variety of systems from one MR fluid recipe. These materials innovations allow us to explore novel soft actuation architectures based upon MR fluids.

Direct-write is a bottom-up fabrication approach where material is added to a substrate in well-defined locations. With the advent of 3D printing and the need for inexpensive, printable and flexible electronics, direct-write patterning is attracting more attention for its ease to use for fewer processing steps. In this work we demonstrated a direct-write, electrochemical approach to the formation and dissolution of silver filaments through a new type of multifunction polymer electrolyte consisting of a UV-crosslinkable polymer, polyethylene glycol diacrylate (PEGDA), and an ionic liquid (IL), 1-butyl-3-methylimadozolium hexafluorophosphate ([BMIM]PF₆). A conductive atomic force microscope (C-AFM) is used to form and dissolve the filaments at pre-programmed locations using a custom script. Filament formation and dissolution kinetics are measured at various IL compositions and formation biases. The IL strongly impacts filament formation kinetics by controlling the local PEGDA structure. For example, in a highly crystalline PEGDA film with a low IL concentration (10 wt%), silver filament formation kinetics vary significantly with XY location and exhibit highly asymmetric formation time distribution; in contrast, when the IL concentration is increased to 30 wt%, PEGDA crystallization is suppressed and the filament formation times exhibit a normal (Gaussian) distribution with respect to XY location. In addition, we show that a competition between electric double layer (EDL) screening, ion transport, and electrochemical reactions gives rise to a non-monotonic dependence of formation time on applied voltage. Time-dependent analysis of formation current along with scanning electron microscope (SEM) characterizations suggest that filament structure is directly related to the magnitude of formation voltage, which can be tuned to improve the filament switching capability. Our results provide deeper understanding of the kinetics of filament formation through a crosslinkable polymer electrolyte, which is potentially useful for multiple material functionalities including the development of new metamaterials with reconfigurable optical properties, and non-volatile, on-board resistive random-access memory (ReRAM) for printable and flexible electronics.

Light-driven cholesteric liquid crystals (CLCs) exhibit unique selective reflection, originating from their inherent self-organized helical superstructures, and dynamic reflection tuning in response to light, which has unique advantages for remote, temporal, local, and spatial manipulation. Such elegant systems may represent ideal candidates for use as “photonic inks” to realize changeable information in color reflective displays, especially those providing paperlike viewability in sunlight where backlit devices perform poorly.¹ To this end, phototunable reflection across the visible spectrum has been demonstrated for CLCs and was induced by photoresponsive chiral motors and switches with tetrahedral, axial, or planar chiralities.^2-4 These triggers undergo photoisomerization, giving rise to both the variations in helical twisting power (HTP) and the color change.
In this report, we demonstrate several new strategies for manipulating the structural colors of CLCs.^5-6 We design a tristable chiral switch by incorporating two different azobenzenes into one chiral structure. Three stable configurations of the chiral switch endow the CLC with two continuous and adjacent tuning periods of the reflection, covering not only entire visible spectrum, but also one more wide period within near-infrared region. The resultant CLCs are capable of creating images of RGB colors with a black background, which is realized based on piecewise reflection tuning. In addition, we proposed a novel tuning mechanism based on a partial photochemical phase transition to enable continuous patterning of photostationary RGB colors in a CLC system, which contains nonresponsive chiral dopants and o-fluoroazobenzenes (Fazo) to serve as the photoswitch. Distinct isomer ratios of Fazo result in precise light-directed RGB colors for the photostationary states, and, thus, a fixed relationship is established between the light stimulus and the reflection color. Accordingly, the RGB color patterns can be continuously erased and rewritten under light irradiation with different wavelengths.

[1] J. Ge, Y. Yin. Angew. Chem. Int. Ed. 2011, 50, 1492.
[2] H. K. Bisoyi, Q. Li. Chem. Rev. 2016, 116, 15089.
[3] H. K. Bisoyi, Q. Li. Acc. Chem. Res. 2014, 47, 3184.
[4] Y. Wang, Q. Li. Adv. Mater. 2012, 24, 1926.
[5] L. Qin, W. Gu, J. Wei, Y. Yu. Adv. Mater. 2018, 30, 1704941.
[6] L. Qin, J. Wei, Y. Yu. Adv. Optical Mater. 2019, 1900430.

Closed-loop drug delivery strategies have proven to be a practical tool for homeostatic regulation, by tuning drug release as a function of biosignals relevant to physiological and pathological processes. Among them, a glucose-responsive “closed-loop” insulin delivery system mimicking the function of pancreatic cells holds great promise to improve quality of life and health in people with diabetes. In this talk, I will introduce our ongoing efforts in developing formulations and related devices for glucose-responsive insulin delivery. I will first discuss the transdermal microneedle patches integrated with glucose-sensitive components for self-regulated insulin delivery tested on both mice and pigs. I will further introduce integration of beta cells and microneedle patch loaded with the synthetic “glucose-signal amplifier” for releasing insulin with a glucose-responsive manner. In addition, synthetic beta cells with vesicle fusion-mediated mechanism for glucose control will also be presented.

Two dry surfaces can be instantly adhered upon contact with each other by intermolecular forces such as hydrogen bonds, electrostatic and van der Waals interactions. However, it is extremely challenging to form such instant adhesion between wet surfaces such as biological tissues, because water separates molecules from the two surfaces to form instant interactions. Existing tissue adhesives, mostly in the form of liquids or gels, rely on diffusion of their molecules into the polymer networks of the tissues for bonding, which can take significant time and give weak adhesion. Consequently, these limitations have severely hampered the scope of applications of existing tissues adhesives and their efficacy in practice. In this talk, we introduce a new mechanism to realize instant strong adhesion of a broad range of wet tissues and devices, implemented in various form factors including double-sided tapes, tissue-mimicking patches, and injectable pastes. Our new tissue adhesives boast unprecedented capability of forming instant adhesion less than 5 s with superior adhesion performance over 1,000 J m^-2 interfacial toughness, 120 kPa shear and tensile strength, surpassing commercially-available solutions. This work not only reveals a new paradigm in wet adhesion but also provides new opportunities and solutions in applications as diverse as tissue adhesives and sealants, bioscaffolds, drug delivery, and wearable and implantable devices.

The emerging generation of drugs is dominated by biotherapeutics, such as antibodies, hormones, and other proteins, for critical treatment applications ranging from cancer to autoimmune diseases to vaccine development. However, many of these drugs suffer from short half-lives in vivo, leading to the need for frequent administrations in order to maintain their concentrations at therapeutic levels in the body. In addition, these large complex-structured macromolecules are inherently unstable in formulation, requiring cold-chain transportation and storage and limiting their long-term viability in in vivo depots. To address these challenges, we have developed a multifunctional, injectable delivery system utilizing supramolecular hydrogels that can sustain the release of these drugs over an extended period of time while simultaneously maintaining their stability, even at high loading concentrations. This work will focus on assessing the ability of these supramolecular polymer-nanoparticle hydrogels to improve the thermal stability of biotherapeutics. In vitro plate assays conducted under accelerated aging conditions are used to investigate how the hydrogel formulation influences the biostability of various model protein drugs, including hormones, enzymes, and antibodies. In addition, correlation between hydrogel mechanical properties and their ability to act as a stabilizing agent is explored. We demonstrate that these hydrogels are capable of extending the thermal stability of sensitive biotherapeutics at even at high concentrations, potentially enabling new drug formulation strategies.

Advances in bioinspired design principles and nanomaterials have led to tremendous progress in autonomously moving synthetic nano/micromotors with diverse functionalities in different environments. However, a significant gap remains in moving nano/micromotors from test tubes to living organisms for treating diseases with high efficacy. Here we present the first, to our knowledge, in vivo therapeutic micromotors application for active drug delivery to treat gastric bacterial infection in a mouse model using clarithromycin as a model antibiotic and Helicobacter pylori infection as a model disease. The propulsion of drug-loaded magnesium micromotors in gastric media enables effective antibiotic delivery, leading to significant bacteria burden reduction in the mouse stomach compared with passive drug carriers, with no apparent toxicity. Moreover, while the drug-loaded micromotors reach similar therapeutic efficacy as the positive control of free drug plus proton pump inhibitor, the micromotors can function without proton pump inhibitors because of their built-in proton depletion function associated with their locomotion.

Bioresorbable structures can be used as drug eluting platforms in various biomedical applications. Soy protein is a new natural material in the medical field with very promising properties. It has been used in our lab as basic material for wound dressings designed for pre-hospital treatment, mainly of burn injuries. Our dressing design consists two layers: a porous layer in contact with the skin, which allows better water permeability and accommodates newly developed tissue, and a top, dense layer, preventing pathogen penetration. In the current study the porous layer was loaded with the hemostatic agent tranexamic acid for bleeding control, and the dense layer was loaded with both an antibiotic drug (Cloxacillin) for infection prevention and with an analgesic drug (Bupivacaine). The whole soy protein structure was crosslinked by glyoxal and plasticized by glycerol.
A film containing higher crosslinking density achieved better strength and modulus, while a film with lower crosslinking density and higher plasticizer concentration exhibited a higher maximal strain. The water vapor permeability, the most important property of burn dressings, was also affected by the film’s formulation: increasing the crosslinking agent resulted in a lower water vapor transmission rate. The swelling ratio and weight loss were higher for the less crosslinked film as well.
A cytotoxicity test was performed with samples containing 3% Cloxacillin (w/w of dense layer). No significant difference was found between the drug loaded film and the neat film without drug. Both did not show any cytotoxic effect.
In conclusion, our novel wound dressing holds a promise to be a most effective measure for casualty pre-hospital treatment, as multi-drug releasing platform, which may also support tissue regeneration.

The materials chosen for use in soft devices tend to be compliant elastomers whose function is to deform in a way that meets the mechanical requirements of the application. In recent years, a new idea has emerged: namely, that the strains that naturally occur during device function can be harvested to drive chemical changes and add function to the devices. One strategy toward capturing strain is to use tension in polymer molecules to trigger the covalent response of an embedded mechanophore. This talk will discuss structure-activity relationships in mechanophore design and their application in multi-responsive materials and devices.

Smart materials with tunable properties have opened new avenues for studying the fundamental, dynamic behavior of cellular systems. The behavior of biological cells is strongly dependent on their mechanical micro-environment. To date, efforts to study this dependency have relied on the use of mechanically static materials with stiffness that can be changed through preparation. This approach provides only half the story though as cells and tissues are dynamic in nature. We have developed a composite extracellular matrix platform with dynamically tunable mechanical properties and have used it to assess the response of cardiomyocytes and fibroblasts to dynamic changes of their mechanical environment. The key material in this platform is a magnetorheological elastomers (MRE) that is composed of an elastomer (polydimethylsiloxane) and ferritic particles. This MRE is a soft (E~10-100 kPa) active material with mechanical properties that can be manipulated through the application of a magnetic field. We have characterized the change in modulus, friction, adhesion, and surface roughness of these MREs that occur due to an applied magnetic field. The effect of the magnitude of the field, the material composition, and material synthesis method on the response were characterized. The stiffness, friction, and adhesion changes were characterized via indentation and sliding tests at the millimeter scale. The results show that the magnetic-induced changes in viscoelastic modulus (up to ~5x) lead to changes in the tribological behavior (friction and adhesion) of the materials. Surface roughness and geometry changes resulting from the strong magnetostrictive response of these MREs to weak fields was also characterized. Finally, the severity, spatial uniformity, repeatability, and time-dependency of the MR effect were also examined. The knowledge gained through indentation and tribology experiments as well as through roughness characterization of these MREs will lead to the design of new stimuli responsive materials that enable more accurate study of dynamic, biological systems.

Macroscopic rotating engines powered by electricity or fuel are very common devices that are generally used to produce mechanical energies. However, it is very difficult, to integrate them into microdevices. Making high-speed and strong miniaturized engines with simplicity, robustness and low cost is always very challenging. Up to now, the strongest rotary motors ever reported are based on the concept of twisted fibers. [1] The concept of twisted fiber can actually be used to develop rotary motors by involving several mechanisms, such as entropic elasticity of polymer chains, [2] solvent swelling in CNT yarns,[3] or the expansion/contraction of GO via water adsorption and desorption.[4] Here, we study the shape memory effect by twisting polymer fibers and explore their application for strong engines.
To make strong microengines, it is necessary to reinforce the torsional properties of polymer fibers by inclusion of nanoparitcles. We prepared carbon nanotube (CNT)- or graphene oxide (GO)-doped polyvinyl alcohol (PVA) fibers by using wet-spinning method. As compared to pure PVA fiber, CNT and GO nanosheets have nearly the same reinforcement efficiency on the tensile properties. However, GO nanosheets have more significant effect on the improvement of torsional properties because of its unique two-dimension nanostructure. We used such strong GO fiber to prepare torsional motors. By measuring the recovered angle against an applied constant torque, we achieved a maximum generated energy density as high as 2800 J/kg. To our knowledge, this is actually the first report of the use of graphene to reinforce torsional properties of polymer composites and the greatest energy density observed in rotary motors.
[1] Haines CS, Lima MD, Li N, Spinks GM, Foroughi J, Madden JDW, et al. Artificial Muscles from Fishing Line and Sewing Thread. Science. 2014;343(6173):868-72.
[2] Yuan J, Poulin P. Fibers Do the Twist. Science. 2014;343(6173):845-6.
[3] Lima MD, Li N, de Andrade MJ, Fang S, Oh J, Spinks GM, et al. Electrically, Chemically, and Photonically Powered Torsional and Tensile Actuation of Hybrid Carbon Nanotube Yarn Muscles. Science. 2012;338(6109):928-32.
[4] Cheng H, Hu Y, Zhao F, Dong Z, Wang Y, Chen N, et al. Moisture-Activated Torsional Graphene-Fiber Motor. Advanced Materials. 2014;26(18):2909-13.

Miniaturization of electromechanical devices will bring a revolution to humanity in the coming decades synonymous with the effects of miniaturizing electronic devices in those previous [1]. They promise and deliver a myriad of applications within industry, including those within the automotive, electronics, aerospace, environmental, and defence. An electromechanical actuator — a device that converts electrical energy to mechanical deformation or motion — is the core component of many such devices. Consequently, research interrogating mili-, micro-, and nano-actuation has, and will continue to become increasingly essential.

In this talk, I will first present a quick overview of my team's density functional theory based computational materials design for high-performance two-dimension (2D) actuation materials [1-5]. 2D materials have a combination of several desirable properties for actuation at a small scale, e.g., atomistic thickness, excellent mechanical strength and flexibility, superior electronic properties, and excellent tunability [6,7]. Various actuation mechanisms are explored in our studies, such as piezoelectricity, electroactive, quantum mechanical effect, and shape memory effect. We will use several material systems to demonstrate these different actuation mechanisms briefly.

My presentation will focus on the shape memory effect (SME) of 2D materials [2-3]. Shape memory materials (SMM) have a unique feature of programmability. This stimulates novel device design concept, so-called material-as-machine, in which SMM can be programmed for actuation/motion following a pre-determined sequence, just like machines but with higher intelligence and flexibility whereby the materials can sense and react accordingly. This concept is particularly appealing at small length scale. However, the conventional shape memory alloy will lose its reversible martensitic phase transformation (origin of the shape memory effect) below a critical size (4 – 60 nm). Our recent study discovered a set of promising 2D shape memory materials. The physical mechanisms of their SME are fundamentally different from conventional SMMs. The external stimuli to trigger the shape memory behaviour are also different from conventional SMMs, i.e., electric field, charge doping, and mechanical force, versus the thermal field. These new stimuli will enable quick response (up to GHz) and precise control (down to nm), which are highly desirable for actuation devices at small length scale.

References
[1] J. Z. Liu, J. Hughes, Electromechanical actuation of pristine graphene and graphene oxide: origin, optimization and comparison, Carbon Nanotubes for Actuators, Nanostructure Science and Technology series, Springer (in press) arXiv:1903.02729
[2] Z. Chang, J. Deng, G. G. Chandrakumara, W. Yan, and J. Z. Liu, Two-dimensional shape memory graphene oxide, Nature Communications 7, 11972 (2016)
[3] J. Deng, Z. Chang, T. Zhao, X. Ding, J. Sun, and J. Z. Liu, Electric field induced reversible phase transition in Li-doped phosphorene: shape memory effect and superelasticity, Journal of the American Chemical Society 138, 4772-4778 (2016)
[4] G. W. Rogers, and J. Z. Liu, High-performance graphene oxide electromechanical actuators, Journal of the American Chemical Society 134, 1250 (2012)
[5] G. W. Rogers and J. Z. Liu, Graphene actuators: quantum-mechanical and electrostatic double-layer effects, Journal of the American Chemical Society 133, 10858 (2011)
[6] X. Kong, J. Deng, L Li, Y. Liu, X. Ding, J. Sun, and J. Z. Liu, Tunable auxetic properties in group-IV monochalcogenides monolayers, Physical Review B 98, 184104 (2018)
[7] L. Qiu, J. Z. Liu, S. L. Y. Chang, Y. Wu and D. Li, Biomimetic superelastic graphene-based cellular monoliths, Nature Communications 3, 1241 (2012)

Improving the state of the art of treatments in regenerative medicine demands for materials that are capable of accomplishing multiple tasks, e.g. providing mechanical support while releasing a drug and then vanishing from the body. Such highly multifunctional materials require distinct properties which are achieved by tailored molecular architectures. Mechanical properties and thermal transitions are adjusted by e.g. joining different building blocks. Cell recognition motifs can be provided by grafting functional side chains or modifying chain-ends, drug loading capability enhanced by strategically placing functional groups to optimize the binding energy between drug and matrix. Cross-linking is a common approach to create polymer networks capable of forming hydrogels or to obtain rubber-like materials. However, while the material properties are a result of the synthesis and the processing of the material, functionalities arise from its interaction with the environment. For example, a hydrogel requires the presence of water and a cell binding motif is useless without cells. Quite often, the different functions are also not orthogonal in a sense that one environmental interaction can trigger multiple functionalities. For example, the swelling of a material in water triggers both drug release and degradation. Ensuring that all material functions are executed as intended therefore requires an understanding and a holistic prediction of the material behavior when responding to a stimulus. Especially predicting material degradation, which has a drastic impact on all material properties and therefore also functions, remains a great challenge. Without such a prediction, designing a biodegradable multifunctional material with a specified lifetime is only possible on an empirical basis.

To support the predictive design of multifunctional materials, a theoretical model for the interplay of cross-linking and molecular degradation kinetics is presented. It is elaborated how the degree of crosslinking affects the degradation kinetics of macromolecules. This model also predicts the decrease of the degree of cross-linking with proceeding degradation in dependence on the molecular fragmentation mechanism, which could be e.g. a random fragmentation or a preferential cleavage of certain bonds. Using the established theories of rubber elasticity, the evolution of the material’s mechanical properties can be deduced from the degradation models.
Such an analytical model provides a qualitative understanding for the impact of cross-linking related molecular parameters on the material behavior during degradation. Taking into account the inhomogeneous microstructure of processed, real-world materials and the complex geometries of medical implants, a lifetime prediction of multifunctional medical devices will require multiscale computational simulations. Moreover, all models rely on input parameters such as reaction rate constants, which have to be determined experimentally.
The Langmuir monolayer degradation technique is an established way to determine these parameters for materials degrading in aqueous environments in experiments that take only a few hours¹. Here, it is presented how the technique was used to verify the analytical models and to determine the kinetic parameters for poly(ε-caprolactone) based networks which were prepared in-situ on the Langmuir trough. In such a system, the cross-linking density can be varied by compressing the layer, and the decrease of the cross-linking density during degradation is registered as a decrease of the storage modulus by means of interfacial rheology.
Literature
1. Machatschek, R.; Schulz, B.; Lendlein, A., Langmuir Monolayers as Tools to Study Biodegradable Polymer Implant Materials. Macromolecular Rapid Communications 2019, 40 (1), 1800611.

The increasing energy demand worldwide must be addressed with sustainable technologies to mitigate further climate change. In particular, the energy employed for heating and cooling covers 79% of the total energy consumed in the European households. Both reducing the cooling demand and improving the efficiency of the energy conversion processes could limit the environmental impact of building cooling. On the one hand, novel materials for personal thermal management can be adopted to shift upwards by few degrees the set-point of room temperature, therefore reducing the cooling load at fixed thermal comfort. On the other hand, the energy consumption of traditional vapour-compression systems can be significantly reduced by achieving sub-ambient temperatures in the condenser thanks to passive coolers.

Recent developments in materials science allowed to reinvent two long-standing passive cooling technologies, namely radiative and evaporative cooling, thus increasing their performances and expanding their application field. We combine the complementary evaporative and radiative cooling features to overcome the intrinsic limitations of conventional polymeric textiles for personal thermal management. Polymeric films and fabrics with tailored optical properties have already been proposed for daytime radiative cooling, reaching a specific cooling capacity up to 100 W m^-2 and acceptable wearability. These composite organic-inorganic nanoparticle-filled polymer materials combine strong spectral selectivity of nano-particles with unique lateral heat-spreading capability of semi-crystalline polyethylene films and textiles. However, their radiative cooling potential is strongly limited by the ambient humidity; additionally, these textiles are not yet optimised to favour the typical skin cooling by sweat evaporation. We optimize the material, sizes and plot of the fabric to enhance both radiative and evaporative cooling performance via multi-physical modelling, which considers water wicking and evaporation, vapour permeation and spectrally selective optical properties. The optimized multi-functional textiles, including dual-mode, reversible or ambient-responsive materials, could be employed for more effective personal thermal management, thus allowing a substantial reduction of the economic costs and environmental footprint of building cooling.

This work is supported by the MIT International Science and Technology Initiatives (MISTI-MITOR), US Army Research Office (via the CCDC Soldier Center and the MIT Institute for Soldier Nanotechnologies), and the Advanced Functional Fabrics of America (AFFOA).

In this work, we present a robust hierarchical mushroom-like structured surfaces by using novel and low-expertise fabrication method. The microscale re-entrant mushroom-shaped structures were fabricated on a substrate by a replica molding technique using a polydimethylsiloxane (PDMS) and an ultraviolet (UV)-curable polyurethane acrylate (PUA) containing inorganic nanoparticles. The tiny inorganic particles were used to make nanoroughness on the top of the re-entrant structures by using plasma polymer etching process. Finally, we have successfully obtained hierarchical mushroom-shaped structures without any structural failure, and the nano/micro multiscale re-entrant features demonstrated remarkable superomniphobic properties repelling water and oil. It is expected that the hierarchical structures are to be applied in a wide range of applications requiring self-cleaning and antifouling surfaces.

Polymer nanocomposites possess unique sets of properties that make them suitable for applications, including structural materials, aerospace, flame retardant material, electromagnetic wave reflector, strain/solvent sensor, thin film transistor, flexible display, and many more.¹ The properties of these nanocomposite are dependent on nanofiller dispersion and bonding with polymer matrix (i.e. particle-matrix interaction). Thermal imaging is a non-destructive method that may be used to gain insight into dispersion and particle-matrix interaction.² Infrared (IR) radiation emitted from these nanomaterial polymer composite depends on the emissivity of the individual components. In addition, during flash heating and cooling, thermal conductivity of components in the nanocomposite can influence IR radiation being emitted. Moreover, during in-situ incorporation of filler with polymer and during curing of thermoset nanocomposites, exothermic and endothermic reactions representing bond formation can be investigated with IR camera³. Even for nanoscale phenomenon as electron transport and energy dissipation, nanomaterials like graphene can be characterized by IR imaging⁴. We have used an economical mid wavelength IR camera Fluke RSE600 equipped with a close up macro lens and algorithm based on MATLAB image processing toolbox to analyze dispersion, voids, thermal diffusivity and energy dissipation of patented graphene polymer nanocomposite materials (G-PMC)⁵ in micron scale. These G-PMCs can act as a standard material to determine the potential of our IR thermography technique due to their homogeneity and lack of impurity due to unique fabrication process. Thermal diffusivity and dispersion of nanoparticles in our G-PMCs was estimated after irradiation with a xenon flash lamp by spatially mapping transient IR radiations with time from different G-PMCs using a Fluke RSE600 thermal imager. Our thermography technique was used to study nanomaterial agglomeration, energy dissipation or thermal transport during sensing application of G-PMCs. Interpretation of the thermal image will be verified by performing scanning electron microscope (SEM), Rheometry, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). We believe this low cost, fast, non-destructive technique will provide valuable insight into functional polymer nanocomposite fabrication and corresponding mechanical, electrical, and thermal properties.

Cellular structures based on Triply Periodic Minimal Surfaces (TPMS) are structures in three-dimensional (3D) space with a locally net zero curvature and a unique architecture that locally minimizes the surface area. They can be divided into two main categories; solid and sheet networks. The special morphology of TPMS, along with their low density and yet high surface area has led them to demonstrate enhanced electrical, thermal, and mechanical properties. The objective of this paper is to computationally evaluate the effective electrical and thermal conductivity of three cubically symmetric TPMS cellular structures – namely Gyroid, IWP and Diamond over a range of relative densities and morphological parameters using the Finite Element Method (FEM). Particularly, it compares the solid cellular structures with each other and investigates the inter-relation between the solid and sheet networks. Results show the effective conductivity to vary linearly with increasing relative density for the three shapes, with the sheet networks demonstrating higher conductivities than the solid networks at all relative densities. The IWP and Gyroid exhibit similar trends while the Diamond shows a lower conductivity for the same values of relative density. Among all the structures, the IWP presented the highest value of 0.17 for the sheet networks and 0.13 for the solid networks, both at a relative density of 25%. The second parameter that is investigated in this study is varying the morphological parameter c-value, which changes the ratio of the two volumes divided by the minimal surface, and at a critical value, alters the geometry such that TPMS-based tube-networks are formed. As observed for the Gyroid, at the same relative density, increasing the c parameter decreases the effective conductivity of the structures due to a decreased surface area available for heat transfer. The effect of varying the c value for the Diamond and IWP tube-networks show similar trends to the Gyroid. The findings of this work are to be used as a validation for measuring the thermal and electrical conductivities of TPMS-based graphene 3D lattices synthesized experimentally where the minimal surfaces of polymer material will be fabricated using additive manufacturing, coated with graphene oxide and subsequently etched via thermal methods to obtain pure 3D graphene architectures.

Simultaneous sensing, visualizing and memorizing magnetic field provide a useful human-interactive platform allowing for easy access and manipulation of the information that human is rarely sensible, making human-interactive displays where sensible but invisible information such as touch, smell and sound is visualized further extended. Here, we present a novel single-level magnetoactive display capable of sensing, visualizing, and storing the information of magnetic field. Our magnetoactive display is successfully developed by employing a magnetoactive conductive fluid of multi-walled carbon nanotubes decorated with superparamagnetic ferrite nanoparticles in hexadecane into an alternating current (AC) electroluminescent (EL) display consisting of an AC field responsive emissive layer with two parallel electrodes. With magnetic field exerted on the device, a magnetoactive conductive channel is formed which serves as a magnetic field gate, giving rise to the characteristic EL upon AC field. The impedance of the magnetoactive conducting channel decreases with the magnetic field, and thus the luminance of the device increases with the field, allowing for facile sensing in impedance and visualization in EL of the degree of magnetic field. More importantly, the magnetic field dependent EL is readily stored and retrieved since a magnetoactive conducting channel remains after the removal of the field due to collective fixation of the channel with the networked carbon nanotubes. The EL is erased by destroying the channel with the opposite magnetic field and another EL is developed and stored with a different magnetic field, making our non-volatile magnetoactive EL display (NV-MED) rewritable. Moreover, by constructing the mechanically flexible arrays of NV-MEDs, we are able to realize a pixelated EL display mounted on skin where a variety of static and dynamic information of magnetic field is simultaneously detected, stored, erased and rewritten many times.

With the advent of massive telecommunications networks and the expansive development of wireless electronics operating in the gigahertz range, “electromagnetic pollution” has risen to unprecedented levels. To mitigate the effects of electromagnetic interference (EMI) from spurious radiation, improved EMI shields are needed. Shields composed of solid metals or metal-based coatings oftentimes exhibit high shielding efficiency (SE) but have issues such as poor wear and corrosion resistance and high rigidity. Foaming of these materials has demonstrated higher broadband EMI absorption as compared to the non-foamed material due to minimization of the air-to-shield impedance mismatch. However, the pore morphology inside the foam is highly dependent on the specific foaming conditions and materials involved. The final pore morphology can drastically affect EMI shielding efficiency resulting in significant resources being spent on optimization of the foaming process. Herein we present an approach that relies on the introduction of periodically placed air-filled pores into conducting polymer composites in order to reduce material requirements and maximize microwave absorption. The presented research will demonstrate experimental validation of a novel route for the development of highly efficient EMI shields based on a magnetically functionalized graphene composite material. First, constitutive electromagnetic properties of bulk composite material are retrieved from scattering parameter measurements. The constituitive properties are manipulated throught variable addition of magnetioelectric filler material. Second, electromagnetic properties are utilized in finite element method-based optimization to establish optimal periodic geometry that have high EMI shielding for a desired range of frequencies and incidence angles. Finally, optimized geometries are realized via compression molding. We demonstrate the validity of this approach using two different polymer systems, one of which includes a segregated conductive network.

This work focuses on the development of kirigami-patterned, passive resonant sensors that operate in the short-wave radio frequency range (1-150 MHz) to wirelessly monitor the deformation of materials in closed systems. At first, the sensors are rapidly prototyped out of Pyralux©, a copper-coated polyimide substrate. The Archimedean spiral design is masked by drawing on the copper with an indelible marker (using a craft XY plotter) and the unwanted copper is etched away with hydrochloric acid and hydrogen peroxide. The samples are then rinsed with acetone to release the mask, coated with polydimethylsiloxane (PDMS), and laser-cut to add the kirigami-inspired pattern to the sensor. The onion ring-shaped resonant sensor is wirelessly coupled to external, two-loop reader antennas to report the extent of material deformation. The reader antennas are connected to a benchtop vector network analyzer (VNA) which can capture both the reflection and transmission scattering parameter signals. We have defined the sensor response as the resonant frequency, which is the minimum of the sigmoidal feature in the transmission scattering signal (S₂₁). The resonant frequency of the sensor is modulated by changing the physical parameters of the resonator such as coil length and spiral pitch. The resonant frequency of the sensors are tracked over an extension range of 0-22 cm and a major shift in the resonant frequency is observed. For instance, a 90 MHz shift in the sensor response is observed by stretching the sensor to 10 cm. Moreover, the effect of the pitch size of the resonator on the sensor’s linear span and gain value (MHz cm⁻¹), which is defined as the linear slope of the resonant frequency-stretch curve, is studied. In order to confirm the repeatability of the gain of kirigami resonant sensor, a 96 cycle hysteresis experiment is conducted for sensors with different pitch sizes. Furthermore, the coated sensors are placed in a pipe to test the ability of kirigami resonators to wirelessly report different flow rates. The sensor with 1 mm PDMS coating exhibits the highest flow gain value (0.17 MHz.s mL⁻¹) and largest linear span (10–100 mL s⁻¹). Finally, since Pyralux© is a relatively expensive substrate and the etching process produces unwanted waste, we demonstrate scalable, sustainable fabrication of resonant sensors with screen printing using conductive silver paste. The resonators are characterized in terms of their electrical and magnetic properties (e.g. resistance, quality factor) as well as their physical properties (using microscopy). Also, the quality of screen-printed resonators is compared to copper-etched and ink-jet printed resonators. We will also discuss current work to print on soft, compliant materials such as Tegaderm™ (3M product). In conclusion, flexible, passive, kirigami-patterned resonant sensors can be fabricated for many proposed applications in healthcare, motion and deformation tracking, virtual reality, and soft robotics.

1. Charkhabi S, Chan YJ, Hwang D-G, Frey ST, Bartlett MD, Reuel NF Kirigami-Enabled, Passive Resonant Sensors for Wireless Deformation Monitoring. Advanced Materials Technologies, 0(0):1800683. https://doi.org/10.1002/admt.201800683

Magneto-Active Elastomers (MAEs) are an important class of soft, shape-recoverable materials that exhibits a stiffness increase in response to an applied magnetic field. Using magnetic field to tune material stiffness is advantageous due to the fast, remote and reversible switching, which is relevant for applications in areas of soft actuators, adaptive vibration dampers and acoustic filters. 1D and 2D architected MAE composites, such as laminates and periodic inclusions, have been predicted to possess novel mechanical instabilities, due the spatial distribution of stiffness mismatch and the ability to dynamically tune the mismatch with magnetic field. We fabricated MAE composites using a commercial silicone as the non-responsive soft matrix and a silicone loaded with iron microparticles for the stiff, magnetoactive regions to experimentally demonstrate these concepts. The silicone matrix formulation was modified to increase the stiffness contrast between the soft encapsulating matrix and the stiff MAE regions, including tuning of the crosslinker to polymer ratio, and addition of silicone oil to further reduce crosslinking. 3D printed templates were used as molds to construct laminates and 2D periodic MAE architectures. Magnetic field induced stiffening was characterized using a custom compression test jig that was designed and 3D printed to systematically load the specimen within a 2 Tesla electromagnet. The study provides experimental feedback on the sensitivity of the buckling strain to experimental specimen sizing/edge effects and provides broader insight on the practical integration of MAE instabilities into functional devices.

Conducting polymers have received considerable attention in various fields, including electronic devices, sensors, energy materials, anti-corrosion coatings, and biomedical applications. Not only through their tunable electronic properties, but also the soft organic material nature and facile functionalization process render these materials as versatile platforms. Via the hybridization with inorganic compounds, such as metal nanoparticles (NPs), a further enhanced electrochemical properties as well as synergistic effects, could be realized. With these improvements, they can be utilized in the rapid identification of certain biomarkers for early detection of various diseases.
In this work, we report a single-step fabrication route, which exploiting the simple electrosynthesis process of conducting polymers, to construct composite sensors with metal NPs incorporation. In addition to their deposition on the planar electrodes, both the deposition bath recipe and processing parameters are explored and optimized for the conformal coating on metal-based inverse opals with flexible substrates support. The composite coating on such bio-inspired 3-D nano-scaffold as the sensing layer could fully utilize the increased specific surface area and improved mass transport brought by the intriguing honeycomb structure. Meanwhile, the enclosed metal inverse opal is employed as the current collector to ensure a highly conductive pathway for signal transduction. The sensing performance for these 3-D sensors is evaluated by the selective detection of ascorbic acid (AA), uric acid (UA), and dopamine (DA). Relevant structural and compositional characterizations are conducted by SEM, EDX, XPS, and Raman spectroscopy.

Ionic liquids (ILs), or room temperature molten salts, composed entirely of low molecular weight cations and anions, have attracted great attention in a broad range of electrochemical devices owing to their physicochemical and electrochemical properties such as non-flammability, non-volatility, high ionic conductivity, and large electrochemical stability windows. The use of highly viscous ILs in electrochemical devices often limits the performance of the IL-based devices due to slow ion transport. To enhance the mechanical integrity of the liquid electrolyte, structuring polymers are often blended to form a chemically or physically cross-linked network, resulting in solid polymer electrolytes known as ion gels. However, the addition of a polymer network in ILs even lower the ionic motion, which leads to slow response of the ion-gel-based devices to an external signal. Mixing organic solvents with ILs is an effective strategy to alleviate the issue mentioned above. In this work, we blended the four different kinds of organic solvents with the ion gels and investigated the effect of the blend composition on the electrical and thermal properties of the solid electrolytes. The electrical properties depended on the viscosity and dielectric constant of the organic solvent, whereas the thermal properties depended on the vapor pressure of the component materials. When these mixed ion gels were applied in electrochemical thin-film device, the mixed ion gel-based devices showed superior performance to the pure ion gel without organic solvents owing to the enhanced ionic motion.

With increasing importance of human-machine interface along with the rapid growth of Internet of Things (IoT), integration of sound generation and visual display in a stretchable form of single sound-in-display device has attracted great attention to connect human with machines via a visualization of auditory system. Herein, synesthetic bimodal senses of sound and color is demonstrated by stretchable sound-in-display devices consisting of strain-insensitive silver nanowire electrodes and field-induced inorganic electroluminescent (EL) phosphor emissive layers. While sound-in-display devices embedding EL phosphors in a dielectric elastomer matrix produce the light emission under alternating-current (AC) bias, audible sound-wave is generated via an actuation of dielectric elastomer matrix along with input sound signals simultaneously. The stretchable sound-in-display devices show highly robust and reliable EL sound performance that can be repeatedly stretched and released without severe degradation due to the use of strain-insensitive silver nanowire electrodes. This study demonstrates stretchable electronics including light emission and acoustic system in a single device, which could be further expanded for the realization of sound-in-display electronics.

Stimuli-responsive smart materials are promising for the detection of various stimuli, such as temperature, pH, or light intensity. Under the external stimuli, the smart materials abruptly change their physicochemical properties. Above all, colorimetric smart materials have great advantages in direct detection and real-time visualization of stimuli. Here, we present a thermoresponsive colorimetric sensor based on the hybrid structure of plasmonic gold nanoparticles and thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) microgels. The color of smart hydrogel film shifts from ruby red to grayish violet with a large extinction peak shift of 176 nm in 1 second for the temperature change from 25 to 40°C. Through the analysis of color shift, the colorimetric sensor array shows a high thermal resolution of 0.2°C. Furthermore, the thermoresponsive colorimetric sensor can be stretchable up to 90% when the hybrid plasmonic microgels are embedded in a stretchable polyacrylamide. In addition, both color- and texture-tunable smart surfaces can be fabricated by using shape memory polymers (SMPs) and thermochromic dyes. We design a thermoresponsive color- and texture-changeable smart surface based on polylactic acid/polyurethane SMP and thermochromic dyes. Here, the pyramid-patterned SMPs (py-SMPs) with fluorinated silica nanoparticles exhibit thermoresponsive change of surface texture and wettability (water contact angle change from 98° to 144°), and thermochromic dye displays thermoresponsive color change. The suggested concept of smart surfaces can be extended to the fields of sensors, actuators, and smart coating by using various adaptive polymers.

Hydrogel has been attracted great attention in biomedical field since this material resembles the feature of extracellular matrices (ECMs). For the successful application of hydrogel for cell culture or tissue engineering, not only providing the stable substrate but also considering the cryogenic preservation of cells or organs is essential to prevent unwanted cellular degeneration. In cryogenic preservation of cells, it is essential to make the water molecules in hydrogel unfrozen during the freezing process. To this end, synthesized the triblock copolymer hydrogel composed with hydrophobic block, zwitterionic block and quadruple hydrogen bonding moiety was investigated in this research. Due to the synergistic effect of super-hydrophilic nature of zwitterionic polymer and nanoscale domain formation of hydrogen bonding moiety, the large amount of water in this hydrogel did not freeze below the temperature 223K. Furthermore, capitallizing on these dynamic bond, this triblock copolymer hydrogel shows injectable and self-healable property. In addition, it shows plateau modulus in the range of soft tissue. We hope that our basic finding give the design principle on hydrogel for biomedical application such as a tissue engineering.

Bottlebrush polymers (BBPs) consist of a linear backbone and grafted side-chains. The high branch-to-backbone ratio in these systems causes BBPs to adopt different conformational behavior compared to linear polymers, making them a topic of interest. The most widely used synthetic method for BBPs is the ring opening metathesis polymerization (ROMP) of macromonomers. Here, we synthesized diblock macromonomer via atom transfer radical polymerization and nitroxide radical coupling, and then synthesized core-shell bottlebrush polymer via ROMP. Our diblock macromonomers consist of poly n-butylacrylate (PBA) and poly ethylene oxide (PEO). Here, PBA acts as a rubbery core and PEO acts as an epoxy miscible shell. With only 3 wt% of BBPs addition, epoxy toughening effect of 200% was achieved. The results show that the application of BBPs to the epoxy toughening industry can be expected.

Since the fabrication of flexible anti-reflective (AR) structures has great attention for application, such as solar cells, display, wearable devices and so on, various methods, especially moth-eye inspired technologies, have been developed in decades. However, there is limited study to explain difference of optical properties depending on structure dimensions and materials fabricating ultra-violet (UV) curable polymers or thermal curable polymers. In this works, we fabricated moth eye inspired conical structures with three different-sized dimension using various materials. To compare the dimension and material dependent AR properties, we successfully fabricated 300 nm, 500 nm and 1000 nm moth-eye structures by using UV curable and thermal curable polymers. As a result, we have demonstrated that the anti-reflection effect of the fabricated surfaces is improved depending on the structural dimension and consisting materials of the nanostructures.

Shape morphing from two-dimensional (2D) planar sheet to three-dimensional (3D) structure have been attracted great attention for the number of application including packaging, assembly, transport, and mechanical actuation. To obtain programmable 3D structure from a 2D polymer sheet, various types of external stimuli have been used including light, heat, electric/magnetic field, and chemicals. In particular, photo-triggered strain engineering used pre-strained thermoplastic polymer sheet has been widely researched due to its ability to local actuation by harmless near infrared (NIR) light with simple and low cost processes. Generally the ink patterns are printed on the polymer sheet for local heating over glass transition temperature (T_g) of polymer with inducing local shrinkage at the pattern regions.
To control the morphed shape of 3D structures, many kinds of pattern design strategies have been studied. For example, pattern width and spacing of hinge patterns were handled for adjusting the folding angle of 3D folding structures. Moreover, different color of hinge patterns was used with different light sources for sequential folding actuation. Recently, using the large size of hinge patterns, global curvatures were controlled according to pattern location, gradient, and its combinations. However, most of the previous works have limited to morphing the folding shapes or the global curvatures based on simple hinge pattern because they considered the deformation of the pattern region, only. To morphing the complicated 3D structures using photo-triggered strain engineering, the pattern design should be done in advanced considered the deformation of non-pattern regions as well as pattern regions. Furthermore, the analyzation of intermediate shapes at each time interval should be done because the final morphed 3D structure is defined according to an intermediate one.
In this study, we demonstrated the pattern design strategy for 3D shape morphing considering the deformation of the non-pattern region by localized shrinkage of pattern regions with employing radial hinge patterns and round facet on bi-axially pre-strained polystyrene (PS) sheet with a circular boundary condition. According to pre-designed radial pattern conditions and the existence of the round facet, photo-triggered 3D shape morphing was experimentally discussed. Furthermore, we introduced the finite element modeling (FEM) simulation with consideration on temporal/positional stress distribution and their stress competition effects. Interestingly, the hidden mechanisms of the strain re-distribution effect at the non-pattern regions, associated with the final 3D curvature structuring, could be experimentally visualized with polarizing optical transmittance images of the photo-triggered birefringent PS films and they also could be analytically computed. Based on systematic experimental results and computational analysis for pre-determined radial patterns, complex 3D shape morphing having bio-mimetic shapes of soft-turtle shell and sea shell shapes could be successfully implemented, where the PS sheet actuation behaviors at the non-pattern regions were as important as the photo-actuating pattern regions in the formation of final 3D structures. The results of local curving actuation with quantifiable stress imply to take applicability forward for self-folded architectures embodying curved and linear geometric surface coexist.
Acknowledgement: This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No 2019R1A2C1005531) and the BK21 Plus project funded by the Ministry of Education, Korea (21A20131600011).

Cell alignment is an important factor in the exertion of specific mechanical function originated from its anisotropic structure. Especially, myoblast alignment is critical to form paralleled and organized myotubes in muscle regeneration. Diverse approaches have been proposed in cell alignment based on photolithography, electrospinning, laser-guided cell micropatterning, microfluidic patterning, acoustic cell patterning, and 3D bioprinting. However, there is still a need for an easier method that does not require complicated equipment to increase the efficiency of cell alignment. Here, we propose a facile method for magnetic assembly of arginine-glycine-aspartic acid (RGD)-modified alginate-coated magnetic microparticles for cell alignment, in particular myoblast arrangement. The particles could be aligned along the direction of a weak external magnetic field and alginate chains on the surface of microparticles could be cross-linked via ionic cross-linking. By these effects, stable linear bundle structures of the particles in centimeter-scale could be formed even after removal of the magnetic field. In addition, incorporation of RGD into alginate chains on the surface of microparticles could lead to myoblast adhesion onto cross-linked, anisotropic bundles. The efficient myoblast alignment on the bundles was confirmed by filopodia detection followed by analysis of filopodia orientation. As a proof-of-concept, in vivo demonstration of the alignment of alginate-coated magnetic particles was performed without complicated surgery by subcutaneous injection of the particles followed by an additional injection of a calcium solution for in situ ionic cross-linking under the external magnetic field. In histologic examination, the anisotropic bundle structures of the particles in subcutaneous space were observed even after 1 day of injection. This facile process could be one of the options to fabricate aligned architecture, which could further supply an aligned microenvironment to the cells; for example, myoblasts for muscular system in regenerative medicine and tissue engineering. Moreover, the properties of being able to be simply injected through a needle without extra surgery and being in situ cross-linked can be strong points when this platform is applied to in vivo system.

Epithelial keratin protein, a type of intermediate filament protein, is the key component of epidermis in skin which is the largest organ in human body. The epithelial alpha-keratin intermediate filaments feature a hierarchical structure, ranging from alpha-helical protein, a dimer composed of alpha-helical coiled coils and two globular C- and N-terminal domains, to full-length intermediate filaments. Epithelial keratins dominate the structural stability and mechanical properties of the skin, also help lock in moisture and bear the external pressure. At the molecular level, the alpha-helical coiled coils are stabilized by clusters of hydrogen bonds. Here we report a study on building a bottom-up molecular based model of one epithelial keratin protein by using the full human keratin type K5 and K14 amino acid sequence. A detailed analysis of geometric and mechanical properties of the full-sequence epithelial protein at different water contents by fully atomistic simulation is presented. We analyze how the protein structure and its properties vary with hydration and investigate the role of water molecules in the epithelial protein. Our results suggest that water molecules play a significant role in achieving the characteristic molecular behaviors, including filament assembled arrangement and mechanical properties of this protein material. We further compare our results with the latest experimental measurements and discuss the opportunity of studying disease states associated with genetic mutations and other structural defects in keratin.

Electrospinning fibers have allowed for the creation of nanoscale structures with high surface to volume ratio which are ideal for next generation wearable electronic and textile applications. Conductive electrospun films are typically constructed by incorporating conductive nanoparticles such as graphene nanoplatelets (GNP) and carbon nanotubes (CNT). Inherently conductive polymers such as polyaniline or polypyrrole have also been used to fabricate conductive electropsun fibers. However, these methods of creating conductive pathways are insufficient as their conductivity remains several orders of magnitudes lower than any metal. Recent developments have used electroplating to coat the fibers with a thin layer of metal. Herein, an alternative electroplating method has been developed that allows for a coating of copper to be uniformly electroplated throughout the entirety of a highly stretchable electrospun styrene-butadiene-styrene (SBS) film. SBS is a copolymer rubber that possesses high elasticity and durability. When made into an electrospun film, the high aspect ratio amplifies the material's elastic properties and can reach strain ratios greater than 1000% without breaking. In this study, various conductive nanoparticles were explored to identify their effects on electroplating coating properties. The SBS film was ultrasonicated in an aqueous solution of the nanoparticles at varying weight percent to prepare the film for electroplating. The ultrasonication process assisted the conductive fillers to diffuse through the thickness of the film and adhere to the individual fibers. This provided an initial conductive pathway for the copper to deposit onto the fibers. As the conductive fillers were evenly coated on each fiber, the copper was also uniformly coated onto the underlying nanoparticle layer. The resulting conductive electrospun film retains its high elasticity through the mechanical properties of SBS, while the conductive copper and nanoparticle layer provide relatively high conductivity to the film even at high strain ratios. These properties make the film suitable for use as large strain sensors in electronic skins and smart textiles.

Shape-morphing micromachines have demonstrated significant potential in drug delivery, minimally invasive surgery, cell manipulation, and stenting applications [1]. With current fabrication methods, most micromachines are limited to a single type of transformation determined by their geometric design, which cannot be altered once fabricated [2]. In this work, we have developed a strategy to encode multiple shape-morphing information into transformable micromachines making use of the magnetic configurations of single-domain nanomagnet arrays. Inspired by origami, our micromachines consist of rigid panels carrying the arrays of nanomagnets separated by structured soft creases. The nanomagnets have tailored magnetic switching fields and, by applying a sequence of magnetizing fields, the arrays can be set into a particular magnetic configuration. By customizing the micromachine designs, we can obtain micromachines that perform specific shape transformations in an applied magnetic field. Based on this strategy, we have built a simple four-pad micromachine with 2⁴ possible magnetic configurations, demonstrating four distinct conformations when actuated by a magnetic field. Further, multicomponent micromachines were constructed by assembling modular units and, by customizing each individual unit, we have engineered a micromachine that can transform between two alphabet letters. We have also created complex folding behaviors, such as bending and twisting, and have implemented these folding modes in a microscale ‘origami bird’ capable of several different flapping modes. This work paves the way for the development of future intelligent microsystems that are reconfigurable and reprogrammable, which is required for biomedical applications and is also of interest for 3D magnetic and optical metamaterials. [3]

[1] B. J. Nelson, I. K. Kaliakatsos, J. J. Abbott, Microrobots for Minimally Invasive Medicine. Annu. Rev. Biomed. Eng. 12, 55–85 (2010).
[2] M. Z. Miskin, K. J. Dorsey, B. Bircan, Y. Han, D. A. Muller, P. L. McEuen, I. Cohen, Graphene-based bimorphs for micron-sized, autonomous origami machines, Proc. Natl. Acad. Sci. 115, 466–470 (2018).
[3] J. Cui, T.-Y. Huang, Z. Luo, P. Testa, H. Gu, X.-Z. Chen, B. J. Nelson, L. J. Heyderman, manuscript under review

To overcome lack of functionality and limitation in conventional soft robots, we demonstrate a highly anisotropic color changeable soft actuators for the first time. Due to the huge anisotropic thermal expansion mismatch, the suggested actuators has a highly anisotropic bending with very large curvature (2.5 cm−1) at considerably low temperature (≈40 °C) compared to the previous electrothermal soft actuators. Low temperature operating condition enables the remarkable long-term durability during more than 10000 times actuating at the maximum curvature. In addition, the optical transparency of metal nanowire network heaters and polymer bilayer allow the incorporation of the thermo-chromic dyes to fabricate color-changing actuators. We demonstrate various color-changing biomimetic soft robots such as color-changing blooming flower, flapping butterfly, and color-changing twining tendril. Along with high anisotropic behavior, large bending curvature with low temperature operating, long-term durability, color-changing function, the actuators offer tremendous possibility for biomimetic soft robotics.

The ability to create 3D printed structures containing living cells is providing a route to the creation of "living" systems that might be useful for bench top drug testing or implantables that facilitate tissue regeneration.

However, the realisation of a useful printed structure based on hydrogels is not a simple task. While we can build on the extensive knowledge that has accrued through cell-gel interaction studies to date, there are a number of dimensions that add to the challenge.

Central to these is that the gel containing the cells must undergo a reasonably rapid phase transformation. In addition, with some applications multiple cells and other bioactive entities need to be strategically distributed in 3 dimensions. Sterilisation of the components and/or the final structure is also of critical importance and finally knowing what we have created without destroying it remains a challenge.

Returning to the start of this process we encounter perhaps the most neglected aspect - most of the emerging hydrogels finding use in bioprinting are naturally occurring. So where do we find them - how do we ensure a reliable high quality source?

Current 3D printing uses a wide range of plastic, metal, and ceramic materials, with no significant effort to integrate these techniques for multi-material fabrication. We previously developed a novel method to deposit non-viscous ink through a stable continuous jet formed by gearing-enhanced peristaltic pumping. This ink deposition technique was used to deposit graphene oxide (GO) ink in a binder jetting (BJ) process to fabricate GO/polyvinyl alcohol composites. In this technique, ink particles are accelerated to speeds of 2-10ms^-1 to overcome surface tension forces tending towards pendant drop formation. Gearing is applied to achieve mechanical advantage (MA)<1, enabling high pump velocity. Motor acceleration made up for the lost torque. In recognizing that gearing could be used to increase torque with MA>1, we realized the potential to perform Direct Ink Writing (DIW) using our ink deposition system. To this end, we DIW-printed viscous graphene/nanocellulose inks. We also recognized that DIW and BJ shared similar layer change, material transport, and gantry motions, allowing the 2 techniques to be implemented in the same system. We designed and built the hybrid 3D printer, implementing transmission to switch gearing ratios. The hybrid printer was demonstrated to print Graphene/polymer composites using both DIW and BJ printing modes.

Material scientists have now developed an extensive library of nano-sized building blocks, offering a vast panel of properties (optic, magnetic, plasmonic, catalytic, etc.). Nevertheless, combining these building blocks for the realization of multifunctional materials while controlling their structure from the nano- to the micro- and all the way to the macroscale still remains an open challenge in order to fully exploit their potential. In parallel, new material processing techniques such as 3D printing technologies are emerging for the fabrication of macroscopic highly engineered parts and devices. In this work, newly discovered silica nanocages are combined with digital light processing 3D printing technique for the rapid fabrication of mesoporous parts with arbitrary shapes and tunable internal structures. Complementary strategies are then deployed for the implementation and deliberate positioning of various functionalities throughout 3D printed objects with high control on the microstructure and macroscopic architecture of the superstructures. This approach paves the road for innovative device concepts and designs, that will benefit from the unique properties of nanomaterials and from the micro- and macroscale manufacturing capability of 3D printers.

Water contamination, either chemical or biological, is one of the main problems for public healthcare in many parts of the world. Contaminated water is a source of a great number of diseases caused by pathogens or by chemical agents. Many techniques are available to improve water quality, but in many cases these methods are not entirely environmentally friendly. Current research efforts are directed toward the use of harmless substances and safer methods. From the pathogens control point of view, silver is one of the most used non-antibiotic agents. Regarding chemical pollutants elimination, one of the most promising techniques is photodegradation mediated by titania (TiO₂). This material photocatalytically generates reactive radicals able to oxidize pollutants upon exposure to an electromagnetic radiation. Functional layers of silver and titania can therefore be used to provide efficient water remediation.

An interesting approach consists in manufacturing multifunctional materials that exhibit both antimicrobial and photocatalytic activities. A fabrication technique able to yield this type of materials is electrolytic codeposition of particles with metals or alloys [1]. For example, thanks to this wet deposition technique, a matrix of silver with embedded titania particles can be easily obtained. The final composite layer exhibits both antibacterial and photoactive properties. Water cleaning possibilities can be further expanded if the antibacterial and the photodegradation action is performed by microdevices covered with silver/titania composites. An example of such devices are the so-called microrobots [2], which can be wirelessly guided using magnetic field and placed exactly where the water decontamination action is needed. Examples of microrobots presenting photocatalytic [3] or antimicrobial activity [4] are available in literature, but none of them combines these two actions on the same device.

The aim of this work is the realization of cylindrical shaped microrobots combining biokilling and photodegradation thank to the presence of a bifunctional composite on their surface. Such microrobots are produced using 3D printing, more specifically microstereolithography, and are subsequently metallized using wet techniques. Two functional layers are applied on the surface of the 3D printed device: a CoNiP magnetic alloy and an Ag/TiO₂ composite. The first makes possible the movement of the device under the influence of an external magnetic field, while the latter imparts the biocidal/catalytic activity to the device. We demonstrate that these devices exhibit antimicrobial activity toward methicillin resistant Staphylococcus aureus bacteria. Moreover, from the pollutants removal point of view, we prove that they can efficiently photodegradate a model molecule like rhodamine B when exposed to ultraviolet radiation.

[1] M. Musiani, Electrochim. Acta 45(20), 3397-3402 (2000)
[2] Nelson et al., Springer Handbook of Robotics, pp. 411-450 (2008)
[3] Musthaq et al., Adv. Funct. Materials 26(38), 6995-7002 (2016)
[4] Hoop et al., Adv. Funct. Materials 26(7), 1063-1069 (2016)

The double network concept has been revolutionary in its ability to turn soft, brittle hydrogels into tough, robust materials with mechanical properties that match the best synthetic elastomers. Double network hydrogels consist of two interpenetrating networks, where each network has a specific mechanical response: the “first network” acts as a sacrificial network, consisting of a rigid, extended network, and the “second network” is a globally percolated, stretchable network. When a double network hydrogel is stretched, covalent bonds of the first network break, dissipating energy; this process continues with increasing strain, until the sacrificial network is completely broken and the second network ruptures. The goal of this research is to demonstrate that the “sacrificial bond concept” is applicable at length-scales beyond the molecular scale. We aim to incorporate this design concept universally for application in structural and medical devices.

Like double network hydrogels, our system consists of a rigid “first network,” 3d printed polyurethane/polyacrylate grids, embedded in a soft and stretchable “second network,” silicone rubber. We found that when the strength of the matrix exceeds the strength of the grid, local fracture occurs in the grid, and stretching is isolated to the rubber in the fractured region. As stretching increases, the force increases, and when the local force exceeds the global strength of the grid, fracture will occur elsewhere in the composite. This process continues sequentially throughout the sample until all grid fracture sites are exhausted, and the matrix ruptures. By tuning the stiffness of the grid, we can independently control the yield strength and fracture strain of the composite, until a point where the grid strength exceeds the matrix strength, and the multiple fracture process no longer occurs.

We also systematically studied the interfacial interactions between the matrix and the reinforcing grid. Both interfacial adhesion as well as topological interlocking are important towards developing a robust composite. By adhesive interactions alone, only minimal fracture of the reinforcing phase occurs; topological interlocking is required to maximize fracture. Based on this result, we systematically change the grid size to modify the number of fracture events. In the optimized form, an increase in work of extension of ~50% over the neat matrix was achieved, representing a ~70% toughening efficiency versus the calculated maximum toughness. These results demonstrate that macroscale double networks can dramatically increase the toughness of soft materials.

Hydrogels represent a class of engineering materials that have great promise for integration within the human body; particularly by optimising and functionally grading their biophysical and biochemical properties. The ability to construct complex architectures through 3D printing is now common place but introducing the ability to transform a planar architecture into a new configuration once manufactured opens up the potential to minimise manufacturing complexity but maximising the design potential. This presentation will detail our latest design thinking utilising a multifunctional materials design methodology and 4D printing research for producing a diverse range of complex architectures utilising thermoplastic and hydrogel trilayer constructs. This unique methodology permits the viable construction of dynamically robust and complex bilayer and trilayer origami architectures for a new generation of active structures. In our study the resulting creations transform from flat 2D parts to 3D structures through submersion in water and return to their original configuration through dehydration. This technique uses commercially available materials and printers to enable a controlled and predictable actuation method that is more accessible and affordable than previous examples of hydration triggered 4D printing. We show the ability to create tessellated origami patterns, such as the Miura-ori origami fold pattern and the waterbomb configuration; the latter being a design that has not previously been realised with 4D printing. These new designs demonstrate how the integration of multiple trilayers into a single 3D print enables through-thickness control of actuation resulting in the formation of active structures with complexity beyond what has previously been achieved with 4D printing. The research will now be extended by the generation of curved-layer morphing origami architectures (i.e. individual layers with variable z-component actuation) to enable selective structural buckling; the generation of tubular bilayer/trilayer architectures; and, the generation of sequential actuation through the addition of porogens (i.e. dissolvable particles used to create porous hydrogel structures) such that the rate and magnitude of actuation can be further programmed in the design phase.

While human tissues and organs are mostly soft, wet and bioactive; machines are commonly hard, dry and biologically inert. Bridging human-machine interfaces is of imminent importance in addressing grand societal challenges in health, security, sustainability, education, and joy of living. However, interfacing human and machines is extremely challenging due to their fundamentally contradictory properties. At MIT Zhao Lab, we propose to harness “extreme hydrogel technology” to form long-term, high-efficacy, compatible and seamless interfaces between humans and machines. In this talk, I will first discuss the fundamental mechanisms to design extreme properties for hydrogels, including extremely tough, resilient, adhesive and anti-fatigue, for long-term robust human-machine interfaces. Then I will discuss a set of novel hydrogel technologies, including i). hydrogel bioelectronics capable of electro-opto-fluidic interrogating single neurons and continuously monitoring gastric physiological conditions over the long term; ii). tissue double-sided tapes that give instant strong adhesion of wet tissues and devices. I will conclude the talk with a perspective on future human-machine convergence enabled by extreme hydrogel technology.

Synthetic polymer hydrogels as soft-wet materials, consisting of three-dimensional cross-linked networks and a large amount of water (50–90%), possess many unique properties such as swelling/deswelling, stimuli-responsiveness, shock absorption, and low sliding friction, making them as potential excellent biomimetics for substitution of soft living materials. However, conventional hydrogels often suffer from weak mechanical properties, which greatly limit their extensive uses for many other applications. In this talk, we will present different design strategies to prepare tough and multifunctional hydrogels with unconventional polymer network architectures and extraordinary properties. Guided by our design principle, we will demonstrate different hydrogels with high mechanical properties, self-healing, actuation, antifouling, and/or wound healing to mimic cartilages, artificial muscles, and mussel-inspired glues. In parallel, molecular simulations will be presented to given atomic-details of structure-properties relationship. Finally, several unique aspects for future development of tough hydrogels will be suggested.

Dynamically crosslinked hydrogels received increasing interest for their adaptive mechanical behaviors under stress and deformation and wide applications for cell scaffolding and delivery. We present a new concept of modulating the dynamics of hydrogel systems crosslinked by hydrazone bonds via a biocompatible organic catalyst. The catalyst accelerates the exchange kinetics of hydrazone bonds for over two orders of magnitude, resulting in identical network structure with widely tunable viscoelastic behavior. The catalyst control of network dynamics enabled quantitative and unambiguous correlation between the network parameters and mechanical properties of dynamic polymer networks, which can be generalized to provide design principles to engineer their viscoelastic properties. We also applied this system for 3D bio-printing to modulate the dynamic properties of hydrogels at different time points of application to have both high injectability and high stability. The incorporated catalyst enhanced the exchange of dynamic crosslinks to achieve high injectability during printing process, but rapidly diffused away from the hydrogel after ejection to retard the exchange and improve the long-term stability for cell culture.

Soft robots can be untethered by carrying a chemical fuel of pneumatic actuators. However, it has a fundamental design restriction; the fuel pressure should be higher than the actuator pressure to transport the fuel. Given that the fuel part occupies most of the volume, the robot becomes pressurized as much as the actuating pressure and requires stiffer materials for the fuel part, making entire robots stiffer. Here, inspired by the pit in plants, we decouple the pressures of the fuel part and the actuator while providing a fuel against the pressure gradient by introducing an isolator between them, thereby liberating from the design constraint. This isolator consists of a hydrophilic nano-porous membrane made of a hydrogel and a micro-porous wall made of a nylon mesh, that correspond to the pit membrane and the cellulose wall at the pit respectively. The mechanical integrity of the structure according to the geometry is studied by finite-element analysis to establish a design rule and the pneumatic power is extensively characterized experimentally with various parameters. Finally, the isolator is implanted to the conceptual soft robots to demonstrate the merits of the isolator.

Surfing is an iconic sport that is extremely popular in coastal regions. Current surfboard fin manufacturers produce high end products using an expensive injection moulding process to create hydro-foil shaped fins. This process, however, does not allow for easy customisation or rapid prototyping.

Hydrogels are smart and multifunctional materials with a real potential for use novel
applications including soft robotics, (edible) sensors and bionic implants. Consisting of a highly swollen polymer network, hydrogels are typically soft and brittle meaning they are not compatible with many traditional techniques used to process materials into structures.

I will demonstrate a variety of (extrusion-based) 3D and 4D printing techniques for processing soft materials (hydrogel inks) alongside other inks of structural polymers to create composite architectures including a smart valve, an artificial cartilage meniscus, an artificial tendon, brain-like structures, edible electronic circuits, stretchable devices, soft robotic devices and edible/living hydrogels.

I will discuss the development of surfboard fins (a hard material) using a performance feedback loop. This loop involves the unique combination of computational fluid dynamics, computer aided design, 3D printing of hard materials, stiffness/flex testing, ocean testing (surfing the waves), embedded sensors / wearables, the Internet-of-Things, and surfers’ perceptive experiences.

Time permitting I will finish my talk with our progress on measuring the mechanical flex behaviour of surfboards, including vibration analysis.

Insects adopt phenolic molecules as molecular cross-linkers that tether internal proteins and/or polysaccharides (such as chitin) to form mechanically strong cuticles functioning as protective armor. The tethering mechanism is triggered by ambient ‘oxygen’ which induces oxidative polymerization between the phenols and the amine-based polymers (proteins or chitin) at the air/water interface. Motivated by this mechanism, we designed a new type of 3D printing system that can be controlled by an unusual external stimulus, ‘oxygen’. The ink for 3D printing is a mixture of pyrogallol (representative phenol), polyethyleneimine (amine-rich polymer), and a scaffolding material. It is initially fluid but immediately hardened after extrusion. By adjusting the air/water interfacial rheology, we were able to control the ink to be cured in 1 second in ambient air conditions. This was a suitable condition for the material to be stacked without falling. The advantage of this 3D printing system is material independence. Activated carbon has been applied to the system to print conductive 3D objects for demonstration, but it can be applied virtually to any colloidal materials on demand.

Multi-material, layer-by-layer additive manufacturing approaches provide a route to the fabrication of complex, structured, and multi-functional composite materials. These composites can be applied in many spaces, including using biomaterials for tissue scaffolding, zeolites for reversible gas capture, and various stimuli-responsive materials for a range of sensing applications.

Here, we present examples of additively manufactured multi-functional materials, including co-printing of conductive and non-conductive adsorbent paste formulations using a direct-ink writing approach to produce devices capable of performing thermal-swing reversible CO₂ capture and release. These printable composites show gas adsorption characteristics in-line with what is expected from the bulk material. Additionally, when an external potential is applied, the printed composites resistively heat to sufficient temperature to desorb captured CO₂. This potentially enables reduced mass and complexity, as well as in-situ manufacture for life-support systems in remote, enclosed, off-planet environments.
This approach is further extended beyond the two discrete materials described above through the integration of inline mixing hardware. Multiple pre-functionalized inks were combined within a print head to enable digitally controlled continuous gradient blending of several different functional materials in order to deposit a programmable multi-functional composite. Components of varied resistivity across a spatial region are demonstrated allowing a high degree of thermal control to be achieved post print. This enables the coupling of desired thermal effects to specific chemistries in the design phase to optimize devices for performance, as well as energy efficiency. This is a key step to unlocking the higher potentials of simulation and multiscale modeling approaches used in prototype design.
Finally, implementation of basic closed-loop analysis of the deposition of these multi-functional materials was studied, by including in-line electronic and optical metrology tools on the print platform. By taking account of the specific effects of additive manufacturing processes, such as spatial resolution and geometry, on-the-fly design optimization is achieved, allowing for the degree of ink functionality to be measured and calibrated. This technique should be applicable to a wide range of functional inks thus unlocking the ability to rapidly prototype parts optimizing for multiple complex physical/chemical properties.

Additive Manufacturing (AM) is nowadays employed in a wide range of industries utilising various materials alongside constant developments in terms of geometrical complexity. However, in addition to exploiting geometry, a multi institutional and multi industry project [1] seeks to augment these products three-dimensional functionality through the co-deposition of both functional and structural materials contemporaneously. Material jetting is key for developing such next generation multi-material/multi-functional AM due to their ability to jet a wide range of materials from polymers, to inks containing metal nano particles (MNPs). In recent years, the use of inks containing silver MNPs has been explored for printing multi-material 3D objects by means of contemporaneous in-situ curing of a polymer and sintering of MNPs using near infrared (NIR) or ultraviolet (UV) light that is absorbed by the NP, triggering their sintering process [2, 3]. As a consequence of their high surface-to-volume ratio, silver MNPs are sintered typically at 120–200 °C, which is as low as 20% of the melting temperature of the metal [3]. Such an advantage enables the printing of metal structures on flexible polymer substrates such as PET or polyimide [4]. A common problem involving low temperature inkjet printing of MNPs is poor conductivity of 3D printed structures and the reason for such problem may lie on the chemistry and morphology evolution during the low-temperature sintering process. Past works have reported conductivity change as a function of annealing temperature and related it to morphological changes [2, 3], however, none has carried out a thorough chemical characterisation of these printed materials. This work describes the development of a protocol for assessing, chemically and morphologically, the sintering process of 3D printed silver nano-particles under different sintering conditions and strategies. Single-layer silver samples were produced by inkjet printing a commercial MNP ink and sintering at different temperatures and high specificity, surface sensitive techniques (time-of-flight-orbitrap secondary ion mass spectrometry - ToF-Orbi-SIMS and X-ray photoelectron spectroscopy – XPS) were employed to track chemical changes. Ambient scanning electron microscopy (SEM) has also been carried out to track in-situ morphological changes in function of sintering temperature.

[1] “Enabling next generation additive manufacturing” http://gtr.ukri.org/projects?ref=EP%2FP031684%2F1
[2] Saleh, Ehab, et al. "3D inkjet printing of electronics using UV conversion." Advanced Materials Technologies 2.10 (2017): 1700134
[3] Vaithilingam, Jayasheelan, et al. "3-Dimensional inkjet printing of macro structures from silver nanoparticles." Materials & Design 139 (2018): 81-88.
[4] Zhang, Fan, et al. "Reactive material jetting of polyimide insulators for complex circuit board design." Additive Manufacturing 25 (2019): 477-484.

Arming nanoelectronics with mobility and self-awareness opens new opportunities in macromolecular science. Originally referred to as electronics based on chemically synthesized nanostructures, nanoelectronics today can also be fabricated following conventional top-down approaches that scale with Moore’s law. Although the subject has been studied intensively for the past two decades and finds application in a variety of disciplines from computing to energy generation, examples of nanoelectronics with mobility and on-board logics remain elusive. As an emerging paradigm that calls for several scientific and engineering disciplines to work in unison, it is necessary to establish a strong narrative that sets the field apart from similar concepts with explicit, unambiguous functions. In this context, I will discuss how the growing library of 2D-soft material composites, with the suite of exotic properties they command, has facilitated the symbiotic engraftment of electronics onto mobile colloidal particles,^[1] thus paving the way towards next-generation microrobotics with both low energy consumptions as well as complex functions.^[2]

I will focus on our recent efforts in synthesizing such 2D-macromolecular heterostructures, using a novel fabrication technique named autoperforation, owing to the spontaneous perforation of the grafted 2D materials around a pre-designed polymer template.^[1] This method lay the foundation of building the proposed colloidal state machines. We have demonstrated, for the first time, that nanoelectronic devices can be grafted onto and/or embedded within colloidal microparticles, creating autonomous machines capable of complex operations in a particulate form.^[1] The characteristic mobility of a colloidal system integrates seamlessly with the modularity that comes with modern digital electronics, enabling information collection and recording in enclosed spaces – such as the human gastrointestinal (GI) tract,^[1] microfluidic channels, and chemical/biosynthetic reactors – as well as remote locations like oil and gas conduits, waterbodies, soil, or the atmosphere.^[1] Ultimately, we envision an intelligent colloidal microrobot that collects, manipulates, and stores information autonomously, extending electronic systems into traditionally inaccessible environments.

[1] Liu, A. T.^†; Liu, P. ^†; Kozawa, D.; Dong, J.; Yang, J. F.; Koman, V. B.; Saccone, M.; Wang, S.; Son, Y.; Wong, M. H.; Strano, M. S.* Nature Materials 2018.
[1] Liu, A. T.; Hampel, M.; Yang, J. F.; Pervan, A.; Koman, V. B.; Zhang, G.; Kozawa, D.; Murphey, T. D.; Palacios, T.; Strano, M. S.* Nature Reviews Materials 2019.

Soft materials capable of transforming between three-dimensional (3D) shapes in response to stimuli such as light, heat, solvent, electric and magnetic fields have applications in diverse areas such as flexible electronics, soft robotics and biomedicine. In particular, magnetic fields offer a safe and effective manipulation method for biomedical applications, which typically require remote actuation in enclosed and confined spaces. In this talk, we will present ferromagnetic soft robots capable of untethered remote actuation, model-guided design, and AI-based control. We fabricate the soft robots by 3D printing the soft-robot bodies together with programming ferromagnetic domains in the robots. We develop a physics-based model capable of quantitatively predicting the deformation of the robots under applied magnetic fields. Based on the model, we obtain a massive amount of simulation data of various applied magnetic fields and deformed configurations. By training deep neural networks with the simulation data, a machine-learning algorithm is further developed to autonomously navigate the soft robots in complicated environments such as vascular systems. We will demonstrate multiple previously-inaccessible functions of the ferromagnetic soft robots, such as autonomous minimally invasive surgeries, enabled by the synergy of 3D printing, quantitative model and AI.

4D printing, i.e. the application of 3D printing technology to stimuli-responsive materials, and in particular to shape memory polymers (SMPs), is gathering large attention among the researches on smart materials. Such an approach would lead to important improvements towards design flexibility, allowing to achieve complex or customized 3D printed structures with externally-triggered shape evolutions. The behavior of SMP-based structures consists in significant dimensional variations occurring when the polymer, after being deformed and fixed in a given temporary shape, recovers its permanent shape thanks to an external stimulus, typically involving heating above specific temperatures [1]. Inspiring aims of 4D printing pioneering works were the realization of active structures based on origami theory and of mechanisms capable of sequential self-folding motions [2].
In order to obtain sequentially moving structures, i.e. structures in which different parts undergo dimensional changes at different times upon the application of the same external stimulus, various approaches may be adopted. Research efforts were mainly based on technological and design tools, as the employ of multi-material 3D printing techniques and the realization of functionally-graded structures [3]. An interesting alternative approach to achieve sequential motions is based only on the material, by employing specific SMP families, as in the case of multiple shape memory polymers (i.e. polymers possessing more than one glass transition or melting temperature) or of polymers featuring the so-called temperature-memory effect. These latter systems, thanks to a broad distribution of the glass transition or melting region, are able to “memorize” not only a shape but also the temperature at which the deformation of the temporary shape was performed, so as to trigger the recovery of the permanent shape at a temperature strictly correlated to the deformation temperature [4,5].
In this work the temperature-memory effect, displayed by a commercial resin, featuring an inherent broad glass transition region, was investigated, with particular interest towards the characterization of the effect and its exploitation for sequential motions of 3D printed geometries. A comprehensive experimental characterization is carried out on simple material specimens and on more complex structures (bars; cubes; self-locking mechanism; reverse-honeycomb auxetic structures) printed by stereolithography. In particular, their shape memory behavior was studied after thermo-mechanical deformation history (or “programming”) properly designed to investigate the material response in case of different deformation temperatures and of multi-step deformation histories. Multiple deformations performed at different parts of a same specimen/structure and at different deformation temperatures enabled in fact the achievement of a controlled recovery process with the presence of distinct and sequential motions. The shape memory response was studied as a function of temperature and in isothermal conditions, these latter being employed to attempt, through the application of a time-temperature superposition scheme, a master curve full description of the time-dependent shape recovery process. The aim is to depict the dependence of the recovery on the deformation temperature both on the temperature and time scales in order to identify best conditions for multiple deformations allowing sequential recovery motions. As a final proof-of-concept and application example, a self-locking clamp was realized and properly “programmed”, so that locking motions were triggered on distinct time scales by the same thermal stimulus applied.

References
[1] M. Behl, A. Lendlein, Mater. Today 10 (2007), 20-28.
[2] Q. Ge et al., Smart Mater. Struct. 23 (2014), 094007.
[3] F. Momeni et al., Mater. Des. 122 (2017), 42-79.
[4] T. Xie, Nature 464 (2010), 267-270.
[5] K. Kratz et al., Adv. Mater. 23 (2011), 4058-4062.

Gallium-based liquid metal nanoparticle inks have shown great potential in creating printed soft and stretchable electronics. Despite their metallic composition, as-printed liquid metal nanoparticles form a nonconductive film because the liquid metal cores of each particle are surrounded by a nonconductive metal oxide shell. Hence, these films require a sintering process to recover their conductivity. Our group previously demonstrated mechanical sintering of liquid metal nanoparticles, although this sintering process put a lower bound on both the size of the particles and softness of the substrate that may be utilized. In this work, we present two thermally involved sintering methods - laser and thermal sintering - to attain conductive liquid metal nanoparticle films. By comparing laser and thermally sintered films with respect to electrical conductivity, surface morphology and elemental composition, crystallinity and surface composition, we reveal the oxide rupture-induced mechanisms that enable electrical conductivity of liquid metal nanoparticles using both methods. We show that thermal and laser sintering under different conditions generate highly conductive liquid, solid or solid-liquid composite films with desired properties that can be used for different applications such as soft robotics, wearable electronics, or broader semiconductor and electronics applications. We also demonstrate high-resolution laser sintered patterns that can be implemented to create high-density electronic devices on soft substrates.

3D printing is an emerging additive manufacturing technology poised to transform both design and manufacturing due to its ability to customize design and generate structural complexity not possible using traditional manufacturing processes. Commercial examples of 3D printed objects using monolithic materials, such as GE’s fuel nozzle, illustrate early success of this technology by enabling new designs and significantly reducing the number of parts and supply chain required for manufacturing. However, only marginal progress has been made to demonstrate multi-material printing and as such it remains a low technology readiness level research endeavour at the moment with enormous potential for innovation and commercial impact. Multi-material 3D printing would increase the complexity and functionality of printed objects and pave the way for 3D structural electronics. The challenge is that most 3D printing techniques cannot print multiple disparate materials into one object. For instance, 3D printing techniques of stereolithography (SLA) and digital light processing (DLP) can generate 3D printed objects with high resolution, high quality surface finish and dimensional accuracy, and it does so using photo-active polymerizable resins as precursor material. However printing objects with functional coatings that are distinct from the core of the object has not been developed. Examples of multi-material 3D structures made from SLA and DLP have been made but the approaches typically result in a composite structure throughout the object and if functional surfaces are desired, this typically involves coating the objects post-printing with functional materials. The drawback of coating post-printing is that it requires multiple steps with different coating apparatus and does not consistently yield coatings with the desired function or robustness, which will depend greatly on adhesion. In this presentation, we demonstrate multi-material printing using SLA 3D printing yielding an object with a functional coating.

Multifunctional metal oxides represent an important class of materials used in modern society. These materials exhibit unique properties such as piezoelectricity,superconductivity, and semiconductivity, rendering them useful in virtually every type of micro/nanosystem device technology. Most current device designs utilize metal oxides as thin film stacks because patterning these materials have mostly been limited to using traditional planar lithography, or various casting methods, which substantially limits the geometries that can be achieved. However, in recent years, 3D printing of these multifunctional metal oxides has become a significant area of interest as new experimental devices that have been able to utilize these 3D materials have demonstrated substantial improvements in performance. While many different techniques have been developed to achieve these architected materials, additive manufacturing (AM) has recently emerged as a frontrunner for the fabrication of three-dimensional metal oxide structures with almost arbitrary geometries.


In particular, additive manufacturing processes involving photolithography have emerged as one of the most promising ones due to the high resolution and small feature sizes achievable. These photolithography systems typically consist of photosensitive slurries, where metal oxide nanoparticles are dispersed in a photosensitive organic binder. The slurry is then patterned using a variety of lithography techniques to create 3D nanocomposite structures, which are then calcined to burn off the organic matrix and to sinter the metal oxide particles together. The advantages of these systems are that it’s simple and versatile – as long as the desired metal oxide nanoparticles can be obtained, the slurry can be made and the part 3D printed. However, the high loading of nanoparticles needed results in a host of other issues, such as increased viscosity, homogenous dispersion of the nanoparticles, and light scattering. To circumvent these, hybrid inorganic-organic photoresins, which contain polymers with metal hetereoatoms in their backbone, have been developed. These photoresins can be patterned and then calcined in the same way to produce 3D metal oxide structures, but without the challenges associated with the inclusion of nanoparticles. A key disadvantage of this approach is that these photoresists are often not commercially available and sometimes require a complex multi-step synthesis. To fabricate arbitrarily shaped 3D metal oxide structures, a process that combines the beneficial aspects of existing approaches: (1) the simplicity and versatility of the slurry method and (2) the high resolution afforded by the organic-inorganic photoresists, has to be developed.


In this presentation, a new photopolymer system that circumvents the problems of both existing techniques is demonstrated. The photopolymer system is facile to prepare and can be easily modified to fabricate various multifunctional metal oxides. As an example of this technique, we demonstrate the printing of a few different metal oxides at a variety of scales by fabricating zinc oxide (ZnO) and lithium cobalt oxide (LCO) architected structures with sub-micron and sub-millimetre features respectively. Characterization of these structures using X-ray diffraction, energy-dispersive spectroscopy and transmission electron microscopy indicate that the structures are indeed comprised of the appropriate material. Compression of the ZnO structures results in a voltage response, exhibiting the piezoelectric behaviour of these structures. Electrochemical cycling of the LCO structures showed efficient performance as a lithium ion battery cathode over greater than 100 cycles. This ability to fabricate these multifunctional 3D materials could open up the field of smart devices and change how we design them.

Nanocarbon-polymer composites offer the advantages of functional electronic response combined with facile processing, thermal stability, and mechanical flexibility. In this presentation, we consider two nanocarbon morphologies, carbon nanotubes and nano-carbon spherical particles, and four polymer matrices, two of which are entirely aliphatic and two of which are rich in aromatic rings. We find that simple current-voltage curves, thermoelectric responses, and perturbations by the oxidizing vapor NO₂ are consistent with the best interconnection and greatest responsiveness associated with carbon nanotubes in aliphatic matrices. In particular, these latter composite types using poly(methyl methacrylate) (PMMA) matrix showed bulk conductivities >1 S/cm and small, concentration-independent Seebeck coefficients <5 µV/K at or below the percolation threshold <5%. At <1% incorporation in epoxy, conductivity was injection-limited rather than bulk-limited, with currents consistent with a 1 S/cm conductivity. Exposure of 1% carbon nanotube-in-PMMA samples to 10 ppm NO₂ resulted in a steady, cumulative p-doping response of about 2% per hour. No such response was observed from nano-carbon spherical particles mixed into PMMA at the same concentration. Insulating polystyrene and semiconducting poly(bisdodecylquaterthiophene) (PQT12) matrices resulted in much lower conductivities with carbon nanotubes, with the polystyrene samples essentially insulating with 1% carbon nanotubes, and PQT12 showing moderate conductivities and increased Seebeck coefficients consistent with significant traps, barriers, and aggregates formed by the carbon nanotubes. The results taken together suggest that moderately polar but nonaromatic matrices yield the highest and best controlled environmental responses from nanocarbon composites.

We report a method to create 3D liquid crystal elastomers (LCEs) that exhibit programmed shape morphing capabilities which can be ‘locked-in’ on demand via dynamic bond exchange. Specifically, we have created printable inks composed of oligomer-based LCEs with main-chain rigid mesogens and allyl dithiol chain extenders. Their programmed director alignment, which is uniquely defined by print path, gives rise to a reversible actuation response when thermally cycled above and below their nematic-to-isotropic transition temperature, T_NI. By incorporating light-activated dynamic bonds, we ensure that the external stimulus for bond exchange is orthogonal to that required for their reversible actuation. When actuated above T_NI, UV light can be used to “trigger” allyl disulfide bond exchange within these printed LCEs in response to the pre-programmed internal stress to “lock-in” their actuated state. Our results offer a pathway towards reconfigurable, adaptive actuators with controlled shape-morphing capabilities and high specific energy density.

Thermoset polymers and composites exhibit excellent specific stiffness and strength, thermal stability, and chemical resistance. However, the manufacturing of high-performance thermosets and composites typically requires lengthy cure times at elevated temperatures, which presents significant challenges for 3D printing. Recently, we demonstrated a technique that combines frontal polymerization (FP) with extrusion-based direct ink writing to simultaneously print and cure neat polymer parts with minimal energy input. This system relies on the ring-opening metathesis polymerization (ROMP) of partially cured endo-dicyclopentadiene (DCPD). Here we expand this approach from the printing of neat polymers to the printing of nanocomposites. We investigate the shear and extensional rheology of nano-inks composed of DCPD monomer and either carbon or silica nanoparticles. From these data, we define a suitable window for direct ink writing in terms of monomer degree of cure and nanoparticle loading. We also use thermal imaging to characterize the FP of printed nano-inks, including front velocity and front temperature, in a variety of printing conditions. Finally, we report on the multifunctional properties of printed nanocomposites, including enhanced mechanical and electrical properties, as well as potential applications based on their multifunctionality.

Electrochemically active bacteria (EAB) such as Shewanella and Geobacter are capable of performing long-range charge transport through a variety of evolutionally developed electron pathways. While these bioderived electroactive systems represent intriguing building blocks for a range of bioelectronic applications, their applications to date are still limited by the lack of effective structural and functional integration at meaningful scales. Here we present our recent effort toward the multi-dimensional assembly of these living materials. Core-shell, EAB-encapsulated hydrogel fibers were manufactured by the multi-inlet coaxial microfluidic devices for 1D assembly. Inside these core-shell fibers, the cellular interactions and microenvironments can be precisely modulated to engineer the developments of the protein-based conductive materials. Based on the results, closely contacted bacteria promote the development of high-density, sub-micron protein structures at cellular interfaces which can be directly translated to the increase of conductivity (16.2 mS/cm) as compared with low-density, micrometer long protein structures generated by the isolated bacteria (6.4 mS/cm). Furthermore, bioprinting was applied to assemble these bacterial cables into functional bioelectrochemical systems, where the 3D structure, including xx, yy and zz, can be programmed and optimized to overcome the intrinsic charge and mass transport limits in native biofilms. The current work represents an important strategy to achieve spatial organization of electroactive living materials with precisely engineered functions and could open up new possibilities to design and construct a biosynthetic functional system from the bottom-up.

Biosensing accuracy suffers from low signal above background at low analyte levels and random variations in sensor performance at higher analyte levels which limit quantitation. Conventional detection schemes, e.g. enzyme-linked immunosorbent assays (ELISA), overcome low analyte level challenges through enzymatic signal amplification, however these assays typically measure the bulk signal from a single or few reactions, leading to compromised detection sensitivity and accuracy. Microfluidics has provided promising tools for uniform compartmentalization of a sample fluid volume into many smaller reactions, however skilled users or specialized and costly commercial instruments are required for implementation. Here, we present a versatile platform to compartmentalize and perform reactions in uniform nanoliter-scale volumes based on the fabrication of microscale multi-material particles (e.g. hydrophobic outer layer and hydrophilic inner layer ring-shaped particles) that form a single droplet per particle with design flexibility of particle structure and droplet shape. Our “dropicle” system provides uniform compartmentalization, customizable shape-coded particle for multiplexing, flexibility to be scaled up, and ease of implementation with existing amplified assay workflows, enabling hundreds to thousands of parallel reactions.

We manufacture the multi-material particles using a 3D printed device to run a hydrodynamically stable co-flow of four different streams of fluids including polymer precursors. The inlet ports of the device are connected using intricate channels such that the outlet flow streams take a cylindrical co-axial shape. Density-matched flow streams consist of Poly(propylene glycol) diacrylate (PPGDA), PPGDA and photo-initiator (PI), Poly(ethylene glycol) diacrylate (PEGDA) and PI, and PEGDA, from the outermost to the innermost stream, respectively. At the device outlet, a square glass capillary is attached to provide a region where fluid streams are exposed to UV source through a patterned mask when the flow is stopped. The two streams with PI are cured into ring-shaped multi-material particles with the inner and outer layers made of PEGDA and PPGDA, respectively. The size of particles are readily controlled by adjusting the fluid-flow rate ratios at the inlets and mask design; whereas the shapes are altered by customization of 3D printed device and mask design for UV exposure.

We have fabricated particles with four distinct cross-sectional shapes and different thickness. These particles with a hydrophilic inner hollow layer and hydrophobic outer layer provide a versatile and scalable platform to form highly uniform aqueous droplets in the center of the particles suspended in an oil phase holding a volume of 1-6 nL depending on the particle design. Capture antibodies for target analyte or other immobilization anchors such as biotin are added to the PEGDA layer during the fabrication process. We successfully implemented an HRP-based fluorescent immunoassay using the dropicle system and demonstrated a limit-of-detection of 10 pg/ml (i.e., 100 fM) with a dynamic range of at least 3 orders of magnitude. Fluorescent-based imaging of the dropicles after reaction enabled both end-point measurements and real-time amplification with simultaneous tracking of large numbers of single particles over time. Furthermore, multiplexing was shown without crosstalk, where two types of particles with different outer polymer shapes and inner droplet shapes maintained their individual fluorescent signals. In addition to be used as a “swarm” of analog assays by correlating fluorescent intensity with target analyte concentrations, our dropicle system is also promising to serve as digital platform by scaling up the number of particles and reducing their size. Finally, signal readout using a portable imager are being explored to extend assay capability to point-of-care settings without relying on expensive instrumentation.

In contrast to sight and hearing, we are relatively weak at recreating the sense of touch. To address this gap, we have conducted several studies to decompose tactile (touch) sensations into their fundamental components, with the goal of recreating arbitrary tactile sensations. Using micropatterned elastomeric slabs of precise thicknesses and psychophysical testing with human subjects, we systematically investigated the role of indentation depth and contact area on the human perception of softness.¹ By decoupling the indentation depth from the contact area, we developed explicit equations to design and tune the perceived softness of haptic interfaces so that, for example, one object feels twice as soft as another. We provide strategies such as designing materials to feel “softer”, while keeping the Young’s modulus constant. These findings provide specifications for designing new materials to interface with the sense of touch and how these materials can be actuated to reproduce tactile sensations.

1. Dhong, C., et al. “Role of Indentation Depth and Contact Area on Human Perception of Softness for Haptic Interfaces”. Science Advances, Accepted.

Conventional microfluidic devices are often limited to enclosed channels and planar geometries, which hinders their usefulness in multiphase reaction or transport processes. We present a novel platform based on capillary fluid flow in three-dimensional open-cell lattices. Using deterministic cell and lattice design and additive manufacturing, we fabricate complex 3D structures with tuned porosity. This approach enables selective placement and direction of liquid flow into predetermined continuous paths through the structure, as well as optimizing the occurrence of gas-liquid or gas-liquid-solid interfaces. We demonstrate the application of lattice fluidics for CO2 capture by incorporating a liquid sorbent into a 3D lattice with high gas-liquid interfacial area. ***This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 within the LDRD program 19-SI-005. LLNL-ABS-778327.

Chitin structures can be found in a variety of organisms in nature and show unique mechanical and optical properties in combination with biodegradability and nontoxicity. One of those species is Penaeus setiferus (King Prawn) with an exoskeleton made of chitin which is conformed in to a bouligand/helicoidal structure that is a photonic crystal. Penaeus setiferus uses this structure mainly to form a strong network as a part of exoskeleton and the optical appearance of the shrimp seems to do not reveal the interesting chiral optics of such organisation. However, when the proteins and calcium minerals were removed from the shrimp exoskeleton, the residual chitin film show quite remarkable iridescent appearance with strong circular polarization. This isolated helicoidal framework is much more porous than the starting material and provides an exciting foundation as a template for exploring chiral photonics using different deposition methods. With the goal of transfering this intricate network, the iridescent chitin shell is used in this study to decorate with metal nanoparticles using wet chemical methods and in a separate study conformally coated with TiO₂ using atomic layer deposition techniques. It is shown that the helicoidal organization of the iridescent shrimp shells can be conformed and transferred in to higher refractive index materials with distinctive macroscopic combination of optical effects.

We are experiencing a global environment under stress and if not ‘capped’, will lead to both a biodiversity failure in addition to global warming and adverse greenhouse gas content in the atmosphere. Looking at natural material design we can see a vast range of intertwined materials and biocomposites performing an enormous and impressive range of tasks, utilising often easily obtained and renewable resources. Biological systems are argued to be superior to technological ones in terms of biology’s utilisation of information and structure over energy and materials. There are many opportunities for biogeochemical cycles to inspire a Design:STEM approach that can simultaneously address the opportunities and challenges created by the global resource and waste crises, greenhouse gas emissions, expanding urban populations and environments, and consumer engagement in environmental behaviours.

As part of our work in BioDesign:STEM Integration, we are examining the role that both biology and botany can play in replacing synthetic single use polymers for plastic packaging of foods, consumer products and luxury items. The paper will outline the choice of bio and phyto materials development and the development of multi component composites that are both resilient, have controlled release and targeted delivery behavioural characteristics, and through an LCA methodology can be reused, refunctioned and recomposted after primary use. We are investigating the creation of a biomimetic yarn drawn from examination of the cross sections of plant stems, where each element is analysed and then substituted for a biomaterial with tailored and enhanced properties.

Natural materials are presumed to have enhanced biocompatibility with humans and, from a financial and timing perspective, provide a good material base for enhancement and modification to fit the current manufacturing methods. Their use allows for aims to include desirable and complex materials properties with biodegradable and biocompatible characteristics, as well as providing the opportunity to identify resources that are naturally abundant, renewable and cost effective. Currently major issues for bio-based packaging are the requirements for water and oxygen barriers and so the project aims include identification of structures, processes and biodegradable materials that can achieve water and oxygen barriers for flexible materials, preferably from a renewable source. Another way to ensure cost-effectiveness and resource sustainability is to use the least amount of material possible through enhancement of material properties and through investigation into structures such as foams. From a design perspective, charismatic effects and aesthetics are being explored through investigations into ideas of elegantly simple, traditionally crafted and overtly natural fabrications concealing a novel, non-intuitive responsive element that adds great functional and experiential value. This interactive behaviour, drawn from our work with thermoresponsive gels, ensures easily repurposable packaging fabrications that engage the consumer. The facile efficiency which the resultant packaging fabrications can achieve serves to inspire the consumer with the potential of natural materials and the natural environment at large.

As a promising candidate for photothermal therapy material, gold nanorods (AuNRs) having high photothermal conversion efficiency, strong absorption and scattering in the near infrared region excellent in biotransparency have been studied. However, one of the problems in practical photothermal therapy application is a burning of organs and/or skin by heating upon light irradiation. Previously, we demonstrated the mechanism which can avoid the overheating even if AuNRs is overirradiated (Autonomous overheat suppression mechanism); namely phase transition of the polymer modified on AuNRs upon heating induced an aggregation of AuNRs and resulted in the shift of AuNRs photoabsorption wavelength [1]. However, in the living body, diffusion of AuNRs is slower compared to that in solution, and rapid aggregation might be difficult. Therefore, in this research, in order to achieve the mechanism of suppressing the overheating of AuNRs itself without involving the change of the aggregation state, we focused on the shortening of AuNRs by the oxidative elution of Au ion from the AuNRs surface [2]. Since the longitudinal absorption wavelength of AuNRs depends on the aspect ratio, the absorption peak will shift to a shorter wavelength by the shortening of AuNRs, and it is considered that the absorption of the irradiation light decreases to suppress the overheating. Therefore, in this study, we studied the shortening temperature of AuNRs depending on the size of modified polymer, in which the density of the polymer coating on AuNRs is expected to change the stability of the Au on AuNRs.
Polymers (RAFT-PEG188, RAFT-PEG500, RAFT-PEG1500) were synthesized by Reversible Addition-Fragmentation Chain Transfer (RAFT) polymerization using polyethylene grycol methyl ether methacrylate (PEGMA) (M_w= 188, 500, 1500) having different ethylene grycol length. After the reduction of the polymers to generate -SH group in the polymer terminate, the polymer solution was added to AuNRs aqueous solution. The obtained AuNRs aqueous solution (PEG188-AuNRs, PEG500-AuNRs, PEG2000-AuNRs) was heated from 35 to 115 °C, and the change of the longitudinal absorption peak upon heating was monitored by UV-vis spectroscopy. A blue shift of the longitudinal absorption peak was observed in the PEG-modified AuNRs, while shift of the longitudinal absorption peak was not observed in the excess CTAB-removed AuNRs (CTAB-AuNRs) measured as a comparison. The peak shift onset time was earlier as the side chain length of the polymer was longer. We found that the onset temperature of the AuNRs with RAFT-PEG2000 was lower than that of AuNRs with RAFT-PEG500.

Conclusion
AuNRs was modified by SH terminated polymers having different side chain length synthesized by RAFT polymerization. Heating experiment of AuNRs solution revealed that the onset temperature of the shortening of AuNRs was lowered when the AuNRs was modified by the polymer with longer side chain. We considered that the lowering of the modification density lowered the stability of Au on the surface of AuNRs, resulting the lowering of the shortening temperature.
References
[1] Shimoda, K.; Fujigaya, T.; Nakashima, N.; Niidome, Y., Spontaneous temperature control using reversible spectroscopic responses of PNIPAM-coated gold nanorods. Chem. Lett. 2013, 42 (10), 1247-1249.
[2] Zou, R.; Zhang, Q.; Zhao, Q.; Peng, F.; Wang, H.; Yu, H.; Yang, J., Thermal stability of gold nanorods in an aqueous solution. Colloids Surf. Physicochem. Eng. Aspects 2010, 372 (1-3), 177-181.

Adhesives are one of essential materials for manufacturing industry, especially for that of composite products. Different kinds of parts made from metals, ceramics or polymers are adhered by adhesives, which contributes to designing, processing, and weight saving. For adhesion of two adherends of dissimilar materials, modification of their surface with laser, plasma or chemicals has been used in general. On the other hand, adhesives having catechol or its analogue moieties have been paid attention, because polymers having catechol moieties show high adhesive strength toward various kinds of aherends. Adhesives of this type are inspired by proteins having DOPA residues in adhesive components of mussels.
2-Mercaptopyridine has a similar chemical structure with catechol, while it is not found in chemical structures of natural proteins. Nevertheless, it has a pyridine ring and a sulfur atom, and these chemical moieties would also interact with kinds of adherends including late transition metals. In this work, a disulfide dimer derived from 2-mercaptonicotinic acid (compound 1) is used as a diacrylate cross-linking reagent for radical UV curing of 2-hydroxyethyl acrylate (HEA). The curing system is applied to photoadhesion of dissimilar materials, which enables to adhere two different substrates quickly and selectively under mild temperature conditions.
Quantitative consumption of acryloyl groups was confirmed after 4 J/cm2 of UV irradiation, by FT-IR spectral measurement (decrease of peak area at 1637 cm-1). The UV-cured products were found to be insoluble to THF. Shear stress of in the range from 0.27 to 1.2 MPa was recorded, and the value for glass was higher than for metals. Triple value for the glass-copper sample comparing with glass-aluminum sample would indicate better interaction of sulfur (and nitrogen) atoms from compound 1 with substrate of late transition metals.
Samples preparing with compound 1 showed much higher adhesive property than the control samples. Shear stress was apt to be kept during extension in the cases of glass-glass samples. This is probably due to hydrophilic interaction between glass substrate and hydroxyl groups of the adhesive layer. Furthermore, the UV-cured adhesive layer was stretched before breaking of the sample. This would be due to exchange reactions between disulfide bonds. On the other hand, the difference was much clear in the cases of glass-copper samples. Cross-linking moieties of compound 1 would contribute to both cohesion in bulk of the adhesive layer and interaction in the interface. Intertacial fracture was observed on the glass-copper sample of compound 1, which the UV-cured residue was remained on the both sides.
To investigate chemical states of the nitrogen and sulfur atoms in the UV-cured glass-copper sample of compound 1, XPS spectral measurements were performed. A model compound for compound 1 had simple spectral charts where a peak at 398.8 eV for N1s and a peak pair at 163.4 eV for S2p were observed. The former peak is assigned to nitrogen atom of pyridine. The latter peak pair is assigned to sulfur atom of disulfide. In the N1s spectra of UV-cured adhesive sample of compound 1, new peaks are observed at 400.5 and 402.6 eV on the side of copper substrate. This indicates that a part of nitrogen atoms of the dipyridyl disulfide moiety from compound 1 would interact with the copper surface. In comparison, new peaks are observed in the lower binding energy region, around 162 eV in the S2p spectra of the adhesive sample. This implies the presence of electron-rich sulfur atoms on the both sides. Although the mechanism for generation of such sulfur atoms is still unknown, these sulfur atoms may contribute to the adhesion via hydrophilic interaction (on the glass side) and coordination (on the copper side).

Chitosan-based coatings turned out to be very promising for the development of sustainable and safe multifunctional systems for the corrosion protection of metal artifacts. A promising strategy to achieve long-term efficacy and specific action against corrosion is represented by the encapsulation of corrosion inhibitors inside stimuli responsive nanostructure. With this aim, herein we investigated the effect of the addition of Layered Double Hydroxides (LDHs) smart nanocarriers on the protective performance of chitosan-based coatings. These systems consist of stacks of positively charged layers between which the inhibitor compound can be intercalated. LDHs act as inhibitor reservoir and allow to control its release only in the presence of corrosion related stimuli, i.e. presence of chloride species and acidic pH. Moreover, these systems are able to slow down the photodegradation of the guest molecules, thus prolonging their protective action. Benzotriazole (BTA) and mercaptobenzothiazole (MBT) were used as inhibitor compounds since they possess a recognized anticorrosion efficiency for different metal substrates. In addition, alkaline nanoparticles, deposited at the coating/metal interface, were used to contrast the acidity coming from the environment and/or produced during corrosion pathways. To assess the efficacy of these nanostructured polymer layers accelerated corrosion tests were performed on the coated and uncoated bronze substrates. The coatings with the inhibitors freely dispersed into the polymer matrix were used as reference. The surface properties of bare alloy and of the alloy with the protective coatings were investigated before and after the accelerated treatments.
The obtained results showed that the encapsulation of inhibitors inside LDHs smart nanostructures allow to achieve a specific action against corrosion and also protect the active molecule from photodegradation, thus improving the stability and the protective performance of the coatings. Alkaline nanoparticles with high surface area and reactivity to acids are also able to provide a local buffer action against pH changes at the metal surface, further enhancing the corrosion resistance of the system. It is worth noting that the developed protective materials possess better performance compared to commercial products based on acrylic resins and are also easy to be applied and removed by using not toxic (water-based) solvents.
The multifunctional active coatings containing LDHs smart nanocarriers, corrosion inhibitors and alkaline nanoparticles guarantee a long-term, safe e sustainable protection of metal works of art exposed to indoor environment conditions. These systems combine different functional capabilities: the physical barrier properties of the polymer matrix and the UV/light shielding action of the inorganic fillers, the stimuli responsiveness of the smart nanocarriers and the chemical protective action of corrosion inhibitors.
This research activity has been carried out within the EU H2020 Nanorestart project “NANOmaterials for the REStoration of works of ART” and has also received the “Young Investigator Award 2018” prize in the area of Chemistry for Cultural Heritage from the Department of Chemical Science and Materials Technology (DSCTM) of the Italian National Research Council.

The ability to convert an electrical field into a mechanical perturbation and vice versa makes piezoelectric materials versatile components for industrial applications in a range of fields covering vibration control in airplanes, ultrasound applications in marine and medical devices or pickups for musical instruments [1].
In recent years, the value of piezoelectric materials for biomedical applications has been unfolding [2-4]. They can act as self-sustained suppliers of charge for nerve and bone tissue repair or as autonomous in vivo energy harvesting components powering electronic implants. Depending on the specific application, biocompatibility and stable performance in the presence of body fluids determine a materials potential for the task. In some cases, it is necessary that living cells form a close interface with the implanted material and when hard- and/or soft-tissue integration of the implant material is desired, a piezoelectric implant that provides large, open pores allowing the ingrowth of cells and blood vessels, provides a clinical benefit.
The potential areas of application for piezoelectric materials in the biomedical context are manifold, but for their transfer into clinical routines safe and reliable functionality has to be ensured. A fundamental step on this way is to clarify the influence of the rather unusual biochemical boundary conditions of the body as well as the standardized pre-surgery handling routines on chemical and functional stability of the materials.
We have been investigating two promising piezoelectric ceramic systems – BaTiO₃ and (K,Na)NbO₃ - regarding their potential as functional implants due to their low degree of cytotoxicity. Microstructural features, such as grain size and porosity, influence the dielectric and piezoelectric performance. While a high degree of open porosity is necessary to allow tissue integration and the development of a stable tissue-implant interface, it can be detrimental for the piezoelectric properties. This can be counteracted by grain size adaption allowing optimization of the materials functionality.
The fluidic environment at an implant site triggers chemical interactions that can influence the implants surface chemistry, functionality and reliability. This is especially important for porous materials providing a large surface to volume ratio. The sensitivity of the functional properties on soaking differs significantly for the two systems investigated. This holds promise that both long-term stable as well as bioresorbable compositions can be developed.
Apart from reliable functional performance and low cytotoxicity, compliance with pre-surgery routines has to be guaranteed, to transfer a novel material from the lab bench to the surgery room. We investigated the impact of disinfection routines and plasma sterilization on the piezoelectric performance of both material systems. The distinct differences between them are correlated to their Curie temperatures and their electromechanical response.

References
[1] J. Rödel, et al., J. Europ. Ceram. Soc. 35 (2015) 1659.
[2] A. Marino, et al., ACS Appl. Mat. Inter. 9 (2017) 17663.
[3] A.H. Rajabi et al., Acta Biomat. 24 (2015) 12.
[4] F.R. Baxter, Ann. Biomed. Eng. 38 (2010) 2079.

Harvesting electronic energy from biomechanical motions of a living body is important for health monitoring and biomedical applications. Most tissue surfaces are inherently soft and constantly in motion. Piezoelectric devices enable new electromechanical interfaces with human tissue for monitoring motion signals. However, the electronic devices should be ideally soft and conformal to the tissue surface. Silk protein is one of the finest biopolymer with intriguing properties such as softness, biocompatibility, flexibility in thin film form, and potential to fabricate wearable and implantable electronic devices.
Herein, we present a stretchable, bendable, and biocompatible piezoelectric nanogenerator using silk protein and ZnO nanorods (NR) to monitor and harvest electrical energy from biomechanical motions. Silk protein without ZnO NR produced an open-circuit voltage of ~1.5 V and a short-circuit current of ~5 nA. With the incorporation of ZnO nanorods into silk protein matrix, the output electrical performance is enhanced 8-fold (open-circuit voltage of ~12 V and a short-circuit current of ~0.04 μA). Due to the noncentrosymmetric structure in the wurtzite form and large electromechanical coupling of ZnO, it can produce large piezo-potential in the crystal under strain condition thus lead to higher output performance for ZnO-silk devices. With this high output electrical performance, it can activate small power consumed commercial electronic device (stop-watch). Owing to the softness and stretchability of the devices, they can be contacted conformally to the biological tissue to generate an output voltage of ~7 V from the tissue motions. The study indicates the potential use of biocompatible ZnO-silk devices in harvesting the power from the human body and tissue motion that may be provide an alternative power source for implantable biomedical devices.

Controlled or sustained release of a drug from nanfibrous patches provide flexibility in site specific delivery and the ability of triggered release based on a feedback control. Electrospun submicron and nanofibers have the ability to carry the required drug payload and can serve as a flexible implant particularly when the fibers are made from FDA approved biodegradable materials. However, the proper formulation of the drug-polymer composite and the ability to control their release require a better understanding of the polymer-drug interaction which would determine the kinetics of release.
Mechanism of drug release can also be influenced by the intrinsic properties of the encapsulated drug, such as its molecular weight, hydrophobicity and the drug-polymer formulations. In these cases, the choice of the polymeric matrix and method of electrospinning, play a crucial role in the final release pattern. In the same vein, combining electrospinning with other fabrication techniques, can provide a multifunctional property as well as various means of control over the release mechanism of the enclosed drug.
As a first step we focused on electrospinning process parameters namely flow rate, applied voltage and capillary to collector distance. The voltage field and combination of the polymer/drug and solvent concentration that determines the viscosity, surface tension and electric conductivity were evaluated to obtain the proper fiber morphology with the drug blended in it. We have demonstrated that by applying proper means of control, various stages of drug release can be manipulated, such as initial burst release, final plateau stage and on demand release. Control over the initial burst release of the drug, was applied by controlling the diameter and morphology of the obtained fibers, as well as the level of dispersity of the loaded drug. Meanwhile, the sustained release of the drugs were manipulated by choosing the proper polymeric matrix with appropriate disintegration time. Finally, on demand release of the loaded drugs were investigated by utilizing combinatory techniques with electrospinning.
In this study, we have evaluated the influence of polymer choice with different molecular weights ranging from 40,000 to 240,000 (PLGA 50:50, PCL, PLGA 85:15) , morphology of the electrospun polymers, and the combination of various technique with electrospinning, for obtaining desired release mechanisms of three hydrophobic drugs, namely biphenol containing small molecule cancer drug, Honokiol, and peptide based, nitroxide radical containing antioxidants JP-4-039 and XJB-5-131,with different molecular weights, from 200 to more than 900. Drug release is characterized through first order burst release followed by controlled release over time using various techniques. Our choice of drug was driven by their applications. XJB and JP are mitochondrial targeting antioxidants being explored for the treatment of cardiac recovery post myocardial infarction. Honokiol is a natural drug being tested for kidney cancer. Sustained and controlled release locally from patches would be beneficial for these drugs. The effectiveness of each polymer used and combinatorial technique, in providing various spatiotemporal control over the release of the aforementioned drugs have been demonstrated.

In this work, we demonstrate poly(3-hexylthiophene) regio-block copolymers (block-P3HTs) that show both great electrical performance and mechanical robustness. block-P3HTs are composed with crystalline regioregular block (rre block) for providing efficient charge transport and the amorphous regiorandom block (rra block) for flexibility. To clarify the architecture effects of block-P3HTs, a series of block-P3HTs was prepared to have similar number-average molecular weight (M_n) of rre block with different M_n of rra block, while the regioregularity (RR) of each block are the same. The hole mobility (µ_h) of all the block-P3HTs are comparable high because the rre blocks confined with the rra blocks provide efficient crystalline domains resulted in fast charge transportations. Especially, the highest µ_h (1.5 × 10^-1 cm² V^-1 s^-1) is obtained in block-P3HT, rather than rre P3HT. The mechanical robustness of block-P3HTs are highly improved with the higher M_n of rra block. The elongation at break of block-P3HT finally reach at 100 times higher values than that of brittle rre P3HT. The study of block-P3HTs serves an efficient strategy of organic active materials for the coexistence of electrical performance and mechanical robustness.

On-demand drug delivery devices (DDDs) have been widely investigated for spatiotemporally controlled therapy with greatly improved patient compliance. However, the power system to operate the DDDs is still a serious limitation, constraining their clinical applications. Here, we developed implantable solar cells using upconversion nanoparticles (UCNPs) for on-demand controlled DDDs. Although skin-penetrating near infrared (NIR) light cannot be used for flexible organic solar cells, UCNPs can convert NIR light to visible light for their operations after implantation to the body. We designed the UCNPs of NaYF₄:Yb/Er@NaYF₄:Yb, which were doped on flexible organic solar cells [PEN/ITO/ZnO(ETL)/Pbdbt:itic(active layer)/MoO3(HTL)/Au]. They could generate current flow upon NIR irradiation and used for on-demand DDDs based on the gold (Au) dissolution to AuCl₄^- by the applied electrical current. The on-demand DDD was fabricated with a SU-8 photoresist on the flexible polyethylene terephthalate (PET) substrate. After that, the on-demand DDD was interconnected with the UCNP coated flexible organic solar cell and passivated with a flexible PET substrate. The successful fabrication of NIR-triggered implantable DDDs was confirmed by TEM, SEM, photoluminescence and absorbance spectrum, current density-voltage (J-V) characteristics, and drug release tests. This new paradigm on-demand DDD might greatly contribute to the progress of light-triggered medical devices and the relevant phototherapy.

One of the biggest challenges in stretchable electronics is to achieve high-performance stretchable semiconductors. Here, we introduce an innovative concept of nanomeshed semiconductor nanomembrane which can be regarded almost as intrinsically stretchable to conventional microelectronic layouts. The nanomembrane is a dense network of fully connected, high quality, inorganic semiconductor traces of nanoscale line width. By making a silicon film into homogeneous nanomeshes with spring-like nano traces from a lift-off and transfer process using a Si-on-insulator (SOI) wafer, we demonstrated a high electron mobility of 50cm²/Vs, and moderate stretchability with a one-time strain of 25% and cyclic strain of 14% after stretching for 1000 cycles, further improvable with optimized nanomesh designs. A simple analytic model covering both fractional material and trace sidewall surfaces well predicted the transport properties of the silicon nanomesh transistors, enabling future design and optimizations. Besides potential applications in stretchable electronics, this semiconductor nanomesh concept provides a new platform for materials engineering and is expected to yield a new family of stretchable inorganic materials having tunable electronic and optoelectronic properties with customized nanostructures.

Unmanned aerial vehicles have received tremendous attention for potential use in various real time intelligent systems. Also, many people use these kinds of systems for their hobbies and business using autopilot technology. Due to the increase in number of unmanned aerial vehicles, several accidents happened in recent years due to loss of control. To solve this problem, researchers mimicking the dragonfly wings. Dragonfly gets attraction due to its rapid acceleration, rapid turning, hovering. Therefore, development of a microminiature flying object that imitates the shape and flight method of the dragonfly is being promoted. However, there is a problem with the miniaturized dragonfly type vehicle currently under development. It is said that, the attitude of the projectile becomes unstable and falls when taking off. Thus, continued flight is difficult. Therefore, to maintain the attitude of the flight, wings pressure needs to be precisely monitored without adding much weight to the wings. Hence, this research work is focused on developing lightweight, thin and ultra-flexible P(VDF-TrFE) nanosheet based pressure sensor. Spin coating and thermal evaporation technqiues were used to prepare nanosheet and contact electrodes. Finally, bulge tester was used to apply pressure to the nanosheet and evaluated the electro motive force (emf). Also experiments were performed with various thickness of P(VDF-TrFE) to identify the desired pressure sensor with high capability.

Regenerative medicine, which has been extensively studied in recent years, requires a large amount of cells. Therefore, development of a method for efficiently culturing cells is actively promoted, and a three-dimensional culture method is attracting attention. In the efficient culture method of cells, it is not only just culture of a large amount of cells, but also efficiently collecting cells cultured in a large amount without damaging the cells is also an important issue.
A cell culture substratum for controlling the culture and recovery of cells by changing temperature has been studied as one of the efficient culture methods, but many conventional cell culture substratum having temperature responsiveness are limited to use in two-dimensional cell culture (e.g. flat culture), and there are few reports that can be applied to three-dimensional (3D) cell culture (e.g. suspension culture). Therefore, in this study, we performed the preparation of a thermally reversible liquid culture medium composition that is possible to culture cells three-dimensionally in a floated state at 37°C and further to be easily recovered cells without damaging the cells in a room temperature, and then we developed novel 3D cell culture method using the medium composition. The preparation of the medium composition was performed by blending xyloglucan from which galactose residues was partially degraded byβ-garactosidase into a basal liquid medium at a specific concentration. By using the medium composition, (1) cells can be preferably cultured in a 3D state maintaining liquidity at temperature over the sol-gel transition point, and (2) it has been found that the cells and the medium composition can be efficiently separated at temperature below the sol-gel transition point.

In this study, we propose a new system concept of 3D-printed modular compliant bipolar electrostatic chuck for handling large film. The prototype of the system consists of 3D-printed modules of bipolar electrostatic chuck with surface flexibility by collective elastically-deformable beam structure. The proposed system is expected to effectively grip thin film-like objects because the compliance avoids any excessive stress which results in damage of target objects. The module performance was experimentally evaluated to investigate influence of beam compliance on attractive force to a target object.
New handling techniques of large thin film/textile materials such as polymer films and papers have been required to manufacture devices using Organic Electro-Luminescence and many other applications. However, conventional electrostatic chucks cannot handle those objects because they typically aim to handle flat and hard wafer in semi-conductor fabrications. Recently, our research group has been developing compliant bipolar electrostatic chucks. Previous researches validated a concept of module of bipolar electrostatic chucks with surface flexibility by collective elastically-deformable beam structure, which has been prototyped by 3D-printer. In addition, other studies shows that the attractive force is greatly increased by smoothing the beam tips. As a next step toward handling large film, it is necessary to increase effective area of attractive surface of grippers. Therefore, this research proposes stacking the modules by layers for that purpose and investigate influence of stacking the modules on attractive force.
For proof of the concept, the authors developed two types of bipolar electrostatic chuck modules which have either high or low compliant beams. By stacking five each of those modules by layer, we synthesized a compliant bipolar electrostatic chuck having 3D-printed elastically-deformable beams for handling large film. We determined the maximum attractive force per unit area of each of the single modules and the stacked modules by obtaining force curves for glass surface.
Both modules have 3D-printed beam structure and consist of four-sublayer (conductor-insulator-conductor-insulator) structure. The outer insulation layer prevents the beams from contacting each other and energizing when modules are stacked. Carbon-mixed and PLA (poly lactic acid) resin are used for conductor and insulator, respectively. Each module consists of 11 beam-assembly and a support board connected with beams. The 80mm-long bipolar beams are arranged at 45-degrees to effective surface which corresponds array of beam tips. In low-compliance module, both a cross section of a beam and a tip of the beam are rectangle of 1.2 mm × 2.0 mm. In high-compliance module, a cross section of the beam is a rectangle of 0.6 mm × 2.0 mm and each tip of the beams is a rectangle of 1.8 mm × 2.0 mm. By this difference of beam width, high-compliance module has greater compliance than low-compliance.
The results validated that the concept increases the effective area and absolute values of attractive force. In addition, we confirmed that the slide glass (4.2 g) was lifted by the high-compliance system which has the smoothed beam tips. However, the results show stacking modules decreased the attractive force per unit area of a system from a single module regardless the compliance because the beam tips of each module are not perfectly aligned to a flat surface. Especially, the reduction ratio of low-compliance was 30% while that of high-compliance was 10%. This indicates that increasing the beam compliance is a valid design strategy in enlarging the effective area by stacking the modules.
In conclusion, our concept, layer-by-layer bipolar electrostatic modules, was verified to increase the effective area of attractive force. The results suggest that it is necessary to increase beam compliance for the concept to maximize performance of compliant bipolar electrostatic chuck.

To realize self-regulation for robot automation, robots are usually equipped with sensors, actuators and data-processing component to operate synchronically. Particularly, the signal (i.e. position, image and temperature) is gathered by sensor and processed, finally sent to actuators for a specific action. In spite of many new soft sensors and soft actuators, self-sensing materials that can monitor their own motions are highly desirable but proven challenging to realize. In this work, we present a photothermally-responsive electrically conductive soft material that can serve as a strain sensing and a photo-actuation, simultaneously owning two key functions essential to artificial muscle materials. The nanostructured hydrogel is synthesized into interpenetrating double network, leading to great enhancement of stretchability and responding speed. Photo absorbers are integrated into the hydrogel, enabling to be controlled by remote illumination and achieve various complex photo-driven anisotropic locomotion. At the meantime, the strain produced from the controlled motion can be sensed by the actuator itself in real time. With this unprecedented capability of sensing the magnitude of the strain that the actuator produces, the robust, stretchable, and ultra-sensitive conductive hydrogels will lead to the next-generation soft robots with self-diagnostic feedback-controlled, higher level of autonomy.

Electro(fluoro)chromic devices (EFCD) have received increased research attention in investigation in the past years because of their potential applications in multifunctional optical devices. Particularly, their simple device architecture, low power consumption, and processability by industrial relevant printing techniques provide great opportunities for the fabrication of low-cost displays and smart window devices. Furthermore, these exceptional properties can be extended with the use of biocompatible and biodegradable materials for the fabrication of transient devices aimed to the reduction of electronic-waste or potential medical applications.

In this work, we report on the fabrication of inkjet-printed EFCDs consisting of biocompatible and biodegradable components on cellulose/gelatin flexible substrates. The electro(fluoro)chromic layers were comprise of two different polymer materials, either a polyindenofluorene-8-triarylamine (PIF8-TAA) or poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). Additionally, we compared the performance of two different solid polymer electrolytes, on the basis of gelatin or Poly(D,L-lactide-co-glycolide) (PLGA) in combination with the non-fluorinated biodegradable salt tetrabutylammonium bis-oxalato borate (TBABOB). The devices were fabricated in a planar architecture utilizing inkjet printed Au electrodes. The fabricated devices were characterized in terms of contrast, efficiency and lifetime.

Finally, by subjecting the devices to a standardized composability test, we demonstrate their potential application in short-lifecycle biodegradable electronics.

Eye tracking through novel eye-based assistive wearable devices is considered as a valuable input modality to be used in different sorts of applications; e.g. medical applications such as visual fatigue, sleep studies and diagnosing a variety of disease states; as well as human-computer interface applications. However, the most popular method to detect eye movement is video-based eye trackers in which, generally, a video camera is mounted on a headset to record the images of the eye, and then, the images are processed to calculate the gaze position. Due to the considerable computational power cost, this technique cannot be applied for portable on-batteries long term applications. As an alternative, electrooculography (EOG), through a more convenient wearable device, was considered as a lightweight, accurate eye-tracking method with low-power consumption. This technique is based on measuring the corneoretinal biopotential of the eyes, which can be modeled as a constant electrical dipole. The eyeball rotation leads to the change in the dipole orientation which subsequently gives rise to the change in the EOG signal amplitude. This signal is generally measured through two pairs of electrodes located in periorbital positions close to the eyes with respect to a ground electrode.
Different variety of wearable EOG devices have been attempted recently, however, due to ergonomic issues and limitations exposed by the current bioelectrodes to be mounted close to the eyes, there still exists a tradeoff between comfortability and the detection of the signal with a high signal to noise ratio. Although the presence of gel is necessary to improve the signal acquisition, wearing the conventional Ag/AgCl electrodes is not aesthetically pleasing. In addition, since the signal decades, once the gel is dried out, these electrodes are disposable and cannot be applied for long-term applications. Considering all the wearable devices recently developed for detecting eye motion using EOG, none of them allows for an accurately long-term monitoring along with comfortability and low motion artifact caused by daily activity. Herein, the role of the electrodes, i.e. the interface between the body as the signal source and the computers as the processing units, is profoundly important. This is the electrode who receives the charges in the ionic form from the body and injects them as electrons through the wires. Since in EOG, the electrodes must be attached close to the eyes, designing a pleasing electrode, both aesthetically and comfortably, which is capable of damping artifacts for efficient data acquisition is still a dire need to be fulfilled.
In the current study, we introduce a novel methodology to fabricate a smart eye mask embedded with a first-in-its-kind fabric-based hydrogel electrode which can be feasibly adopted to daily life. We synthesized a mechanically stable, biocompatible, and fully recoverable hydrogel, through initiative chemical vapor deposition of poly(hydroxyethyl acrylate) on the silver gel. In the retro-design of this electrode, we got inspiration from the conventional Ag/AgCl electrodes, which, despite all the drawbacks, is still second to none in the market. We have successfully addressed all those drawbacks in our hydrogel electrode along with reaching to high signal to noise ratio in long-term data acquisition, wash-stability, breathability, no skin irritation, and is capable for further miniaturization to be embedded in other wearable platforms rather than the sleep eye mask. The success of the proposed wearable hydrogel-based EOG device is illustrated through several controlled experiments revealed by a comparative study between the designed bioelectrode, the standard electrodes, and the dry silver plated fabric ones based on their biopotential strength and the corresponding signal to noise ratio.

Membrane distillation (MD) has attracted significant attention as a rapidly emerging water treatment technology owing to its utilization of low-grade energy. Extensive studies have been carried out in both theoretical and experimental aspect of this technology. These previous studies, however, focus only on either theoretical or experimental aspect rather than incorporating both sides for a deeper understanding. It is impossible to perform a comparison study between theoretical and experimental results without being able to reliably control crucial MD membrane parameters, namely the pore size. This remains a critical limitation of most superhydrophobic membranes that the membrane parameters are not versatile once the fabrication process is set. Here, we suggest a stretchable superhydrophobic membrane of which the pore size can be readily controlled through the application of mechanical strain. The membrane was fabricated through simple electrospinning/electrospraying process and was tested of various membrane parameters including pore size, contact angle, and liquid entry pressure. The MD performance of the membrane according to the applied mechanical strain was studied both theoretically and experimentally by comparing the experimental separation flux to that of the predicted value from the computing simulation of MD. As expected, the separation flux was enhanced with increasing the pore size of the membrane. However, the lifespan of usage was shortened with larger pore sizes as it was wetted easily compared to its counterpart with smaller pore sizes. By varying the applied mechanical strain, the optimal pore size in terms of both separation flux and lifespan was found for the MD process.

Vanadium dioxide (VO₂) under goes insulator-metal phase transition (IMT) at 68 °C, accompanied with giant electrical, optical and lattice changes. Combining high Young's modulus (around 140 GPa), large IMT strain shrinkage and moderate IMT temperature, the distinct performance before and after phase transition makes VO₂ a competitive candidate for multi-functional MEMS actuators. For VO₂ actuators reported to date, lateral structures were used where two electrodes are placed above the phase change material, and current flows via in-plane direction. In this work, a vertical multilayer VO₂ MEMS micro-actuator device is reported. Though such configuration is being actively studied for memory devices, there is currently no literature discussing VO₂ vertical stack actuators. Here we will report on experimental and simulation studies of the vertical stack on the performance of the VO₂ actuator, toward the goal of IC integration for applications benefiting from reduced size, weight, power, and cost.
The VO₂ actuator is composed of 3 vertically stacked layers, where a 150 nm thick VO₂ layer is sandwiched between top Pt and bottom ITO electrodes. An equivalent thermal circuit is developed with a thermal response time of 0.39 ms. With the IMT of VO₂ generating volume change, a 35 μm long VO₂ actuator experiences 2 μm deflection across the phase transition driven by heating, and 0.22 μm deflection when electrothermally actuated. COMSOL finite element analysis is performed to determine spatial distribution of current flow and temperature profile, and to verify experimental measurements of strain induced bending in this multilayer vertical structure. The obtained experimental result shows a good fit with simulation analysis, which can in the future be utilized to develop a generic understanding of such vertical MEMS devices incorporating phase changing systems.

Self-assembly of block copolymer (BCP) serves as a powerful tool to fabricate complex 2D nanopatterns. Block copolymer are comprised of two or more chemically distinct subchains, which are linked together by covalent bonds. Upon annealing, these different blocks are phase separated into regimes, which forms nanostructures of different morphologies such as spheres, cylinders and lamellae. By introducing graphoepitaxy such as trenches, post arrays, researchers can ‘direct’ the self-assembly process to form uniform and device-oriented 2D nanopatterns. Over the past two decades, researchers have achieved all different thin film patterns through directed self-assembly of BCP. Despite the various 2D structures obtained from BCP, the variety of 3D nanostructures that have been so far achieved is limited. In this work, we present a novel way to fabricate uniform 3D nanostructures using a layer-by-layer approach. We test this new method using dissipative particle dynamics (DPD) to show its promise. Various multilayer structures consisting of spheres, cylinders and lamellae aligned and stacked on each other were achieved. Furthermore, different experimental parameters, which affect the uniformity of the structures, have been studied in the model.

Supramolecular assemblies of dendrimers, with defined structures and tunable functionalities, are promising functional materials. Here we report a ternary system (lanthanide ion/bis-ligand/PAMAM dendrimer) capable of assembling in a cooperative way by forming a complex between anionic (metal−ligand) coordination polymers and the cationic PAMAM dendrimers. In off-stoichiometric mixtures, charge-stabilized spherical nanoparticles of ∼100 nm appear; they have either negative or positive surface charges depending on what the excess component is. Introducing different trivalent lanthanide ions, Ln(III), in the coordination allows tuning both the luminescence emission spectrum and the magnetic relaxivity without affecting the assembly process or the final structure of the particles; this makes them interesting in the context of application. Moreover, the incorporated dendrimer allows us to add functional nanocargo, for example, Au nanoparticles in the cavities of these molecules, again without disturbing the assembly. In this novel way, we obtain versatile, multilevel hierarchical supramolecular dendrimer- containing assemblies with good control over their structures and functionalities. This is very difficult to achieve with conventional covalent compounds but becomes possible because of the supramolecular nature of the coordination polymers and the strong cooperative assembly.

Light-driven and photo-curable polymer based additive manufacturing (AM) has a huge potential due to its high resolution and precision. Unlike point- and layer-wise photopolymer AM technologies, volumetric AM forms the entire part all at once, which produces parts much more rapidly and overcomes such as stair step surface artifacts and inhomogeneous mechanical properties. Acrylated radical chain-growth polymerized resins are widely used in photopolymer AM due to their fast kinetics, and volumetric AM technology readily leverages this set of materials. However, for successful control of the reaction in 3D, the molecular basis of polymer network formation must be understood in detail. We present an optimized ReaxFF force field for acrylates polymer resin to account for the radical polymerization thermodynamics and kinetics, and the polymer network structure and composition. The force field is trained against our extensive training set including density functional theory (DFT) calculations of reaction pathways along the radical polymerization from methyl acrylate to methyl butyrate, C-C and C=C bond dissociation energies of methyl acrylate and methyl butyrate, and structures and partial charges of all molecules and radicals. The parametrization process utilizes a parallelized search algorithm, and the resulting model is able to study polymer resin formation, crosslinking density, chain length and distribution, and residual monomers of the more complex poly(ethylene glycol)_n diacrylate (PEGDA)/bisphenol a glycerolate (1 glycerol/phenol) diacrylate (BPAGDA) mixture.

While microparticle (MP) assemblies have long attracted academic interest, few practical applications of assembled MPs have been achieved because of technological difficulties related to MP synthesis, MP position registration, and absence of device concepts. The precise positioning of functional MPs in a proper stencil can produce flexible/stretchable electronic devices, even when the MPs themselves are rigid. In recent years, remarkable progress has been made in the programmable position registration of MPs, production of functional MPs, and concepts for MP-based, pixel-type electronic devices. For example, flexible tactile sensors have been intensively studied for healthcare and electronic skin devices.
Non-close-packed MP assemblies on a flexbile electrode act as a pressure sensing material like a cartridge film. The cartridge film is made by filling the holes of a stencil film (one MP in each hole) with conductive microparticles (MPs). Using the cartridge film, the sensing material can be cut-and-pasted on electrodes and transferred to other electrodes for reuse. This study analyzes the electrical responses of the sensors made of the cartridge film on the basis of the Hertzian contact theory, and also correlates the sensing performance of the sensors with the conductivity of the MPs and the degree of protrusion of the MPs from the stencil surface.
On the other hand, stretchable strain sensors are manufactured with close-packed MP assemblies. We proposes a dry process of fabricating single crystal-like monolayer which consists of conductive MPs in large area of rubber substrate. Due to their complete two-dimensional assembly, the current map measured by a conductive atomic force microscope (C-AFM) provides information to understand the rapid resistance change in small elongation deformations. Within 15 % of elongation strain, the stretchable sensor distinguishs 0.3 % fine strain due to high gauge factor (average value ~ 124.5) and detects sensitively the pulse on a wrist.

A challenge faced in the creation of increasingly complex and miniaturized sensing platforms is the need for multiple lithographic masking steps to achieve a particular pattern. In this work, we design and manufacture microscale arrays of one-dimensional photonic crystals without masking via electrohydrodynamic jet printing. Transfer matrix simulations are first used to design interference-based, polymer optical filters with reflectance exceeding 60% in imaging-relevant bands of the visible wavelength range. We describe the material selection rules and process conditions allowing for multilayered micro-filters with individual layer thickness control from 0.1 to 1 μm, filter edge length less than 50 μm, and compositions using commercially-available polymers with varying refractive index. A microspectrophotometry tool and process are developed to aid the characterization ex and in situ, allowing for rapid iterative processing to negotiate optical, interfacial, and rheological constraints of the system.

Fish skin is covered with a lot of scales which have microstructures on surfaces. It is considered that surface microstructures are functioned as antifouling property, self-cleaning ability and reduction of fluid resistance. In the conventional study, antifouling property and self-cleaning ability were evaluated by static wettability analysis. However, it is not sufficient for the practical evaluation because actual liquid movements cannot be determined by the static method. Therefore, we suggested a novel experimental method, called “dynamic wettability analysis in liquid media”, to observe behaviors of air bubbles and micro-droplets in liquid media. The values of dynamic wettability improved evaluations of antifouling property and self-cleaning ability. We fabricated a series of micro-structured water channels on silicon wafers by photolithography. The surfaces of water channels were modified hydrophilic by an excimer lamp. It is thought that antifouling property and self-cleaning ability are changed not only by surface microstructures but also by surface wettability changes. The surface wettability was measured by static water/hexadecane contact angles. The abilities of antifouling and self-cleaning of the micro-structured surfaces were evaluated by the behaviors of the air bubble and the hexadecane droplet in water media. In addition, we investigated how long hexadecane droplet was easy to invade within micro-structured surface in water media. The surface microstructures enhanced the water/hexadecane wettability and the movements of the air bubble in liquid media. The sir bubble behaviors in liquid media on micro-structured and flat surfaces were differed unexpectedly. It is generally thought that liquid droplets or bubbles move easily on surfaces having larger static contact angles, but these results were not agreed so. We tried to control the movements of the air bubble and the droplet in liquid media by gradually hydrophilic treatment. The movements of the air bubble and the hexadecane droplet in water media were improved by hydrophilic treatment. These results indicate that the movements of the air bubble and the droplet in liquid media become able to evaluate the antifouling property and the self-cleaning ability.

Stem cell based tissue engineering requires increased stem cell retention, viability, and control of differentiation. The use of biocompatible scaffolds encapsulating stem cells typically addresses the first two problems. To achieve control of stem cell fate, fine-tuned biocompatible scaffolds with bioactive molecules are necessary. However, given that the fine-tuning of stem cell scaffolds is associated with UV irradiation and in situ scaffold gelation, this process is in conflict with injectability. Herein, we develop a fine-tunable and injectable 3D hydrogel system with the use of thermosensitive poly(organophosphazene) bearing β-cyclodextrin (β-CD PPZ) and two types of adamantane-peptides (Ad-peptides) that are associated with mesenchymal stem cell (MSC) differentiation that serve as stoichiometrically controlled pendants for fine-tuning. Given that complexation of hosts and guests subject to strict stoichiometric control is achieved with simple mixing, these fabricated hydrogels exhibit well-aligned, fine-tuning responses, even in living animals. Injection of MSCs in fine-tuned hydrogels also results in various chondrogenic differentiation levels at three weeks post-injection. This is attributed to the differential controls of Ad-peptides, if MSC preconditioning is excluded. Eventually, our fine-tunable and injectable 3D hydrogel could be applied as platform technology by simply switching the types of peptides bearing adamantane and their stoichiometry.

‘Negative mechanical materials / metamaterials’ refer to materials and/or engineered systems that exhibit anomalous macroscopic thermo-mechanical properties that emerge due to the structure of their subunits, rather than the specific chemical composition. As a result of their design/construction, they may exhibit anomalous macroscopic properties such as zero or negative Poisson's ratios (auxetic), moduli and/or indices. Such zero/negative properties are not normally manifested by their conventional counterparts and may thus potentially be used in applications where typical materials cannot. This work will look into some of the more recent developments made in this field, focusing on how existing materials (e.g. crystals) are providing the blueprint for the design and manufacture of novel 'negative materials'.

Liquid crystal elastomer (LCE) films can be programmed by an array of stimuli, such as light, heat, interaction with alignment layers and mechanical deformation. Well aligned, monodomain films can produce large mechanical strains via order-disorder transitions caused by heating and, thus, high power – density actuations can be realized with low-cross-linked LCEs. Here, we focus on developing the material composition, alignment via mechanical deformation and Joule heating for achieving a low-voltage (<5V), high power-density (~kW/m³) response using LCE actuators. The material design process involved modulating the cross-linker and spacer monomer structure, as well as varying the molar concentrations among mesogenic matrices to simultaneously achieve optimal actuation and stability of the mesophase. To elicit ultrafast actuation by Joule heating, we developed the elements of the microfabrication protocols to integrate electrodes (2nm Ti + 30nm Ag), patterned onto a curved PET shell in mechanical designs. By utilizing non-linear mechanical instabilities (snap-through) in curved shells, an experimental platform was developed for creating millisecond scale actuation. In our experiments, 50um thick LCE films were synthesized and attached to a curved, electrode-patterned 23um PET shell by silicone glue. An Arduino system was used to provide current pulses for periodic heating and a current sensor was integrated to track the actinic current as a function of time. To characterize the actuation, USB digital cameras were used to record the deformation from front and side views and a FLIR infrared camera was positioned to monitor the actuator temperature variation from above. The dynamics of snap-through time (ms) was characterized using high speed imaging. Repetitive actuation over tens of cycles was demonstrated.

There is a growing interest in creating untethered soft robotic matter that can repeatedly shape-morph and self-propel in response to external stimuli for use in exploratory robots and adaptive structures. Towards this goal, we use multimaterial 3D printing to fabricate active hinges composed of liquid crystal elastomer (LCE) bilayers with orthogonal director alignment that interconnect polymeric tiles. When heated above their respective actuation temperatures, printed LCE hinges exhibit a large, energy-dense, and reversible bending response. Their actuation temperature and bending angle are controlled by employing LCE inks with disparate nematic-to-isotropic transition temperatures (T_NI) and hinge geometry, respectively. Through an integrated design and additive manufacturing approach, we demonstrate passively controlled, untethered soft robotic matter that adopts task-specific configurations on demand, including a self-twisting origami polyhedron that exhibits three stable configurations and a “rollbot” that assembles into a prism and self-rolls in programmed response to thermal stimuli.

Covalent crosslinking of a polymer network forms a distinct reference state, with respect to which the changes in liquid crystalline order in elastomers (LCE) could produce significant and reversible actuation. However, it was difficult to process the LCE materials into useful actuating shapes. Vitrimer networks offer a way to make processable plastics with shape-memory properties: with the plastic regime above vitrification temperature, re-shaping and re-alignment of LCE is now possible. Also possible is the joining-together and assembling of complex actuator structures via the bond-exchange reaction across the contact interface. In this talk we present a range of new (exchangeable) xLCE materials, including different bond-exchange chemistry, and also the dual vitrimers where a certain fraction of the polymer network remains permanent – and demonstrate their remarkable physical properties in large reversible actuation, and switchable dynamic adhesion. This new generation of the LCE and xLCE materials, showing both nematic and smectic phases of main-chain LC polymers, is very robust: with strain to break exceeding 150-200% and stress to break exceeding 0.8-1 MPa. The Young modulus of 0.7-1 MPa is found both in the non-aligned polydomain state, and in the aligned monodomain. With the reversible (equilibrium) thermal actuation strain amplitude of over 100%, the density of mechanical work delivered on the full thermal cycle reaches MPa levels, with the speed of response is only limited by the rate of heat diffusion into the elastomer body. We present and discuss practical thermo-mechanical devices using the heat-moulded xLCE as reversible actuators.

Shape memory polymers (SMPs) are promising candidates in the emerging fields of biomedicine, aerospace, flexible electronics and nanofabrication thanks to their programmable deformation.¹ To date, the shape adaptations in most SMPs are triggered by external heat, which is not favored or feasible in bio-applications. Light-induced SMP has shown potentials owing to its temporal, localized, remote and isothermal triggering and actuation.^2,3 However, the current light-induced SMP requires long activation time and the shape fixity rate remains low.
Herein, we develop a new strategy to activate shape memory effect (SME) by light. Unlikely triggering the thermal SMP by changing the external temperature, we switch the transition temperature of the photoresponsive polymer by light under ambient temperature to realize SME. To demonstrate this strategy, an azobenzene-based liquid crystal elastomer (azo-LCE) with dynamic covalent bonds is designed and synthesized via ring-opening metathesis polymerization. Upon sequential UV and visible light illumination, azo-containing mesogens undergo trans-cis-trans photoisomerization,⁴ varying the glass transition temperature of azo-LCE,⁵ thus to allow for the athermal processing of temporary shape. By exploring the SME of LCE, we realize various light-induced actuations with high shape fixity and recovery rate in 2 minutes without generating significant heat. In particular, we demonstrate the programmable shape recovery of artificial mimosa from the temporary shape to the original shape upon UV irradiation, mimicking the stimulus-response performance of natural mimosa. Moreover, the employment of dynamic covalent bonds is capable of altering the topology of the network, endowing this cross-linked LCE with excellent processability.⁶ Therefore, we manage to obtain and reshape different 2D and 3D structures from the same azo-LCE, solving the manufacture issue of conventional SMPs. We expect this light-programmable SMP provides potential applications for the future soft robotics and automation equipment.
References
[1] A. Lendlein, O. Gould. Reprogrammable recovery and actuation behaviour of shape-memory polymers. Nat. Rev. Mater., 4, 116–133 (2019).
[2] X. Qing, L. Qin, W. Gu, et al. Deformation of cross-linked liquid crystal polymers by light – from ultraviolet to visible and infrared. Liq. Cryst., 43, 2114-2135 (2016).
[3] J. Lv, Y. Liu, J. Wei, et al. Photocontrol of fluid slugs in liquid crystal polymer microactuators. Nature, 537, 179-184 (2016).
[4] T. Ikeda, J. Mamiya, Y. Yu. Photomechanics of liquid-crystalline elastomers and other polymers. Angew. Chem. Int. Ed., 46, 506-528 (2007).
[5] H. Zhou, C. Xue, P. Weis, et al. Photoswitching of glass transition temperatures of azobenzene-containing polymers induces reversible solid-to-liquid transitions. Nat. Chem., 9, 145–151 (2017).
[6] Z. Pei, Y. Yang, Q. Chen, et al. Mouldable liquid-crystalline elastomer actuators with exchangeable covalent bonds. Nat. Mater., 13, 36–41 (2014).

Stimulus-responsive polymers are attractive for microactuators because they can be easily miniaturized and remotely actuated, which enables untethered operation. Inspired by biology, artificial cilia have been investigated for applications in sensing, microfluidics, and controlled wettability. Functional artificial cilia usually respond to applied stimuli but require maintaining the applied stimulus or are programmed to perform one-way processes that cannot be reset. Reconfigurable artificial cilia are desirable, whose shape can be set, locked, unlocked, and reconfigured. In this work, magnetic iron microparticles were dispersed in a thermoplastic polyurethane shape memory polymer matrix and formed into artificial, magnetic cilia by solvent casting within the vertical magnetic field in the gap between two permanent magnets. In this template-free method, interactions of the magnetic moments of the microparticles, aligned by the applied magnetic field, drive self-assembly of magnetic cilia parallel to the field direction. The resulting magnetic cilia respond simultaneously to magnetic fields and light. Temporary shapes obtained through combined magnetic actuation and photothermal heating can be locked by switching off the light and magnetic field. Subsequently turning on the light without the magnetic field drives recovery of the permanent shape of the magnetic cilia. These cilia are therefore reconfigurable rather than merely responsive. The permanent shape of the cilia can also be programmed after fabrication by applying mechanical constraints and annealing at high temperature. Spatially controlled actuation of cilia is demonstrated by applying a mask for pattern transfer into the array of magnetic cilia. Developing a theoretical model to predict the response of shape memory magnetic cilia elucidates physical mechanisms behind observed phenomena, enabling the design and optimization of ciliary systems for specific applications. Remote reconfiguration enabled by combining applied magnetic fields and light enhances the capabilities and broadens the applications of magnetic cilia.

Friction force on soft material usually is not linearly dependent on normal load because of the nonnegligible adhesion force or surface energy. As the adhesion force is proportional to the real contact area, friction force can be switchable by changing the surface roughness of the material. Here, we introduce a shape memory photonic crystal (SMPC) which is polymeric inverse opal structure and made of polyethylene glycol diacrylate (PEGDA) and ethoxylated trimethylolpropane triacrylate (ETPTA) co-polymer. The original ordered structure of SMPC providing a smooth surface can be programmed into a temporary disordered structure providing a rough surface by water swelling. The disordered structure can be recovered by ethanol swelling. Both programming and recovery are under room temperature.
The previous studies demonstrate that this unusual athermal shape memory effect is caused by the competing between the elastic modulus (E) of material and the surface tension (µ) of the chemical solution. During the swelling, the porous structure is order because the polymer chains are lubricated by chemical solution and have high mobility. In this case, polymer chains trend to recover to their original conformation which is ordered porous structure. During the evaporation of the chemical solution, the capillary force from the surface tension (µ) of the solution will deform the porous structure into disordered status if µ is large (such as water) enough to compete with E. On the other hand, the structure will stay order if µ is not large (such as ethanol) enough.
In this work, we first characterize the optical property of both ordered and disordered SMPCs by reflection spectra. The SMPCs show an obvious photonic band gap with ~530 nm wavelength in ordered (recovered) status and no photonic band gap in disordered (deformed) status. Then, atomic force microscopy (AFM) and micro-indentation are used to characterize surface roughness and adhesion, respectively. The adhesion force on recovered SMPCs with a smooth surface is about three times larger than that on deformed SMPCs with a rough surface. Finally, a reciprocating sliding test is conducted on SMPCs by a spherical stainless steel tip under different normal load (0.5mN ~ 7mN). The friction coefficient on the recovered SMPCs can be 14 times higher than that on the deformed one. The mechanism behind this friction coefficient change will be discussed in this presentation.

Metal-halide perovskites have become appealing materials for optoelectronic devices. While the fast advancing stretchable/wearable devices require stability, flexibility and scalability, current perovskite still suffers from ambient-environmental instability and incompatible mechanical properties. To break the hindrance, recently perovskite−polymer composites have shown improved in-air stability with the assistance of polymers as the embedding media. However, their stability remains unsatisfactory in high-humidity environment or when immersed in water. These methods also suffer from limited processability with low yield (2D film or beads) and high fabrication cost (high temperature, air/moisture-free conditions), thereby limiting their device integration with complex structures and broader applications. Herein, a one-step scalable method is developed to produce freestanding highly-stable luminescent organogels, within which perovskite nanoparticles (NPs) are homogeneously distributed. The perovskite-organogels present a record-high stability, maintaining their high quantum yields for > 110 days immersing in water at different pH and temperatures. This paradigm is universally applicable to broad choices of polymers, hence casting these emerging luminescent materials to a wide range of mechanical properties tunable from rigid to elastic. With intrinsically ultra-stretchable photoluminescent organogels, flexible phosphorous layers were demonstrated with > 950% elongation. Rigid perovskite gels, on the other hand, permitted the deployment of 3D-printing technology to fabricate arbitrary 2D/3D luminescent architectures.

Photodeformable liquid crystal polymers (LCPs) that adapt their shapes in response to light have aroused a dramatic growth of interest in the past decades, since light as a stimulus enables the remote control and diverse deformations of materials.^1-3 LCPs, especially the ordered ones, have demonstrated their potentials to dramatically increase the photodeformation extent and construct light-driven soft actuators because they possess fascinating features combining the entropic elasticity of polymeric elastomers and the ability to undergo a reversible and alignment dependent shape-change behavior of liquid crystals (LCs). Much effort was made to develop new photodeformable LCPs, including their basic actuation mechanisms, the various deformation modes, the newly designed molecular structures, and the improvement of processing techniques.^4-6 In this report, special attention is devoted to the novel molecular structures of LCPs, which allow for easy processing and ordering. The soft actuators with various deformation modes in response to light are also covered with the emphasis on their photo-induced bionic functions and potential applications in optofluidics and optoelectronic devices.

[1] G. Stoychev, A. Kirillova, L. Ionov. Adv. Optical Mater. 2019, 1900067.
[2] Y. Yu, M. Nakano, T. Ikeda. Nature 2003, 425, 145-145.
[3] J. Lv, Y. Liu, J. Wei, E. Chen, L. Qin, Y. Yu. Nature 2016, 537, 179-184.
[4] T. J. White, D. J. Broer. Nat. Mater. 2015, 14, 1087-1098.
[5] C. Ohm, M. Brehmer, R. Zentel. Adv. Mater. 2010, 22, 3366-3387.
[6] T. Ube, T. Ikeda. Adv. Optical Mater. 2019, 1900380.

Wearable computers, stretchable electronics, soft robotics, healthcare, and other areas of research that require physical human-machine interactions demand materials that are inherently multifunctional. Human-made materials typically lack diverse multifunctionality that is more widely observed in nature, where a material can be soft and stretchable as well as responsive and adaptable to its environment. One promising class of materials is liquid crystal elastomers (LCEs), which are compliant, deformable, and undergo a thermally-activated liquid crystal phase transition resulting in macroscopic shape change.. However, LCEs are electrically insulating with low thermal conductivity. Rigid fillers can improve relevant materials properties of LCEs and introduce additional functionalities, but at high loading (greater than a few weight percent), rigid fillers reduce shape-morphing capabilities of the LCE.

In the multifunctional composite described in this work, functionality is retained at 50 vol. % (83 wt. %) loading of liquid metal microparticles (LM). Mechanical properties were characterized by mechanical testing and dynamic mechanical analysis. The LM inclusions do not degrade the compliance nor deformability of the LCE matrix, while rigid inclusions increased stiffness and prevented actuation. Thermal conductivity measurements showed improved heat dissipation capabilities of the LM-LCE composite relative to the unfilled material, critical for thermally-activated shape-morphing. Electrical conductivity of the LM inclusions enabled the possibility of Joule-heated actuation. Joule-heated actuation is uniform, robust, and resilient; the composite could actuate even after significant physical damage and could actuate for >15,000 cycles at 50 % strain and >100,000 cycles at 2.5 % strain. Shape change can be programmed for zero-stress actuation of irregular form factors. A soft crawling entity and architectures that demonstrates sensing, actuation, and traditional electronics interfacing highlight the potential use for this multifunctional composite in active areas of research.

Stimuli-responsive systems are attractive since their properties can be controlled by external stimuli and/or surrounding environment. Recently, more than one stimulus is utilized in order to enhance the performance of systems, or to bypass undesired effects. However, most of previous research on multi-stimuli has been focused on enhancing or inducing changes in one type of response. Herein, we developed a nanocomposite material with independent multi-states composed of photo-responsive polymer and quantum dots (QDs), in which its properties can independently be controlled by different wavelengths of light. More specifically, azobenzene-incorporated poly(dimethylsiloxane) (AzoPDMS) triggers photobending (PB) by 365 nm light and uniformly dispersed methylammonium lead bromide perovskite (MAPbBr₃) QDs show photoluminescence (PL) by light below 500 nm. The PB and PL could be simultaneously and independently controlled by the wavelength of applied light creating multi-states. Our approach is novel in that it creates multiple independent states which can further be used to transfer information such as logic gates (00₍₂₎, 01₍₂₎, 10₍₂₎, 11₍₂₎) and possibly widen its application to flexible and transparent opto-electric devices.

Elastomeric lattices are widely applicable for energy absorption, impact protection, and signal propagation, due to their capability to undergo large, reversible strains and energy-dissipating buckling instabilities. In particular, architected liquid crystal elastomers (LCEs) combine the structural properties of lattice-based design with programmability of the material stiffness, offering tailored energy absorption properties. The stiffness of the LCE is locally programmed by the applied strain field, which orients the director (mesogen) of the LCE. However, the set of physically accessible strain profiles is regulated by the shape and spacing of the LCE beams within the lattice, creating a large design space to navigate. To address this challenge, a Bayesian optimization framework is utilized to design the shape of the LCE beams to achieve specific spatial strain distributions under applied loading. The beams are parametrized with a Fourier-series expansion, which controls the thickness as a function of beam length in terms of the magnitude, periodicity, and phase of the top and bottom layers. The Bayesian optimizer utilizes the posterior distribution of the response surface that is obtained by a Gaussian process, creating a less expensive surrogate model for optimization and visualization. Representative 2D lattices for both bending and stretching dominated behavior under uni-axial loading were prescribed. The strain field within the designed LCE beams was calculated using a nonlinear finite element simulation to capture the geometric and material nonlinearities of the model. After calculating the strain field, statistics of the spatial distribution were compiled to predict the average stiffness increase of the lattice due to LCE director programming. The mean, variance and number of modes of the stain distribution were evaluated as objective functions for optimization. Preliminary results suggest uniform thickness beams with a range of lower periodicity (< 4) increases the variance of the strain distribution in the LCE. In contrast, beam designs with regions of narrow thickness result in lower variance of the strain distribution, but have larger differences in the maximum to the minimum strain difference, as the strain fields become more localized. Collectively, this design tool provides an initial framework to explore the coupling between geometry, strain and material programmability in the LCE system and has potential to inform the design of other material systems with strain-based patterning mechanisms.

There has been substantial research interest in ionic liquids and polymerized ionic liquids (PILs) over the past decade due to their potential applications in energy storage, ion exchange membranes, gas/liquid separation membranes, and stimuli-responsive devices. Typically, a trade-off is observed between ionic conductivity and mechanical properties. Polymers provide a route to improve flexibility and mechanical properties of electrolytes but generally at the expense of conductivity. Here we report a new class of electroactive polymer that was designed and synthesized based on covalently crosslinked network PILs (n-PILs) to decouple conductivity and mechanical strength. Through molecular engineering, we are able to precisely control the spacing between ions, crosslinking density and linker polarity (hydrocarbon or oligoether). The resultant n-PILs exhibit low T_g (~ -40°C), tunable ionic conductivity (> 10^-5 S/cm under ambient conditions), and are self-standing (Young’s modulus 0.2-2.2 MPa) at room temperature. These n-PILs were investigated as dopant-free, single ion conducting actuators and showed bending strains as large as 0.9% under DC testing conditions which is comparable to the best performing ionic liquid swollen block copolymers. A large electrochemical window (±3 V) and absence of water or solvent allows our n-PIL actuators to retain >85% of the original bending strain after 1000 cycles under 3V, 0.1 Hz AC current. Modulus controls the response under DC conditions while the AC measurements are dependent on the ionic conductivity as well.

The ice formation processes on solid surfaces are complex and diverse, which makes it a daunting challenge to design an icephobic material functional under different icing conditions in complex varying real-life environment.^1-4 Developing an effective icephobic surface with multiple anti-icing functions through simple design and large-scale production is highly desirable. Biological antifreeze proteins (AFPs) offer a great example of multifunction integrated anti-icing materials that excel in all the three key aspects of anti-icing process, i.e., they can depress the freezing temperature, prevent the ice growth, and inhibit the ice recrystallization simultaneously by tuning the structures and dynamics of interfacial water.¹ Inspired by antifreeze proteins (AFPs), a multifunctional anti-icing platform based on polydimethylsiloxane (PDMS)-grafted polyelectrolyte hydrogel is reported. The properties of interfacial water can be controlled via tuning the synergy of hydrophobicity and ion-specificity, which provides us a promising route to integrate various icephobic advantages into one material. The controllability of interfacial water grants the polyelectrolyte hydrogel coating high performance in inhibiting ice nucleation (ice nucleation temperature lower than -30 ^oC), preventing ice propagation (ice propagation time higher than 500 s/cm²), and decreasing ice adhesion (ice adhesion strength lower than 20 kPa). These low-cost hydrogels can be large-scale coated onto different inorganic and organic materials, such as metals, plastics, oxides and ceramics. The simplicity, mechanical durability, and versatility of these smooth hydrogel surfaces make it a promising option for a wide range of anti-icing applications.

References
He, Z.; Liu, K.; Wang, J*. Acc. Chem. Res. 2018, 51 (5), 1082-1091.
He, Z.; Xie, W. J.; Liu, Z.; Liu, G.; Wang, Z.; Gao, Y. Q.*; Wang, J.* Sci. Adv. 2016, 2 (6), e1600345.
Jin, Y.; He, Z.; Guo, Q.; Wang, J*. Angew. Chem., Int. Ed. 2017, 56 (38), 11436-11439.
Wu, S.; He, Z. *; Zang, J.; Jin, S.; Wang, Z.; Wang, J.; Yao, Y.; Wang, J. * Sci. Adv. 2019, 5, eaat9825

Soft materials deform in a distributed fashion and in various modes. Although stretchable sensors have been developed to sense the deformations of soft-bodied robots or human organs, each sensor can only sense one deformation, and offers limited knowledge about the deformation’s mode and location. Advanced mechanical sensing with richer information is usually achieved through sensor networks, or machine learning techniques, which are complex on a systematic or computational level. In a step toward reducing complexity associated with advanced mechanical sensing, we present a compact and low-cost design of a stretchable optical waveguide sensor, which achieves the goal through sensing the rich information carried by light. The waveguide, composed of multi-core structure and patterned with absorbing dyes, differentiates the deformations’ modes among stretching, bending and pressing, and senses deformations’ location and magnitude. Furthermore, the sensor is capable of decoupling deformations happening at multiple locations at the same time, and decoupling different modes of deformations. These features are demonstrated in a 3D printed glove, which can use one waveguide sensor to sense in real time the bending angles of the three joints on a finger, and simultaneously detect location and magnitude of an external press.

Introduction: There is a critical need for a safe, non-contact, and dynamically activated trigger for actuating implantable devices. Inducing on-demand degradation of these devices enables tuning treatments to the needs of individual patients, diseases, and recovery schedules. Triggers based on other stimuli, such as heat, pH, or enzymatic chemicals, have been employed in some in vivo applications, but come with many restrictions that limit their use for several disease use cases. Light-triggerable materials offer non-contact on-demand degradation with high spatial and temporal resolution. We have developed a tough light-triggerable hydrogel with tunable mechanical properties and modular design that can be degraded in a safe and non-contact manner in vivo. We apply these materials to two applications in the gastrointestinal tract: a bariatric balloon and an esophageal stent. We demonstrate biocompatibility and on-demand triggering of the material in vitro and in vivo. We characterize performance of the system in a large animal model with an accompanying ingestible LED. This is, to our knowledge, the first demonstration of light-degradable hydrogels in vivo.
Methods: We custom-manufactured an acrylated ortho-nitrobenzyl (oNB)-based compound and used it as a linker to polymerize hydrogels from a range of materials, including polyacrylamide (PAAM) and poly (2-acrylamido-2-methylpropane sulfonic acid) (PAMPS) single network gels and tough PAMPS/PAAM double network gels. Cytotoxicity of the materials and degradation byproducts was evaluated on two cell lines. Mechanical properties were measured using rheological testing and compression testing. Materials were degraded in vitro and in vivo (porcine model) using custom-made LED arrays and ingestible light-emitting pills.
Results & Discussion: The mechanical properties of our material far exceeded previously reported properties for light-degradable gels (>100 times stronger) and enabled, for the first time, their in vivo use. The mechanical properties and degradation timelines of these materials could be tuned using a variety of parameters, such as gel composition and light wavelength, intensity, and distance from the material. The material could be dissolved within minutes of irradiation and its degradation byproducts, as well as degradation light wavelengths (365-405 nm) were proven biocompatible. We showcased the advantageous properties of our material in two use cases: a gastric resident bariatric balloon and an esophageal stent. In the gastric resident device, we triggered light-activated reduction in the size of an ingestible space-filling balloon in vivo using an ingestible LED pill. If employed in a patient, this functionality could enable on-demand passage of the space-filling device when residence is no longer required. This would provide a significant advantage over the current clinical standard, which requires an invasive endoscopic procedure to retrieve the balloon. Similarly, we have developed a triggerable gel-linked esophageal stent in which light irradiation provides a non-contact method for safely dissolving and removing the stent from the esophagus without risking off-target detrimental effects to the tissue lining that arise from mechanical-, heat-, or chemical-based triggers. This could be used to treat benign and malignant stenoses or strictures. Our material enables dynamic, biocompatible, spatially controllable, and non-contact degradation in vivo.
Conclusions: Triggerable materials stand to transform our capacity to precisely control biomedical device activity and performance while reducing the need for invasive interventions. Our light-triggerable hydrogels have the potential to be applied broadly throughout the GI tract and other anatomic areas. By demonstrating the first use of light-degradable hydrogels in vivo, we provide engineers and clinicians with a novel, safe, dynamically deliverable, and precise tool to design dynamically actuated implantable devices.

Stimuli-responsive hydrogels have been widely used in many fields, including soft robots, bioengineering, and smart sensors, due to their excellent flexibility, stimuli responsiveness, and shape change performance, which have attracted extensive attention. However, the tedious and time-consuming preparation process, low response speed, and requirement of toxic additives/solvents severely limit their practical application. Here, we reported a cost-efficient two-step synthetic method for stimuli-responsive Poly(N-isopropylacrylamide) (PNIPAM) hydrogel with additive-free, fast response, large swelling ratio, and high fatigue resistance. Results show that the overall performance of the as-synthesized PNIPAM hydrogels is among the top level compared with other reported work despite the significantly shortened preparation time. Moreover, we have also achieved large photo-thermal response and remote control capabilities by introducing multi-wall carbon nanotubes (MWNTs) into the PNIPAM hydrogel, demonstrating precise tuning of the bending angle and deformation geometry of the nanocomposite hydrogel under infrared laser irradiation. Lastly, we designed and integrated the stimuli-responsive hydrogels with stretchable circuits to make an electric-driven soft actuator, which is capable of multi-mode programmable electric-driven actuation. It is expected that the electric-driven soft actuator could have great potential for the application of artificial muscles and aquatic soft robots.

The development of smart biomaterials is a challenging task. Via the promising high-energy electron treatment, biological relevant hydrogels such as gelatin can be engineered to become smart materials. Due to their original biocompatibility and cytocompatibility, they show a high potential for applications in biomedicine and related fields. Therefore, reagent-free methods to develop smart hydrogels are required. A highly favorable technique is high-energy electron treatment, which can be used to develop smart and stimuli-responsive hydrogels.^[1,2]
Within this contribution, we will present two different preparation processes utilizing high-energy electron treatment to develop effective thermo- and hydration-responsive gelatin hydrogels. Since high-energy electron treatment is highly advantageous for reagent-free modification of biological hydrogels, the resulting smart hydrogel materials have a great potential for applications in biomedicine and related fields.

^[1] S. Riedel, S.G. Mayr, Reagent-Free Programming of Shape-Memory Behavior in Gelatin by Electron Beams: Experiments and Modeling, Phys. Rev. Appl. 9 (2018) 024011.
^[2] S. Riedel, B. Heyart, K.S. Apel, S.G. Mayr, Programing stimuli-responsiveness of gelatin with electron beams: basic effects and development of a hydration-controlled biocompatible demonstrator, Sci. Rep. 7 (2017) 17436.

During tissue formation and regeneration, the dynamic mechanical force transmitted through microenvironments continuously impacts on the mechanics of cells. Cellular mechanical properties are closely related to genes and proteins expressions [1, 2]. The mechanical properties would alter during the procedure of stem cells differentiating into different lineages. At different stages of stem cell differentiation, the cells display varying levels of mechanical properties in response to surrounding microenvironments, which depends on the composition and organization of subcellular structures, especially the cytoskeleton and nucleus. The mechanical properties of cell nucleus affects the proteins folding and transport as well as the condensation of chromatin [3], which further regulates cell fate. However, few studies have assessed stems cells mechanical property during differentiation. In this study, the mechanical properties change of human bone marrow mesenchymal stem cells (hBMSCs) during the procedure of adipogenic and osteogenic differentiation were determined by atomic force microscopy (AFM) at different time points. Simultaneously, the change of histone modification level and cytoskeleton were characterized by laser confocal microscopy and flow cytometry. Through comparing the mechanical properties of the nuclei at different stages of cell differentiation found that the stiffness of nuclei increased with the induction time prolongation. Immunofluorescence results show that the intensity of H3K27me3 significantly increased over the differentiation. Our results indicate that AFM is a facile and effective method to monitor stem cells differentiation.
Key words：stem cell, cell mechanics, AFM
Reference
[1] R.D. Gonzalez-Cruz, V.C. Fonseca, E.M. Darling, Cellular mechanical properties reflect the differentiation potential of adipose-derived mesenchymal stem cells, P Natl Acad Sci USA 109(24) (2012) E1523-E1529.
[2] A.E. Ekpenyong, G. Whyte, K. Chalut, S. Pagliara, F. Lautenschlager, C. Fiddler, S. Paschke, U.F. Keyser, E.R. Chilvers, J. Guck, Viscoelastic Properties of Differentiating Blood Cells Are Fate- and Function-Dependent, Plos One 7(9) (2012) E45237- E45246.
[3] M. Guo, A.F. Pegoraro, A. Mao, E.H. Zhou, P.R. Arany, Y. Han, D.T. Burnette, M.H. Jensen, K.E. Kasza, J.R. Moore, F.C. Mackintosh, J.J. Fredberg, D.J. Mooney, J. Lippincott-Schwartz, D.A. Weitz, Cell volume change through water efflux impacts cell stiffness and stem cell fate, P Natl Acad Sci USA 114(41) (2017) E8618-E8627.

Wood in nature has well-defined vertical structure with low tortuosity to facilitate the mass transport. Inspired from the wood structure, we designed anisotropic hydrogels with alignment to increase the ionic conductivity of materials. The pore size can be rationalized and reduced even smaller than natural wood to increase the specific area, while maintaining the alignment. Conducting polymer, owing to its mesoporous structure and high electrical conductivity has been widely used for supercapcitors. By incorporating the conducting polymer in hydrogel-based matrix, the all-solid-state supercapacitor with high electrochemical performance can be fabricated. Such conducting polymer-hydrogel composites exhibit unprecedented ionic conductivity, areal supercapacitance, power density, energy density, capacitance retention and cyclic stability. Besides, the hydrogel matrix also provides excellent flexibility under cyclic bending, making it possible for flexible electronics.

Given their intrinsic hierarchical micro-/nano-structures, unique chemical/physical properties and tailorable functionality, hydrogels and their derivatives have emerged as an important class of materials for many exciting applications beyond their traditional biomedical applications. Bottom-up synthetic strategies to rationally design and modify their molecular architectures enable functional hydrogels to address critical challenges in renewable energy and environmental technologies.

In this talk, I will present our recent advances made in nanostructured functional hydrogels, particularly those based on conjugated polymers, as an emerging material platform for sustainable energy and environmental technologies, including high-energy-power batteries and supercapacitors, and solar water desalination and atmospheric water harvesting. I will further illustrate ‘structure-derived multifunctionality’ of this special class of materials.

Introduction
Many animals including humans have a lot of hairs on their body surface in order to protect their body surface. The outermost surfaces of the hair have cuticle structures in a scaly overlapping manner from the root to the tip of hair. The cuticle plays an important role as protection of the interior of the hair against external irritation. Furthermore, it is said that it plays a role of transporting the sebum secreted near the root to the tip of hair. Anisotropic surface structure such as cuticle greatly contributes to wettability. However, we have a question about the direction of sebum transport phenomena due to the fine cuticle structure.
In this research, we tried to investigate dynamic wettability of the cuticle structure, to clarify regularity in this fine structure, and to consider correlation with the liquid transport phenomenon. To elucidate the wettability of anisotropic surface structures can be expected to apply to microfluidic devices, hair cosmetic products, and antifouling coatings.

Experimental Method
Dynamic wettability toward water droplet of 3 to 40 pL such as a receding angle and a droplet evaporating behavior was measured by using Microscopic Contact Angle Meter (MCA-3 type I). Distilled water, which is a volatile liquid, evaporates in less than 30 sec. The receding angle can be measured during the evaporation process. The amount of the droplet during the measurement is kept much smaller than the capillary length at which the liquid begins to be affected by gravity, it is possible to measure dynamic wettability of the cuticle structure excluding the influence of gravity.

Results and Discussion
The dynamic wettability of the cuticle structure toward to picolitter-scaled water droplets indicated that, an anisotropic pinning effect was observed at the cuticle structures in the case of the longer diameter of water microdroplet than the interval of cuticle. The receding angle from the tip side to the root side of the hair was measured during evaporation of the water microdroplet. This result also indicated that the anisotropic water spreading from the tip to the root of hair was depended on commonly consideration of sedum transporting on the cuticle from a root to a tip of hair surfaces. The water manipulation learning from this mechanism will help to produce biomimetic fluidic devices.

We report the synthesis method of ultra-stretchable soft materials for effective light modulation of optoelectronic devices such as solar cells and light emitting diodes. We controllably generate multi-scale pores within soft materials (e.g., silicone rubber) to effectively control their light reflection properties by using the water-streaming method, which can be extended to ultra-stretchable soft materials. Specifically, formation of the pores on the surfaces of soft materials enables to fabricate the anti-reflective soft materials with light reflection of less than 4% in the visible wavelengths. In addition, multi-scale pore generation within the soft materials leads to achieve light reflection of more than 95% in the visible wavelengths without incorporation of metallic or ceramic components. The fabricated soft materials exhibit ultra-stretchable properties of up to ~300% engineering strain. Those layers are assembled to commercial organic solar cells as anti-reflective and back-reflective layers as such they significantly increase the light absorption and the light energy conversion efficiency of the solar cells due to the enhanced light trapping effects. Our all-polymer platform with effective light managing properties can be readily applied to commercial optoelectronic devices for their enhanced performance with diverse applications.

Acknowledgement
This research was supported by the International Research and Development Program (NRF-2018K1A3A1A32055469) through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT of the Republic of Korea.

Magneto-responsive materials are emerging sources for packaged shape reconfigurable devices owing to its rapid contactless actuation by the external magnetic field. While programmability of magneto-responsive materials enables multi-modal actuation such as bending, twisting, and their hybridized actuation mode, most reports are limited to demonstrate of single actuation mode in a single sample. Herein, we report patternable actuation modes within a single sample by utilizing the patterned magnetic field to align the magnetic component. Furthermore, we also demonstrate programmability of actuation modes in a single sample by adapting a masking technique for arbitrary patterned actuation of the microarray. Remarkably, reversible magnetic actuation of patterned microarrays is achieved 100 actuation cycles. The programmable magneto-responsive microarrays could be served as a general platform for shape reconfigurable tunable microdevices.

Elastic composite-based piezoelectric energy harvesting technology is highly desired to enable a wide range of device applications, including self-powered wearable electronics, robotic skins, and biomedical devices. Recently developed piezoelectric composites are based on inorganic piezoelectric fillers and polymeric soft matrix to take the advantages of both components. However, there are still limitations such as the weak stress transfer to piezoelectric elements and the poor dispersion of fillers in matrix. In this talk, a highly-enhanced piezocomposite energy harvesters (PCEH) is representatively developed using a three-dimensional (3D) interconnected electroceramic skeleton by mimicking and reproducing the sea porifera architecture (although the speaker will introduce other research examples and achievements). This new mechanically reinforced PCEH is demonstrated to resolve the problems of previous reported conventional piezocomposites, and in turn induces stronger piezoelectric energy harvesting responses. The generated voltage, current density and instantaneous power density of the biomimetic PCEH device reach up to ~16 times higher power output than that of conventional randomly-dispersed particle-based PCEH. This work broadens the further developments of high-output elastic piezocomposite energy harvesting and sensor application with biomimetic architecture.

Dielectric elastomers are a type of electro-active polymers that have been investigated for its use in artificial muscle-like stretchable actuators. Dielectric elastomers are characterized by their high energy density, large strain rate, fast response, softness, lightweight, and low cost [1]. There have been many attempts at harnessing and utilizing these characteristics. To apply elastomers in various conditions and structures, numerous actuator configurations were designed, such as spherical, cylindrical/tubular, and zipping actuators [2][3]. Also, to produce a larger linear motion or to maintain stability, soft actuators combined with other actuation mechanisms, such as hydraulics and magnetism, have been fabricated [4][5]. A spring roll actuator is composed of a thin dielectric elastomeric sheet wrapped around a spring core. This configuration converts the dielectric membrane’s expansion into linear motion. As a result, upon activation, a muscle-like movement is produced. Designing of spring roll actuators based on models has been attempted, to obtain an optimal design and to increase the performance [1][6-8]. Although the model-based approach was effective, experimental results did not completely match with model predictions, due to nonlinear properties. We propose a model-based spring roll actuator design, which considers both static and dynamic conditions. Using strain energy functions, a viscoelastic material model of the actuator is established. Then, overall governing equations are derived from the Helmholtz free energy equation and the viscoelastic model. With fabricated spring roll actuators, the proposed actuator model is experimentally verified in static and dynamic conditions. In conclusion, we present a general model of spring roll dielectric elastomer actuators and its optimized fabrication parameters for specific operating conditions.

[1] J. Zhang, H. Chen, L. Tang, B. Li, J. Sheng, and L. Liu, Appl. Phys. A. 119, 825-835 (2015).
[2] D.Q. Tran, J. Li, F. Xuan, and T. Xiao, Mater. Res. Express. 5, 065303 (2018).
[3] L. Maffli, S. Rosset, and H.R. Shea, Smart Mater. Struct. 22, 104013 (2013).
[4] H. Boys, G. Frediani, S. Poslad, J. Busfield, and F. Carpi, in: Proceedings of Electroactive Polymer Actuators and Devices (EAPAD) 2017 (SPIE, Portland, OR, 2017), p. 101632D.
[5] C. Cao, X. Gao, and A.T. Conn, Appl. Phys. Lett. 114, 011904 (2019).
[6] S. Zhigang, Acta Mech. Solida Sin. 23 (6), 549-578 (2010).
[7] M. Moscardo, X. Zhao, Z. Suo, and Y. Lapusta, J. Appl. Phys. 104, 093503 (2008).
[8] J. Zhang, H. Chen, J. Sheng, L. Liu, Y. Wang, and S. Jia, Appl. Phys. A. 116, 59-67 (2014).

Ant colonies in nature are able to cooperatively accomplish complex tasks that are beyond the capabilities of individuals through self-organizing into sophisticated and functional structures. For example, to traverse difficult terrain, ants grip firmly the bodies of each other, and constitute a living, flexible and robust chain-like ant bridge to march across the gaps beyond the reach of individuals.

Emulating natural collective behaviors promises benefits in various engineering fields, and has been partially realized through elaborate algorithm and physical designs in traditional large-scale robotic swarms. Further downscaling the swarms to micro-/nanoscale is envisioned to expand their applications in the hard-to-reach regions for humans, such as targeted delivery, microelectronics, and so on^{[1, 2]}. However, to date, developing microswarms with group-level functionality still remains a challenge.

Previously, our group has developed various magnetic actuation strategies for microrobotic systems^[3-5]. Herein, we present a magnetic microswarm that emulates the collective behaviors of ant bridges for electronic applications^[6]. The building blocks of microswarm are fabricated by functionalizing Fe₃O₄ nanoparticles with a continuous gold surface layer, so that they are both paramagnetic and electrically conductive. Under a programmed oscillating magnetic field, the building blocks are reconfigured into a ribbon-like microswarm, which can perform reversible elongation with a high aspect ratio. Through elaborately tuning the magnetic field parameters, we apply the microswarm to self-assemble a chain-like conductive pathway for electrons between two disconnected electrodes with the bodies of building blocks, thus mimicking both the structure and function of ant bridges. We demonstrate that the microswarm is capable of serving as a microswitch, repairing broken microcircuits and constituting flexible circuits with the advantages of customizable controllability, high precision and long-term stability. This work provides an example of how science and technology can be inspired by nature. Further adjusting the surface functionalization process may endow the microswarm with new collective behaviors and functions, thus paving the way for better understanding the complex collective behaviors of living systems.

ACKNOWLEDGMENT
This work is financially supported by the General Research Fund (Nos. 14203715 and 14218516) from the Research Grants Council of Hong Kong, and the ITF project (No. MRP/036/18X) from the HKSAR Innovation and Technology Commission.

REFERENCES
[1] Felfoul, O. et al., Nat. Nanotechnol. 2016, 11, 941-947.
[2] Gracias, D. H. et al., Science 2000, 289, 1170-1172.
[3] Yan, X. et al., Sci. Robot. 2017, 2, eaaq1155.
[4] Zhang, Y. et al., Sci. Adv. 2019, 5, eaau9650.
[5] Yu, J. et al., Nat. Commun. 2018, 9, 3260.
[6] Jin, D. et al., ACS Nano 2019, 13, 5999-6077.

Cartilage consists of a collagen network coupled with a hydrated matrix of negatively charged sugars known as glycosaminoglycans (GAGs). GAGs are responsible for attracting and immobilizing water within the tissue as well as providing high resistance to compression due to charge repulsion. A decline in GAG content is an early indication of osteoarthritis (OA), a disease that deteriorates the mechanical integrity of cartilage. To date, early diagnosis of OA remains nearly impossible. Using contrast enhanced computed tomography (CECT), tissues such as cartilage can be visualized to ascertain properties such as thickness, morphology, and biochemical states of various tissues. Nanoparticles (NPs) are of particular interest as a CECT contrast agent due to their modifiable properties such as composition, diameter, high surface area, and confined electronic structure. NPs containing gold, bismuth, and tantalum have been used as X-ray contrast media for CECT. Tantalum is biocompatible, can be functionalized with a variety of silane ligands, and absorbs a greater fraction of X-rays compared to conventional iodinated contrast agents, making it an attractive contrast agent material for CECT. We have synthesized a new positively charged tantalum-oxide nanoparticle (Ta₂O₅ NP) as a contrast agent for CECT assessment of cartilage health and integrity. The NPs were synthesized with positively charged tetra-ammonium ligands to bind to anionic GAGs and a short polyethylene glycol layer to improve biocompatibility. We have successfully imaged naturally occurring osteoarthritic defects in ex vivo human metacarpal phalangeal joints using CECT with NPs with different surface charges. Additionally, we measured NP diffusion into tissue and subsequently characterized the biochemical and biomechanical state of the entire cartilage.

Self-assembly of biopolymers like proteins and polysaccharides, through their liquid crystalline (LC) state, provides reconfigurable structures in nature. These are effectively mimicked by researchers to develop highly ordered architectures through various self-assembly processes.
We reported the self-assembly of polysaccharides, sacran and xanthan gum upon drying their aqueous LC solution from a limiting interface as an example of instability-driven pattern formation. By controlling the cell width, the polysaccharide deposited to form multiple vertical membranes, bridging the millimeter-scale gap between the substrates, partitioning the available space.
The interesting aspect is the size of the LC structural unit (mesogen) of sacran. It has been reported to be 1 µm in diameter and < 20 µm in length, the aspect ratio being more than 20, when compared to other popular biopolymers like CNF, DNA. The size and interactions between these mesogenic units have not been considered. The basic theory is that as the receding air-water evaporative interface reaches their location, the domains are formed like a crust/ skin-layer. In order to create a new surface, energy is needed which comes from the supplied temperature as thermal energy. They experience capillary forces towards the substrate-wall as well as strong interparticle capillary interactions. In this competition of forces, the interparticle interaction is long-ranged and also stronger, resulting in bridging depositions. In this study, we have explored the effect of the size of the LC domains of the polysaccharide solution in the space partitioning phenomenon.

[REFERENCES]
1. K. Okeyoshi: M. K. Okajima; T. Kaneko. Scientific Reports 2017, 7, 5615.
2. K. Okeyoshi; G. Joshi; M. K. Okajima; T. Kaneko. Advanced Materials Interfaces 2018, 3, 1870013.
3. G. Joshi, K. Okeyoshi, T. Mitsumata, T. Kaneko. Journal of Colloid and Interface Science 2019, 546, 184.

[ACKNOWLEDGEMENTS]
G. J. is grateful for the JSPS Fellowship and the KAKEHNI Grant #JP18J11881.

Current fabrication process for high aspect ratio nanostructures has limitations; realization of randomly stooping feature, and lack of applicability of organic materials, although they possess attractive applications, Here, we present a new fabrication process of randomly bended polymeric nanohair structure by irradiating the polymeric vertical nanohair structure with flood electron beam under ambient pressure. Also, the bending degree was controlled by increasing irradiation time. This behavior can be explained by scattering of flood electron beam. Due to air molecules, electrons are severly scattered, and collided with the hairs from random direction. These electrons causes the oxygen-assisted radiolysis of PUA which result in outgas of carbon dioxides and water and new hydrogen bonds, hence mass loss and volum shrinkage occurs. These facts are verified by fourier transform infrared spectroscopy and monte carlo simulation of electron trajectories. This noble, and simple method has promissing applicability of fabrication of nanostructured surface with random feature for diverse applications, such as antireflection and dry adhesion.

Lattice structures have been actively studied for engineering applications due to their desirable properties such as high specific stiffness. Beyond existing properties, there have been new studies that have demonstrated mechanical behaviors which do not exist in natural materials or in the bulk forms of materials (“meta-materials”). To enhance versatility of meta-materials, there have been studies to make tunable systems using stimuli-responsive materials. Nevertheless, they exhibit properties predetermined by the initial design of lattice structures, requiring the change of the geometry for changing their mechanical behaviors. There is knowledge gap to manipulate the mechanical behaviors of lattices through a simple programming procedure without changing geometry for multifunctional materials.

To overcome the current knowledge gap, we hypothesized that if a lattice is made of a non-linear material that changes local properties depending on the local strain, one might be able to control the overall mechanical behaviors of lattices by applying different global strains that change modulus distributions within lattices. To test our hypothesis, we have utilized liquid crystalline elastomers (LCEs) as a model material to make lattice-based meta-materials because their molecules can change alignments depending on applied strain, resulting in change of their mechanical properties. For design of such multifunctional materials, we have utilized a Bayesian optimization framework to determine the shape of the LCE beams to achieve specific spatial strain distributions under applied strain followed by finite element simulations to understand how the strain-dependent material modulus change affects the overall mechanical behaviors of lattice structures.

Then, we have fabricated LCE lattice structures based on the design guidelines and characterized their mechanical behaviors. We synthesized main-chain LCEs in a replica mold of the desired shape through a two-stage thiol–acrylate reaction. Before the second stage reaction, the LCE structures were detached from the mold and different amount of strain was applied to the structures. In accordance with generated strain distribution, mesogens were differently aligned inside the structures. As a result, different modulus distribution was achieved. After that, the alignment was fixed with UV light and the structures were restored to their original shape by heating. Then, we investigated mechanical behaviors of differently “programmed” structures using universal testing system and found that the structures show different mechanical behaviors depending on the changed modulus distribution as a result of “programming”. For example, a structure with the same shape changed its behavior from positive stiffness to almost zero stiffness, i.e. stresses maintained nearly constant within broad strain range, after programming. In addition, we will present our characterization results of strain distribution in the LCE lattices and resulting modulus change to compare with the prediction from Bayesian optimization as well as our studies of combining different types of programmed structures to achieve various mechanical behaviors.

We envision that our findings can contribute to enabling the next generation meta-materials by providing the capability to manipulate the mechanical behaviors of lattices through a simple programming procedure with applications including load bearing (positive stiffness), energy absorbing (negative stiffness), and large actuation with minimum input energy (near zero stiffness). It can also contribute to improving an engineering system efficiency by enabling multi-functionalities from one component.

Wrinkling rendered by the buckling of a strained stiff layer attached to a soft elastomer substrate has been widely used in various applications such as smart adhesion, optical grating, precision metrology, surface engineering, stretchable electronics, and antifouling coating. This is because it is an efficient and low-cost strategy to control surface morphology. There were many researches on the formation of wrinkle surface in film/substrate bilayers through compressive stresses by various factors such as mechanical compression, thermal expansion mismatch, lattice mismatch, solvent-induced swelling, capillarity force, environmental stimulus, and bubble inflation, etc. Especially, the method of strain mismatch leads to thermal stress from a difference in the coefficient of thermal expansion between thin films and soft substrates for producing a wrinkled structure which has been extensively investigated throughout theoretical and experimental approaches. Bowden et al. first reported that complex surface patterns are formed by depositing a metal thin film onto a polydimethylsiloxane (PDMS) due to thermal contraction of the soft substrate by electron beam evaporation¹. Stafford et al. observed that the formation of complex surface patterns can be controlled by elastic modulus depending on the difference in thermal expansion when the ultrathin amorphous polymer on a soft elastic substrate². Im et al. have theoretically studied that the viscoelastic properties of thin polymer films play an important role in fabricating ordered structures by modeling³. However, rheological properties of viscoelastic substrates for developing wrinkle structures by the sputtering system are still insufficient up to now.
In this research, we report the controlled surface morphologies of fluorocarbon thin films deposited on soft elastic substrates by a mid-frequency sputtering using the sputtering target of carbon nanotube/polytetrafluoroethylene composite polymer. The fluorocarbon thin films deposition and particle bombardment can produce heat the PDMS substrates greatly during the sputtering process. We demonstrate a one-step method to obtain the micro/nanostructured wrinkles by changing the viscoelastic properties of PDMS substrates. The viscoelasticity of substrates was controlled with various amount of curing agent and different curing conditions such as temperature and time. The surface morphology for these samples strongly depended on the viscoelastic properties of PDMS substrates. The rheological properties and surface morphologies were systematically studied and discussed. This study provides a facile and effective method for fabricating different wrinkle structures by controlling the viscoelasticity of PDMS substrates.

References
1. Bowden, N., Brittain, S., Evans, A. G., Hutchinson, J. W., Whiteside, G. M., Nature 1998, 393, 146-149.
2. Stafford, C. M., Vogt, B. D., Harrison, C., Julthongpiput, D., Huang, R., Macromolecules 2006, 39, 5095-5099.
3. Im, S. H.; Huang, R., J. Appl. Mech. 2005, 72. 955-961.

The nanocomposite coating system was constructed by a composite film composed of inorganic polymer and graphene for metal protection. The anti-corrosive technology for metal protection is essential in contemporary industry. Although the metal species such as copper (Cu), aluminum (Al), stainless steel, etc., have a very important role in wide commercial application fields including building, automobiles, electronics, etc., they are susceptible to corrosion; spontaneous degradation reaction showing similar mechanism to electrochemical reaction at the interface between electrode and electrolyte [1]. This kind of reaction leads to undesirable deterioration of own functional properties by structure deformation of materials and a lot of financial losses. So far, most researches have been focused on the fabrication of insulating coating barrier as one of the candidates to break through this problem [2,3]. However, the necessity which requires multifunctional roles not only defending main materials but also having additional functionality such as electrical conductivity and thermal conductivity came to the fore. Furthermore, selectivity properties against various environmental factors for protective barrier layer are issues in recent semiconductor electronics, many devices including anti-icing, electromagnetic shielding (EMI) and energy storage systems [4-6].
With this consideration, we studied about dual function behaviors of electrically conductive anti-corrosion coating layer which is composed of inorganic polymers such as polysiloxane (PSX) or polysilazane (PSZ) and graphene. Inorganic polymer, PSX or PSZ, was used as a main barrier matrix with excellent chemical stability and defect covering agent for graphene and graphene, a 2-dimensional carbon allotrope, was applied as a conductive filler and a stress relaxation agent of composite matrix. The Inorganic polymer-graphene nanocomposite shield layer was fabricated on metal substrate such as Cu or Al by a simple coating process using a metering rod or a doctor blade. After curing process, the inorganic polymer-graphene nanocomposite barrier film showed enhanced corrosion inhibition properties when they were exposed to seawater (3.5 wt% NaCl) or sulfuric acid (H₂SO₄) comparing to both of bare Cu or Al substrates. To be specific, the corrosion rate of inorganic polymer-graphene nanocomposite film was prominently decreased (minimum 1/40^th compared to bare Cu in 3.5 wt% NaCl solution and 1/2000^th compared to bare Al in 0.5M H₂SO₄ solution) and charge transfer resistance was noticeably improved (minimum 2×10⁴ times higher than bare Cu in 3.5 wt% NaCl solution and 2.77×10⁶ times higher than bare Al in 0.5M H₂SO₄ solution). Furthermore, this coating film exhibits the electrical conductivity enhancement as increase of conductive carbon filler to maximum 1.70×10³ S m^-1 on Cu and to 35 S m^-1 on Al. With the result of this study, the inorganic polymer-graphene nanocomposite coating layer exhibits superior multifunction properties including anti-corrosion and electrical conductivity with the synergetic effect between inorganic polymer and graphene.
We believe that further understanding and modifying inorganic polymer-graphene nanocomposite coating system has the potential to broaden the area of application which needs multifunctionality in the field of thermal interface materials, EMI, anti-icing and etc.

References
[1] E. McCafferty, Introduction to Corrosion Science, Springer, 2010, pp. 1–11.
[2] S. An, M.W. Lee, A.L. Yarin, S.S. Yoon, Chem. Eng. J. 344 (2018) 206–220.
[3] A.A. Nazeer, M. Madkour, J. Mol. Liq. 253 (2018) 11–22.
[4] P. Pokharel, Q.-T. Truong, Compos. Part B: Eng. 64 (2014) 187–193.
[5] H. Kim, Hyemin Lee, H.R. Lim, H.B Cho, Y.H Choa, Appl. Surf. Sci. 476 (2019) 123–127.
[6] Y. Tong, S. Bohm, M. Song, Appl. Surf. Sci. 424 (2017) 72–81.

Solidified ionic liquid electrolytes, known as ion gels, have recently attracted considerable research interest owing to their great merits of high ionic conductivity, good mechanical property, non-volatility, flexibility, and thermal stability. These ion gels are typically fabricated by generating three-dimensionally interconnected polymer networks within in ionic liquids of interest. We employed a polymer precursor with chemically cross-linkable moieties and cross-linkers to make solid-state chemical ion gels. We fabricated stretchable ion gels that can be applicable to various electronic/optoelectronic devices by controlling the crosslinking density of the network polymer. By modifying the interface of the target substrate, stretchable devices could be stick to various substrates including SiO₂, metal, plastic, and rubber surfaces, which clearly demonstrates versatility of the adhesive ion gels for E-skin devices. We introduced adhesive ion gels to fabricate flexible strain sensors. Electrical properties of the flexible sensors including sensitivity, linearity, transmittance, and durability were systematically investigated. The resulting sensors using adhesive ion gels performed better than normal ion gel sensors without adhesive functionality. Furthermore, we controlled the structure and morphology of the adhesive ion gels to enhance the sensing performance.

Since any electrochemical reactions occur at surface of electrodes, an electrode with well-defined porous structure, and therefore high surface area, would be preferred. Upon crosslinking with phytic acid, polyaniline (PANI) forms a conducting hydrogel with a hierarchical 3-D porous structure. Such a PANI-based hydrogel could be a promising electrode for various electrochemical applications. Here, we present the effect of compositions in preparation of PANI on its pore morphology and electrical property. It turns out that the composition of monomer, initiator, and crosslinker in preparation has a significant influence on the morphology of the PANI hydrogel. As initiator/crosslinker increase or monomer decreases, the PANI conducting hydrogel has denser morphology with decreased pore size, resulting in higher electrical conductivity. The PANI conducting hydrogel with 3-D porous morphology could serve as an efficient electrode of an electrochemical capacitors. In the 3-electrode configuration, the PANI hydrogel electrode prepared at the optimized compositions exhibited 294 mF/cm2 of capacitance with ~50% retention rate after 5000 cycles. Finally, we fabricated a practical capacitor with two symmetric PANI hydrogel electrodes, which shows 195 mF/cm2 of capacitance with improved cycle stability of 80 % retention rate.

Theranostics is a combination of the terms diagnosis and therapeutic. This concept was further developed to Nano-Theranostics with advancements in nanotechnology over the last decade. In the Nano-Theranostics, nanoscale imaging module, targeting module, or therapeutic module were incorporated into a single system by chemical conjugation or encapsulation methods. However, the multiple compositions and complex structure of these Nano-Theranostics agents (we call this “Type 1 Nano-Theranostics agent”) have several hurdles (i.e., low reaction yield, high synthetic cost, and difficulty in verifying their toxicity) for biomedical applications. Here, we introduce next-generation of Nano-Theranostics agent, called “Type 2 Nano-Theranostics” which is MRI guided hyperthermia using magnetic softness tuned g-iron oxide (γ-Fe₂O₃, MSTIO) Nanoprobes. While the conventional magnetic nanoparticle-based agents are optimized for the individual function of MR effect or heat induction power, MSTIO possesses both exceptionally high intrinsic loss power (ILP, ~ 7.0 nHm²kg^-1) at a biologically safe range of AC magnetic field (H_appl f_appl = 5.0×10⁹ Am^-1s^-1) and a significantly enhanced r₂-relaxivity of MRI (r₂ = 647.94 mM^-1s^-1). The enhanced hyperthermic antitumoral effects and T₂-MR contrast imaging of MSTIO tested in rat models are primarily due to the dramatically increased saturation magnetization (M_s), resulted from the precisely controlled occupation of Ni²⁺/Zn²⁺ cations in T_d and O_h sites. We also found that 20-30 nm of the γ-Fe₂O₃, nanoparticles with ultra-thin surface layer shows best heat induction performance under the bio-safe range of AC magnetic field (f=100 kHz, H=120 Oe) from the numerical simulations and experimental results. Due to their excellent dual functionalities implemented in a simple system, we believe that MSTIO nanoprobe will be one of the best candidates of Type 2 Nano-Theranostics for future nanomedicine.

Many organisms in nature have a photonic epidermis composed of an assembly of iridophores, iridocytes, or iridoplasts rather than a monolithic photonic layer. The cell assembly enables the organisms to reorganize the photonic surfaces during dynamic transformation and growth. Inspired by the organisms, we propose the two-dimensional (2D) assembly of amphiphilic photonic tiles at the air-water interface to provide unprecedented reconfigurability that has never been achieved with a conventional film format of the colloidal lattice. The photonic tiles are prepared using a photocurable dispersion of silica particles in a carefully-selected resin as a photonic ink. In the ink, the silica particles spontaneously form nonclose-packed face-centered cubic (fcc) lattice due to the interparticle repulsion caused by the solvation layer. The nonclose-packed lattice is instantly captured in a polymeric matrix upon photopolymerization of the resin, where the shape of the colloid-polymer composite is featured to a hexagonal disc by photolithography. The silica particles are selectively etched out from the hexagonal disc, which results in a porous internal structure with strong iridescence. To render the photonic discs amphiphilic, the top side surfaces of the tile are subjected to reactive ion etching with sulfur hexafluoride gas, which makes the surfaces highly porous and hydrophobic according to Cassie-Baxter model. As a result, the photonic tiles sit on the air-water interface while exposing the body of the tile to the air. This configuration significantly deforms the interface by the action of gravity, which leads to the strong capillary attraction between the tiles. Therefore, the tiles assemble to form a dense photonic layer without large voids under gentle agitation. The assembly of photonic tiles rapidly adapts to the dynamic undulation of the interface and shape transformation of the container as the individual tiles can rearrange while the capillary force holds the tiles assembled. The assembly can be applied to a shape-shifting reflective display. The assembly can be also transferred onto a solid substrate by either using the Langmuir-Blodgett method or forming an elastomer on the top of the assembly. The two methods construct a highly reflective photonic coating on a wide range of substrates, which can also make a flexible photonic device. In addition, the tiles can be assembled on the surface of the water drop, forming a photonic liquid marble. It potentially serves as a reservoir for cells and algae and helps the organisms to be photo-protected and photosynthetically efficient, which is modeled after nature mentioned in the introduction. We believe that the interfacial assembly of amphiphilic photonic tiles will provide new means to create high-quality photonic coatings on wide solid supports as well as highly reconfigurable photonic surfaces at free interfaces.

A here-to-fore unexplored property of two-dimensional (2D) electronic materials is their ability to graft modular electronic functionality onto colloidal particles so as to access local hydrodynamics in fluids to impart mobility and enter spaces inaccessible to larger electronic systems. Herein, we demonstrate the design and fabrication of fully autonomous state machines (only 100x100x1 µm³ in size) built onto a SU-8 particles powered by a 2D material-based photodiode. The on-board circuit connects a chemiresistor element and a memristor element, enabling the detection and storage of information after aerosolization, hydrodynamic propulsion to targets over 0.6 m away, and large area surface sensing of triethylamine, ammonia and aerosolized soot in inaccessible locations. An incorporated retro-reflector design allows for a facile position location using laser-scanning optical detection. Such state machines may find widespread application as probes in confined environments, such as the human digestive tract, oil and gas conduits, chemical and biosynthetic reactors, and autonomous environmental sensors.
Reference: Nature Nanotechnology volume 13, pages 819–827 (2018).

Recently, microfludic devices are much paid attention, because these are used many ways such as bio analysis, chemical synthesis and heat pipe devices. However, current microfludic devices have some probrems, that these need high pressure to transport liquid, since these are composed of some closed tubes. And more, these are susceptible to bubble entrapment, inpurities, and consequently variation in the metered volume. In order to solve these probrems, we focused on a coastal animal wharf roach that has open-type flow micro-passages on the legs which can transport water to their gills spontaneously by the surface free energy. It was found out that the flow passages were composed of micro-blades oriented in several parallel lines. We fabricated a series of flow passages composed of micro-scaled epoxy blades on silicon wafer by photolithography inspired by those on legs of Wharf Roach. Fabricated samples can also transport liquid spontaneously against gravity. The purpose of this research was to clarify the factors controlling the velocity of liquid transport by changing several parameters defined the size, gap and arrangement of the micro-scaled blades. The velocity through these flow passages was experimentally determined by measuring the vertical rise of liquid column across a series of vertical microstructure surfaces with varying characteristic dimensions. The plot of transport distance to elapsed time is accurately approximated by the equation of motion for the capillary rise of liquid in a porous medium using Darcy law.
From these results, it was found out that the velocity of liquid transport through these flow passages was determined by the balance of the capillary pressure, the weight of the liquid column, and the pressure loss defined by the kinematic viscosity, the porosity and the permeability. Furthermore, it is suggested that the capillary pressure, the porosity and the permeability can be controlled by several parameters of the sample, and the liquid transport velocity can also be adjusted.

Pressure-sensitive touch panels provide an intuitive and natural method to sketch and write with new levels of control and interactivity. However, they require a combination of sensors or a stylus-based interface to identify 3D signals, which prevents their implementation in a wide spectrum of applications. Here, we report a transparent and flexible 3D touch which operates in a single device with the assistance of multiscale structures and a nanowire percolation network. The device could assign functionalities to objects without reference to any varying surfaces. Rigorous theoretical analysis allowed us to achieve the target pressure sensitivity, and successful 3D data acquisition was carried out through the 6-wire measuring technique

Tasking polymeric materials with functionalities beyond their primary (often load-bearing) role has gained significant interest in the development of smart materials. We have recently developed a reconfigurable shape memory elastomeric composite (Re-SMEC) featuring a water-degradable, elastomeric polyanhydride (PAH) matrix that, unlike most polymeric shape memory systems, features an original geometry that can be thermomechanically altered at will. In our past work, we reported that this reconfigurability was possible since the constituent bonds of the polyanhydride elastomeric network undergo dynamic covalent exchange between neighboring anhydride groups. This exchange enables one to customize the geometry of the “target” shape during shape memory activation. Taking advantage of these new properties, we present a new shape memory elastomeric composite featuring elastic fibers as the permanent, memory retaining phase, and a polyanhydride-based elastomer matrix as the fixing phase. Unlike other fiber-reinforced shape memory systems, where the fibrous phase typically serve to temporarily fix geometry, this design utilizes a reconfigurable matrix as the shape-fixing phase. Moreover, this new design enables recovery of the original shape in response to degradation of the matrix. We report on the degradation profile of this composite, with quantification of mechanical properties and the effect of fiber orientation on this new shape memory phenomenon.

Electronic skin realizes seamless interfaces between human and computers, enabling mechanical and chemical sensing on human skin with applications for healthcare/monitoring devices and user interfaces for augmented reality. Multifunctional devices that can map high-resolution pressure distribution over arbitrary surfaces would enable novel applications such as skin prosthesis, artificial nerve systems for soft robotics, and advanced human-machine interfaces. For this reason, many studies on conformable force sensors have tried to map spatial pressure by employing matrix design and sensor pixels. However, they show poor spatial fidelity mainly due to their low pixel density, crosstalk among pixels, and bulky electrical wires for data acquisition. Furthermore, pressure distribution could be severely distorted by device structures such as uneven or thick sensing layers, structural inhomogeneity, and limited conformability. Therefore, the new homogeneous and conformable design should be developed to bridge the fidelity gap. However, existing methods for flexible or soft pressure sensors show limited design freedom to satisfy the demand due to their impractical fabrication process. Although pressure sensors exploiting contact resistance between engineered micro-/nano-structures and conductive films are promising due to their high stability and fast response time, reported works cannot offer viability because they need bulky micro-fabricated or pre-established structures such as a sponge and tissue paper.
In this work, we propose a homogeneous and ultrathin device structure to autonomously capture and image pressure distribution over 3D surfaces with high spatial fidelity, and appropriate materials and a manufacturing method for highly sensitive and transparent pressure sensors that can be readily integrated into the proposed device. Specifically, we develop a solution-processable nanohybrid network of nanocellulose and conductive nanowires for ultrathin and transparent piezoresistive pressure sensors. As compared to previously reported cellulose-based piezoresistive pressure sensors where microfibers are coated with conductive nanowires, our nanohybrid network features a nanostructured surface morphology where dense nanocellulose encircles each conductive nanowire. This unique nanostructured surface results in unprecedentedly high sensor sensitivity (> 1000 kPa^-1), a fast response time (< 1 ms), and high transparency (~80%). We combine the transparent piezoresistive network coated on an ultrathin (~1 μm) colorless polyimide (PI) film with a quantum dot-based electroluminescent film. The two functional films conform to each contact object and effectively form conductivity distribution in a continuous domain with minimal distortion of contact pressure. This patterned conductivity brings out high-resolution (> 1000 dpi) electroluminescent imaging of the pressure distribution without the need for pixel structures. The spatial resolution depends only on the thickness of the films, whose effect on output images is systematically investigated by a finite element analysis and measuring images of spatial pressure applied with micropillar arrays. We further demonstrate the feasibility of our approach by constructing high-information-density human-machine interfaces such as a transparent touch interface that can identify the user in addition to touch information. This study provides a new pathway to high-fidelity stimulus imaging with potential applications for bio-imaging, wearable human-machine interfaces, and force-sensing deformable displays. The detailed methods and results will be discussed later.
This work was supported by Institute for Information & Communications Technology Promotion (IITP) grant funded by the Korean government (MSIP) (No.2017-0-00048, Development of Core Technologies for Tactile Input/Output Panels in Skintronics (Skin Electronics)).

Smart adhesive system which easily adhere to and release from a target surface on demand by external signals can be employed in broad applications in medical industry, robotics, industrial transporting system, and smart printing. By employing light-responsive actuation of hydrogel composites and octopus-sucker-like microstructure of elastomer, here, we demonstrate a high-performance light-responsive smart adhesive pad, in which the adhesive properties can be actively and remotely controlled by external light stimulus. The light-responsive hydrogel composite, which consists of a thermo-responsive hydrogel (poly(N-isopropylacrylamide) (pNIPAM)) and photothermal carbon materials, acts with a switchable motion of shrinking/swelling by turning on/off a near IR light. This hydrogel composite on the octopus-sucker-like microcavity-patterned elastomer (polydimethylsiloxane (PDMS)) can generate/remove a differential pressure between the inside and outside of microcavity, which can induce/withdraw an adhesive force to grab/release a foreign target surface. Finally, the light-responsive smart adhesive pad shows a switchable adhesive performance through the control of irradiation of near-IR (NIR) light, enabling the switchable adhesive strength from 0.15 kPa (NIR light ‘off’) to 26.32 kPa (NIR light ‘on’) with an on/off switching ratio of adhesion of 175 in fast response to the remote NIR light without any preload. Thanks to these superior adhesive properties, the smart adhesive pad can be applied to broad macroscopic/microscopic applications such as an adhesive patch which can endure a weight or a micromanipulation to easily pick and release micro/nano-membranes of semiconductors by the remote control of NIR light.

Buckled structures originated from the compressive stress on a film have been exploited to generate randomly or regularly grating patterns, or as a method to fabrication of foldable or stretchable devices. Laterally buckled structures, which is resulted from the compression of high aspect ratio line patterns have been reported for an academic interest or an application about the anti-counterfeit patterns generated by a mechanical response. In the presentation, we show the control of the features of laterally buckled patterns by the manipulation of the compressed area in the bilayer system. In addition, we demonstrate a potential application to absorb the mechanical stress by using the unique spring-like structures of lateral buckling.

Injun Lee, Wonryung Lee_, Yong Ho Kim, and Byeong-Soo Bae
Wearable Platform Materials Technology Center (WMC)
Dept. of Mater. Sci. & Eng., KAIST, Daejeon 34141, Republic of Korea
The barrier is a key component of bio-integrated electronics, protecting the device from the bio-fluid environment and enabling high performance without degradation over time. Recently, the bio-fluidic barrier on the ultra-thin device offers reliable measurement of various bio-signals from even on skin or organ due to the defect-free passivation layer[1]. To meet the requirement of low water permeability, inorganic material based bio-fluidic barriers such as thermal grown SiO₂ [2] and bilayer of SiO₂/SiN_x[3]have been exhibited superior barrier performance. However, the inorganic materials for the barrier have process incompatibility, including high processing temperature and harsh etching conditions. Thus, the organic materials based on bio-fluidic barriers, such as polyimide(PI)[4] and SU-8[5] have been also investigated due to their process compatibility. But such organic-based barriers are unstable under the water environment, resulting in unreliable ultra-thin devices for the bio-applications. Therefore, hybrid material for the bio-fluidic barrier that has advantages of both organic and inorganic is needed.
Here, we demonstrate the siloxane(inorganic) based fluorinated epoxy(organic) hybrid materials(FEH) for the bio-fluidic barrier and confirm the barrier performance for the flexible system by using the solution-processed oxide thin-film transistor(TFT)s on ultra-thin polyimide film. Our sol-gel derived FEH is inorganic-organic hybrid materials for the bio-fluid barrier, which is capable of simple spin-coating and UV-patterning by cationic polymerization without additional etching process. Furthermore, FEH exhibits superior water repellency and hydrophobicity compared to other conventional organic films due to the fluorine functional group, which can be confirmed by magnesium soaking test and water contact angle. To evaluate the electrical stability of the barrier in the bio-fluidic environment, we confirm no leakage through defects of films using electrical impedance spectroscopy analysis. To verify the barrier performance in real-time, we demonstrate the solution-processed indium oxide TFTs with the FEH barrier and measure the transfer characteristics in the phosphate-buffered saline (PBS). The oxide TFT, which is vulnerable to water, passivated by FEH barrier films exhibits transfer characteristics with no dramatically change during 16hours in the PBS. Furthermore, to realize the FEH barrier for flexible systems, we demonstrate the solution-processed oxide TFTs on 1μm-thick polyimide film with the FEH barrier and successfully measure the transfer characteristic, which is consistent with the result of TFTs on rigid glass wafer. In conclusion, we envisage the potential of our FEH as a bio-fluidic barrier for future bio-integrated devices and advanced electronics.
[1] S. Park, S. W. Heo, W. Lee, D. Inoue, Z. Jiang, K. Yu, H. Jinno, D. Hashizume, M. Sekino, T. Yokota, K. Fukuda, K. Tajima, T. Someya, Nature 2018, 561, 516.
[2]H. Fang, J. Zhao, K. J. Yu, E. Song, A. B. Farimani, C.-H. Chiang, X. Jin, Y. Xue, D. Xu, W. Du, K. J. Seo, Y. Zhong, Z. Yang, S. M. Won, G. Fang, S. W. Choi, S. Chaudhuri, Y. Huang, M. A. Alam, J. Viventi, N. R. Aluru, J. A. Rogers, Proc. Natl. Acad. Sci. 2016, 113, 11682.
[3] E. Song, H. Fang, X. Jin, J. Zhao, C. Jiang, K. J. Yu, Y. Zhong, D. Xu, J. Li, G. Fang, H. Du, J. Zhang, J. M. Park, Y. Huang, M. A. Alam, Y. Mei, J. A. Rogers, Adv. Electron. Mater. 2017, 3, 1.
[4] J. H. Koo, S. Jeong, H. J. Shim, D. Son, J. Kim, D. C. Kim, S. Choi, J. I. Hong, D. H. Kim, ACS Nano 2017, 11, 10032.
[5] H. R. Cho, D.-H. Kim, T. Hyeon, Y. S. Hong, S. H. Choi, C. Song, T. Kang, H. Lee, K. Shin, M. S. Kim, Sci. Adv. 2017, 3, e1601314.

Piezoelectric materials are extensively used as actuators in various sectors such as biomedical, manufacturing and robotics. This is due to its piezoelectric property that allows the material to actuate when an electrical field is applied. Compared to traditional electric motors, piezoelectric polymer actuator, Polyvinylidene Fluoride (PVDF), offer advantages such as conformability, ease of processing, better biomimicking ability, lower cost, higher power-to-weight ratio, increased control, and response time. PVDF is a semi-crystalline polymer where its zigzag all-trans (TTT) b crystal phase is responsible for the actuation ability. To promote this unique crystal phase, there has been research on processing methods, such as the addition of fillers to align and stabilized the TTT conformation on the surfaces of the nanofillers. The current study investigates the use of single-walled carbon nanotubes (SWCNT) in a PVDF matrix to increase: (i) its piezoelectric property for enhanced actuation and (ii) its mechanical property to withstand the environmental conditions of various actuation applications. The weight percentage (wt.%) of SWCNT within the PVDF matrix and its dispersion, enhanced actuation displacement, and response time due to higher conductivity were explored with parametric studies. This study also reports on the effects of popular processing methods (i.e., mechanical stretching) in promoting the alignment of the fillers, resulting in an alignment of the crystal structures. Initial results found an optimal weight percentage of SWCNT to be 0.5 and 3%, where both mechanical, electrical, and actuation properties excelled. At 1 wt.% CNT, the composite increased its conductivity by 4 magnitudes, and its density and ultimate yield strength increased by a factor of 70%. While its b content at 1 wt.% had no significant change, at 2 wt.% CNT, the b phase increase to 40%, 10% higher than that of the pure PVDF sample. With an increase in conductivity and piezoelectric property, the material’s actuation can be performed with greater displacement and lower power. This study provides insight to future research utilizing piezoelectric materials for actuation application that can advance into soft robotics.

We present advancements to a water-based digital fabrication and design platform that allow for the continuous gradation of mechanical properties, biocompatibility, and biodegradability in pectin-based biopolymer hydrogels. Continuous gradation of these properties across scales ranging from centimeters to meters are achieved using the same fabrication methods and computational workflow. Fabrication parameters including extrusion pressure and feedrate are assigned and varied without discretization, allowing material proportions to be precisely tuned by graded computational inputs. Localized diffusion of extruded materials further increases the continuity of multi-material transitions beyond the limits of mechanical resolution.

Both functionally graded and homogeneous combinations of silk, pectin, and chitosan hydrogels are presented and characterized with a focus on the ability to tune stiffness, dissociation rate, and the proliferation rate of biological agents as independent variables The implemented digital-fabrication system further enables the real-time modification of extrusion parameters through feedback-driven control logics, thereby allowing the further customization of hydrogel properties in response to environmental parameters. These capabilities constitute a set of methods by which a diverse array of material properties can be precisely tuned and spatially templated from a relatively limited material palette for the creation of functionally-graded multiscale hydrogels.

It is important to record thermal history in our daily lives. Although conventional digital-based thermometers have a high accuracy of temperature measurement and its recording, they usually consist of electronic circuit board, battery, and display as well as temperature sensor, which are expensive and not disposable. Moreover, the electronic thermometers have difficulties on applying to an infant skin for monitoring long-time fever or applying to packages of edible products and cosmetics for checking staleness, causing intense demand for disposable, patch-type thermal recorders. The non-electronic, disposable thermal recorders can be prepared by using materials that have colorimetric response for temperature. Metallic nanoparticles, thermochromic dyes, fluorescent dyes, or liquid crystals have been used as constituent materials for the temperature recording. However, it is elusive to decouple temperature and time from color change of the materials.
Here, we design photonic films that record thermal condition through irreversible structural deformation and intuitively display the thermal condition as color patterns. The photonic films are polymeric inverse opals whose frameworks are made of negative photoresist. When the polymeric inverse opals are heated up, they experience creep deformation due to the large surface energy at the pores, causing shrinkage. Polymeric inverse opals attached on a solid substrate show the shrinkage along the direction normal to the substrate while maintaining regularity of their cavity array. This anisotropic shrinkage leads to a blue-shift of the structural color. The rate of the blue-shift or equivalently rate of deformation strongly depends on the temperature. The relation between the rate and temperature can be described by time-temperature superposition principle or Williams-Landel-Ferry (WLF) model. That is, time and temperature are equivalent so that it is difficult to separately estimate time and temperature from the single magnitude of the blue-shift. To decouple and separately estimate temperature and time for isothermal heating, crosslinking density of the negative photoresist is regioselectively adjusted by controlling ultraviolet (UV) dose, which determines thermal and mechanical properties of the photoresist. As the different crosslinking density provides different time-temperature relation, several independent relations can be obtained from a set of distinct UV doses. For isothermal heating, an invisible pattern with regioselective UV doses turns into a multicolor pattern. Using the multiple structural colors of the single inverse opal film, multiple superposition equations are deduced, from which temperature and time are separately estimated. To the best of our knowledge, there has been no thermal recorder that is able to decouple temperature and time. Our patch-type inverse opal is potentially useful as the disposable thermal recorders for various applications.

Bio-inspired compound (BIC) eyes have been emerged as a main component of optical systems, and many researchers have been interested in their unique optical characteristics such as wide field-of-view, low-aberration, and high sensitivity to light ^[1,2]. To fabricate BIC eyes structures, several methods are generally used such as precision machining, thermal reflow, and femtosecond laser writing ^[3-5]. However, these methods are time-consuming and involve high-cost associated with photolithography and etching. Self-assembly of microparticles in liquid can be an alternative method ^[6] because it does not require vacuum system. But it is not appropriate for large-area fabrication and has a disadvantage in that the process control is difficult.
In this work, we report a facile fabrication method for BIC eyes with printing and dry-rubbing assembly process. Firstly, a hemispherical lens is fabricated by dispenser printing method, which is suitable for rapid-processing of optical components ^[7]. After that, we adopt dry-rubbing process, which is one of the methods for arranging microparticles in dry-phase ^[8], to form microparticle monolayer onto the surface of hemispherical lens. This hierarchical microstructure is used as a template of BIE eyes, and replicated in soft materials including polydimethylsiloxane and ultraviolet-curable epoxy resin. Because the BIC eyes structure is fabricated from soft materials, it has stretchability, thus it is expected that the optical properties can be easily tuned by applying mechanical strain. We believe that our method can be applied to the various imaging systems such as cameras, endoscopies, and light-emitting devices. Detail fabrication process and experimental results will be discussed at the conference.

Acknowledgments:
This research was supported by the MOTIE (Ministry of Trade, Industry & Energy) (10051971) and KDRC (Korea Display Research Corporation) support program for the development of future devices technology for display industry. The authors thank to Prof. Unyong Jeong at the Pohang University of Science and Technology (POSTECH) for the help in dry-rubbing assembly process.

References:
[1] K. -H. Jeong, J. Kim, and L. P. Lee, Science 312, 557 (2006).
[2] G. J. Lee, C. Choi, D. -H. Kim, and Y. M. Song, Adv. Funct. Mater. 1705202 (2018).
[3] L. Li, and A. Y. Yi, Opt. Express 18, 18125 (2010).
[4] S. Huang, M. Li, L. Shen, J. Qiu, and Y. Zhou, Opt. Commu. 393, 213 (2017).
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[6] T. Wang, W. Yu, C. Li, H. Zhang, Z. Xu, Z. Lu, and Q. Sun, Opt. Lett. 37, 2397 (2012).
[7] S. Lee, S. Lee, H. Yoon, C. -K. Lee, C. Yoo, J. Park, J. Byun, G. Kim, B. Lee, B. Lee, and Y. Hong, Opt. Express 26, 824 (2018).
[8] C. Park, T. Lee, Y. Xia, T. J. Shin, J. Myoung, and U. Jeong, Adv. Mater. 26, 4633 (2014).

Natural polymer is one of the most promising material to reduce dependence on petroleum-based polymer. Cellulose is the most abundant natural polymer on the planet. In particular, the use of cellulose is not only a fundamental solution to the focused microplastic problem, but also is high utilization value as industrial material due to high strength, biodegradability and thermal stability.
However, it is well known that cellulose does not have T_g and melting temperature because of their strong hydrogen bonding network and chain rigidity. These limitation makes difficult to be thermally formed as certain shape and control mechanical properties to apply industrial fields. Therefore, it is necessary to the develop of technology capable of controlling strength, flexibility, and stretchability by inducing thermoplastic properties. Many researchers have studied methods of microstructural change to develop thermo-plasticized cellulose by introducing macromolecules on cellulose backbone. However, those methods have critical limitation because of low efficiency of plasticization and complex process that precedes the synthesis of cellulose derivatives.
In this study, we developed method to efficiently plasticize cellulose via change of grafting architecture which composed of ester molecules. To control chain flexibility and free volume, three different types of grafting molecules were employed; ε-caprolactone (ε-CL) / Cell-g-PCL, ε-decalactone (ε-DL) / Cell-g-PDL, and L-lactide / Cell-g-PLLA. The grafting molecules were synthesized at hydroxyl groups on cellulose backbone via ring-opening polymerization in 1-buthyl-3-methyl-imidazolium chloride, which was observed by ¹H NMR and FTIR. Furthermore, degree of polymerization (DP) of grafted molecules was controlled to confirm effect of side chain size on plasticization performance. The microstructure of cellulose was significantly disrupted by grafting molecules. This deconstruction behavior became more clear when the size of grafting molecules was larger. Despite of similar molecular weight of grafted molecules, the branched architecture easily dissociated the cellulose crystalline. This results led to decrease of glass transition temperature (T_g) of cellulose. ε-DL-grafted cellulose exhibited T_g at 30 ^oC, while T_g in ε-CL and L-lactide-grafted cellulose was not observed in similar DP. This results suggested that the grafting molecules with branched structure was more effective to hinder intra- and inter-chain network of cellulose, compared to linear structure.

Clear endoscopic vision is essential for laparoscopic surgery. However, body fluids such as blood and peritoneal fluid cause sight loss, which make the surgical operation difficult. Conventional methods such as irrigation, rubbing lenses, and particle-based porous coating infused with lubricant have been conducted to prevent sight loss, but functional stability issues are not solved[1]. Here, we present directly engraved nano-microstructure lubricating (DENL) method, which demonstrates anti-biofouling and anti-fogging ability without any additional device and strong physical and chemical durability due to engraved nano-microstructure. DENL method involves the formation of robust nano-microstructure on the endoscope lenses via etching with a femtosecond laser. After the process, Fluorine-based self-assembly monolayer (SAM) was applied on the substrate to enhance the chemical affinity of the substrate to perfluorocarbon-based lubricant. We further demonstrated that the developed lens maintained a transmittance of 80% in the visible light region and confirmed its anti-biofouling and anti-fogging ability via dipping (>5 cycles) and fogging (>30 mins, >RH 90%) test using various body fluids. Also, the clear vision was secured even in extreme condition where various attempts were made to damage the developed lenses via exposing it to various chemical solutions and mechanical stresses. We believe that the endoscopic lenses produced by DENL method bring excellent benefits in endoscopic surgery compared to a conventional method by securing clear sight for stable operation and miniaturizing the endoscopic instrument for minimally invasive surgery.

Reference
[1] Sunny, Steffi, et al. Proceedings of the National Academy of Sciences 113.42 (2016): 11676-11681.

Acknowledgement
This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government(MSIT) (No. 2019R1C1006720) and the Yonsei University Research Fund of 2019 (2019-22-0014).

Radiative cooling enables passive cooling of terrestrial objects to sub-ambient temperatures by rejecting thermally emitted infrared radiation to the cold outer space through the infrared (IR) transparent window of the earth’s atmosphere (8-13 µm). However, achieving low sub-ambient emitter temperatures and high cooling power during the day under direct sunlight remains a challenge due to significant absorption of solar irradiation and high parasitic heat gains from the ambient environment. In this work, we address these challenges by developing polyethylene aerogels (PEAs) covers that are optimized to achieve high solar reflection, near-perfect infrared transmittance and ultra-low thermal conductivity which can minimize solar absorption and parasitic heat gains at the emitter. The PEA samples were fabricated using thermally induced phase separation of polyethylene in a solvent followed by supercritical CO₂ solvent extraction. The optical and thermal properties were optimized by altering the nanoporous structure of the PEA using different solvents (decalin, paraffin oil or paraffin wax) and varying the density (between 10 and 80 kg/m3) of the aerogel. The optical characterization of the fabricated samples revealed a solar-weighted reflectance as high as 92% and a mid-infrared (8-13 µm) transmittance as high as 80% for a 6 mm thick sample. We also performed a detailed thermal characterization of PEA samples using a custom-made guarded hot plate thermal conductivity setup and measured thermal conductivity as low as 28 mW/mK. By performing measurements under different gas pressures and boundary conditions (optically black or reflective boundaries), we were further able to experimentally decompose the total thermal conductivity k of PEA into its three subcomponents – solid k_s, gaseous k_g, and radiative k_r. Finally, we performed outdoor experiments to demonstrate the benefits (ultra-low thermal conductivity and high solar reflectivity) of our optimized PEA for daytime radiative cooling. Under direct sunlight at solar noon, we measured a sub-ambient cooling of up to 13 °C for an emitter covered with 12 mm thick PEA – greatly surpassing the performance (1.7 °C sub-ambient cooling) of a similar emitter without PEA.

Vanadium dioxide (VO₂) is an ideal inorganic driving material for actuators with outstanding performance due to its giant power density (7 J/cm³) and ultrafast response (∼ picosecond). Single-crystalline VO₂ nanowires (NWs) have demonstrated supreme actuation capabilities while the VO₂-based flexible devices up to centimeter-size toward macroscale robotics are rarely explored. Here, we develop a kind of macroscopic, flexible and all-inorganic bimorph actuators composed of super-aligned VO₂ NWs and carbon nanotube (CNT) films for the first time. Super-aligned VO₂ NW films in large scale (several square centimeters) were achieved by assembling and post-annealing ultra-long H₂V₃O₈ NWs. The as-grown highly-anisotropic VO₂@CNT films showed tailoring direction-dependent bending morphologies and actuation performance, in which giant displacement/length of 0.83, high power density of 3.2 J/cm³ —-2 orders of magnitude higher than mammalian muscle, fast response up to ∼15 Hz, and long lifetime more than 1 million actuation cycles were demonstrated. The excellent thermal/electrical conductivity and light absorption of CNT thin films enable the actuators highly responsive to multiple stimuli including heat, light, and electricity. Notably, the whole-inorganic structure as well as remarkable anisotropy allow the remarkable actuation of VO₂ NWs in a macroscopic scale mechanical device with fantastic performance for versatile applications, including biomimetic geometer, mini jack, inspect wing, mini elephant trunk, torsional artificial muscle, etc.

Our bodies and smartphones will be connected to the bodyNET in the near future [1]. Electronic devices that can stretch, from circuits and batteries to sensors and screens, will realize with the demand of such bodyNET and will extend our senses and abilities. To fabricate devices within our clothes and accessories, attached to our skin and implanted in our bodies, a new platform transfer technology is required. In particular, the technique of forming conformal contacts, which remove air at the interface, is of paramount importance. Air trapping at the interface cause air to bulge due to small thermal changes during the device driving and even during post-processing such as vacuum, ultraviolet curing, heating and plasma processes, etc. The interfacial air-bulging problem could lead to not only delamination but also the breaking of films and metal interconnections in the devices. As a result, the interfacial expansion of air damages the electrical characteristics of the device. Meanwhile, the degree of air-bulging at the interface could be increased as Young’s modulus of a stretchable materials is low.
In this talk, we introduce how to remove air in the interfaces for the fabrication of skin electronic devices (skintronics). It is possible by using a gapless vacuum laminator with a stretchable jig. Skintronics were designed to the wrinkled structure, to impart stretchiness in one axis direction without destroying the function of the device while stretching or compressing the device. The gapless laminating process consists of a first step of removing air from the interface and a second step of applying pressure. Skintronics are fabricated by four essential fabrication steps. First, polyimide (PI) is spin-coated on a carrier glass. Second, the functional layers constituting the device are individually fabricated on a sample of glass/PI. Third, a sacrificial film (SF) is fabricated on a sample of glass/PI/device, followed by a laser lift-off process to detach a glass from a sample of glass/PI/device/SF. Finally, a sample of PI/device/SF is totally transferred on pre-stretched elastic substrate by a gapless vacuum lamination [2]. Spontaneous wrinkles are formed on skintronics, which has the structure of elastic substrate/PI/device, after both removing a SF and relaxing a stress. Here, we prove that the devices fabricated by a new total transfer method are stable and reproducible in the electrical property during a device driving. Also, we demonstrate that this excellent electrical property of the device is due to the reduction of a long-range-order deformation as well as a formation of conformal contact at the interfaces.

This work was supported by Institute for Information & Communications Technology Promotion (IITP) grant funded by the Korea government (MSIP)(No.2017-0-00048: Development of Core Technologies for Tactile Input/Output Panels in Skintronics(Skin Electronics)).

Energy saving in buildings is a critical problem due to the poor thermal insulations, especially for windows in cold climates. The conventional approach mainly relies on a double-pane design. We have previously reported a concept that by applying photothermal coating on single-pane windows, the thermal insulation property (U-factor) can be dramatically lowered. Both Fe₃O₄ and Fe₃O₄@Cu_2-XS nanoparticles coatings have shown promising photothermal effect, maintaining good transparency. By comparison of the same average visible transmittances (380-760 nm) of Fe₃O₄ and Fe₃O₄@Cu_2-XS coatings, Fe₃O₄@Cu_2-XS shows better photothermal effect under simulated solar irradiation (0.1 W/cm²). This is due to the better NIR absorbance of Fe₃O₄@Cu_2-XS nanoparticles compared to Fe₃O₄ nanoparticles. Similar results were also found through monochromic irradiations (785 nm laser, 0.1 W/cm²). Therefore, under the same requirement of visible transmittance, a photothermal coating with better NIR absorbance will perform the better photothermal effect, as well as better thermal insulation improvement for the coated single-pane window.

Synthetic microparticles have been widely used in drug delivery, imaging, light scattering, pigmentation, cell mimicking, and understanding of cell phagocytosis. Surface patterns could play important roles in their functions, yet it remains challenging to (re)produce spherical microparticles of diverse surface patterns with submicron resolutions. In contrast, nature uses a bottom-up mechanism, via phase separation of extracellular material mechanically coupled to an elastic cell membrane, to create infinitely replicable but diverse surface patterns on spherical cells, such as fungal spores, insect cuticles, and pollen grains. Here, taking the biological pathway that nature has perfected over evolutionary history, we design and fabricate liquid crystal elastomer (LCE) microparticles (diameter, 1 ~ 10 um) with various surface patterns including holes, stripes and spikes, recapitulating the key features in pollen pattern formation that involves phase separation and kinetic arrest of polysaccharides of different chemistry and elasticity at the extracellular membrane. Our approach takes advantage of the anisotropy of liquid crystal oligomers (LCOs) and mixture of different chain lengths in a single droplet. While the chain length of LCOs determines the surface energy and elasticity, thus surface anchoring behaviors at the interface; the heterogeneity of LCOs leads to chain segregation within droplets, thus, facilitating kinetic arrest of LCOs at the interface. Diverse surface patterns are formed after UV curing of the LCO droplets, which are not seen from non-LCOs. Our study also confirms that heterogeneity can be a feature but not a bug in self-assembly. The ability to form diverse and complex surface patterns on microparticles could not only improve our understanding of the general rules about self-assembly in micro- and nano-environments, but also open doors to mass production of functional nano-/micromaterials.

For centuries, optics and photonics have been key enabling technologies in art, design, and architecture in a manner that architects and designers, in their struggle to enrich visible light with color, have experimented with adding pigments, textures, and nanoparticles to construction materials. However, the sunlight not only brings bright visual illumination and color to the building exteriors and interiors, but also radiative heat, which can either be used to warm the buildings or needs to be reflected to avoid overheating. Ideally, the two functions can be combined in one material or a single structural design concept. Recent development of spectrally-selective nano-structured materials and meta-surfaces has opened opportunities to manage both visible light and radiative heat year-round with conventional window and rooftop designs. In this regard, lightweight, flexible, and durable polymer materials, as well as organic-inorganic composites are increasingly replacing conventional natural materials across different sectors of economy, including new construction, historical buildings retrofitting, and design of new multi-functional wearables. Here, we report on the design, fabrication, and characterization of polymer-based organic-inorganic composites with tailored broadband spectral properties, and controllable thermal conductivity. We show that by varying the degree of crystallinity of ultrahigh molecular weight polyethylene (UHMWPE) and the composition of nanoparticle fillers, we can achieve simultaneous control over optical and thermal properties of the resulting composite material. The development of new optical functionalities that go beyond normal light diffusion in disordered polymer-based materials are also explored by introducing pseudo-random order to the material internal meso-structure.

Iridescence due to a structural organization is seen in nature in many organisms. Comb jellies are sea animals of phylum Ctenophora. In this study two species, namely Mnemiopsis leidyi (M. leidyi) and Beroe cucumis were used to study the internal arrangements of iridescent structures or comb rows. The Refractive index (RI) of the tissues of these comb jellies are close to the RI of salt water (~1.34) and the RI of comb rows is higher making them much more visible than rest of the body (~1.57). The internal structures of comb rows are hexagonally packed and consist of a central microtubule pair. Reverse engineering these submicron structures throws light on the arrangements and will help in designing a novel photonic template. Photonic crystals are periodic arrangements of different dielectric constant materials and if their periodicity changes due to external stimuli their maximum reflectance changes too and this principle can be used in sensing applications. There is an increasing need for a point of care diagnostics, demands the production of label-free and highly sensitive detection. The traditional analytical systems are time-consuming, labor intensive and expensive. Replacing these methods with simple but advanced detection mechanisms would transform the medical field as it could save billions of dollars, assay time as well as patients who need early stage detection.
Surface-enhanced Raman spectroscopy (SERS) is a powerful technique for detection of analytes. The information of chemical bond vibrations that cause Raman shifts is gathered even when an analyte is in trace amounts. It is widely known that SERS activity is large in areas with a high electromagnetic field, known usually as “hot spots”. These hot spots are found in closely packed metal nanostructures. The use of metal coated (Ag, Au) nanostructures as a SERS substrate can increase the Raman signal of analyte tremendously. Recently, many studies have demonstrated that metal coated nanopillars act as efficient SERS surfaces. The spacing between the structures and substrate excitation plays a crucial role in the Raman signal generation. The above-mentioned comb rows like nanostructures, when coated with Au or Ag, could act as a SERS active surface, giving rise to several hotspots for analyte detection.
In this study, we observed the nanoscale arrangements of the comb structures under a transmission electron microscope using ultratome cross-sections of the same. The design of these nanostructures was recreated using AutoCAD and RAITH software. These were then replicated using two-photon lithography and ebeam lithography techniques. These were later characterized with scanning electron microscope (SEM) for their reflectivity, Raman signatures, both with and without gold molecules. Finally, these golds coated photonic templates were utilized as a SERS active surface for biomolecules.

Fibronectin (FN) fibrillogenesis plays crucial roles in vivo by orchestrating embryogenesis, tissue organization by promoting the assembly of other extra-cellular proteins such as collagens, fibrillin, and tenascin-C and cell adhesion and growth [1]. This process is initiated by binding of FN to the cell surface through integrins and subsequent association with polyanionic proteoglycans (PGs) such as chondroitin sulphate resulting in FN unfolding from compact form to an extended form [2]. FN-self association through N-terminal domains and additional binding sites after FN unfolding result in fibril growth stabilized through non-covalent FN-FN interactions. To realize FN fibrillization artificially in vitro, the assembly of FN at the air-water (A-W) is an attractive solution [3]. The 2D confinement and high local concentration at the A-W interface enhances the FN-FN association essential for fibril growth and the acidic pH of the subphase can mimic the negatively charged PGs to promote FN unfolding. It is hypothesized that FN assembly at the A-W can simulate the FN assembly on cell membranes and result in fibril formation. FN was spread as droplets from concentrated solution (1 mg/mL) on subphase pH 2 in a circular trough (diameter 9 cm) and the assembly process was followed using in situ characterization tools. Surface pressure increases with time plateauing at 11 mN/m after 350 min and this indicates that surface adsorption is favorable on the subphase with pH 2, which is a pre-requisite for self-assembly. In parallel, the assembly process was investigated by polarization-modulation infrared reflection absorption spectroscopy (PM-IRRAS) to get information about the conformation of the FN layer. Amide I peak shifted from 1627 cm^-1 to 1621 cm^-1 after 30 min indicating unfolding of the FN from the compact native form. Finally, FN self-crosslinking was proven using interfacial rheology by the increase in interfacial elastic modulus and interfacial loss modulus with time (upto 16 h). The elasticity of FN fibrils was confirmed from the much higher elastic modulus (6 mN/m) than loss modulus (1 mN/m). Therefore, FN fibrillation can be realized in a cell-free environment using the A-W interface as a platform for assembly and such fibrils can be produced artificially in a facile manner on large-areas (12 cm²). We envision that such FN fibril networks can be transferred onto substrates for stem cell differentiation or as biomimetic scaffolds for tissue engineering and regenerative medicine.

References
1. Mao, Y.et al., Fibronectin fibrillogenesis, a cell-mediated matrix assembly process. Matrix Biol, 2005. 24(6): p. 389-99.
2. Ahn, S., et al., Self-organizing large-scale extracellular-matrix protein networks. Adv Mater, 2015. 27(18): p. 2838-45.
3. Bhuvanesh, T., et al., Langmuir–Schaefer films of fibronectin as designed biointerfaces for culturing stem cells. Polymers for Advanced Technologies, 2017. 28(10): p. 1305-1311.

Always there is great demand for in vivotesting to understand more about body metabolism to provide effective diagnosis and therapy. Currently no industrial technology available for single cell especially for pH, temperature or other cell metabolites. Compared to conventional sensors, research on single cell microneedle sensor is still in its infancy due to their difficulty in fabrication, poor flexibility, toxicity, scarcity of nanomaterials, instrumentation difficulty and poor stability. Meanwhile painless micro/nano needles have been widely used for extraction skin interstitial fluid, vaccine and drug delivery over the past two decades, but their potential as sensor remains largely unexplored. Therefore we aim to develop single microneedle based sensor for detection of pH and other cell metabolites in single cell. A ~4.8 µm pH sensor was fabricated and tested it in-vivo/in-vitrosensing capability was demonstrated. High stability and sensitivity make this novel pH sensing microneedle is a cost effective and easy fabrication tool for biological sensing especially at the single cell level. The developed sensor exhibited the Nernstian response of -46 mV/pH. The fabricated microneedle sensor ability is proven by in vivo testing in mice cerebrospinal fluid (CSF) and bladder. The pH sensor reported here is totally reversible and results were reproducible after several routine testing. This type of sensor development definitely will bring new innovative ideas that have the huge potential for drug development while continuous metamorphosis observation.

Microfluidic paper-based analytical devices (µPADs) represent a promising platform for fast, portable, low-cost and easy-to-use analytical tools for point-of-care (POC) devices. Cellulose’s hydrophilicity, combined with patterned hydrophobic microfluidic channels generate sample flow from the inlet to a defined location for subsequent analysis. Nevertheless, the entry of µPADs into a real-life application is still minimal, mainly due to the inherent limitations of the materials used for the manufacture of µPADs, including their passive role as support element with no control on the fluid flow.
The present work develops microfluidic substrates based on piezoelectric electrospun poly(L-lactic acid) – PLLA membranes, optimised and properly characterised in terms of morphology, physicochemical properties and capillary flow rates. Oriented PLLA electrospun membranes were first produced to mimic the structure of commercially available Whatman® papers, commonly used in the fabrication of µPADs. Further, oriented PLLA membranes were also produced to study the effect of fibres orientation. As proof of concept, a disposable PLLA microfluidic system was designed and fabricated for the detection and quantification of glucose.

Acknowledgements
Portuguese Foundation for Science and Technology: UID/FIS/04650/2019, UMINHO/BI/86/2019, UID/EEA/04436/2019, UMINHO/BI/445/2018 POCI-01-0145-FEDER-028159, and grant SFRH/BD/140698/2018 (RBP). EuroNanoMed, 2016: LungChekENMed/0049/2016. Spanish Ministry of Economy and Competitiveness (MINECO): MAT2016-76039-C4-3-R (AEI/FEDER, UE); Basque Government: ELKARTEK, HAZITEK and PIBA programs.

Silicone elastomers are widely used in “stretchable” technologies (e.g., wearable electronics) that require the elastomeric components to accommodate varying magnitudes of mechanical stress. Understanding how mechanical stress influences the surface chemistry of these elastomeric components is therefore critical to the performance of these materials. We treated silicone films (polydimethylsiloxane; PDMS) with oxygen plasma and systematically exposed these films to various magnitudes of tensile stress while studying the associated surface chemical changes using contact angle measurements, X-ray photoelectron spectroscopy, and gas chromatography-mass spectrometry. We discovered that mechanical stressing oxidized PDMS films resulted in the on-demand restoration of the film’s hydrophobicity due to: i) cracking of the brittle surface oxide layer, ii) migration of uncured monomers from the bulk towards the surface, and iii) surface rearrangement. We utilized these understandings to develop a facile method for the rapid, on-demand switching of surface wettability and the generation of surface wettability patterns and gradients. These findings are broadly applicable to the fields of microfluidics, soft robotics, printing, and to the design of adaptable materials and sensors.

Non-healing, chronic wounds have placed an enormous stress on both patients and the healthcare systems that served them. Severe complications induced by these wounds can lead to limb amputation or even death. Treatment of the hostile wound environment requires effective drug delivery systems able to overcome current limitations. Electrospun biomaterial scaffolds have showed a great potential for in both wound healing (i.e. as wound dressing materials) as well as controlled drug delivery applications. More specifically, electrospun gels due to their high moisture adsorption capacity and ability to interact with wide ranges hold a lot of promise. Previously, we developed bio-waste derived chitin-lignin gels, and demonstrated that they can be integrated as a native tissue-like fibrous membrane. However, their clinical application was limited by solubility and undesired burst release. Here, we developed a coaxial electrospinning approach to first encapsulate the gels with polycaprolactone (PCL). Presence of a PCL shell layer provided longer shelf life for the chitin-lignin gels in moisture environments and provided a sustainable release of drug molecules. Model drug and antibiotics were loaded into core-shell fibrous platform, which effectively inhibited both gram -positive and -negative bacteria without inducting observable cytotoxicity. Therefore, these PCL coated chitin-lignin fibrous gel platforms may be a good candidate for controlled drug release based wound dressing applications.

We have been producing and testing aqueous amphiphilic copolymer polyether solutions, formulated with varying amounts of a third constituent added with the notion of forming higher-throughput, drug-loaded gels. These gels have also shown potential in localized drug delivery and displace drug-eluting bone cements and spacers. So long as there are no structural requirements for the spacers, the cement matrix can be loaded with more than a few percent of the mass of the spacer with an antibiotic. To establish baselines of drug release in drug eluting cements, their transport attributes have been assessed either in terms of directly qualitatively observing an infection response clinically, or by measuring drug release into a tissue, or a receiving solution to mimic the tissue.¹ Direct assessments of reduced infection by imaging or indirect protocols using a spacer interacting on a bacterial culture plate and resolving a zone of death emanating from the spacer are both indications of transfer of some antibiotic from the spacer and into the surrounding medium allowing some sort of assessment of a minimum inhibitory concentration (MIC).² To assess the elution features of gentamicin and vancomycin incorporated into bone cements, we probed the literature to resolve instances where actual measurements of drug release from drug-loaded cement constructs were executed and corresponding mechanical responses from these same systems. The viscoelastic response of these drug-eluting polymers were also subjected to creep, stress relaxation, and fatigue. We compared the relative rates of drug release and mechanical strength from structures. We have performed a review on the strength and comparative efficacy of drug loaded bone cements and determined that after loading there is an average 15% drop in strength in bone cements with an average 6.55ug of antibiotic release corresponding to an overall decrease in strength to amount released, but when compared relative to amount loaded is on average less than 10%. We will present an overview of the comparative strength and release characteristics of antibiotic loaded bone cements.
[1] Nandi, S. K., S. Bandyopadhyay, P. Das, I. Samanta, P. Mukherjee, S. Roy & B. Kundu (2016) Understanding osteomyelitis and its treatment through local drug delivery system. Biotechnology Advances, 34, 1305-1317.
[2] Anagnostakas, K. & C. Meyer (2017) Antibiotic elution from hip and knee acrylic bone cement spacers: a systematic review. Biomed Research Interanational, 4657874.

Chemical versatility of polymers provides a wide range of functionalization inputs onto the shell of the nanocapsules that play an essential role in the interactions with their surroundings.^[1-3] Moreover, the polymeric shell enhances the lifetime of the encapsulated drugs by protection from harsh environment factors such as pH value, enzyme activity, and avoids side effects of the cargo molecules to the living environment by decreasing rapid leakage.^[2] For this purpose, the development and engineering of smart polymeric nanocapsules have gained a high interest. Various materials have been adopted for encapsulation,^[3] and a variety of chemical and physicochemical methods have been developed in order to prepare hollow spheres with controlled size and shape. ^[4-5] Although each method has its own merits and demerits, they all need either a preorganized structure or template to shape a hollow shell structure, and furthermore require time-consuming and laborious multi-step processes including removal of core or templates. Moreover, in polymers, dye/drug release can be achieved by introducing a photo-sensitive segment, whose activation leads to either rupture or modification of the diffusive properties of the capsule shell, allowing the delivery of the encapsulated material.^[6] Considerable efforts have been thus devoted to prepare stimuli-responsive hollow capsules which undergo a structural transition in response to small changes in the environmental conditions such as pH, temperature, redox-state, medium, and ionic strength.^[7] However, polymer nanocapsules which change the morphology from 3D nanocapsule to 2D nanowire-network on UV light exposure are not reported.
Herein, we have developed a new, direct synthetic method for polymer nanocapsules without need of any template, pre-organized structure, or core removal. Wherein, introduction of the ferreocene-based moiety into the copolymer induced the formation of the nanocapsules. We demonstrate the switchable encapsulation and release of a fluorescent dye, when exposed to UV light. This process which is fully reversible and is due to transformation of spherical morphology into nanowire network.
Polymer nanocapsules were obtained by self-assembly of poly(styrene-b-vinylpyridine) (PS-b-P2VP) block copolymer and poly(chlorostyrene-co-vinylferrocene) (ClPS-co-PVF) in a mix solvent of THF/methanol without addition of any surfactant. The nanocapsules are paramagnetic in nature; this helps easy separation of polymer nanocapsules from solution by application of external magnetic field. Encapsulation of the fluorescent dye occurs during self-assembly step. Upon triggered with UV light for 2 h, the capsules gradually shrink and fuse into each other to transform into a nanowire-network and release the fluorescent dye gradually. The polymer nanocapsules were treated with human blood, which showed good hemocompatibility and did not cause any platelet aggregation. This has good implications for the development of the drug carriers.
In conclusion, we have synthesised a new hemocompatible, hybrid magnetic light responsive polymer nanocapsules with a controlled dye releasing capacity by a facile and robust preparative protocol in one pot. It is anticipated that this material will find applications in target specific drug delivery systems responsive to light and other external stimuli.

References
1. M. W. Tibbitt, J. E. Dahlman and R. Langer, J. Am. Chem. Soc., 2016, 138, 704-717.
2. K. Baek, I. Hwang, I. Roy, D. Shetty and K. Kim, Acc. Chem. Res., 2015, 48, 2221-2229.
3. J. Cui, J. J. Richardson, M. Bjrnmalm, M. Faria and F. Caruso, Acc. Chem. Res., 2016, 49, 1139-1148.
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7. S. Nayak, L.A. Lyon, Chem. Mater. 2004, 16, 2623-2627.

Hydrogels are an important class of materials and have until now spread over a variety of fields in modern sciences. Other than covalent networs, non-covalent hydrogels consist of transient physical cross-links and have the inherent advantages that they are flexible and show self-healing as well as shear-thinning behaviour. Specific binding motifs have to be chosen to render a hydrogel non-covalent. Beside hydrogen bonding, electrostatic interactions or metal complexations, the self-assembly between a host and a guest molecule can be a powerful tool to mediate gelation in a given material. Cucurbit[8]uril represents such a host molecule and can complexate a variety of guest molecules. Recent reports have shown, that depending on the aromatic guest structure, complexes of 1:1:1, 2:1, 2:2 and even 2:3 (guest:host) stoichiometry can be formed. In this work we harvest the capacity of Cucurbit[8]uril to form 2:2 complexes, where now 2 modified viologen derivatives are stacked and handcuffed by 2 Cucurbit[8]uril macrocycles. The used guest molecules are fluorophores of aromatic nature and show unique optical and electrical properties. Once brought together, charge transfer complexes are formed that are glued together by the Cucurbit[8]uril macrocycles and therefore the optical and electrical properties dramatically change. By copolymerizing acrylamide with only little amounts of these fluorophores, polymers are obtained that readily form hydrogels upon addition of Cucurbit[8]uril to the system. The resulting highly fluorescent hydrogels show unique mechanical properties that are supported by rheological data. Due to their high elasticity and fluorescent properties, hydrogel materials based on these 2:2 Cucurbit[8]uril host-guest complexes hold promising potential for imaging applications in biomedical systems or as self-reporting materials.

Intrinsically stretchable conductors are essential components for soft electronics, a new field of electronics, which includes deformable displays, stretchable transistors, energy storages, and health care devices. Most of the cases, they were usually made in the form of the conductive composite using percolation networks; conductive filler and intrinsically stretchable polymer matrix. Although they show great performance with high conductivity and large deformability, in terms of the fabrication process, their process is far from the conventional electronic fields where sputtering deposition is widely used. If the sputtering process can be applied to the manufacturing process of soft electronics, the potential for industrialization and commercialization will be greatly enhanced.

In this presentation, therefore, a bridge between the industry field and the new electronics will be suggested; stretchable conductors are made by metal deposition method on strain releasable structured substrates [1-3]. The intrinsically stretchable substrates (Styrenic block copolymers (SBC)) dissipates strain during the elongation through their surface network structures (microfibrils network, nanofiber network).

With these substrates, the deposited brittle conductive metal lines can maintain their network and conductivity during harsh deformation condition (up to biaxial stretched ~ 100 %, ~ 20 Ω/sq). To demonstrate the advantages of the deposition method, tunable conductivity (i.e. strain sensitivity), patternability with various pattern width, areal uniformity and practical application are proposed. In addition, in order to clarify the fundamental mechanisms for maintaining the conductivity during the deformation, various experimental results and finite element method (FEM) focusing on mechanical deformation were investigated. Finally, a novel but simply designed tactile sensor fabricated only through metal deposition method on a single substrate will be presented that reacts to pressure and detects 2-D position information.
Reference
[1] Moon et al., Advanced Materials (2018)
[2] Moon et al., in preparation
[3] Unyong Jeong et al., Acc. Chem. Res. (2019)

Spatial variations in the wettability of surface-chemical gradients has been used to transport liquid droplets along predefined paths at predictable velocities. In these demonstrations the chemical gradients were synthesized, almost exclusively, on rigid, planar substrates which limit their adaptability. We have pioneered a set of techniques which enable the facile synthesis of large-area surface-chemical gradients on soft elastomers (e.g., PDMS) with mechanically switchable surface microtopography. These advances enabled the fabrication of, for the first time, mechano-adaptive soft surfaces capable of controlling the transport of liquid droplets dynamically. We provide an analytical model which predicts droplet velocity based on critical parameters such as strain state, droplet radius and viscosity, surface microroughness, and steepness of the wettability gradients. Further, we demonstrate the use of these mechano-adaptive gradients in the performance of functions directly relevant to surface-fluidic applications. We believe these findings are generally applicable to the generation of mechano-adaptive surfaces with dynamic, programmable surface-liquid interactions and chemical reactivity and directly useful to, for example, the design and fabrication of surface fluidic systems, adaptive surface coatings, and smart textiles.

In a ligament rupture reconstruction, a tendon autograft is used to restabilize the bones around it. This procedure requires: surgically removing a portion of a tendon adjacent to the site of injury, drilling holes in the bones at the ligament insertion sites, funneling the tendon through the bones, pulling them taut, and restraining them with bone anchors. In addition to being fraught with limitations, this procedure and reconstructed joint cannot recapitulate the functionally-graded biochemical and biomechanical bone-ligament interface. Precise control of material properties and architecture could be the solution to reproducing native tissue properties at the bone-ligament interface.

3D bioprinting (3DBP) has shown promise for creating tissue engineered scaffolds with excellent resolution and controlled architecture. Commonly made from bioinks of biocompatable polymer-based solutions, these 3DBP scaffolds can be optimized to match the structural competency needed for bone tissue regeneration. Additionally, near-field electrospinning (NFE), an additive manufacturing technique, can produce smaller feature sizes than 3DBP. By applying a voltage between the build surface and the needle of the bioink syringe, the solution can be drawn from the syringe using electrostatic potential and thinning of the bioink filament. This system produces highly controlled, high-tensile resistant fibers very similar to ligament tissue fibers. Using a custom platform that merges the two manufacturing systems, we can fabricate complex composite scaffolds with fully integrated bone (3DBP) and ligament (NFE) phases. The current study focuses on optimization of the biochemical and biomechanical properties of each distinct phase of the composite scaffolds and characterization of the mechanical capability of the composite.

Poly(caprolactone) (PCL) in chloroform with decellularized bone particles was used as a bioink for the fabrication of the 3DBP bone phase scaffold. PCL in chloroform was mixed with Hexafluoro-2-propanol (HFIP) as a bioink for the NFE ligament phase. 3DBP and NFE scaffold deposition parameters (extrusion rate and print speed) were characterized as a function of viscosity and solvent evaporation using an Anton-Paar rheometer. Bone phase 3DBP scaffolds of PCL only, PCL w/10% bone, and PCL w/40% bone were mechanically tested for compressive strength using an MTS servohydraulic actuator. Ligament phase NFE fibers were evaluated for tensile strength in 0° uniaxial, 90° biaxial, and 45° biaxial configurations using dynamic mechanical analysis. Cell viability of 3DBP and NFE scaffolds using NIH/3T3 fibroblasts was conducted along with cytoskeletal structural analysis through immunocytoskeletal staining and confocal imaging. Furthermore, the mechanical response of the 3DBP/NFE composite scaffolds were mechanically characterized and the microscopic structure examined using scanning electron microscopy.

By combining the 3DBP and NFE additive manufacturing techniques, we’ve created a structurally integrated composite scaffold for bone and ligament phase tissues. The hybrid system can create functionally graded architectural features that mimic bone and ligament tissue by altering scaffold geometry. Adapted bioink composition can tune the mechanical properties of the scaffold for fabrication of biologically relevant bone-ligament tissues.

Integration of various nanomaterials into one multi-component system is prerequisite to produce multifunctional materials. In this study, a self-assembly protein of α-synuclein (αS), an amyloidogenic protein responsible for Lewy body formation found in Parkinson’s disease, has been employed to fabricate the multi-component nanofilms containing carbon nanotubes (CNTs), gold nanoparticles (AuNPs), and magnetic nanoparticles (MNPs). Ultra-thin 2D film of CNTs was prepared with the αS-CNT conjugates in which the N-terminal region was demonstrated to form α-helix on the hydrophobic CNT surface while the acidic C-terminus was exposed outward as determined by CD and NMR spectroscopy. Following a slow vacuum filtration of αS-CNTs through a polycarbonate membrane filter, chloroform was then used to unleash the CNT film by dissolving the underlying filter membrane, which also facilitated the αS-αS interactions by forming enhanced anti-parallel β-sheet and α-helix as evaluated with FT-IR. The light-responsive CNT film ornamented with or without αS-AuNPs in the presence or absence of αS-MNPs was transferred to the surface of a thermo-responsive double network hydrogel sheet composed of poly-N-isopropylacrylamide (PNIPAAm) and alginate, and sandwiched with a passive polymer layer of Ecoflex. Upon a near infra-red laser irradiation to trigger the photothermal effect of CNT, the entire triply structure exhibited a distinct shape deformation via a heat-induced shrinkage of the CNT immobilized area. In addition, the MNP co-localized films were shown to cause unique locomotions in the triply form under a rotating magnetic field. These multi-component nanomaterial films are therefore suggested to be utilized as a stimuli-responsive element to cause the shape deformation of hydrogels, which could serve as a critical part for the development of various areas including soft robotics, theranostics, and human-machine interfaces.

Wearable wireless sensor technologies are of greater concern for delivering the real-time healthcare information through personalized smart mobiles. Despite significant developments in active components, device geometry, sensors and efforts have been made to introduce new forms of natural inspired mechanical architectures that can accommodate large strains and geometrical deformations that are subjected to complex stress environments. Herein, we introduce, a fully integrated wearable wireless sensory patch system with strain-free mechanically robust structures inspired from both natural kirigami and serpentine patterns that are sticky, conformable, and mechanically robust to achieve high-levels of sensing
performances. The present work addresses the challenge of all-day continuous monitoring of human body biological signals by introducing the well-equipped breathable (water permeability ~ 80 gm-1h-1), excellent adhesion to the skin (peel strength < 200 gf/12mm), bio-compatible, and conformable smart patch that can absorb the moisture (sweat) generated from the skin without any harshness and allowing the users’ to continuously monitor the early detection of diagnosis. Moreover, the heterogenous stretchable temperature and humidity sensors have been introduced with high electrical properties and sensitivity under various temperature and relative humidity (%RH) scales. Theoretical and experimental results highlight the importance of sensor structural designs under various mechanical loading and deformations. The integrated sensory systems are equipped with breathable, bio-compatible patch, and protective layers, so that the user can conformably wear through the day for continuous analysis of early diagnosis, thereby allowing the patients to improve healthcare problems at different stages through mobile monitoring. Furthermore, the proposed integrated sensor enables the wireless sensing capabilities in response to a rapid variation equipped with customized circuit design, low power Bluetooth (BLE) module and signal processing integrated circuit (IC), thus, establishing a unique platform for multifunctional sensors to interface with hard electronics and emerging opportunities in the biomedical field and internet of thing (IoT) applications as well.

With their abilities of self-renewal and pluripotency to differentiate into all three germ layers, human induced pluripotent stem cells (hiPSCs) are promising cell sources for cell-based drug and implant testing [1, 2]. However, the large-scale expansion and maintenance of hiPSCs require adhering to strict conditions [3, 4]. Sample systems for the cultivation of high-quality hiPSCs are highly demanded to meet the application requirements. In this study, we probe the possibility of modifying the polymeric substrates for maintaining the self-renewal and pluripotency of hiPSCs. Here, polydopamine (PDA), typically used to join two materials including a wide range of inorganic and organic materials [5, 6], was employed to immobilize the Laminin 521 (LN521) onto the surface of polyethylene terephthalate (PET). An aqueous solution of dopamine with concentrations ranging from 0 to 2.0 mg/mL was applied on PET surfaces. These PDA-modified surfaces were further functionalized with LN521. Surface wettability was evaluated by measuring the water contact angle (WCA) and surface properties of the modified substrate were analyzed using an atomic force microscope (AFM). Initial hiPSC attachment (1h after seeding) and cell proliferation were evaluated by counting the total cell number. The maintenance of pluripotency was evaluated at different time points. WCA of the PDA-LN521 surfaces gradually decreased from 62.1°±6.3° to 8.1°±2.9°. The maximum peak-to-valley height roughness (Rt) of PDA-LN521 modified surfaces determined by AFM increased in a dopamine-concentration-dependent manner, ranging from 43.9±1.6 nm to 126.7±7.6 nm. Young's modulus of PDA modified surfaces was substantially increased from 0.980±0.36 GPa to 4.810±2.41 GPa. There was a significant enhancement (13.0±7.2% and 24.2±8.1%) of hiPSC adhesion on PDA-LN521 (dopamine concentration at 0.125 and 0.25 mg/mL). When increasing the dopamine concentration to 0.5 and 1.0 mg/mL, there was no further increase in hiPSC adhesion on PDA-LN521 surfaces. Moreover, hiPSCs proliferation was remarkably enhanced on PDA-LN521 surface (dopamine solution at concentration from 0.125 to 1.0 mg/mL). Pluripotent gene expression of hiPSC, including Oct-4, Sox2, and SSEA4, was not affected by PDA treatment. PDA modification did not impair the pluripotency of hiPSCs. In conclusion, polydopamine-mediated surface modification is an effective approach for the robust expansion and maintenance of hiPSCs on polymer substrates.

Reference
1. Bantounas, I., et al., Generation of Functioning Nephrons by Implanting Human Pluripotent Stem Cell-Derived Kidney Progenitors. Stem Cell Reports, 2018. 10(3): p. 766-779.
2. Wei, M., S. Li, and W. Le, Nanomaterials modulate stem cell differentiation: biological interaction and underlying mechanisms. Journal of Nanobiotechnology, 2017. 15: p. 75.
3. Rodin, S., et al., Clonal culturing of human embryonic stem cells on laminin-521/E-cadherin matrix in defined and xeno-free environment. Nature Communications, 2014. 5: p. 3195.
4. Kanninen, L.K., et al., Laminin-511 and laminin-521-based matrices for efficient hepatic specification of human pluripotent stem cells. Biomaterials, 2016. 103: p. 86-100.
5. Zhou, P., et al., Simple and versatile synthetic polydopamine-based surface supports reprogramming of human somatic cells and long-term self-renewal of human pluripotent stem cells under defined conditions. Biomaterials, 2016. 87: p. 1-17.
6. Park, H.J., et al., Bio-inspired oligovitronectin-grafted surface for enhanced self-renewal and long-term maintenance of human pluripotent stem cells under feeder-free conditions. Biomaterials, 2015. 50: p. 127-39.

All electronic devices require a power source to operate. The need to have portable power sources becomes more crucial for miniaturized bioelectronic devices that detect biological signals such as the heartbeat, muscle movements, as well as critical biomarkers. We herein present an all-polymer enzymatic biofuel cell to power such bioelectronic devices. The anode is an NDI-T2 copolymer (P-90) consisting of alternating naphthalene dicarboximide (NDI) acceptor and bithiophene (T2) donor subunits with randomly distributed alkyl and ethylene glycol side chains, while the cathode is a p-type thiophene-based copolymer P(EDOT-OH-EDOT). The enzyme (glucose oxidase) has efficient electrical communication with the n-type polymer film, rendering P-90 suitable as an anode for the enzymatic biofuel cell. The p-type cathode material demonstrated stable catalytic activity towards oxygen reduction reaction (ORR). Upon introduction of glucose into PBS, the former is oxidized to gluconolactone by GOx, producing electrons that are transferred to the P-90 anode. These electrons then travel through the external circuit to the cathode which reduces dioxygen to water generating power from glucose and oxygen in aqueous media. The biofuel cell exhibited a cell open circuit potential of 0.3 V when operated at physiologically relevant glucose concentrations, enough to power organic electrochemical transistors (OECTs), state-of-the-art sensor configuration of organic bioelectronics. The powering device is stable for 35 days in a membrane-free configuration and yields a power density of 20.7 mW.cm^-2 at 100 µM of glucose. Implementing an OECT sensor that can be indefinitely powered by glucose throught the biofuel cell can lead to self-reliant devices.

4D printing is a technology that makes the 3D printed structures deformed by responding to external stimuli such as temperature, pH, UV, and magnetic field. Recently, 4D printing has been actively explored for the application in several field such as soft robotics or biomedical devices such as a stent or a sensor that detects and reacts under the biofluidic environment. However, there are still many challenges. One is that it is difficult to control the deformation speed and the other is irreversible deformation which changes only in one direction.
In this study, we present a temperature-responsive 4D printed structure deformed by controlling the two distinct memory effect of ‘strain memory’ and ‘stress memory’. Shape memory has two concepts: one is 'strain memory' and the other is 'stress memory'. 'Strain memory' means to remember the shape of the structure and to be restored to that shape by the stimuli condition. 'Stress memory' means that the structure accumulates and memorizes the stress, not just the shape. Even if the same structure deforms to the same strain, the stress that acts on the structure can also be programmed differently by the material of the structure, 3D printing conditions, and additional processes.
When a 3D printed structure is deformed, the external strain applies to each of the printed thermoplastic fibers composing the structure. The strain applied to a 3D printed SMP (shape memory polymer) with a rubbery state at Tg or higher would be stored in a glassy state when cooled. Stress memory inside the printed structure can be residually controlled by stacking output layers with different recovery stresses. By programming the stress acting on each layer in the process of returning to the memorized shape, it is possible to make the stress more than necessary in the shape recovery process differently for each layer. We shows that by alternatingly programmed with the layer with stress memory effect on top of the upper layer with strain memory effect, it is possible to make a reversible structure in deformation. By relieving the stress memory, the structure in the high temperature is transitionally deformed into programmed shape with a faster speed, then by the strain memory effect, the programmed shape returns to the original shape that was initially memorized at the 3D printing process. Through this study, we demonstrate this concept for a structure similar to the stimuli responsive plants behavior like Mimosa, which rapidly self-deforms to instantaneous external stimuli, and gradually restores to its original structure even when the external conditions are intact.

Nanomaterials with high specific surface area and nanoscale detection capability via reversible process is promising for real-time monitoring. In nanoscale detection, the system needs to show long-term stability, rapid response, precise detection, and high ON/OFF ratio. Herein, we present a nanoscale switch which is reversible with short response time and stable for many cycles. Switch is composed of gold nanoparticles(NPs) functionalized with carboxylic functional group (11-mercaptoundecanoic acid; MUA) and tert-ammonium functional group ((11-mercaptoundecyl)-N,N,N-trimethylammonium bromide; TMA) with 5:1 ratio. These NPs were stable in both acidic (pH 3) and basic (pH 11) conditions, and surface charges rapidly changed by changes in the environmental pH. We propose two models to monitor changes in surface charges upon changes in environmental pH via zeta potential: ‘dilution model’ and ‘conservation model’. In dilution model, the pH control solution was directly injected into the NP system, which showed rapid response (< 30 s) with ~30 cycles. In conservation model, NPs were isolated in a semipermeable membrane in order to avoid accumulation of counterions. Conservation model showed relatively slower response time (< 5 min) compared to the dilution model, but the stability improved to 45 cycles. NP-based nanoscale system showed high ON/OFF ratio of 1.3 due to the high surface area, and reversibly switched with fast response time (< 30 s) with ~30 cycles. We believe this system will provide significant advances in the field of real-time nanoscale monitoring (e.g. in vivo monitoring where the environment changes in real time due to homeostasis) and receptors for molecular communications which quickly respond to continuously delivered messenger molecules.

3D structures formed from carbon nanotubes could present interesting mechanical and electronic properties [1]. Some studies have shown that the electronic and mechanical characteristics of these structures are dominated by the topology of the carbon nanotubes networks, which makes their properties tunable [1]. However, up to now the synthesis of such structures has been very limited [2,3]. It has been previously shown that it is possible to grow carbon nanostructures inside the channels of the zeolites [2,3]. Among the large number of possible zeolites [4], good candidate structures to allow the synthesis of 3D carbon nanotubes network are the beta zeolites [3], as they have interconnected channels. In this work we report a preliminary study, based on molecular dynamics simulations about 3D carbon nanotube networks that could be formed inside beta zeolites. We investigated their structural stability and mechanical properties. Our results show that from all possible carbon nanotubes that can be embedded inside the channels of the beta zeolite, the one with chirality (6,0) is the most stable. Using the carbon nanotube (6,0), it is possible to built 3D structures with both all (higher density) and only partially (lower density) filled zeolite channels. The 3D low-density carbon nanotube networks are anisotropic and can be stretched along the direction in which all nanotubes are perpendicular up to 130% of strain without fracture. Also, the porosity and network stiffness can be tuned depending on the amount of carbon nanotubes filling the zeolites channels.

References:
[1] J. M. Romo-Herrera, M. Terrones, H. Terrones, S. Dag, and V. Meunier, Nano Letters 7 (2007) 570.
[2] H. Nishihara, T. Kyotani, Chem. Commun. 54 (2018) 5648.
[3] K. Kim et al., Nature 535 (2016) 131.
[4] http://www.iza-structure.org/databases/.

We propose a new functional paper containing fullerene nanowhiskers (FNWs), i.e., an “FNW-composite paper.” It is known that FNWs have an n-type semiconducting property and are used in a diverse range of applications, including field-effect transistors, solar cells, chemical sensors, and photocatalysts. Therefore, many studies have been conducted until now by lots of researchers. However, because the FNW is a nano-scaled material, so that it is difficult to handle, generally. In this study, we develop an “FNW-composite paper” by mixing FNWs with pulp fibers (raw materials of papers) and solve the problem. Since a paper is lightweight, easy to process, inexpensive, and familiar material for us, the “FNW-composite paper” can be expected to be applied to various things.
It is well known that the FNW is prepared using the method of liquid-liquid interface precipitation (LLIP). In this method, it is necessary to put a poor solvent of fullerenes above a good solvent saturated solution of them and form an interface between them. After a while, thin cylindrical shape substances are grown at the layer and FNWs are educed.
In this study, we use the LLIP. As a first step of fabricating our “FNW-composite papers,” pulps (150 mg) are stirred in pure water (10 ml) for 60 minutes to prepare a pulp dispersion. Then, C₆₀ (fullerene, 40 mg) is dispersed in m-Xylene (10 ml), which is a good solvent of fullerenes, to prepare a fullerene dispersion. After that, the pulp dispersion and the fullerene dispersion are poured in a square case. Since water has a greater specific gravity than m-Xylene, the layer of the fullerene dispersion is above it of the pulp dispersion. Then, isopropyl alcohol (IPA, 10 ml), which is a poor solvent of fullerenes, is poured from above the dispersions carefully to form an interface between the fullerene dispersion and IPA. After that, the prepared liquid is left for 112 hours at 4 °C. Next, the liquid is heated to evaporate moisture. Finally, the material in the case is pressed to finalize the making process.
As results, we could gain a sample in this way and confirm that FNWs existed on the pulps by SEM. FNWs have a lot of great features as we showed above. We expect to prepare the paper which has an n-type semiconducting property and use it as a field-effect transistors, chemical sensors, and so on.

Infections are a major concern in orthopedics. Bacteria colonization is often the reason for prosthetics failure that causes biofilm formation and induces bone degenerative diseases. The emergence of resistant bacteria has hindered the ability of common antibiotics to fight these infections. For example, Staphylococcus aureus (S. aureus) is able to encode methicillin (i.e MRSA strains) and it is responsible for 60% of sepsis implant failure. The elevated morbidity and mortality associated with resistant infections support the need for innovative approaches that not only improve treatment outcomes but also reduce the risk of developing further antibiotic resistance. Antibacterial agents such as silver ions are of great interest as broad-spectrum biocides to overcome and prevent the development of resistance in many pathogenic strains. We have developed Ag containing bioactive glass-ceramics with advanced antibacterial and bioactive properties. The synthesis of bioactive nanoparticles (BGN) with complicated composition remains a big challenge. In this work, this challenge is addressed, as we deliver nanoparticles in the desired composition. These nanoparticles are expected to show enhanced antibacterial and bioactive behavior compared to their microsize counterparts due to the increase in their surface area. Here, a modified Stöber method is presented for the successful incorporation of ions that play a key role in the bone regenerative properties of the BGNs. Synthesis parameters were systematically modified in terms of solvent, reagent addition order and stirring time to accomplish particles of the nominal composition being below 100 nm in size and with moderate dispersity. A final protocol was optimized for the synthesis of silver-doped BGN (Ag-BGN) containing SiO₂-CaO-P₂O₅-Al₂O₃-Ag₂O. Characterization techniques such as SEM-EDS, TEM, FTIR, XRD, and solid-state MAS-NMR were used to demonstrate the composition, morphology and structure of the BGN and Ag-BGN synthesized. The antibacterial properties were also evaluated against MRSA by colony forming unit quantification after direct exposure. The cell-material interaction was studied using human marrow-derived mesenchymal progenitor cells. In conclusion, this work addresses the challenges in the development of nanoparticles with multiple ions in nominal concentrations and presents the advancements in antibacterial and bioactive characteristics.

Mimicking the native extracellular matrix (ECM) using multifunctional materials is a promising approach to direct tissue regeneration in vivo. In particular, pure biomaterial-based strategies without further incorporation of growth factors or surface functionalization are desirable, owing to lower production cost and complexity.

Targeted towards clinical translation of an implant capable of modulating regenerative processes in vivo, a one-pot synthesis of 3D-architectured gelatin-based hydrogels was designed, in which the biomolecule is chemically functionalized [1]. These structured hydrogels exhibit essential properties and functions including presentation of cell adhesive sequences, interconnected porous architecture, degradability, dimensional stability upon swelling, as well as tailorable elastic properties. The gelatin-based hydrogels were manufactured in a cleanroom facility. While it is known that such scaffolds are degradable in vivo, there is limited understanding on the contribution of different degradation mechanisms, particularly in relation to the role of crosslinks.

In this study, samples of 1.5 x 1.5 cm² with thickness of ~3.5 mm were incubated at 37 °C with mild agitation in solutions simulating pure hydrolytic degradation (phosphate buffered saline, PBS), oxidative degradation (3 % v/v H₂O₂) and enzymatic degradation (0.2 U/mL Collagenase I), which are supplemented with 0.01 % w/w sodium azide to exclude microbial contamination. The hydrolytic and oxidative buffer conditions simulate real-time degradation [2]. Collagenase I was selected to elucidate enzymatic degradation due to its presence in damaged tissue and reports of degrading other gelatin-based materials [3]. The influences of the three degradation conditions on mass loss, morphological and chemical properties of the scaffolds were investigated.

The scaffolds degraded rapidly under oxidative and enzymatic conditions, with endpoint of >95 % mass loss achieved in 2.5 weeks. In contrast, the scaffolds were relatively resistant to hydrolytic degradation, with merely mass loss of 20 % after 20 weeks. SEM analysis indicated varied degradation behavior among the different sample groups based on changes in porous structure alongside crack formation.

We discuss degradation mechanisms and products in relation to the chemistry of the scaffold, specifically on the role of the involved crosslinks. Oxidative and enzymatic degradations were shown to be the key mechanisms for in vivo degradation of our gelatin-based hydrogels. Such analysis is vital for biodegradable implants to elucidate degradation behavior and products, both of which are essential for translation of novel biomaterial-based implants.

Reference:
1. Neffe, A.T., et al., Adv Mater, 2015. 27, 1738-1744.
2. Weems, A.C., et al., Acta Biomater, 2017. 59, 33-44.
3. Kishan, A.P., et al., J. Mater Chem B, 2015. 3(40), 7930-7938.

Reversible shape-reconfiguration of magnetic composites has been demonstrated by pre-programming the alignment of magnetic particles within micropillar arrays. The alignments of magnetic particles determine the magnitude and directionality of magnetic-actuation dependent to the offset angle from the external magnetic field axis. Previous reports on magnetic microstructures have mostly been employed symmetric cylindrical or rectangular geometry, resulting in balanced stress distribution for actuation by the external magnetic field. Herein, we demonstrate the effects of asymmetric geometry on magnetic actuation with the rectangular and triangular form factor. Upon the external magnetic field, the magnetic torque generates concentrated magnetic momentum in anisotropic micropillars, resulting in enhanced magneto-mechanical actuation. To elucidate the relationships between geometry factors of pillars and magnetic-actuation, we will discuss structure-property relationships of triangular and rectangular micropillars for both bending and twisting actuation.

Delivering cargoes at desired time points and positions in nanoscale is necessary in order to precisely control the time-dependent reactions. For example, each drug needs to be delivered at desired time point in order to increase the efficacy of multi-drugs. The delivery time and position also need to be finely controlled if cargoes should be combined before they degrade for activation. However, it is difficult to develop a spatio-temporally controlled delivery system (especially for multi-cargoes, delivery time difference with a short period time (< a few minutes)) due to random walk motion of cargoes, difficulty of applying two different driving forces on the same type of nanoscale delivery system, and an interference between cargoes. Herein, we designed two (or more) types of nanomotor which can travel at different speeds upon a single magnetic stimulus. Nanomotors were composed of nickel head – silver flexible filament – gold tail encapsulated with N-isopropylacrylamide (NIPAm) based hydrogel. The difference in speed was quantitatively controlled by adjusting the length of each compartment whereas the cargo releasing time was regulated by optimizing the thickness of encapsulating hydrogel. Our nanomotor based nanoscale delivery system demonstrated sequential cargo delivery with time-difference of a few minutes. This delivery system can possibly increase the gene editing efficiency (e.g. CRISPR/Cas9 system) and efficacy of multi-drugs by allowing drugs or genetic materials to be activated at different time points. Furthermore, our time-controlled delivery system in nanoscale can also be applied in molecular communication via applying sequential (bio)material transmission as a signal.

Water-responsive (WR) materials that swell and shrink in response to changes in relative humidity could serve as high-energy actuators, providing new engineering opportunities for soft robotics, sensors, and energy harvesting devices. Spider silk has been shown to be a WR material and has a higher energy density than conventional actuators. However, natural silk’s relatively low production efficiency and variations in water-responsiveness limit their practical applications. Bombyx (B.) mori silk is also reported to have a WR property, but B. mori silk has a lower energy density than that of spider silk. Here, we demonstrate that the processing of the B. mori silk can dramatically increase regenerated B. mori silk’s WR energy density. To control the grain size and volume ratio of Silk II structures, we treated regenerated B. mori silk films with water vapor and methanol under various conditions which yield higher volume ratios. FTIR and AFM experiments subsequently confirmed the variation of Silk II structures resulted from these post-treatment methods. We found that Silk II structures’ crystallinities, sizes, and distributions define the silk’s WR behaviors. For example, as the volume of Silk II increases, regenerated silk’s WR energy density increases and reach ~500 kJ m^-3, which is comparable to that of spider silk. This work is a proof-of-concept that a powerful WR actuator can be fabricated with cost effective and naturally abundant B. mori feedstocks.

Inspired by a human or animal hair as a natural humidity sensor, two types of humidity sensing microfibers based on an agarose polymer as a hydrophilic matrix and conducting fillers are reported. The microfibers are fabricated with simple extrusion of the agarose composites containing two different conductive nanofillers: (1) graphene oxide (GO, chemically reduced after extrusion)/silver nanowires (AgNWs) and (2) carbon nanotubes (CNTs). Both microfibers at optimum filler content exhibit the enhanced electrical conductivity and mechanical properties, due to intrinsic property of CNT or synergistic contribution of AgNWs and reduced GO (rGO) as 1D and 2D nanofillers, respectively. As a result, the microfibers have 3~4 times higher values of Young’s modulus than commercial nylon-6 and polyamide and are flexible enough to be knotted. The composite microfibers have an ability to be humidity sensors owing to their humidity-dependent conductivity. The microfiber containing rGO/AgNWs shows positive dependence of its conductivity on environmental humidity, upon ionization of water molecules by rGO. On the other hand, the microfiber with CNT shows negative dependence of its conductivity on humidity, due to decreased junction density of CNT resulting from swelling of the hydrophilic agarose matrix at high humidity. In order to delve into the opposite humidity response of two composite fibers, we performed impedance analysis of the fibers at various humidity conditions, which will be discussed. The composite microfibers show reliability, reversibility and feasibility of humidity sensing demonstrated by repetitive changes in humidity and practical usages such as human breathing. The humidity sensing microfibers could have applications to smart textile and wearable devices.

Biocompatible and implantable electronics have gained increasing attention due to growing interest in health care. The advances in the electronics require the development of biocompatible and implantable memory that performs the data processing and storage. However, conventional memory devices are not suitable for this purpose because they are not biocompatible and sometimes even toxic. We present the memory devices and artificial synapses based on natural, biocompatible, and biodegradable materials on flexible polyethylene terephthalate substrates [1]. Multi-bit data storage capability is achieved by controlling maximum reset voltages and compliance current. The switching behavior is thought to be related to the carbon atoms in the active layer, which could form the carbon filament. Synaptic functions including analog switching behavior and potentiation/depression are realized by controlling the formation and rupture of filament [2]. By properly modulating the stimulation pulses, both short-term plasticity and long-term plasticity of biological synapses can be achieved. Moreover, the devices can be stably operated under mechanical bending stress. These researches will offer a new possibility for biomaterials to be used in next-generation memory devices and neuromorphic systems. In this presentation, characteristics of biomaterials for application to memory devices and artificial synapses will be presented in detail.

[1] Youngjun Park and Jang-Sik Lee, ACS Applied Materials & Interfaces 9, 6207 (2017)
[2] Youngjun Park and Jang-Sik Lee, ACS NANO 11, 8962 (2017)

A diversity of self-propelled chemical motors, based on Marangoni propulsive forces, has been developed in recent years. However, most motors are non-functional due to poor performance, a lack of control, and the use of toxic materials. To overcome these limitations, we have developed multifunctional and biodegradable self-propelled motors from squid-derived proteins and an anesthetic metabolite. The protein motors surpass previous reports in performance output and efficiency by several orders of magnitude, and they offer control of their propulsion modes, speed, mobility lifetime, and directionality by regulating the protein nanostructure via local and external stimuli, resulting in programmable and complex locomotion. We demonstrate diverse functionalities of these motors in environmental remediation, microrobot powering, and cargo delivery applications. These versatile and degradable protein motors enable new design, control, and actuation strategies in microrobotics as modular propulsion sources for autonomous minimally invasive medical operations in biological environments with air-liquid interfaces.

Water-responsive (WR) materials that exert significant forces in response to changing hydration levels are receiving growing interest due to their potential applications, including use as actuators for energy harvesting devices, artificial muscles, and soft robotics. Reported examples include biological and synthetic materials with abilities to efficiently convert chemical potential of water into mechanical actuations. However, these systems are typically complex, and consequently, their WR mechanisms are not well-understood thus preventing rational design and optimization. Here, we demonstrate that tri-peptides, which are modular organic building blocks with precisely tunable non-covalent interactions, spontaneously associate to form hierarchical ordered crystalline structures, which exhibit WR behavior that is strongly dictated by their building blocks’ chemical nature and consequent organization. Our tripeptide crystals, with intrinsic water channels in nanoscale, has the ability to swell and shrink in response to changes in relative humidity (RH). The crystals also exhibit outstanding mechanical properties including a stiffness of 0.5 - 2GPa depending on RH, leading to a high WR energy density of more than 80kJ/m³. Due to its biodegradability and relative simplicity, this system could not only serve as an excellent platform to enhance understanding of such material’s WR mechanisms, but also holds much promise for programing better WR materials for future applications.

All-organic electronics have gained increasing attention due to their biocompatibility, intrinsic flexibility, as well as lower cost compared to inorganic materials. It is hypothesized that the similarity of mechanical properties between the electrode and substrate in all-organic electronics, facilitates improved mechanical performance in these structures. Here, we report the comparison between failure mechanism of an all-organic bilayer and a metal-polymer bilayer to demonstrate the effect of inherent properties of layered structures on the overall mechanical performance of the system.

In this work, we are presenting a simple approach for the fabrication of high-performance muscle-like actuators (artificial muscles) for untethered applications. Artificial muscles are exploited in various applications, including soft robotics, bio-medical devices, and even energy harvesting systems, to name a few. One of the limitations of such actuators is the need for wiring, pressurized gas tanks, electrolytes, etc. Here we are demonstrating how we can make wireless actuators that can perform as good as the tethered counterparts.

Molecular robots are all around and inside us – from viruses injecting their RNA and highjacking cellular machinery for replication, to myosin contracting our muscles, to the ribosome translating our DNA. Such invisible machinery is key to us being alive. Can we start growing functional nanomachines artificially? In this talk I will outline progress we have made towards this goal. From creating programmable materials that can move, sense and respond to their environment in complex ways, to artificial morphogenesis – we have the ability to shape particles and our future. & much of this story is based on liquid droplets.

Our work on topological inter-penetration of functional materials[1] replaced unpredictability in multifunctional synthesis with combinatorics - choosing 3 phases of 20 already optimized functions would lead to over 8000 trifunctional materials. We demonstrated new supercapacitor architectures,[2] as well as emerging self-sensing artificial muscles.[3] We also discovered artificial morphogenesis – transformation of liquid droplets into a large variety of complex regular micro- and nanostructures. Our methods of growing from single molecules many shapes, including octahedra, hexagons, rhomboids, triangles and fibers[4] have yielded a polymerization process[5] that could potentially replace the expensive infrastructure and waste of lithography. We have classified dozens of pure[6] and mixed component systems (including triglyceride oils) capable of shape-change[7] which could let us synthesize novel shaped lipids or polymer drug carriers. We use thermodynamic understanding and mathematical modelling to predict and control the observed shapes[8]. Transforming almost 100% of a liquid droplet into a final shape is ideal for sustainability and for space manufacturing.

Current projects aim to move beyond manufacturing static shapes. By combining bottom-up growth with multi-functional polymer synthesis, we aim to produce functional micro- and nanoparticles with autonomous behaviour, e.g. movement, sense and response to environmental stimuli, as well as on-board energy storage. Surprisingly, some of our artificial systems already mimic life by repeatedly harnessing thermal fluctuations in the environment, and storing energy by breaking up into smaller and smaller emulsion droplets.[9] I will outline implications for further fundamental discoveries and for potential applied explorations.


[1] Khaldi A, Plesse C, Vidal F, Smoukov SK*, Designing Smarter Materials with Interpenetrating Polymer Networks, Adv. Mater. 27, 4418–4422 (2015)
[2] Fong KD, et al. Semi-Interpenetrating Polymer Networks for Enhanced Supercapacitor Electrodes, ACS Energy Lett. 2, 2014–2020 (2017) DOI: 10.1021/acsenergylett.7b00466
[3] Wang T, et al. Electroactive Polymers for Sensing, Interface Focus, 2016, DOI: 10.1098/rsfs.2016.0026
[4] Denkov N,Tcholakova S,Lesov I,Cholakova D,Smoukov SK*,Self-Shaping of Droplets via Formation of Intermediate Rotator Phases on Cooling, Nature 528, 392–395 (2015)
[5] Lesov I,et al, Bottom-up Synthesis of Polymeric Micro- and Nanoparticles with Regular Anisotropic Shapes, Macromolecules 51 (19), 7456-7462 (2018)
[6] Cholakova D, Denkov N, Tcholakova S, Lesov I, Smoukov SK*,Control of drop shape transformations in cooled emulsions, Adv. Colloid & Interface Sci (2016)
[7] Cholakova D, Valkova Zh, Tcholakova S, Denkov N, Smoukov SK, Self-Shaping of Multi-component Drops, Langmuir 33 (23) 5696 (2017) DOI:10.1021/acs.langmuir.7b01153
[8] Haas PA, Goldstein RE*, Smoukov SK*, Cholakova D, Denkov N, A Theory of Shape-Shifting Droplets, Phys. Rev. Lett. 118 088001 (2017)
[9] Tcholakova S, Valkova Zh, Cholakova D, Vinarov Z, Lesov I, Denkov N, Smoukov SK, Efficient self-emulsification via cooling-heating cycles, Nature Comm., 8, 15012 (2017)

Tactile sensing is required for a dexterous feedback system of an object in robotic-skin applications. Moreover, an ability to monitor various physical forces such pressure and shear in real time is a key technology for a slip detection with fragile objects. As a way of solving the above, a flexible printed sensor will be invaluable. Because these possess great potential advantages for the robotics-skin applications due to high sensitivity. Previously, fabrication of soft sensors and their application for robotic skins was reported by many groups; however, realization of a multi sensing devices by printing methods remain a challenging task. Recently, we reported flexible and soft sensors that were fabricated using a ferroelectric polymer, P(VDF-TrFE) and Carbon nanotube (CNT) by printing methods for shear and pressure detection. Furthermore, we developed a printed temperature sensor using PEDOT:PSS. Integration of these sensors on a one-tip-substrate will enable realization a physical multi-sensor for tactile signals. Here, we report a wearable and printed soft robotic multi sensor composed of shear, pressure and temperature sensors for detection of tactile signals.
The various shear, pressure and temperature sensors were fabricated on a flexible film by printing methods. First, we fabricated the shear sensor using P(VDF-TrFE) by Screen printing method. A cross-linked poly(4-vinylphenol) (PVP) solution mixed with the PVP and 1-methoxy-2-propyl acetate as the solvent was formed by spin-coating onto the substrate as the planarization layer. Lower and upper electrodes of the sensor were formed using conductive polymeric materials and annealing at 140 °C for 30 min. The P(VDF-TrFE) layer was formed as the detecting layer of shear force by screen printing and annealed at 135 °C for 1 h. The polarization and the coercive electric point of the sensor were 7.0 µC cm^-2 and 50 MV m^-1. These performances are reasonable as printed ferroelectric devices. Next, we fabricated the pressure sensor using the CNT solution mixed with a 4-dodecylbenzenesulfonic acid by Dispense equipment. The electrodes of this sensor were formed by the Ag nanoparticle ink and annealing at 150 °C for 30 min. The CNT layer was formed as the detector of pressure force by Dispensing and annealed at 100 °C for 12 h. The initial resistance value of this sensor was 10 kΩ. Finally, the temperature sensor using PEDOT:PSS was fabricated by Screen printing. After formation the PEDOT:PSS layer, the substrate was annealed as 100 °C for 12 h.
The output voltage of the shear sensor linearly displayed a clear correlation with the applied a shear force and the output voltage. It showed approximately 50 mV in the shear speed of 200 mm s^-1. Similarly, the relationship between applied pressure and output voltage in the pressure sensor was measured. The pressure was applied by using a pressure tester to the sensor. This resistivity was changed from the initial value to 1 kΩ when pressure of 2.0 N applied. These results indicate that the fabricated various devices will be candidate for tactile sensors of a robotic-skin due to high sensitivity.
Robotic controlling experiments were performed demonstration the use of our sensors to monitor tactile signals in real time. The gripper can grip various objects by a pneumatic driving system. Moreover, our multi sensor were attached on a soft robotic gripper. An oscilloscope recorded the signals of output voltage from the sensors. We can estimate tactile signals of shear, pressure and temperature at the same time when the gripper handled objects. From these outcomes, the information obtained from the fabrication of the multi sensor used in this study further illustrates the potential in an elaborate robotics controlling system with a closed loop feedback.

Shape memory polymers (SMPs) can respond to heat by generating programmable movement, which can enable multiple technological advances in deployable structures, biomedical device placement, and sensing applications. Many of these technologies could benefit from miniaturization: deployable micro-sized drug delivery vehicles, neural probes and stents could enable minimally invasive access to targets that are currently surgically inaccessible. The shape change requirements of drug delivery have motivated the development of isolated three-dimensional (3D) SMP structures through molding and emulsion techniques, resulting in relatively simple geometries: spheres, cubes and boomerangs with whose critical dimensions are 1-35 µm^[1-3]. Many other applications require shape transformations to occur in structures with substantially more complex geometries, i.e. a stent or neural probe, which drives the need to synthesize complex architected shape memory structures with sub-micron resolution.
We developed a benzyl methacrylate-based photosensitive resin that polymerizes into programmable 3D shapes with minimal dimensions of 650nm using two photon lithography direct laser wiring (TPL-DLW). We synthesized this resin for shape memory actuation via a glass transition, i.e. the produced structures transform from glassy to rubbery state in response to increased temperature to enable shape programming and recovery. Dynamic nanomechanical analysis (DnMA) was performed through the 22^oC to 87^oC temperature range on individual TPL-sculpted SMP cylindrical pillars with diameters of 10µm and revealed the initiation of a glass transition at 60^oC. We performed shape memory programming by first applying a 400µN load to individual pillars at 77^oC and then cooling them to the glassy state at 42^oC while maintaining the mechanical load. After load removal, the structures retained their shapes over 7 days at room temperature and recovered to their original dimensions when heated to 87^oC within 5 minutes. This shape memory occurred in all 3D micro-architectures that we programmed, including pillars, cubic lattices, and flowers, with a characteristic shape recovery ratio of 86 ⁺/_- 4%.
This technique provides a promising pathway to miniaturize shape memory devices and to develop stimuli responsive microscale mechanical metamaterials. Utilizing shape memory polymers as constituent materials could enable miniaturization of existing macroscale shape memory devices, as well as the development of stimuli responsive materials that display amplified and unusual mechanical properties that stem from emergent nano-size effect in materials.
[1] C. Wischke, M. Schossig, A. Lendlein, Small. 2014, 10, 83.
[2] Y. Liu, M. Y. Razzaq, T. Rudolph, L. Fang, K. Kratz, A. Lendlein, Macromolecules. 2017, 50, 2518.
[3] S. M. Brosnan, A. M. S. Jackson. Y. Wang, V. S. Ashby , Macromol. Rapid Commun. 2014, 35, 1653.

Cephalopods, caterpillars and other soft creatures inspired a broad spectrum of bio-mimetic actuators capable of sensing and adapting to their complex erratic environments. Yet, they are missing a feature of nature’s designs: biodegradability. Soft robots that degrade at the end of their life cycle reduce electronic waste and are paramount for a sustainable future. At the same time, medical (robotic) technologies benefit from biodegradable materials since they are often single-use devices and have to address hygiene requirements. We therefore develop biodegradable hydrogels (biogels) for single-use wearable electronics and transient soft robots that are reversibly stretchable, are able to heal, and are resistant to dehydration. Soft machines and robots – built from biogels with tuned mechanical properties – are designed to be operated in ambient conditions and degrade after use. An equally compostable electronic skin provides our soft actuators tactile feedback and temperature sensing, directly processed with a recyclable on-board computation unit. Besides progressing stand-alone soft machines, our advances in the synthesis of biodegradable hydrogels bring bionic soft robots a step closer to nature.

Electroactive artificial muscles actuators are unique and lightweight devices that will revolutionize automotive applications by their large strain (120%) and high specific power (160 W/kg), but still require improvement in energy density to be commercially viable. Through design aided by finite element analysis (FEA) and material research, these in-house fabricated artificial muscles were improved by recursive optimization. This led to a new origami-inspired design for a compact, foldable electrode stack that consists of an inner zig-zag structure suspended in dielectric fluid, surrounded by an outer double helix of electrode leads. We refined the electrical insulative material to increase the breakdown voltage per micron of film thickness by more than 30%. This improvement enables actuators to operate at higher voltages, thus increasing the maximum actuator force. Our origami-designed artificial muscles (O-DAM) increase the active electrode surface area which enhances the performance of the device. These soft robotics actuators promise to revolutionize the future of human-machine interactions.

This talk presents an approach for fabricating cell-sized robots massively in parallel. By building upon existing microelectronics technology, we show how to overcome the key challenges for miniaturizing robotic systems. We use this approach to build and deploy microrobots that walk, are fully untethered, are individually addressable, and wirelessly receive power and instructions through light. They use a new class of voltage controllable, electrochemical actuators made from nanometer thick membranes of platinum. Our fabrication process is completely compatible with silicon microelectronics processing and results in millions of microrobots per four-inch wafer. Combined, these results present a broad platform that can unite mechanical systems, information processing and control to make autonomous robots the size of cells.

The advancement of stretchable electronics is instrumental for new-generation compliant and wearable devices. High-performing strain sensing technologies have already been realised by exploiting the high gauge factor of graphene-related materials coupled with elastomers [1,2]. Nevertheless, the manufacture of graphene-based electrodes that display outstanding electrical features which remain constant during mechanical deformation, is still challenging [3,4]. On this basis, we fabricated a deformable electrode by simply spray-coating nitrile rubber with graphene-based elastomeric conductive inks. Painting stretchable polymer dispersions carrying graphene nanoplatelets (GnPs) or hybrids of GnPs and carbon nanofibers led to the production of novel electrodes with low sheet resistances (≈10 Ω sq⁻¹). The hybrid electrodes that were prepared in this work, exhibited enhanced electrical conductivity at low nanofiller loadings and upgraded performance after repeated bending and folding cycles, compared to the GnP-based electrodes. Both conductors sustained repeated washing cycles and preserved 50% of their initial electrical conductivity at 12% elongation. The strain stability of their electrical properties was enhanced by pre-stretching the rubber substrate before spraying the conductive ink. With this approach, both GnP- and hybrid-based electrodes preserve more than 70% of their initial electrical conductivity at 12% stretch. In this case, at 80% elongation the hybrid material displays electrical conductivity 4 times higher than the GnPs conductor. This is because the GnP-based coating forms cracks already at 30% elongation while the hybrid shows a crack-free morphology even at 100% strain. Repeated stretch-release cycles produced an electro-mechanical deterioration that can be restored simply through a heating treatment. The healing procedure also restored the electromagnetic interference shielding efficiency that was normally reduced after repeated stretch-release cycles. The developed technology finds application as stretchable parallel-plate capacitive touch sensor [4]. Tactile forces as low as 0.03 N and as high as 5 N can be detected by the device bended over curvilinear surfaces or under elongation.

References:
[1] Jang et al., Advanced Materials, 22, 4184-4202, (2016)
[2] Shi et al., Advanced Functional Materials, 42, 7614-7625, (2016)
[3] Oh et al., ACS Applied Materials & Interfaces, 5, 3319–3325, (2016)
[4] Cataldi et al., Advanced Science, 2, 1700587, (2018)

In the last years, soft robots have been designed and developed to fulfil demands of better malleability and adaptability to changing environment [1-2]. They can be made of various stimuli responsive materials, which respond to magnetic field [3], light [4], temperature [5], electric fields [6], chemicals [7], pressure [8], etc. In contrast to other actuation mechanisms, magnetic fields are appealing for numerous application scenarios (e.g. environmental, biological, medical), where their long-range penetration, easy accessibility, and controllability [2, 9, 10] offer exciting advantages. Despite the significant advances in soft magnetic actuators, real-time monitoring and precise feedback control [11-13] remain a challenge for magnetic soft robots.

Here, we present a soft robotic system capable of precisely controlling its deformation degree by means of embedded highly compliant, high-performance magnetic sensors. Our ultrathin (7-100 μm) and ultrafast soft robots that can be actuated by in external magnetic fields pulsating at rates of up to 200 Hz. The high-performance magnetic field sensor is based on the giant magnetoresistive effect and is prepared on ultrathin polymeric foils [14-17] to assure its high mechanical stability combined with mechanical imperceptibility. The latter is crucial to avoid any disturbance of the soft actuator due to the presence of magnetic sensing device. The self-sensing function is realized by monitoring the change of the sensor signal upon approaching it to a magnetic patch applied to the soft robot. This concept of an entirely soft and integrated sensor-actuator system enables contactless self-tracking of motion for magnetic soft robots and can be readily extended to other stimuli-driven soft actuators. These developments will pave the way towards intelligent soft robots, autonomous and reactive soft devices, and new types of human-robot interaction.

[1] D. Rus et al., Nature 521, 467 (2015)
[2] L. Hines et al., Adv. Mater. 29, 13 (2017)
[3] J. Y. Kim et al., Nat Mat. 10, 747 (2011)
[4] J. Deng et al., J. Am. Chem. Soc. 138, 225 (2016)
[5] Y. S. Kim et al., Nat Mat. 14, 1002 (2015)
[6] T. Mirfakhrai et al., Materials Today 10, 30 (2007)
[7] Q. Zhao et al., Nat Commun 5 (2014)
[8] SA. Morin et al., Science 337, 828 (2012)
[9] W. Hu et al., Nature 554, 81(2018)
[10] Kim. Y, et al., Nature 558, 274 (2018)
[11] T. G. Thuruthel et al., Sci Robot. 4, eaav1488 (2019)
[12] J. A. Lewis et al., Adv. Mater. 30, 1706383 (2018)
[13] W. Zhang et al., Adv Funct Mater. 29, 1806057 (2019)
[14] M. Melzer et al., Adv. Mater. 27, 1274 (2015)
[15] G. S. C. Bermúdez et al., Nat Electron. 1, 589 (2018)
[16] G. S. C. Bermúdez et al., Sci Adv., 4, eaao2623 (2018)
[17] P. N. Granell et al., npj Flexible Electronics, 3, 3 (2018)

High permittivity and efficient electromechanical coupling are critical to perform energy storage or conversion between mechanical and electrical energy for various applications of electrostrictive polymers. We report a giant electrostriction effect in liquid crystalline graphene doped elastomers. The materials are formulated by an original phase transfer method which allows the solubilization of graphene oxide monolayers in non-polar solvents. It is shown in particular that liquid crystal transition leads to an increased percolation threshold. Because of their unique liquid crystal structure, the resultant composites show a giant electrostriction coefficient (M~10^-14 m²/V² at 0.1 Hz) coupled with good reproducibility during cycles at high deformation rates. This work offers a promising pathway to design novel high performance soft dielectric materials for sensing or energy harvesting applications. We will also discuss recent developments concerning dielectric foams and multilayers systems that allow ultra-low pressure sensing via piezo-capacitive effects.

Soft robots have the potential to adapt their morphology, properties, and behavior to different tasks or changing environments. This adaptive capability is often inspired by biological systems. For instance, humans can transition between forceful and gentle tasks by controlling the stiffness of skeletal joints through co-contraction of antagonistic sets of muscles. In another example, the remarkably dexterous motion achieved by skeleton-free animal parts such as elephant trunks, octopus arms, and human tongues is attributed to selective contraction of layers of uni-directional muscle fibers. During this talk, I will present recent work towards programmable composites that address variable stiffness properties and variable trajectory motions inspired by these capabilities in animals. First, I will present a particulate additive designed to undergo a repeatable solid-liquid phase change within a polymeric matrix and demonstrate its use to achieve unprecedented changes in bulk material stiffness and elasticity. The solid-liquid phase change of Field’s metal inclusions allows a composite to dramatically adjust its mechanical response, as demonstrated in two matrix materials: a thermoset epoxy and a silicone elastomer. Second, I will describe a soft composite lamina comprised of an elastic matrix with uni-directionally embedded inextensible fibers and an adhesive backing, which was inspired by soft body control strategies using fiber-architectures. In contrast to existing soft actuators with fixed deformation trajectories, this composite is simply placed on the surface of an inflatable body to govern its deformation trajectory, can be re-arranged in-situ to change this trajectory, and is created using a high throughput, automated manufacturing process. Finally, I will speculate on how these two composites could be combined to achieve new capabilities in next-generation soft robots.

The emergence of soft robotics has given rise to new challenges in both the development of functional materials and the design of innovative versatile manufacturing techniques. Additive manufacturing is generally cited when discussing promising versatile fabrication processes. Indeed, a wide range of materials, such as thermoplastic polymers, metals, elastomers, biomaterials, and yarns, can be used for freeform fabrication and integration into complex structures using different additive manufacturing techniques. Among these techniques, the extrusion of materials is the most commonly adopted due to the its relative simplicity. However, the choice of materials has been limited to materials exhibiting a phase transition at appropriate temperatures (e.g. thermoplastics) or to thixotropic materials that flow under stress. Hinton et al. reported the use of a support bath, made of a microparticulate hydrogel (Carbopol), allowing the freeform embedding of PDMS in the liquid state before reticulation of the elastomer.1 After curing, the hydrogel is dissolved by changing the pH, and the 3D-printed object is released. However, Carbopol is highly sensitive to the ionic composition and pH, thus excluding various materials with incompatible chemical compositions. In this contribution, we present the use of a new aqueous-based support bath made of nanoclay suspension for the printing of functional devices. This new support enables the printing of a wider range of materials, including thermosensitive and UV-curable materials, that can be combined into functional devices. We illustrate the advantages of this economical and reusable support by fabricating dielectric elastomer actuators (DEAs) inspired by the Peano-HASEL actuator published by Keplinger’s group.2 In a facile and fully integrated process, we used the aqueous-based support bath to print advanced muscle-like actuators. First, the dielectric liquid is encapsulated by printing an elastomeric envelope.
Electrodes, made of a UV-curable polyacrylamide hydrogel, are successively integrated into the elastomer before curing. Finally, materials are left for curing at room temperature for about 24 h and the support bath is washed away. This facile method allows the assembly of multiple actuators with various complex forms. We present the rheological properties of the support bath, its compatibility with a wide range of materials, and the fabrication and characterization of a DEA device.
(1) Hinton, T. J.; Hudson, A.; Pusch, K.; Lee, A.; Feinberg, A. W. 3D Printing PDMS Elastomer in a Hydrophilic Support Bath via Freeform Reversible Embedding. ACS Biomater. Sci. Eng. 2016, 2 (10), 1781–1786. https://doi.org/10.1021/acsbiomaterials.6b00170.
(2) Kellaris, N.; Venkata, V. G.; Smith, G. M.; Mitchell, S. K.; Keplinger, C. Peano-HASEL Actuators: Muscle-Mimetic, Electrohydraulic Transducers That Linearly Contract on Activation. Science Robotics 2018, 3 (14), eaar3276.

Polymeric actuator materials are able to shift their shape reversibly and repetitively in response to an environmental stimulus. Shape-memory polymer actuators function by utilizing the crystallization-induced elongation and melting-induced contraction of an actuation domain, the orientation of which is maintained by a rigid skeleton domain.¹ The interconnection between the domain-forming segment chains is provided by a network of cross-links, which are usually of a covalent nature and therefore preventing the reprocessing of the material after fabrication.² The implementation of physical cross-links, based on e.g. hydrogen bonding, thermally stable crystals or ionomers, aims to provide a solution to this problem. In this work, we introduce shape-memory polymer blend actuators, where the cross-links are formed by the physical interaction between a multiblock copolyester and an oligoester. By utilizing this supramolecular interaction, we create a rigid structure, stable up to 200 °C, formed in a one-step process without any post-treatment. The blending approach allows us to tune the actuation performance of the materials simply by adjusting the composition.
1. Lendlein, A. & Gould, O. E. C. Nat. Rev. Mater. 4, (2019).
2. Behl, M., Kratz, K., Noechel, U., Sauter, T. & Lendlein, A. Proc. Natl. Acad. Sci. U. S. A. 110, 12555–9 (2013).

A rich literature exists in bioinspired robotics and recently the use of soft materials and variable stiffness technologies represents an emerging way to build new classes of robotic systems that are expected to interact more safely with natural unstructured environments and with humans, and that better deal with un-certain and dynamic tasks. Despite the big achievements in this field, robotic technologies are still inadequate to mimic the biological system capabilities in changing their morphology and adapting their body and functionality during their lifetime. Growth is a very interesting feature of living beings that can inspire a generation of robots with new and unpredictable abilities of movement. Noteworthy, plants represent an alternative model of movement in robotics based on growing.
We propose a new generation of self-creating plant-like robots that are able to move adding new material to their bodies while adapting to external conditions.
We also focus our research on designing and developing innovative actuation solutions taking inspiration from unexplored biological phenomena, such as osmosis. In this field, we propose the first soft robot mimicking plant tendrils. The robot is able to curl and climb, using the same physical principle determining water transport in plants (osmosis).
The potential impact on society of plant-like self-creating robots could be huge and wide, e.g., in rescue, medical applications, space, or environmental monitoring. Since the design of these robotic solutions is deeply based on a few selected plant features, a new view of robots for biology can be envisaged, with the goal to give insights on the organisms themselves and open new exciting opportunities both in science and engineering.

Plant organs and tissues represent from a materials science point of view hierarchically structured multifunctional adaptive materials systems which in addition typically are equipped with various self-x-functions including for example self-repair. This makes them to interesting role models for many potential applications in high-end technologies including soft robotics, aviation and space flight, automotive, and future-bound green architecture, but also for sports equipment and for prostheses or orthoses. An often overlooked potential of bio-inspiration from plants are complex motions found in the not at all static and immobile plants. These motions can either be actively actuated (by turgor or growth processes) or can be passively actuated (by changes in humidity). In the latter case, motion patterns are imprinted in the structure of fiber-reinforced plant materials systems allowing for one, two and three-phase motions.
Novel methods for quantitative analysis and simulation of the form-structure-function relationship at different hierarchical levels provide fascinating insights into multiscale mechanics and other functions of plant material systems. New production methods such as 3D & 4D-printing, laser sintering and melting, and 3D braiding pultrusion make it possible - similar to biology - to produce from small to large and to functionalize different hierarchical levels. This allows cost-effectively to convert many outstanding properties of biological models into innovative biomimetic products. The examples presented include the development of material systems for a novel type of soft robots that climb like plants and adapt to their environment. The “GrowBot” research groups aim to transfer the skills of climbing plants who can find suitable support structures with their stems in complex, unknown 3D environments. Their different anchoring strategies allow the plants to attach themselves to different surfaces. In a first phase the transfer of stems structure and of the various attachment system (e.g. roots or tendrils) into bio-inspired (self-)adaptive materials systems for soft-robots is intended. A second example are anti-adhesive materials systems and surfaces inspired by plant surfaces on which insects cannot find grip and slip off. These bio-inspired micro-structured surfaces can be embossed on adhesive tapes that can help protect food or medicines from pest insects. Further examples are based on plant movements and aimed for the development of novel bio-inspired motile materials systems, e.g. for architecture. They include one and two phase motion patterns found in pinecone scales (Pinus spp.) and three phase motions occurring in the involucral bracts of the silver thistle (Carlina acaulis). These organs combine sensor, actuator, reactive movable element, and support structure in one materials system, do not consume energy (i.e. move entirely passive), show high level of functional integration and display extraordinary high functional resilience and robustness. Active motion processes served as role model for the biomimetic façade shading system flectofold which was inspired by the trap movement of the waterwheel plant (Aldrovanda vesiculosa), and by the wing folding patterns of the Italian striped bug (Graphosoma italicum). The waterwheel plant together with the Venus flytrap (Dionaea muscipula) served additionally as concept generator for adaptive biomimetic actuator systems reacting to various stimuli and combining two biological snap-trap mechanics. The bio-inspired demonstrators not only incorporate the actuation principles and motion behaviours of the two carnivorous plant species but also show adaptive responses to different environmental triggers. In the presented actuator systems we succeeded to implement several plant movement, actuation and deformation systems into one versatile adaptive technical compliant mechanism.

Cilia are thin hair-like structures that cover living surfaces for motion and swimming. Numerous studies have been focused on replicating the properties of these morphologies by exploring artificial biomimetic cilia for applications in microfluidic propulsion/mixing^[1], surface property modification ^[2], catalytic reactions ^[3], microrobots/swimmer ^[4]among many others.
Among multiple possibilities for actuation, magnetic fields present an opportunity given their advantageous properties for quick response and wireless operation. However, localizing the actuation of only a small area of the cilia structure or even individual pillars, presents a challenge since the magnetic field is not localized and does not present defined confining boundaries.
In this work, we use light as a wireless and localized stimulus to modulate the magnetic force and control the movement of a small fraction of cilia within a large magnetic cilia array. Chromium dioxide (CrO₂) is a black ferromagnetic material with lower Curie temperature than other commonly used magnetic fillers. By taking advantage of the high absorbance and temperature-sensitive magnetic susceptibility of CrO₂, we have demonstrated a novel mechanism by combining light and magnetic field to actuate soft actuators ^[5]. In this work, the technique is applied in the microscale to high aspect-ratio arrays of pillars that form magnetically responsive cilia. The cilia are fabricated with CrO₂ and PDMS mixture using silicon molding techniques and present a 9:1 aspect ratio (i.e. 5 μm in diameter and 45 μm in height) over a 1 cm 1 cm patch.
The cilia move in accordance with the external magnetic field and exhibit a deformation-dependent transparency. Because of the periodic pattern of the cilia, the structure also exhibits far-field diffraction patterns from whose diffraction efficiency can be wirelessly tuned with the magnetic field. With the measurement of the change of diffraction efficiency, a theoretical estimation of the cilia movement can be made. Furthermore, by taking advantage of the high light absorption and good photo-thermal properties of CrO₂, the cilia array can be locally heated through light irradiation. Along with its thermal-demagnetization effect, embedding CrO₂ in the structure grants the uniform magnetic cilia array unique properties: cilia can be actuated locally and at the same time globally with untethered stimuli – light and magnetic fields yielding three distinct modes of controls that can be used to actuate the cilia array- (a) only with light, (b) only with magnetic field, and (c) with both in combination. By using light only, accurate actuations can be made even with individual cilia while the rest remains unperturbed; with the sole use of the magnetic field, all the cilia are synchronized and move together. When using light in concert with the magnetic field, one can modify the cilia movement locally on top of a global cilia movement. This is hard to achieve with either only light or magnetic field on a uniform sample without imposing material constraints to generate a material gradient during synthesis and material fabrication. Among potential applications, this concept cilia composite can add utility in soft-robotic approaches, or biomimetic microrobots with higher control degree-of-freedom when combined with other non-reciprocal cilia designs.

[1] C. L. van Oosten, C. W. M. Bastiaansen, D. J. Broer, Nature materials 2009, 8, 677.
[2] Q. Zhou, W. D. Ristenpart, P. Stroeve, Langmuir the ACS journal of surfaces and colloids 2011, 27, 11747.
[3] W. Wang, X. Huang, M. Lai, C. Lu, RSC Adv. 2017, 7, 10517.
[4] S. Kim, S. Lee, J. Lee, B. J. Nelson, L. Zhang, H. Choi, Scientific reports 2016, 6, 30713.
[5] M. Li, Y. Wang, A. Chen, A. Naidu, B. S. Napier, W. Li, C. L. Rodriguez, S. A. Crooker, F. G. Omenetto, Proceedings of the National Academy of Sciences 2018, 115, 8119.

With a specific stimulus, shape-memory materials can assume a temporary shape and subsequently recover their original shape, a capability that renders them relevant for applications in fields such as biomedicine, aerospace and wearable electronics. Shape-memory in polymers and composites is usually achieved by exploiting a thermal transition to program a temporary shape and successively recover the original shape. This may be problematic for heat sensitive environments and when rapid and uniform heating is required. In this work, a soft magnetic shape-memory composite is produced by encasing liquid droplets of magneto-rheological fluid into a polydimethylsiloxane matrix. [1] Under the influence of a magnetic field, this material undergoes an exceptional stiffening transition, with an almost 30-fold increase in shear modulus. Exploiting this transition, fast and fully reversible magnetic shape memory is demonstrated in three ways, by embossing, by simple shear and by unconstrained three-dimensional deformation. Using advanced synchrotron X-ray tomography techniques, the internal structure of the material is revealed, which can be correlated with the composite stiffening and shape-memory mechanism. Based on this simple emulsion process, this material concept can be extended to different fluids and elastomers, and can be manufactured with a wide range of methods.
[1] P. Testa et al. (In Press), Advanced Materials, 2019

Conductive polymers such as polythiophenes, polyanilines and polypyrroles, have been widely studied for many potential applications, such as organic photovoltaic cells, organic electronics, supercapacitors and actuators. One major barrier that restricts their application is their poor mechanical properties. The poor mechanical properties of conductive polymers are mainly due to their conjugated molecular structure, which makes the main chain very rigid. Inspired by the structure of bones, where rigid hydroxyapatite crystals and soft collagen fibers cooperate to form strong and tough materials, we proposed to incorporate 'soft' polymers into rigid conductive polymers to improve the mechanical properties. The soft polymer ingredients are designed to interact with rigid conductive polymers through supramolecular interactions, such as hydrogen bonds, charge-charge interactions, dynamic covalent bonds and so on. Upon a large stress, the weak supramolecular interactions between soft polymers and rigid conjugated polymers would break to help dissipate destructive energy, which would greatly improve the toughness of the materials. Beyond that, the dynamic nature of supramolecular interactions could also enable the conductive polymers stimuli-responsive properties. Herein, we report two examples of utilizing conductive polymers composite to make programmable soft actuators that are responsive to multiple stimuli.

In the first case, PEDOT, PAA-AMPS and PVA are crosslinked by hydrogen bond, electrostatic interaction and coordination to form a supramolecular network. In response to environmental moisture, the resulted composite PPA can not only generate powerful actuation with a contractile stress up to 13 MPa, but also perform programmable helical motions. PPA films with internal stress along the radial directions were prepared by a simple solution casting method. Driven by moisture, rectangular stripes cut from the same PPA film but with different cutting angles can perform direct bending, left-handed or right-handed helical motions, demonstrating the generation of chirality from asymmetric internal stress. By modulating the distribution of internal stress in PPA stripes, their moving direction and speed are readily prescribed. The powerful and programmable PPA stripes can be used to make soft devices, such as moisture-responsive switches and transporters.

In the second example, we report a multi-responsive polymer composite (PHP) based on poly(N-isopropylacrylamide) (PNIPAm), polyaniline (PANi) and polydimethylsiloxane (PDMS). PNIPAm shows reversible volume change in response to the change of temperature, humidity and ionic strength. PANi can efficiently absorb visible light and convert the light energy to heat. PDMS is a transparent and robust elastomer, with a high positive coefficient of thermal expansion. PNIPAm and PANi are incorporated together to give the PNIPAm-PANi hydrogel, which is coated with a PDMS layer to give the PHP bilayer film. Owing to the synergistic effect of these three functional polymers, the PHP bilayer film can perform rapid and reversible transformation between multiple complex shapes (upon global stimuli) and patterns (upon localized stimuli), driven by four types of stimuli: light, heat, humidity and ionic strength. The transformation of PHP is well programmable by using different orders of sequential stimuli. With its powerful actuation and excellent repeatability, the programmable PHP bilayer actuator can be utilized as environment-sensitive devices, such as switches and smart curtains.

By these examples, we wish to demonstrate that the supramolecular approach could be a general method not only improve the mechanical properties of rigid conductive polymers, but also enable good stimuli-responsive properties to conductive polymer composites. These programmable multi-responsive actuators are promising for fabricating smart soft robotics.

High strength and high modulus carbon fibers are produced by carbonization of polyacrylonitrile (PAN) precursor fibers processed through continuous gel spinning [1]. The density of solid carbon fibers made from PAN precursors is in the range of 1.73-1.93 g/cm³. Further reduction in the density of the carbon fibers and increase in specific surface area are possible by introducing porosity. Controlling the pore size and distribution in the porous carbon fiber are ways to tailor the mechanical and structural properties. This study explores the conditions to introduce porosity in carbon fibers produced by continuous gel spinning of blends of PAN and sacrificial polymer, with good mechanical properties. Sacrificial polymers including poly(acrylic acid) (PAA), poly(methyl methacrylate) (PMMA), poly(styrene-co-acrylonitrile)(SAN), are chosen based on their incompatibility for blending with the carbon source, PAN. Pore size, distribution and morphology in the carbon fibers are found to be dependent on factors including the choice of sacrificial polymer, blend ratio, solvent and coagulation conditions used for spinning. The influence of the above mentioned processing factors on the mechanical and structural properties of the precursor and resulting carbon fibers are evaluated in this study. This comparative study paves the way for identifying the optimal PAN-sacrificial blend system for production of gel spun porous carbon fibers that are strong, light and possess uniform network of porosity. Porous carbon fibers from gel spun precursor, possessing high mechanical strength could create a spectrum of applications of lightweight, self-sustaining structural reinforcements with energy storage or filtering capabilities. One could envision the body of an aircraft or car made with porous carbon fiber that could store energy and lead to energy efficient smart vehicles.

(1) Chae, H. G.; Newcomb, B. A.; Gulgunje, P. V.; Liu, Y.; Gupta, K. K.; Kamath, M. G.; Lyons, K. M.; Ghoshal, S.; Pramanik, C.; Giannuzzi, L.; et al. High Strength and High Modulus Carbon Fibers. Carbon N. Y. 2015, 93, 81–87.

Smart textiles are a topic of growing interest combining traditional uses of clothes with functional properties. The increasing number of antibiotic-resistant microorganisms and consequently its infection diseases frequency, and the rising of skin cancer incidence are two examples of smart textiles applications. Antimicrobial properties and UV blocking could be developed in fabrics by using metallic oxides. The broad range of metallic oxides properties and their stability are of great interest, and the methods for its grafting in textile substrates are divided into two groups: ex-situ and in-situ.
In this work, cotton weave fabric samples were prior treated with enzymatic desizing, and a scouring/bleaching simultaneous process to develop a high absorbing material. A factorial experiment suggested a treatment procedure with 0.2% NaOH and 2% otw of H₂O₂ for best results of weight loss, whiteness index and water absorption rate (warp and weft directions).
Then, a new two-step method is proposed to prepare in-situ copper oxide (CuO) and zinc oxide (ZnO) inside the cotton fibers in the pre-treated textile fabric, and after grafting with a reactive monochlorotriazine (MCT) beta-cyclodextrin. The grafting of MCT-beta-cyclodextrin in cotton fibers was made by the pad-dry method. Copper and zinc sulfates were used as precursors, to achieve concentrations of copper and zinc ions from 1% to 5% inside the fibers (until copper sulfate solubility limit). These methods are low-cost and scalable into the textile industry finishing process.
The main purpose of this work is to prepare a smart textile with a never reported method. Using water-soluble precursors applied by a pad-dry process. Followed by a reduction wet process to prepare nanostructured metallic oxides inside cotton fibers. The change of solubility from the precursors to the prepared oxides is proposed as a mechanism to improve the washing fastness and durability of the treatment.
The new materials were characterized using FTIR, SEM, EDX, TEM, DRX and thermogravimetric analysis to understand the structural properties and nanostructured particle morphology.

We created a kirigami-inspired self-folding robotic finger with a microfluidic capillary force in paper. When water was sprayed on hydrophilic regions patterned on paper, the 2-D sheet of the kirigami-based finger was controllably self-folded and popped up to touch/connect two electrodes and switch on LEDs. When the water in the paper evaporated, the popped-up structure was unfolded into its original planar sheet. The fold-to-pop-up structure can be readily fabricated via a double-sided wax printing method, forming a bilayer structure of the hydrophilic regions and the hydrophobic wax, in which these two layers have different swelling and shrinking properties. This novel activation technique enabled a flat paper finger to self-fold with desired angles by controlling hydrophilic/hydrophobic patterns and their lengths. The patterned paper performed folding actuation with water and unfolding behavior with evaporation without being mechanically manipulated by external forces or moments. This proposed technique will be advantageous for many applications (e.g. humidity sensors) inexpensively and autonomously in remote and resource-limited environments. Soft robotics is recently considered as one of the most exciting research topics because of their deformability, flexibility, and adaptability to environmental changes. Soft actuators have been one of the most significant core technologies to enable autonomous capabilities for various soft robotic applications like rehabilitation and training robots, surgical robots, and diagnostic robots. Several promising soft actuators have been proposed including shape memory alloys, electro active polymers, fluidic elastomer actuators, and electro-magnetic actuators, achieving multiple degrees of freedom and delicate object manipulation. However, these techniques are very complicated, expensive, and inefficient in terms of energy use [6]. This work demonstrated an innovative self-actuating method with a microfluidic capillary force in paper through rapid and low-cost prototyping. Through the prescribed planar design of patterned folds and cuts, we demonstrated a kirigami-inspired programmable self-folding of the robotic finger with defined curvatures. The operating principle of the fluidic actuation in paper, which consists of a swelling process with sprayed water and a drying process with evaporation. This actuation used a two-layer configuration with one passive wax layer and one active water layer. The passive layer developed a negligible mechanical move compared to the active layer with the water-based swelling process. This difference in expansion or contraction between the two layers generates localized bending of the paper finger and touches/connects two pre-patterned electrical wires (conductive PEDOT:PSS polymers) for LEDs lighting. The bilayer of the hydrophobic and the hydrophilic regions had drastically different swelling behavior in response to water spraying, spontaneously folding-up and actuating from the 2-D pattern on the paper, turning on the LEDs. The folded structure can also unfold itself with evaporation, turning off the LEDs. Electronics components (i.e. resistors, LEDs and SN75468 IC) were mounted on the paper printed circuit boards. Under repeated swelling and drying processes, the designed paper successfully folded and unfolded without any mechanical degradation. The length of the hydrophobic wax was controllably increased, reducing the ratio of the wax to the hydrophilic part of the paper and controlling the switching duration with water sprayed. The stability and conductivity of the electrical wires were significantly enhanced by the addition of graphene even under repeated folding and unfolding deformations.

Soft and stretchable electronics present opportunities to change how humans interact with technology, promising improvements to healthcare monitoring, communications, and accessibility. Stretchable devices, particularly those designed to be worn on the human body, require soft, deformable elastomeric substrates that can withstand torsional, shearing, and multiaxial strains in addition to normal wear and tear. The elastomer polydimethylsiloxane (PDMS) has been widely used: It is soft, stretchable, biocompatible, transparent, and easy to mold. Most importantly, PDMS possesses surface properties that make it easy to integrate with functional electronic materials for stretchable device fabrication. Plasma oxidation increases the wettability of the PDMS surface by generating a hydrophilic surface silicate layer, enabling the deposition of functional materials from solution and chemical surface modification via the chemisorption of organosilanes. Still, bulk PDMS suffers from mediocre tear strength, a relatively high Young’s modulus of 1.5-2.0 MPa and an elongation at break of ~140%. Replacing PDMS with other elastomers that offer useful properties such as high dielectric strength, edge-tear resistance, extreme stretchability, and ultra-low modulus is a challenge due since they often lack the ideal surface chemistry of PDMS necessary for device integration.

Our approach to solving this fundamental problem fuses two different elastomers together to form a layered structure, transforming the elastomeric substrate into a multifunctional element that combines different properties, providing functionality that a single elastomer cannot deliver. We previously demonstrated the idea using an organosilane-based “molecular glue” to adhere a thin membrane of PDMS onto the surface of a transparent butyl rubber substrate. The resulting membrane-interface-elastomer (MINE) structures uniquely combine the surface chemistry of PDMS with the intrinsically low gas permeability of butyl rubber for the fabrication of robust stretchable device. This structure enables functionalization of the PDMS surface with conductive metal films while retaining the gas impermeability of the butyl rubber below. Interestingly, metal films deposited on this structure remain conductive to 85% elongation by generation of microcracks in the surface in a way that is not observed in native PDMS. In this presentation, we describe new MINE structures fabricated by adhering a PDMS membrane to the elastomer Ecoflex. The low Young’s modulus (68 KPa) of Ecoflex is similar to human skin, making this elastomer ideal for skin-mounted electronics. However, we show that the silicone oils and low molecular weight petroleum plasticizers that make Ecoflex so stretchable also cause poor surface chemical properties: Plasma oxidation of Ecoflex results in migration of these low molecular weight additives to the surface, disrupting the formation of a hydrophilic silicate layer. The fabrication of PDMS-Ecoflex MINE structures uses the platinum-catalyzed crosslinking chemistry common to both elastomers, producing a covalently-crosslinked interface between the two elastomers.

We show that together, the layered MINE structure exhibits the best properties of PDMS and Ecoflex: The PDMS membrane surface can be plasma oxidized to increase the wettability and support subsequent chemical modification, whereas the mechanical properties of the Ecoflex elastomer dominate mechanical behaviour of the composite. PDMS-Ecoflex MINE structures demonstrate stretchability to 400% elongation before delamination of the PDMS layer, as well as a Young’s modulus at the surface of 100 KPa, comparable to Ecoflex alone. We also demonstrate the use of pre-strained PDMS-Ecoflex MINE structures to fabricate gold films that retain conductivity to 300% elongation.

Ionotronic systems consist of hybrid electrical circuits that use both ions and electrons as charge carriers.¹ The constituent materials of synthetic ionotronic systems, such as hydrogels and dielectric elastomers, often exhibit properties such as softness, transparency, stretchability, and biocompatibility that are desirable in a range of contemporary applications such as soft robotics and biological interfaces. Recent years have seen the development of ionotronic sensors,² actuators,³ and power sources⁴ that leverage these characteristics. Such engineered systems often share their function, morphology, or mechanism with excitable biological tissues, which also use ions as charge carriers in aqueous media.

Membranes are a key component of both biological and synthetic ionotronic systems, owing to their utility as selective barriers and capacitors with variable properties. Electrolyte gradients across selectively permeable membranes provide the driving force for the generation of electrical potentials such as the resting potential of a cell membrane,⁴ and capacitive membranes between electrolyte-bearing reservoirs can laterally transport electrical signals quickly in the manner of a transmission cable or an axonal segment between nodes of Ranvier in a neuron.⁵ In this work, we trigger selective permeabilization events within an insulating membrane in response to various stimuli in order to generate and transmit electrical signals within soft materials in the manner of a dendrite. We compare the voltage decrement along such membranes with that of an electrotonus in excitable tissues. This bioinspired transduction scheme leverages the toolkit of stimuli-responsive chemistry to enable the development of systems that produce fast electrical responses to a range of environmental changes. The ionotronic systems described here may be useful as sensors when interfaced with existing electronics or, when coupled with actuators, may serve as functional elements of autonomous systems exhibiting homeostatic or oscillatory behavior.

References:
1. Yang, C. & Suo, Z. Hydrogel ionotronics. Nat. Rev. Mater. 3, 125–142 (2018).
2. Sun, J.-Y., Keplinger, C., Whitesides, G. M. & Suo, Z. Ionic skin. Adv. Mater. 26, 7608–7614 (2014).
3. Keplinger, C. et al. Stretchable, transparent, ionic conductors. Science 341, 984–987 (2013).
4. Schroeder, T. B. H. et al. An electric-eel-inspired soft power source from stacked hydrogels. Nature 552, 214–218 (2017).
5. Yang, C. H. et al. Ionic cable. Extreme Mech. Lett. 3, 59–65 (2015).

The synthesis of nano and microstructures are an emerging field in chemistry and materials science. They can be made from a large variety of materials, for example metals, semi-metals, or polymeric substances. Usually, these particles exhibit a comparable simple shape, for some are high temperature is required and for many (except polymers) of them no covalent bonds are formed during formation /1/.
Some years ago, we have presented the synthesis of silicone nano filaments in particular for coatings delivering superhydrophobic, superoleophobic, or superamphiphobic surface properties (fig. 1) /2, 3/. Also, nano- and microstructures different from filaments have been synthesized in a reproducible manner /4/.

Recently, we have shown a reaction mechanism, the Droplet-Assisted Growth and Shaping, explaining how this one-dimensional growth is initiated by a delicate interplay between surface properties, phase equilibrium, and reactivity /5/. Based on this new scheme we are able to synthesize nano- and microparticles of different shapes depending on the reaction conditions.

The DAGS approach is not only applicable to silicon containing polymers. Recently, we could show that DAGS also leads to ermaniumoxide structures and Alumina containing nanostructures.

In this presentation, we will give an overview about this novel synthesis scheme. Applying appropriate reaction conditions allows for the directed growth of nano- and microstructures of complex shape. We believe that this reaction scheme is very promising in chemical synthesis and material science, since it enables us to form complex nano and microstructures from polymeric materials at room temperature in aqueous medium. Beyond this, we also draw the attention on multifunctional materials obtained by strategies implementing DAGS chemistry, e.g. wetting and electric conductivity features.

References:
SC Glotzer, MJ Solomon, Nature Materials 6, 557
G. Artus, S. Jung, J. Zimmermann, H. P. Gautschi, K. Marquardt, S. Seeger, EP1644450A2 (2003), Adv. Mater. (2006),18, 2758
J. Zhang, S. Seeger, Angew. Chem. (2011) 50, 6652
Stojanovic, S. Olveira, M. Fischer, S. Seeger, Chem.
Mater. 2013, 25, 2787
G Artus, S Olveira, D Patra, S Seeger, Macromol.
Rapid Comm. 2017, 38, 1600558
/6/ N. Saddiqi, D. Patra, S. Seeger, ChemPhysChem 20, 538–52019
/7/ N. Saddiqi, S. Seeger, Adv. Mat. Interfaces, doi.org/10.1002/admi.201900041 (2019)
/8/ X. Zhang, S. Seeger, doi.org/10.1002/cnma.201900161 (2019)

Thin-film layers deposited on flexible metal foils can offer functionality for many applications, including semiconductors, detectors, refractory shielding, insulators, catalysts, and optical layers. With favorable manufacturability and low cost of thin-film deposition, various stacks of thin-films can be layered to produce multi-functional properties. For processes that require high temperatures, in this case up to 1450°C, it is imperative to limit the diffusion from the underlying metal foil substrate into the functional top layer thin-film, to reduce impurity contamination that may otherwise degrade the performance of the functional layer(s). Here, thin-films of MgO and SiO2 were deposited onto molybdenum metal foil and heated to 1410°C in a controlled vacuum environment with argon gas. Mo impurity concentration was characterized by dynamic secondary ion mass spectrometry (SIMS) depth profiles, both before and after high temperature annealing, and compared for MgO and SiO2 diffusion barriers. The films were also examined in secondary electron spectroscopy (SEM) to assess the impacts of high temperature annealing on film adhesion and cracking, XRD to measure effects of annealing on film crystal structure, and AFM to determine topography.

In a triboelectric system, two different materials with large difference of polarity in triboelectric series are generally required for the enhanced triboelectric output performance. This requirement of contact pairs restricts the selection of triboelectric materials and the use of identical materials for contact electrification. In addition, it impedes the facile fabrication of triboelectric devices with enhanced performances. Here, we demonstrate a facile approach for the development of triboelectric devices based on an identical material for the contact pair by switching the triboelectric polarity of ferroelectric copolymer, poly (vinylidenefluoride-co-trifluoroethylene) (P(VDF-TrFE)). The aligned dipoles in P(VDF-TrFE) have a great effect on the triboelectric polarity, which relies on the applied bias direction during electrical polarization. This approach does not need any additional chemical functionalization or mechanical modification to fabricate identical material-based triboelectric devices with remarkably enhanced output performances. The inversely-polarized P(VDF-TrFE) device exhibits ~106 times higher output currents and ~126 times higher output voltages than those of non-polarized P(VDF-TrFE) devices. Moreover, the high sensitivity of our triboelectric device in the subtle pressure range enables the simultaneous monitoring of weak pulse pressure of the carotid artery. This work demonstrates a facile fabrication to realize identical material-based triboelectric device with outstanding output performances via dipole-alignment of ferroelectric polymers. Our proposed strategy provides the capability to tune the triboelectric polarity of identical material without additional complicated process, paving the way for the development of high-performance triboelectric devices.

Single-walled carbon nanotubes (SWNTs) with semiconducting features show near infrared (NIR) photoluminescence (PL). Recently, locally functionalized SWNTs (lf-SWNTs) that are synthesized by local chemical functionalization of the tube structures have been developed as new types of NIR PL nanomaterials.[1-8] Therein, by the chemical reactions, new emissive sites that have different electronic structures from non-modified SWNTs are created on the tubes. As a result, the lf-SWNTs emit red-shifted PL with high efficiency (E₁₁*) compared to original PL (E₁₁) of the non-modified SWNTs. Furthermore, the E₁₁* PL of lf-SWNTs is found to show different PL wavelengths depending on the modified molecule structures.[1-5] Thus, this feature would be promising to create multifunctional NIR PL nanomaterials based on molecular functionalities of the modified molecules.
Here we report dynamic E₁₁* PL wavelength tuning techniques by covalent modification of functional molecules on the local functionalized moieties of lf-SWNTs. In this technique, driving forces for the wavelength shifts are designed based on molecular functions including molecular recognition[6,7] and dynamic covalent bond formation[8]. It allows us to create lf-SWNTs that response to various external stimuli with NIR PL shifting features.
Firstly, phenylboronic acid (PB), which binds sugar molecules selectively, so-called “sugar recognition”, was functionalized to SWNTs through diazonium chemistry to synthesize phenylboronic acid-modified lf-SWNTs (lf-SWNTs-PB).[6] The E₁₁* PL of lf-SWNTs-PB appeared at 1138 nm. When D-fructose was added to the aqueous solution of lf-SWNTs-PB, the E₁₁* peak was blue-shifted to 1124 nm according to the increase in the D-fructose concentration. This shifting was induced by electronic property changes of the functionalized PB moiety through boronate ester formation with D-fructose. As another molecular recognition motif, azacrown ether groups were functionalized to lf-SWNTs (lf-SWNTs-CR).[7] The lf-SWNTs-CR showed spectral red-shifts of E₁₁* PL by silver ion inclusion and protonation of amine part (pH variation), and, interestingly, the shifted wavelengths were different between these two systems. In the dynamic covalent bonding system, arylaldehyde groups were introduced in lf-SWNTs (lf-SWNTs-CHO).[8] When aniline derivatives having different substituents were mixed with the lf-SWNTs-CHO, wavelength shifts of the E₁₁* PL occurred, which provided different wavelengths depending on the chemical structures of the bound aniline derivatives. This wavelength shifts were induced by the imine bond formation (condensation reactions between amine and aldehyde groups). Moreover, additional chemical reactions including dissociation and exchange reactions of the bound aniline derivatives, and the Kabachnik-Fields reaction realized further wavelength changes in the E₁₁* PL. Thus, the present approach using imine chemistry at the functionalized sites achieves multistep PL modulation.
Therefore, molecular design of the local functionalized sites produces multifunctionalities in lf-SWNTs that response to various stimuli and environmental changes, which would be applicable to biological sensing and environmental monitoring by using their NIR PL features.

References: [1] Schatz, G. C. and Wang, Y. et al., J. Am. Chem. Soc. 2016, 138, 6878. [2] Htoon, H. and Doorn, S. K. et al., Nat. Photon. 2017, 11, 577. [3] Shiraki, T. and Nakashima, N. et al., Sci. Rep. 2016, 6, 28393. [4] Shiraki, T. and Nakashima, N. et al., Nanoscale. 2017, 9, 16900. [5] Shiraki, T. and Nakashima, N. et al., Chem. Commun. 2017, 53, 12544. [6] Shiraki, T. and Nakashima, N. et al., Chem. Commun. 2016, 52, 12972. [7] Shiraki, T. and Nakashima, N. et al., Chem. Eur. J. 2018, 24, 9393. [8] Shiraki, T., Nakashima, N., Fujigaya, T. et al., Chem. Eur. J. 2018, 24, 19162.

3D-printing has become one of the most fascinating subjects of research during the last decades because of the sheer amount of different design strategies and the implied manufacturing philosophies it has enabled.^[1] Crucial to the impact of additive manufacturing is the possibility to freely design devices and structures without the necessity for highly complex technologies by combining standard materials science with standard mechanical engineering on varying levels of technological profoundness.
Especially the fields of biomedical engineering and printed electronics profit from the simplicity of 3D-printing, allowing for sophisticated material design and advanced circuitry.^[2] Additionally, microparticles with complex shapes and integrated functionalities have been used in a broad range of applications since their geometry cannot be easily reproduced with clean room technology to implement structural benefits ina microscopic range.^[3]
Here, combining both of these aspect, we demonstrate multiple, microparticle based architectures for both biomedical and electronic applications. The benefit of using microparticles is the multitude of well grounded, standard techniques for their usage and the possibility to elevate their functionalities by integrating them into 3D structures. Custom geometries of metal-free sensors for different signals have been fabricated, just using metal oxide microparticles from materials science in a common Direct Ink Writing (DIW) approach. As an example, a heterojunction net of CuO/Cu₂O/Cu has been grown by simple step integration of copper microparticles on glass substrates and additional rapid thermal annealing, exhibiting high sensitivity for acetone, enabling its use as a sensor for breath analysis. Another example is the usage of complex-shaped single crystalline ZnO tetrapodal microparticles, which are highly sensitive towards UV light and are used as UV-sensors without the necessity for clean room technology. For the field of biomedical engineering, ZnO-biopolymer composite printed constructs show antibacterial properties for potential applications as functional wound dressing. These findings only hint at the much larger potential of the DIW of microparticles into functional devices which will enable more simple fabrication techniques for future challenges.

References: [1] Advanced Materials 2014, 26, 5930–5935;
[2] Sensors 2017, 17(5), 1166;
[3] Scientific Reports 2016; 6: 20793.

Electrospray deposition is a spray coating process that utilizes a high voltage to atomize a flowing solution into charged microdroplets. These self-repulsive droplets evaporate as they travel to a target grounded substrate, depositing the solution solids. We have classified a regime of self-limiting electrospray deposition (SLED) that enables the coating of surfaces hidden from the spray needle’s line-of-sight. In this regime, the deposited solids are insulative and have minimum mobility at the substrate, causing charge to gradually accumulate. Future generations of droplets are redirected to uncoated areas, yielding more uniform coverage of the entire substrate. In this study, we used stimuli-responsive hydrogel 3D structures fabricated through projection micro-stereolithography as our substrates to demonstrate the effectiveness of SLED for the coating of 4D-printed structures. We first examined model metallic geometries to classify the limits of the SLED phenomenon, including gaps and rapid bends. These revealed that SLED could readily enter gaps of less than 100 µm and undergo bends at a rate of an estimated 500 rad/s. We then coated 3D printed octet-truss lattices. The lattices had edge lengths of ~1 cm and struts of ~250 µm diameters and were coated with hierarchically-structured styrene-butadiene-styrene block copolymer-toughened polystyrene. By monitoring coated and uncoated lattices were enclosed in a camera-monitored humidity chamber, the swelling-driven dimensional changes in lattice over time were recorded. The polymeric coating acted as both a moisture barrier and mechanical coating, both reducing the extent and regulating the rate of hydrogel swelling. This represents a means of decoupling the surface and bulk properties of 4D-printed materials to provide for surface-gated control of the final structures.

The electrospray process utilizes the balance of electrostatic forces and surface tension within a charged spray to produce charged microdroplets with a narrow dispersion in size. By adding dilute solids to the spray, electrospray deposition can be employed for the manufacturing of nano- to micro-scale coatings. We have identified a regime of the spray of insulating materials onto conductive substrates where a limiting thickness emerges where the accumulation of charge that repels further spray. Self-limiting electrospray deposition (SLED) can uniformly cover complex multiscale structures with a variety of morphologies, including nanoshells and nanowires. Here, we investigate the application of polymer blends to modify the morphology and, through nanoindentation, the mechanical properties of the spray films for different applications. On the morphological side, blending immiscible non-self-limiting materials can alter the fill and porosity of the shell structures or the length and alignment of wire structures by tuning the droplet phase evolution. In mechanical properties, we demonstrated that the addition of a miscible curing agent to an epoxy resin can maintain the hierarchical spray structure to result in a tougher and stiffer coating for protective barriers. Further, the porosity of these films can be tuned spatially or programmed into the spray composition. In contrast, to make films that are more flexible for compliant surfaces, blends of plastic homopolymers and elastomeric block copolymers were sprayed. The net result of elastomeric blending was a coating that could enhance adhesion and sustain ~17% strain in the underlying structure.

The emergent field of biohybrid fiber systems has derived several techniques to entrap, encapsulate, or adsorb living or bioactive agents within woven and non-woven constructs, to simultaneously benefit the survivability of the biological agent and augment the functionality of the fiber. However, these techniques remain largely incompatible with existing textile manufacturing technology and lack the robustness of commercial woven fabrics. The incorporation of bacteria-derived [SS1] biosynthesis systems into fibers that can survive industrial spinning, weaving, or knitting processes is a method of producing biocomposite textiles across scales, and further, for using textile patterning methodologies for fiber templating and distribution.

To achieve the necessary preservation of biological activity within industrially-workable threads, we experiment with techniques such as lyophilization and the use of cell-free expression systems. The efficacy of a PURExpress cell-free system soaked into commonly used natural and artificial fibers is first demonstrated using the expression of Green and Red Fluorescent Protein (GFP, RFP). The cell-free system is then preserved on the fibers via lyophilization and the output is compared to that of the fresh system using the difference in the expression of GFP/RFP as determined by the intensity of fluorescence. The expression of more functional genes, such as the one which produces serratiopeptidase, a proteolytic enzyme that dissolves silk and other proteins, is then tested using the cell-free fiber system.

To assess their industrial usability biohybrid threads are used in established textile manufacturing techniques, and monitored for robustness and for the controlled spatial distribution or patterning of biofunctional properties into woven or knit textile structures. We hypothesize that when preserved onto silk fibers, the expression of serratiopeptidase would create a subtractive process by which the biosynthesized outputs of a silk textile would actively alter the geometry of the textile. We envision future textiles with a controlled patterning of biosynthetic compounds via biohybrid threads could have applications ranging from autonomous modificatins in fabric structure, to wound care and the promotion of the migration of other pharmaceutical agents to areas of interest.

Nature is the best pioneer of science based on their optimized functions for thousands of years. Spiders and spider webs, among them, have been tremendously attracted for prey capturability optimized by sensing of prey approaching, vibration cleaning the surface from droplets. Although spider web have provided various inspiration, simultaneous mimicry of the functions in a simple structure meets challenges due to needs of complex mechanism and proper materials. Here, we explored a multi-functional ionic spider web, which is electrostatically capturable, cleanable and self-powered sensible dielectric elastomer actuators optimized by behavioral inspiration of spider web. To combine the multi-functions resulting in increase of capturability, ionic spider web was driven by a stretchable and translucent electroactive structure made of dielectric elastomer and ionically conductive organogel. The electric field generated by the potential difference between a pair of ionic spider tube induces polarization in an adjacent target to realizes electrostatic adhesion. Self-powered sensing by electrostatic induction from a naturally electrificated target to ion in the tube realized switchability to ionic spider web to avoid from undesirable contamination on the surface, resulting in increase of capturability. Furthermore, electrostatic vibration of ionic spider web driven by alternating electrical attraction and repulsion force readily cleaned droplet on ionic web, leads increasing capturability. Plasma and (heptadecafluoro-1,1,2,2-tetrahydrodecyl)trichlorosilane treatment on dielectric elastomer readily increased (sensibility) and cleanability and it prevented the evaporation of organogel, which leads increase of durability of ionic spider web. We demonstrated the integrated approaches with autonomous ionic spider web sensing approaching targets and robustly capturing various materials after cleaning the surface. Ionic spider web lays the foundation for multi-functional robots inspired by nature.

Materials that respond to stimuli by moving and/or changing modulus are needed for emerging applications in fields ranging from soft robotics to medicine. To fill this need, we create composite materials consisting of regions of heterogenious physical phases: liquid or gas vesicles encapsulated in a solid or complex fluid matrix. Through incorporation of energy transferring nanoparticles and coatings at the interphase of these phases, we are able to actuate microscale phase transitions that result in a macroscale change in morphology/modulus of the material. This property may lead to tetherlessly actuated robotics, and new medical devices.

Spiders are abundant in most ecosystems in nature, making up more than 47,000 species. This ecological success is due to the web architectures and the exceptional mechanical properties of spider silk. Silk’s combination of strength, elasticity, toughness, and robustness originates from its hierarchical structure and has been a template for high-performance material design. In particular, spiders have optimized and adapted their web architecture to survive in their environment.

The most studied and familiar spider web is the 2D orb web which is composed of radial and spiral threads. However, 3D webs, such as sheet, funnel, or cob webs, are more common in nature. In contrast to 2D webs, where the spider is vulnerable to attacks, 3D webs surround the spider and offer a defensive advantage by warning the spider of intruders, blocking its predators and entangling prey.

Here, we investigate the mechanical properties of a Cyrtophora citricola 3D web, the architecture of which has been digitally modeled with micron-scale details from images of full-scale laboratory experiments (Su, Qin, Saraceno, Krell, Mühlethaler, Bisshop, Buehler, Royal Society Interface, 2018). Extending this work, we use a coarse-grained bead-spring model based on the 3D spider web network model and silk fiber properties to study the response of a realistic web structure to mechanical loads and the interplay between material and performance.

Understanding the roles of structure, material, and web spinning process, in the functionality and evolutionary fitness of spider webs could lead to innovative 3D spider web-inspired structures such as high performance light-weight long-span structures or fiber reinforced composite materials.

A soft shear force tactile sensor is essential for sensitive stretchable e-skin as well as pressure sensor. Especially, small size shear sensor has large potential of development in surgical robots which need delicate movement and grasping. However, capacitive type shear sensor has limit to miniaturization because the signal is weak in pF when it gets smaller. Here, we enable miniaturization of capacitive shear sensor using ion gel. Ion gel constructs electrical double layer (EDL) so that the sensor can make big signal at a small size. It provides nF scale capacitance which is about 10³ ~ 10⁵ times bigger than general polymer dielectrics. Also, our sensor has simple structure composed of well-shaped wall and pillar in the center. The ion gel located between wall and pillar make it possible to detect 4 different directions with high accuracy according to movement of pillar. Moreover, the sensor itself is made of conductive Ag ink and polydimethylsiloxane (PDMS) so it has high mechanical flexibility and stability. The single sensor has 5 x 5 mm² area and 2 mm height pillar and produces up to 100 nF. Finally, we demonstrate practical application of shear force sensing with 3 x 3 array in 27 x 27 mm². This flexible tactile sensor shows great promise for delicate robot finger which needs careful touch and sensitivity.

Dixa Longistyla is a family of flies and the larvae can float for a long time on water. A hydrophobic-hydrophilic pattern presents on the surface of larvae’s abdomen. The hydrophobic region is ring-shaped and the inside is hydrophilic. When the larvae float on water, a water droplet is held inside of the hydrophobic ring. Due to the drop, it is considered that the larvae sink down to water easily and need lower energy than the completely hydrophobic surface. Moreover, a bubble ring is formed on the hydrophobic region in water and the maggots can float up more easily than completely hydrophilic objects. Therefore, they have a both hydrophobic and hydrophilic region in terms of floating and sinking to water. Applying the pattern, we can control sinking and floating properties. The purpose of this study was to mimic the hydrophilic-hydrophobic pattern and to examine the effect of the pattern on water sinkability.
Sample were fabricated by oxygen plasma treatment of hydrophobic sheets through ring-shaped masks. The sheet surface under the mask was not oxidized, so that a hydrophobic region was remained after the plasma treatment. The sinking position, which was related with interaction on the hydrophilic-hydrophobic pattern, was measured using by surface tension balance. If the sinking position is shallow, it seems that the sample easily sinks into water. Two different shapes of mask, annular and disk, were prepared and the samples were fabricated by using of each mask. Moreover, in the case of measurements of the annular sample, volume of water held inside the hydrophobic ring was changed systematically.
There was almost no difference in sinkability between ring pattern without any water droplet inside the ring and disc pattern. On the other hand, the sinkability of the sample improved as volume of water inside the ring increased. The experimental results indicated that volume of water inside the ring affects the sinkability. The reason why the ring-shaped pattern and the disk-shaped pattern did not have a difference in the sinkability is considered that water was not sufficiently held inside the ring-shaped pattern.

Polymer foams are widely utilized in the aerospace and defense industries for applications including structural support, vibrational dampening, and shockwave mitigation. Through a materials-by-design approach, the Direct Ink Write (DIW) additive manufacturing (AM) method is an attractive approach for the design and fabrication of porous structures capable of achieving controlled mechanical response of the underlying deformation mechanisms. Two geometries of porous, periodic AM pads were printed using new DIW resin formulations containing up to 25 wt.% of functional filler (TiO₂, Al₂O₃, or graphite). All AM pads were characterized using chemical (FTIR, MS, NMR), thermal (TGA, DSC), and mechanical techniques (DMA, compression). Dynamic compression experiments coupled with time-resolved X-ray imaging were performed to obtain insights into the role of filler interactions in the in situ evolution of shockwave coupling in these functional, periodic porous polymers.

Living creatures and artificial objects like engines that possess dynamically varying and highly unconventional geometries are full of elastic waves. Such elastic energy with different frequencies could be power source of devices while few work demonstrates the elastic energy utilization on curved surfaces. The difficulties include that elastic waves in human beings and artificial objects are dispersed and relatively weak at local parts. Meanwhile, unconventional geometries and multiple frequencies of elastic waves require soft materials and more complicated structures of devices.

The acoustic blackhole (ABH), generally made of wedge structures, could damp the induced elastic wave velocity into zero, due to its power-law profile change in the thickness. ABHs have great potential for mitigating vibrations and noise. However, the fabrication limitation of the wedge may greatly affect the ABH performance. Besides, the rigid irregular structure of traditional ABHs reduces the strength of the whole device and limit their application in complex scenarios.

Here, we demonstrated an ABH mode with soft hyperuniform disordered structure that dramatically concentrate elastic wave energy and eliminate reflections on uneven surface. Hyperuniform disordered structures exhibit acoustic bandgap, and its randomness showing potentials to design novel devices. While this topic draw increasing attentions, application based on which is few. We arranged hyperuniform pattern with a smooth power-law profile edge in the soft matrix to realize the hyperuniform disorder acoustic blackhole (HABH). The numerical simulation shows good suppression of reflection and concentration of energy at the tip. The design method of HABH and double layer HABH is discussed. The HABH doesn’t require delicate process build while shows convincing ABH effect. The soft matrix of HABH makes it possible to attach on uneven surface. Our work provides a prominent solution to realize energy harvesting on human beings and noise reduction in automotive or architecture with lightweight, strong compatibility and low cost. Besides, the combination of hyperuniform structure and traditional configurations like ABH bring the unprecedented characteristic of devices, which can be translated to photonic crystals or other wave controlling systems.

REFERENCES
[1] B. M. P. Chong, L. B. Tan, K. M. Lim, H. P. Lee, A Review on Acoustic Black-Holes (ABH) and the Experimental and Numerical Study of ABH-Featured 3D Printed Beams, International Journal of Applied Mechanics 2017, 09, 1750078.
[2] S. Torquato, F. H. Stillinger, Local density fluctuations, hyperuniformity, and order metrics, Phys Rev E Stat Nonlin Soft Matter Phys 2003, 68, 41113.
[3] W. Man, M. Florescu, E. P. Williamson, Y. He, S. R. Hashemizad, B. Y. C. Leung, D. R. Liner, S. Torquato, P. M. Chaikin, P. J. Steinhardt, Isotropic band gaps and freeform waveguides observed in hyperuniform disordered photonic solids, Proceedings of the National Academy of Sciences 2013, 110, 15886.

Interest in natural-based degradable polymers has placed bacterial polyhydroxyalkanoates (PHAs) under the spotlight. PHAs are linear and isotactic polyesters composed of (R)-hydroxyalkanoic acid monomers. The knowledge of degradation and crystallization mechanisms of PHAs, which leads to shifts in their mechanical properties, is of critical importance for application development.
Naturally, biodegradation of a material starts at its surface. Using the Langmuir monolayer degradation technique, combined with in situ Brewster Angle Microscopy (BAM), several aspects of the degradation of polymer materials were directly observable. Since degradable polymer films at the air-water interface form water-soluble degradation products, the concentration of chain segments at the surface decreases during degradation leading to a decline of the surface pressure¹.
Thin polymer films of poly(3-R-hydroxybutyrate) (PHB) and poly[(3-R-hydroxyoctanoate)-co-(3-R-hydroxyhexanoate)] (PHOHHx) were exposed to a degrading medium consisting of i) phosphate-buffered saline (PBS, pH 7.4), ii) KOH (pH 10-13) and iii) KOH plus a PHA depolymerase enzyme (pH 10). In Langmuir layers, both polymers were highly stable in PBS and up to pH 12, demonstrating that the hydrolysis of PHAs ester bonds is only catalyzed at very highly alkaline conditions. At low packing densities of the films, the molecular degradation curves at pH >12 suggested a chain-end scission mechanism with an almost linear decrease of the surface pressure. This process did not induce a drastic shift in the crystallization state and therefore in the mechanical properties of the polymers, as observed by BAM and interfacial rheology measurements.
PHB with high initial degree of crystallinity (Xc = 55–65%), showed slightly faster degradation curves when compared to PHOHHx. Most likely, the amorphous polymer chains entrapped by the PHB spherulites (interlamellae amorphous regions) degraded faster than free amorphous polymer chains, as established in semi-crystalline poly(L-lactide)².
The degradation of PHAs by a specific PHA depolymerase showed a typical and fast random scission mechanism for both polymers. However, the PHA-degrading enzyme was more efficient on PHOHHx with longer side chain and lower degree of crystallinity. Interestingly, the degradation of PHB followed a two-steps mechanism that could be observable at the air-water interface. In the first stage, a decrease in the mechanical strength was observed, which was followed by a second step that agrees with a secondary crystallization process or chemi-crystallization.
We present the Langmuir degradation technique as a potential standard to characterize and compare several functionalities of polymers of different origin, structure and composition.

1. Machatschek, R.; Schulz, B.; Lendlein, A. Langmuir Monolayers as Tools to Study Biodegradable Polymer Implant Materials. Macromolecular Rapid Communications 2019, 40 (1), 1800611.
2. Gleadall, A.; Pan, J.; Atkinson, H. A Simplified Theory of Crystallisation Induced by Polymer Chain Scissions for Biodegradable Polyesters. Polymer Degradation and Stability 2012, 97 (9), 1616-1620.

Since their discovery in 1991, carbon nanotubes (CNTs) have been of great interest for multifunctional materials due to their outstanding electrical, thermal, and mechanical properties. Unfortunately, it has been challenging to translate the excellent properties of single CNT molecules into macroscale materials. A promising technique for obtaining high performance fiber materials is wet-spinning solutions of CNTs in chlorosulfonic acid (CSA). CSA and other superacids overcome the strong van der Waals forces between the CNTs by protonating the sidewalls of the CNTs to individualize the molecules to form a true solution. The CNTs in solution follow classical soft matter physics behavior; the solutions are isotropic at low concentration and liquid crystalline at sufficiently high concentration. The transition between these phases depends on the aspect ratio (the ratio of the length of the CNT to the diameter). Here, we study how the rheology and phase behavior of the solutions affect the spinning process and the electrical and mechanical properties of the resulting fibers. We have examined this experimentally by varying key processing parameters such as solution extrusion rate, CNT solution concentration, fiber draw ratio, and choice of coagulant. We find that spinning at lower concentrations yields significant improvement in tensile strength but no change in conductivity. Preliminary tensile testing data demonstrates that fibers spun from lower concentration solutions have a higher elongation a break. This suggests that the improvement in tensile strength can be attributed to the formation of larger bundles of CNTs within the fiber. Continued research of the fluid behavior will enable us to create the next generation materials for sensors, electrodes and wiring.

SOP: In this paper, we present the development of a novel ultra-flexible tactile sensor that makes use of such organic photo diodes (OPDs) embedded into a soft skin construct, measuring force based on its deformation. Our goal is to integrate this sensor with robotic and prosthetic fingers for improved sensing and control. Developing an electronic skin (e-skin) that is highly flexible, durable and scalable is a highly desired goal. We model the e-skin sensor design and application after human hand and skin. Our skin provides a sophisticated sense of touch, contact-based information, as well as perception of texture, shape, etc. Beneath the skin, mechanoreceptors act as transducers, generating precisely timed spikes that are informative of contact forces and surface properties such as textures, edges and curvatures. A wide variety of sensors based on piezoresistive, capacitive and optical principles have been proposed with varying degrees of resolution, sensitivity and sizes. However, the development of flexible sensors that can be attached to robotic fingers and e-skins is still an unresolved issue. OPDs, especially designed on flexible substrates, constitute a new technology for applications to robotic and prosthetic hands.
Methods: The sensor is composed of 3 layers: The top one is formed by a matrix of 3x2 light-emitting diodes (LEDs), the middle layer is made of a soft elastomeric material (Ecoflex) that serves as the transduction layer and the bottom layer is formed by an ultra-flexible, ultrathin OPD 3x2 array. The transduction layer was painted with black pigment and has six cavities through which each LED target one OPD directly. Deformation of the soft layer induces changes in the light received by the OPDs and is informative of the applied forces over the skin. We performed a compression test to characterize the output voltage of the OPDs. From this relationship, we built a neuron model that mimics the activity of Merkel Cells (SA-I) akin to physiological data.
Results: The compression test demonstrated that it was possible to detect deformations of at least 0.5 mm. The relationship between compression and voltage was mostly linear and the sensitivity can be improved by making use of a programmable amplifier. The firing rate of SA-I afferents is associated with indentation depth according to a sigmoidal function. We applied such function to map indentation to a proper input to the SA-I neuron model. Our results demonstrated that it was possible to obtain firing rates that were similar to the physiological behavior of SA-I, where larger indentation amplitudes led to higher firing rate.
Conclusion: The proposed ultra-flexbile tactile sensor paves way for improved e-skin design in robotics and prosthetics, especially for soft robotics where flexibility is a must. This sensor can also be used for improving the tactile perception of textures and shapes, besides dexterity in manipulation. The conversion of the signals into spiking activity of SA-I afferents that are more faithful their biological counterpart is also promising for delivering more naturalistic touch feedback from prosthetic hands to amputees via nerve stimulation.

Nearly one-fourth of neuro interventions fail to treat cerebral aneurysms, imposing a significant sociological and economic burden. Treatment is beneficial but was limited to surgical clipping until the advent and broad clinical adoption of endovascular coiling [1, 2], now a preferred, relatively inexpensive, and statistically more successful option [3]. It involves deploying platinum detachable coils into the aneurysm through a microcatheter; the coils aid formation of blood clots within the aneurysm, excluding it from circulation. However, the current microcatheters lack the much-needed steerability for precise tip positioning. Magnetic [4], piezoelectric ultrasonic [5], and wire-pulley [6] devices have been proposed in the past, but have not found broad acceptance. The existing panoply of passive guidewires and catheters, cannot be steered in vivo resulting in treatment failure, principally due to the difficulty in navigating tortuous vasculature, accessing, and optimally placing the microcatheter tip in the aneurysm dome for coil deployment.
Balloon catheters, which represent a crude form of soft-robotics, are broadly accepted in clinical use. However, fabrication of soft-robotic devices at length scales between 50 micrometers and 1 mm – the critical length scale which endovascular neurosurgical catheters demand – remains a challenge because both photolithography and 3D printing are inadequate. We combine innovative micro-fabrication techniques with intuitively engineering hyperelastic polymers, and direct hydraulic microactuation to provide steerable catheters for endovascular neurosurgery to overcome the high failure rate of current devices. Our novel fabrication methods enable delivery soft-robotic devices at the small length scales (<100 μm) with aspect ratios over 400. This delivers complete 3D hemispherical and direct handheld control of the microcatheter tip orientation to the neurointerventionist. We further test and validate the performance of the soft robotic steerable catheter in CT-Angiograms based silicone models to provide a representative test bed. The representative ex vivo silicone phantoms of vasculature start from the femoral artery, through the aortic arch to the internal carotid artery and the aneurysm, and include non-Newtonian blood flow analog with pulsatile pumping to mimic the heart. The testing in silicone models is used to iteratively improve performance paving the way for in vivo tests in porcine. The resulting data shows that the technology demonstrates promise through quicker treatment with fewer mistakes in comparison to the existing gold standard devices.

[1] Guglielmi, G., Vinuela, F., Dion, J. & Duckwiler, G. Electrothrombosis of saccular aneurysms via endovascular approach: part 2: preliminary clinical experience. Journal of neurosurgery 75, 8–14 (1991).
[2] Guglielmi, G. et al. Endovascular treatment of posterior circulation aneurysms by electrothrombosis using electrically detachable coils. Journal of neurosurgery 77, 515–524 (1992).
[3] Molyneux, A. J. et al. Risk of recurrent subarachnoid hemorrhage, death, or dependence and standardized mortality ratios after clipping or coiling of an intracranial aneurysm in the international subarachnoid aneurysm trial (isat): long-term follow-up. The Lancet Neurology 8, 427–433 (2009).
[4] Hetts, S. W. et al. Magnetically-assisted remote controlled microcatheter tip deflection under magnetic resonance imaging. JoVE (Journal of Visualized Experiments) e50299–e50299 (2013).
[5] Yun, C.-H., Yeo, L. Y., Friend, J. R. & Yan, B. Multi-degree-of-freedom ultrasonic micromotor for guidewire and catheter navigation: The neuroglide actuator. Applied Physics Letters 100, 164101 (2012).
[6] Feng, W. et al. Highly precise catheter driving mechanism for intravascular neurosurgery. In Mechatronics and Automation, Proceedings of the 2006 IEEE International Conference on, 990–995 (IEEE, 2006).

Microneedles (µNeedles) are an attractive option for painless drug delivery vs. hypodermic needles. µNeedles have gained popularity for cosmetic and medical applications because they create micro-punctures without damaging the skin epidermis and deliver drugs or nutrients deeper into the skin layer. Coating the microneedles is an interesting approach for delivering specific drugs and/or nutrients. Electrospraying is a versatile method to produce micro/nanoparticles and can control the particle size by changing process parameters or solution properties. Electrospraying process was used for producing micro/nano particles of insulin, folic acid, titanium dioxide, antimicrobial agent before. However, limited studies are available on coating of microneedles. In this study, we have demonstrated microneedles can be controllably coated with an electrospraying method.
The effect of electrospraying process parameters (electric field, electrospraying time) and solution parameters (molecular weight, solvent properties) were evaluated using two dermarollers with µneedle arrays 0.25 and 2.00 mm in height. To determine the solution parameters of the electrospraying process, two different molecular weight of poly(ethylene oxide) (Mn 100 kDa and 1000 kDa) and two different solvents (water and ethanol) were used. Water soluble Keyacid Red (KAR) dye was used as a model molecule. For successful electrospraying, a solvent with high surface tension and low vapor pressure, high electric field between nozzle and collector, low polymer molecular weight are required. Because a limited amount of particles can be coated on microneedles, optimizing polymer to drug ratio is critical to incorporate the required amount of drug into microneedles. The loaded dye was released completely within 5 min. As expected, dye loading was increased with electrospraying time up to 60 min, after which loading on the µneedles no longer increases as the particles begin to accumulate and branch on top of each other.
Further research is being carried out to determine the performance of the nanoparticle coated microneedle delivery system in ex vivo and in vivo studies.

It is known that iridescent solid films can be produced from cellulose nano crystals (CNCs) solutions in the presence of the earth Magnetic field, [1] after solvent evaporation. The CNCs have a negative magnetic susceptibility, which allows the production of aligned solid films, with the cellulose nano rods main axis aligned parallel to the air interface, after the evaporation of the solvent.
Cellulose derivatives, for example cellulose acetate (AC), can form homogenous solutions with CNCs, from which films and fibers can also be prepared [2], the CNCs align their main axis along the main axis of the fibers, which translates into the enhancement of the mechanical properties of the electrospun micro/nano fibers [3]. To investigate the broken symmetry of the system CNCs rods were mixed with symmetric particles, spheres of iron oxide metallic nanoparticles (IONs).
The IONs were chosen due to their shape and because they are magnetic [MG2] nanoparticles, with diameters of the order of 10 nm, and can be conjugated with different other agent nanoparticles [4].
We prepared micro/nano fibers from AC with different quantities of IONs conjugated with CNCs and determined the critical concentration of IONs needed to induce magnetic properties to the fibers.
The precursor suspensions and the micro/nano electrospun fibers were investigated by using different techniques as scanning electron microscopy (SEM), atomic force microscopy (AFM), polarizing optical microscopy (POM), X-ray, small angle X-ray scattering (SAXS), and nuclear magnetic resonance spectroscopy (NMR). The mechanical properties as well as water contact angle measurements, of the electrospun membranes, were also investigated, with and without the nanoparticles.
This work demonstrates that it is possible to produce magnetic paper by adding a low amount of magnetic cellulose-based nanoparticles, which opens new horizons to the design and control of mechanical and magnetic properties of cellulosic materials.

References:
[1] S.N. Fernandes, P.L. Almeida, N. Monge, L.E. Aguirre, D. Reis, C.L.P. de Oliveira, A.M.F. Neto, P. Pieranski, M.H. Godinho, Adv. Mater. 2017, 29(2), 1603560.
[2] S. Chen; G. Schueneman; R.B. Pipes; J. Youngblood; R.J. Moon, Biomacromolecules 2014, 15, 3827.
[3] K. Ohkawa, Molecules 2015, 20, 9139.
[4] M.S. Albernaz, S.H. Toma, J. Clanton, E.S. Bernardes, K. Araki, R. Santos-Oliveira, Pharm Res 2018, 35, 24.

A nanofabrication including nanofiber formation gives novel functions to materials. Due to the large surface area, interconnected framework, and pore structures, nanofibers and nanofiber membranes show superior properties in the applications such as sensors, catalysts, filters, protective clothes, and biomaterial scaffolds⁽¹⁾. An electrospinning is a straightforward and versatile fabrication method for the nanofiber membrane from polymer solutions and melts. One major advantage of this method is applicable for a wide range of materials, such as inorganic materials, synthetic polymers and biological materials. Recently, the development of high-throughput and high-quality electrospinning system is strongly required. The process of nanofiber fabrication during electrospinning is too complicate to clarify the mechanism.
Some researchers reported the direct observation of fiber formation during electrospinning by using a high-speed camera. Few reports, however, deal with the analysis of the electrified-jet behavior in bending instability region⁽²⁾.
We performed quantitative analysis of nanofiber fabrication process during electrospinning. The electrified-jet phenomenon from the nozzle to the substrate was observed by a high-speed camera⁽³⁾. To analyze electromagnetic and kinetic parameters, the flying velocities of the electrified-jet were measured and the electric potentials were obtained from a finite element method analysis of an electric field. The charge density and a size of the electrified-jet in the bending instability were determined by solving the equation of motion for the electrified–jet. By using this analytical approach, the effects of the applied voltage and the addition of an electrolyte to the spinning solution on nanofiber formation were demonstrated. The insights obtained here enable precise design of the high-throughput and high-quality electrospinning process.
In addition, we carried out theoretical analysis of liquid impregnation behavior into well-defined nanofiber membranes. The determining factors for controlling liquid impregnation is investigated using numerical analyses based on the Kozeny-Carman equation.
Finally, an application of nanofiber membrane derived from material properties and nanofiber morphology is demonstrated to show the advantages of electrospinning technology.

(1) Yarin, A. L. et al., Cambridge University Press: Cambridge, 2014.
(2) Reneker D. H., Yarin A. L.et al., J Appl Phys. 2000, 87, 4531-4547.
(3) Uematsu, I. et al., Ind. Eng. Chem. Res. 2018, Vol. 57, 36, 12122-12126.

Coupling of reaction and diffusion forms a spontaneous pattern. Turing theoretically predicted that stationary pattern forms in reaction-diffusion systems and stated the formation conditions of stationary patterns. In reaction-diffusion systems, the medium is an important. The diffusion coefficients of the activator and the inhibitor are important for pattern formation. We have tried to control pattern formation in the Ferrocyanide-Iodate-Sulfite (FIS) reaction, which is pH-oscillating reaction, by controlling solute diffusion via the network density of polymer gel.
In this study, we reported the pattern formation in heterostructured gels with different network densities by the FIS reaction. The chemical states of the gel depend on the diffusivity, which in turn depends on the network density of the gel. Consequently, a pH pattern reflecting the heterostructured gel emerged. Furthermore, adjusting the condition produces novel patterns in the heterostructured gel.
A heterostructured gel was prepared by a two-step synthesis method with photo polymerization. Acrylamide (AAm), the cross-linker N,N'-methylenebisacrylamide (MBAAm), and the photopolymerization initiator Irgacure 2959, were used. Two gel precursor solutions with different monomer contents were prepared. The monomer contents of gel precursor (20) and gel precursor (10) were 20 and 10 wt%, respectively. A continuous stirred tank reactor (CSTR) covered with a gel was constructed. The gel was set in the space between reactor. The temperature of the reactor was set at 50 °C with a thermostatic bath. Solution A ([NaIO₃]₀: 75 mM, [H₂SO₄]₀: 3.6 mM, [NaOH]₀: 0.25 mM) and solution B ([Na₂SO3]₀: 89 mM, [K₄Fe(CN)₆]₀: 25 mM) were fed separately into reactor with HPLC pumps.
By controlling the flow rate, the difference in the diffusivities in the heterostructure gel was converted to a difference in the pH states via the FIS reaction. Furthermore, the boundary conditions given by the striped heterostructured gel gave rise to stationary linear patterns, which are formed in the reaction-diffusion system. In this way, pattern formation in the FIS reaction was controlled by the artificially designed heterostructured gel.

The deficient disposition of the pruning waste from grass (Poaceae), has been converted into a considerable environmental problem in Ecuador since it is discarded in common garbage dumps. As a result, gases and lixiviates are generated producing a negative impact on the environment. This project takes advantage of these residues to isolate their chloroplasts, with the aim of subsequently developing bioreactors to make the absorption of CO₂. Several investigations have been carried out in order to encapsulate chloroplasts obtained from other species, in inorganic matrices ^[2,3], since these molecular machines transform light energy into chemical energy, through the process of photosynthesis ^[1]. However, it is still a challenge to find an adequate method to encapsulate them and to maintain their vital function. In this work we present, for the first time, the encapsulation of grass chloroplasts into silica monolith with a hierarchical texture, using high internal phase emulsion (HIPE). Based on the results obtained, it was demonstrated that it is possible to extract chloroplasts from the grass with high yield. The chloroplasts extracted were encapsulated into silica monolith. The synthesized samples were analyzed by optical and scanning electron microscopy, as well as by DRS-UV-Vis and Fluorescence spectroscopy to monitor the photosynthetic activity of chloroplasts and it was shown that it was possible to keep it up to more than 90 days.

^[1]R. E. Blankensip, “Molecular Mechanisms of Photosynthesis”, Blackwell Science Ltd, London, 2002.
^[2] C. F. Meunier, J. C. Rooke, A. Léonard, P. Van Cutsem, B. L. Su, J. Mater. Chem., 2010,20, 929.
^[3] A.E. Sommer-Marquez, D.A. Lerner, G. Fetter, P. Bosch, D. Tichit, E. Palomares Dalton Trans. 2014, 43, 10521.

We propose a new strategy to engineer elasticity in otherwise rigid materials by structuring them with specific patterns. This happens spontaneously at the microscale on stretchable thin gold films on silicone that display dense distributions of Y-shaped cracks to favor out-of-plane deformation. We drew inspiration from these cracks to pattern Y-shaped cuts and engineer reversible elasticity in a multi-layer of metallic and plastic thin films.
First, the geometry and density of the Y-shaped patterns were first optimized using finite element analysis and macroscopic models. Next, we developed the fabrication process enabling the micro-patterning of thin polyimide/platinum/polyimide interconnects with microscopic Y-shaped cuts (branches of dimensions ∼15 μm, thickness < 10 μm). Encapsulation in silicone rubber completed the fabrication of stretchable interconnects that can be easily manipulated.
The micro-structured metallic films exhibit a sheet resistance of ∼15-20 Ω/sq. and display surprising deformability and stability compared to non-micro-patterned interconnects of identical thickness. 200 µm wide, 17 mm long, Y-shaped metallic tracks mechanically fail at 80 % tensile strain albeit do not fail electrically while plain tracks of identical geometry fail both mechanically and electrically at only 3 % applied strain. The micro-patterned interconnects sustain repeated cycling at 10% tensile strain for 1 million cycles with remarkable electrical stability. Moreover, this technology allows for the patterning of tracks down to 20 μm in width and complex layouts on a wafer-level scale. Through pattern optimization, mechanical gradient may be engineered across the structure, defining non-deformable to elastic areas, thereby providing an interesting platform for the hybrid integration of stiff and rigid components with stretchable interconnects. Finally, we verified the micro-structured tracks impact only minimally the mechanical properties of the silicone carrier in terms of apparent elastic modulus (apparent elastic modulus increased from 2.3 MPa to 3.2 MPa).
We have implemented this soft technology to prepare stretchable micro-electrode arrays for neural recordings but we anticipate this strategy will be implemented in a range of wearable and implantable bioelectronic interfaces.

As surface contamination can contribute to transmission of bacteria, the development of surface enhanced coatings that causes sanitization of the surface is an important development in reducing hospital acquired infections. To develop antimicrobial coatings with “sharp” Z-scheme photocatalytic nanoarchitectures. Hematite (Fe2O3) as non-toxic narrow band gap semiconductor with broad absorption in the visible light, will be used as the main element in coating, “sharp” structures offering a long optical path for efficient light harvesting, that will increase photocatalytic efficiency of structures. Similar “sharp” structures proved it effectiveness in bacteria killing by piercing into the bacterial cell wall and as repelling surfaces that resist bacteria attachment. Thereby, in this work an antimicrobial activity of Fe2O3 coatings was studied by Agar diffusion and JIS tests. Hematite coatings were obtained by one step hydrothermal method. Ferric chloride and urea were dissolved in a distilled water, this solution was transferred into autoclave containing an rubber substrate fully immersed into the solution. Then the autoclave was placed in a hot air oven at constant temperature 150 C for 3 hours in air. Finally, substrate with coating was taken out from the autoclave and washed in DI water and dried in air at room temperature. Obtained coating were characterized by SEM, FTIR and XRD. Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 2593, Staphylococcus epidermidis ATCC 12228, Staphylococcus saprophyticus ATCC 15305, Pseudomonas aeruginosa ATCC 10145, Bacillus cereus ATCC 11778, Enterococcus faecalis ATCC 29212, Listeria monocytogenes ATCC 13932, Salmonella typhimurium ATCC 14028 were used as a test cultures. The microbiological testing results show the efficiency of the hematite coatings against all test microorganisms.

Soft Robotics offers solutions to problems where human or animal-like architectures and materials are needed. Tasks requiring strength yet finesse, currently only achieved through human operators, may in the future be automated by developments in soft robotics. Further than just mimicking biological systems in performance, the aim of soft robotics is to develop robots which are both safe and compliant for human interaction. Pneumatic actuators are widely studied in soft robotics as the compliant actuation of these systems is comparable to that found in Nature. However, conventional pneumatic actuators are powered by externally tethered hard air compressors or accumulators.

Gas Evolution Reactions (GER) are widely found in biochemical processes [1,2]. Hydrogen peroxide is a sub-product of cellular metabolism that protects the cell against anaerobic pathogens. Given its reactivity, it must be quickly transformed into less harmful or reactive compounds. In vivo, the decomposition of hydrogen peroxide to water and oxygen is catalysed enzymatically by catalase [3]. Soft, porous catalytic nanocomposites can perform a similar function to enzymes while also mimicking the desirable compliance of biological systems.

Platinum is a catalyst used in the decomposition of hydrogen peroxide [4]. This work reports the development and characterisation of a Platinum nano-catalyst laden 3D printing filament, created by loading a commercially available porous filament (POROLAY LAYFOMM 40) with platinum nanoparticles. The nanocomposite filament is used to create a one-step multi-material 3D-printed GER pneumatic soft artificial muscle. The resulting pneumatic actuator with embedded catalysts converts energy-dense liquid chemical fuel (hydrogen peroxide) into actuating gases (oxygen). Actuator geometries for optimising the amount of oxygen harnessed from the hydrogen peroxide decomposition are explored through finite element analysis. The potential for the configuration to create a fully soft untethered device capable of gentle movements for locomotion or handling of delicate objects is discussed. Developing such advanced methods for manufacturing and powering soft robots is critical in order to realise their potential to generate real societal impact.

[1] Zhang L, Happe T and Melis A 2002 Biochemical and morphological characterization of sulfur-deprived and H 2 -producing Chlamydomonas reinhardtii (green alga) Planta 214 552–61
[2] von Caemmerer S and Farquhar G D 1981 Some relationships between the biochemistry of photosynthesis and the gas exchange of leaves Planta 153 376–87
[3] Jones D P, Eklöw L, Thor H and Orrenius S 1981 Metabolism of hydrogen peroxide in isolated hepatocytes: Relative contributions of catalase and glutathione peroxidase in decomposition of endogenously generated H2O2 Arch. Biochem. Biophys. 210 505–16
[4] Serra-Maia R, Bellier M, Chastka S, Tranhuu K, Subowo A, Rimstidt J D, Usov P M, Morris A J and Michel F M 2018 Mechanism and Kinetics of Hydrogen Peroxide Decomposition on Platinum Nanocatalysts ACS Appl. Mater. Interfaces 10 21224–34

Nature has developed remarkable WR systems that dramatically deform in response to changes in relative humidity (RH), such as the actuation of pine cones opening and releasing their seeds and wheat awns propelling their seeds into the ground. Such WR actuations can be extremely powerful, and have a great potential to power modern engineering systems. Here, we present our discovery of bacterial cell walls that exhibit extremely high energy density of 72.6 MJ/m³ and power density of 9.1 MW/m³, surpassing that of existing actuator materials and artificial muscles. By using our customized AFM, we characterized WR properties of bacterial cell walls from three species, including Bacillus subtilis, Staphylococcus aureus, and Saccharomyces cerevisiae. We found that cell walls from these three species have significant water-responsiveness, and their WR strains reach 27.2%, 19.1%, and 11.2%, respectively. To measure their WR energy densities, we have created a thermodynamic cycle where applied forces and RHs can be varied to maximize cell walls' WR work. Using this method, we have measured their energy densities to be 72.6 MJ m^-3, 47.9 MJ m^-3, and 29.9 MJ m^-3. Considering their cycle period (8s), cell walls’ power densities are estimated to be 9.1 MW m^-3, 5.9 MW m^-3, and 3.7 MW m^-3, respectively. We also note that, while these cell wall structures share similar molecular structures, they possess diverse water-responsiveness, motivating further studies of cell walls’ WR fundamental mechanisms.

Recently, Polymers of Intrinsic Microporosity (PIMs) have attracted attention as a novel class of high free-volume polymers with highly rigid and contorted molecular structure. Most research on PIMs has focused on fundamental material and membrane properties, with only a few studies on materials in fiber form. In this study, PIM-1 polymer fiber mats were fabricated by electrospinning using different solvent systems consisting THF, DMF and toluene. The resulting fiber mats showed excellent breathability and high porosity, indicating potential for applications in protective clothing. The surface area of the PIM-1 fiber mats was typically 650 m²/g, which is close to 750 m²/g measured for the starting neat powder. A problem, however, is that the produced fiber mats have very poor mechanical integrity due to low interchain interactions of PIM-1, hindering their practical use. In our work, we have developed a unique PIM/PAN hetero-structure synthesis approach by incorporating PAN fibers as a structural reinforcing material into the PIM fiber matrix. The as-prepared PIM/PAN composite fibers exhibit 40 times improvement in tensile strength compared to the PIM fibers, with a net surface area of 360 m²/g, indicating only a moderate loss in porosity. In addition, metal-organic framework (MOF) particles with the capability of degrading toxic chemicals, such as chemical-warfare agent (CWA) simulants, were integrated into the composite fibers. The resultant PIM/PAN/MOF composite fibers show 2-3 times higher removal capacity of dimethyl methylphosphonate (DMMP) than the baseline material and demonstrate the detoxification of 4-nitrophenyl phosphate (DMNP) as monitored by UV−vis spectroscopy, among which DMMP and DMNP are both chemical nerve agent simulants. These findings indicate that functionalized PIM-1-based fabrics are a promising material for applications in chemical protection and detoxification.

Anisotropic nanomaterials composed of two halves with different structure, chemistry, or polarity, known as Janus nanomaterials, have distinct properties when compared to symmetrically functionalized analogues. These materials have recently gained significant attention in many applications such as electronic thin films, drug delivery, sensors, optics, oil/water separation membranes, photoactivated micromotors, photocatalysts, and interfacial modification. Among the many Janus structures, two-dimensional (2D) Janus nanomaterials with high aspect ratio in rod-like or planar (i.e., nanosheets) morphologies, are especially intriguing considering their interfacial properties as well as their ability to assemble into higher order and hybrid structures. In this research, we describe an approach to mass synthesis of Janus graphene nanosheets in highly controllable ways via a novel “Interfacial Nanoreactor” system. We have characterized and proven the asymmetric structures of the synthesized Janus graphene nanosheets by Langmuir-Blodgett (LB) surface pressure-area (π-A) curves, fluorescence spectroscopy, contact angle measurement and scanning electron microscope (SEM) characterizations. The Janus graphene nanosheets with two chemically different compartments show very unique behaviors at liquid interfaces. We observed surfactant-like interfacial phenomena of the Janus graphene layer when its surface density increases, which is similar to the way that micelles or lipids form in a bulk phase above the critical micelle concentration (CMC). The one of applications for the nanofluids of Janus graphenes is to be a chemical agent for enhanced oil recovery (EOR). To demonstrate this applications, we used a microfluidic-based reservoir-on-a-chip model to understand oil-water-rock phase interactions and visualize the fluid transport processes in micropores, and more than 10% improvement in oil recovery was observed using the Janus graphene nanofluids in comparison to just using seawater flooding. The 2D Janus graphenes also present great opportunities to further create tailored and functional hierarchical structures of interest to molecular biology and medicinal chemistry.

With the movement towards flexible and transparent electronics[1] for use in displays[2], electronic skins[3] and wearable healthcare monitoring[4], electrical components such as pressure sensors must evolve alongside circuitry and electrodes to ensure a fully flexible and transparent system. In the past, piezoresistive pressure sensors made with flexible electrodes have been fabricated, however, many of these systems are opaque.[5]

For the first time, we present a technology that exploits the natural self-assembly of polystyrene nanospheres to reproducibly create optically transparent pressure sensors with sensing performance comparable to industry standards. We have demonstrated flexible sensors with transparencies as high as 79.3 % transmission, fast relaxation times of <50 ms, and sensing response up to 200 kPa.

The performance of the piezoresistive pressure sensor relies on uniform elastic nano-dome arrays. A thin and homogenous lining of PEDOT:PSS renders the domes conductive and retains the transparent and flexible qualities of the underlying polymer. The highly tunable multi-step fabrication procedure establishes the potential for the mechanical properties of the sensor to be tailored and tuned.

This presentation will include the design, fabrication details and scale-up potential of the sensor. Alongside this, the performance metrics will be demonstrated, and the pressure sensing mechanism analysed with reference to some preliminary in-situ SEM compression testing.

[1] F. Xu, X. Li, Y. Shi, L. Li, W. Wang, L. He, R. Liu, Micromachines 2018, 9, 580.
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Technologies for modification of material surfaces to create specifically envisioned interfacial properties are of high technological interest, particularly when it comes to in situ thin layer coatings with very hydrophilic materials, i.e. hydrogels, on hard materials. While spin coating of precursors and crosslinking of reactive moieties via UV irradiation may be applicable to flat materials [1], alternative approaches are of interest that conceptually would be applicable to any surface shape by initiating hydrogel formation from the surface itself [2]. In this context, the capability of enzymes to crosslink polymeric precursors to form hydrogels [3] may be applied to realize a “coating-from” rather than a “coating-to” approach for functional interfaces.
Based on previous experience of relatively slow conversion of substrates by mushroom tyrosinase after surface immobilization [4], here horseradish peroxidase was selected and successfully coupled to amino-functionalized glass or gold surfaces by use of glutaraldehyde. When exposed to solutions of hydrophilic 4-arm star shaped telechelics from poly(ethylene glycol) bearing end groups derived from aromatic amino acids, the envisioned in situ formation of thin layer hydrogel coatings was achieved.
Contact angle and zeta potential analyses were applied to determine physicochemical properties of the surfaces. A qualitative proof of hydrogel deposition was provided by time-of-flight secondary ion mass spectrometry (ToF-SIMS), showing ethylene glycol repeat units as well as the crosslinkable aromatic moieties at higher concentrations for enzyme triggered crosslinking conditions as compared to pure adsorption of the precursor. A quantitative assessment of the coating thickness was performed by atomic force microscopy (AFM) and quartz-crystal microgravimetry, suggesting very thin homogeneous hydrogel layers of 100 - 250 nm being formed. As a key function needed for hemocompatible devices, low thrombogenicity of the hydrogel coating similar to clinical accepted implant materials was demonstrated with human blood from several donors according to the protocol approved by the ethics committee (# EA2-018-16; Charité University Medicine Berlin, Germany).
This “coating-from” approach may in the future be applied to various shapes of surfaces, e.g. for cell culture, protein/biofilm repellency in technical applications, or in flexible electronics.

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Magnetic soft robots facilitate battery-free contactless control of sub-mm soft robots. However, simultaneous programming of magnetic field is required in both 3-axial direction and magnitude to navigate through obstacles. Hence, parallel control of multiple soft robots becomes prohibitive. Herein, we demonstrate maneuverability of multiple polymeric microbots capable of on-demand orbital navigation inspired by hierarchical rotation and revolution of our Solar System planets. Here, the hierarchical magnetomotility for soft robots is achieved by planar rotations of permanent magnet. Simple change of rotational speed of magnets allows reversible control of trimodal rotation including rotating, pivoting, and tumbling. Remarkably, different orbital radius and/or velocity for each soft robot can be achieved in multi-body system due to aspect ratio dependent magnetic motility of soft robots. The hierarchical magnetomotility promotes adaptable self-correcting locomotion since blocked rotations shift revolution pathway, providing multi-terrain navigation functionality including stairs and uphill climbing as well as underwater and above water swimming. We will also discuss collective behaviors of the magnetic soft robots to accomplish a certain mutual goal.

The growing world population and the related increase of chemicals used in daily life leads to higher concentrations of chemical substances in our water reservoirs. It is therefore crucial to develop green, stable and efficient absorbents for purification of contaminated water. In this work, an anionic cellulose nanofibril (CNF)-based hierarchical aerogel with high specific surface area (up to 430 m²/g) was prepared via a combined directional freeze-thawing (macro-pores) and supercritical drying (meso-pores) method. By adjusting physical and chemical cross-linking, we can obtain a high Young's modulus (711 kPa) and hydrophobic performance (contact angle ~120°), which help to maintain the stability of aerogels in aqueous conditions. The cationic dye methylene blue (MB) was chosen as a model organic molecule to investigate the absorption properties of the aerogels by changing the pH, absorbent dosage, initial dye concentration, and contacting time during the adsorption process. The aerogels showed a maximum adsorption of MB up to 234 mg/g, and remain intact in the dye solution even after 24 h of shaking during the adsorption test. Inspired by the excellent adsorption performance of cationic MB, we selected Ag⁺, a metal ion that has been rarely studied in the literature for ionic adsorption. The maximum adsorption of Ag⁺ was found to be 116 mg/g. A high specific surface area and a strong electrostatic interaction are the prominent mechanisms behind the good adsorption capacities to both MB and Ag⁺. These results indicate that the prepared macro- and meso- dual porous CNF aerogels are promising candidates for wastewater purification. Considering the economic factor, a reduction reaction was performed on the aerogels after the Ag⁺ adsorption enabling a conversion of ionic to metallic Ag. This allows for a recovery of the extracted silver and a potential reuse of the materials within antibacterial or catalytic applications.

Cross-scale micro-nano hierarchical structure in the living systems often provides unique features on surface and serves as an inspiration source for artificial materials or devices. Among them, artificial made broccoli-like structure demonstrates excellent surface performance such as ultra-high hydrophobicity or hydrophilicity in various situations.
In this work, by introducing a solvent-assisted UV laser treatment, we establish a rapid yet facile approach to fabricate self-similar hierarchical broccoli-like micro-nano structures on silicon with super hydrophilicity and high light absorbance. Specifically, through adjusting the operating parameters of the UV-laser (scanning speed, vand space between adjacent scanning lines, ΔL) and immersing solvents, we can tune the surface morphology of the surface, such as surface roughness and height difference, to obtain uniform, robust surface topography. According to micro-views, we observe regular microgrooves consist of abundant “peaks” and “valleys” that stack vast broccoli-like structures. We also investigate the forming mechanism of such broccoli-like structures. It is found that phase change, micro-/nano-particles sputtering and depositing, disintegration and re-depositing, and solvent evaporating etc are important issues during the forming process of self-similar structure.
Through optical test of UV-treated Si samples, the results reveal that such broccoli-like structures have a consistent high light absorbance (>90%) in an ultra-broad spectrum from ultraviolet to infrared spectrum (in 200-2 500 nm spectral range). It may provide a low-cost way to fabricate black Si for solar energy harvesting in common laboratory environment.
Further, the patterned silicon can be used as a master for capillary assemble of soft electronics on elastomeric substrates with water/liquid alloy-amphiphilic zones, or as a self-cleaning surface and a heat transfer surface. The demonstrated facile way for a broccoli-like structure fabrication may encourage more researchers to investigate unique features of self-similar micro-/nano surfaces, and further exploit their great potential in applications towards diverse directions.

To perceive the tactile signals, such as magnitude, strain and especially direction, researchers have developed various types of sensors. However, these devices are either only could obtain single signal or super complex in structure. This work presents a novel soft tactile sensor with capacitance between liquid alloy based hemisphere and planar electrodes. Due to the nature high surface tension and flowability of liquid alloy droplet, the dynamic re-distribution of charges on electrodes can achieve high sensitivity, wide range and abundant functions, e.g. magnitude or direction of external force.
In demonstration, a flexible tactile sensor based on morphological deformation of liquid alloy was fabricated. The bottom electrode was a hemi-sphere liquid alloy droplet pinned on a circle copper pad, which was surrounded with liquid alloy phobic substrate to avoid the adhesion of liquid alloy during deforming. While the upper electrode was made of planar liquid alloy, which was divided into several isolated equal sections. Hence, the entire device can be viewed as several capacitance sensors with a shared fluidic electrode. In intact situation, most of the charges would concentrate on the top of hemisphere at first. With the approaching of the electrodes, the charges would disperse to a wider contacting area, which was reflected on the change of capacitance in each sector. Thus the information of the tactile signal could be calculated according to the results from all of the capacitances, and the magnitude and direction were acquired at the same time. Without the constraint of wrapped materials, the droplet is only limited by its high surface tension, which leads to a high sensitivity. At the same time, the charges dispersion following the deformation also contributes to the sensitivity. The impact parameters including the amount of liquid alloy, the size of bottom and upper electrodes, and the fabricating technique also were studied. The response time, repeatability, hysteresis etc. demonstrated the performance of this novel tactile sensor.

This work presents a facile method to assemble discrete magnetization soft robots via laser-tuned selectively transfer printing different patterned anisotropic magnetized silicone cells. This technique could be simply implemented via anisotropic magnetization, magnetized cells cutting and transfer printing of magnetized cells in three major steps. It is very promising to parallelly flexibly input magnetization information into a three-dimensional structure for diverse applications.
Spatial preset of specific properties in a configurable way is a key to develop active devices running in dynamic scenarios such as that in soft robotics, biomedicine, functional materials and four-dimensional (4D) printing. Despite success in recent development, current fabrication technique still too complicated to implement in a facile and rapid way enabling flexible spatial preset of magnetization in soft materials.
In this work, by introducing a laser-tuned selectively adhesive transfer printing of anisotropic magnetized silicone cells, we present a facile fabrication technique to flexibly preset discrete magnetization in soft materials for making fast-transforming untethered magnetic robots. Such a preset of magnetization pattern can be easily tuned during the transfer process by alignment adjustment or laser parameters tuning. Different magnetized cells can be selectively picking up by tuning the surface morphology and hence adhesiveness of magnetized film with a different laser-treatment parameter setting. Spatial preset of magnetism can be achieved by geometrical alignment and configuration adjustment of different magnetized cells. Moreover, magnetization in each layer can be easily tuned in arbitrary direction on demanded and thus empower the independent addressability to different magnetized cells in a global actuating magnetic field. Further, we can use planar structure to achieve complex 3D structures and the flexibility of the re-assembling based this method enable it ease of geometrical re-configuration, which can totally change its response behavior accordingly.
Finally, two demonstrations are presented: 1) the re-assembling process of sub-robots together with its responding behavior in different geometrical configurations, and 2) a targeted drug delivery of a hollow 3D structure with excellent passibility and flexible steering inspired by tumbleweed.

Nowadays, intelligent home robots are meeting a giant demand in people’s daily life, including healthcare detecting, environment monitoring and so on. Among them, fully Soft robots are attracting huge attentions due to its great adaptability in various environments and enhanced safety, particularly when interacting with people. Therefore, it’s important to improve the comfort level of human-robot interaction rather than a rigid or statistic contacting, where diverse soft functional circuits are needed to be integrated on the 3D complex surfaces for environmental perception and to endow soft robotics with more features. However, present approaches for perception layer are almost based on planar techniques in a very limited area, or costly equipment to print 3D circuits but time-consuming, cannot satisfy the demanding from soft robots with seamless integration without hindering the great adaptability and dynamic 3D morphology. Hence, direct conformal print of perceptive circuits on arbitrary robots’ external surfaces is one of the most effective and convenient solution to achieve excellent environmental perception for soft robots.
In this work, we present a method of fabricating intuitive perceiving layer integrated on soft robots with a conformal masked printing combined with UV-laser patterning and liquid alloy (Galinstan) circuits spraying. Specifically, an ultra-flexible and sticky elastomer is employed as a mask to be conformably attached on the target surfaces under a gentle pressure after laser patterning. Following with liquid alloy sprayed and mask peeled, the liquid alloy circuits are completely conformal printed on arbitrary surfaces of soft robots, including developable/non-developable surfaces, curvilinear surfaces with sharp edges and other 3D complex surfaces. Finally, through connecting with functional component units and sealing via dip-coating, we can obtain the fully soft robot with soft/conformal functional layer.
Upon this technique, we employ a soft robot hand integrated with functional layer, which consists of liquid alloy connections and component units, such as thermistors, to detect pressure, strain or near-field heat source. Further, combining with a feedback circuit and soft actuator, the soft robot hand could help monitor human healthcare signal when we touch/shake with it. In addition, it can be actively away from heat source because of temperature sensor module. That would be a great potential for endowing soft robotics with more functionalities.

The therapeutic potential of mesenchymal stem cells (MSCs) has been demonstrated in regenerative therapies. However, their therapeutic efficacy could be attenuated when undergo cellular senescence caused by various environmental stressors. The senescent MSCs could remain viable but presented an irreversible growth arrest and deficient proliferation. Tissue regeneration would be impaired due to their influence on the function of neighboring cells via altered secretome profile [1, 2]. MSCs can be modulated by not only the biochemical signals but also the physical cues such as the substrate topography [3, 4]. However, little is known about the influence of the topographic cues on cellular senescence of MSCs. In this study, the influence of microscale roughness on MSC senescence was investigated on the poly(ether imide) (PEI) substrates as a model system. Three distinct levels of roughness were created in the bottom of PEI inserts via injection molding: smooth surface R0 (root mean squared roughness (Rq): 0.2 ± 0.1 µm); R1 (Rq: 3.9 ± 0.2 µm) and R2 (Rq: 22.7 ± 0.8 µm). The senescence and proliferation of rat MSCs on the substrates were examined using senescence-associated β-gal assay and a cell counting kit. The paracrine effect of MSCs on different substrates was studied using a transwell system. MSCs were cultured in PEI inserts, then the MSC-laden transwells were put into the insert. The proliferation of cells inside the transwells was assessed via CFSE staining followed by flow cytometry analysis. After 5 days of culture, MSCs in different inserts showed high cell viability and similar spindle-shaped morphology. The lowest senescence ratio was observed in MSCs cultured on R1 (35 ± 4% decreased compared to R0). Cells on R1 presented the highest proliferation rate (5.1 ± 0.2 fold increase of cell number), as compared to cells on R0 (4.3 ± 0.5) and R2 (3.9 ± 0.4). The MSCs cultured on different substrates could effectively influence the proliferation of cells inside the transwell via their paracrine effect. The R0 secretome inhibited cell proliferation inside the transwell as compared to the R1 secretome (1.8 ± 0.2 fold decrease after 20 days of culture). In summary, the PEI substrate with roughness R1 provided a more superior surface environment for MSC culture, which inhibited cellular senescence and promoted cell proliferation. Such a microscale surface roughness can be considered as a key parameter for surface design of stem cell culture device and implants to improve the quality and therapeutic potential of stem cells.
References:
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[2] Coppe JP, Desprez PY, Krtolica A, Campisi J. Annu. Rev. Pathol. 2010, 5, 99-118.
[3] Kilian KA, Bugarija B, Lahn BT, Mrksich M. Proc Natl Acad Sci U S A. 2010, 107, 4872-4877.
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We developed ultrathin films of polyurethane-based shape memory polymer (SMP) as a syringe-injectable and self-expandable platform for implantable medical devices. Free-standing polymeric ultrathin films with the thickness less than 1 μm and the flexural rigidity less than 10^-2 nN m have been demonstrated as a promising material for a minimally-invasive platform for the delivery of molecular and cellular drugs. Despite their potential merits, however, conventional nanosheet technologies based on polymers such as polylactic acid (PLA) and poly(lactic-co-glycolic acid) (PLGA) are yet limited by (1) the size of needle that injects nanosheet from syringe (maximum lateral size of 15 mm could be ejected from a 19G needle (inner diameter (I.D.) = 0.7 mm)), (2) the ability to expand after injection and (3) the ability to control the motion after injection. To address these limitations, we developed free-standing SMP nanosheets embedded with magnetic nanoparticles (MNP), termed MNP-SMP nanosheets. The temperature-mediated shape memory effect (SME) of the SMP with the glass transition temperature (T_g) of 25°C provided following four capabilities to the 710-nm-thick MNP-SMP nanosheet; (1) syringe-injectability through the medical needles (a nanosheet with the lateral size of 15 mm could be ejected from a 20G needle (I.D. = 0.6 mm)), (2) self-expandability after injection to aqueous media, (3) conformability and removability on the biological surfaces, and (4) guidablity in an external magnetic field. In addition, the MNP-SMP nanosheets were readily interfaced with an additional layer of PLGA to extend the functionality as a carrier of molecular and cellular drugs without compromising the demonstrated capabilities. The MNP-SMP nanosheets will contribute to the development of advanced syringe-injectable medical devices as a platform to deliver drugs, electronics, biological cells and engineered tissues to the specific site or lesion in the body for minimally invasive diagnosis, therapy and regenerative medicine.

Harnessing soft materials and compliant structures to build robotic grippers has pushed the boundary in advancing robotic systems and materials science. Mimicking the morphology and grasping mechanisms found in biological system has attracted tremendous attention in the design of soft grippers. Although hand morphology of primates inspired a variety of soft gripper designs, due to the complexity, bio-mimicking the thumb–index hand morphology is limited and challenging. In contrast to the hand morphology of primates, marine tetrapods, such as sea turtles, utilized their flipper-like articulating limbs to capture and manipulate prey. This simple posture for holding and pinching could be effectively achieved by utilizing the underactuated deformation of compliant structures, such as kirigami. In this talk, we present a novel design of an ultra-thin soft gripper that mimicks the grasping posture of marine tetrapods using kirigami shells. Through a combination of mechanical modeling and experiments, we demonstrate the morphology and principle of grasping, and characterize the performance of the kirigami shell gripper by picking up a various objects with different shapes and examining the loading capacity. We find that the kirigami shell gripper can perform a variety of grasping tasks which cannot be easily accomplished by current soft gripper designs. The gripper is low-cost, scalable, ultra-thin, and ultra-lightweight with a payload to weight ratio of 270, and provides a novel approach to the design of soft robotic grippers.

The design of inks for three-dimensional (3D) printing of actuatable structures is of importance since the principles of ink design have a great influence on the response and the general materials characteristics. Thus, creating new types of ink materials with a programmable response is an ongoing challenge. This study demonstrates a new class of stimuli-responsive inks for 3D printing containing microcapsules, which contain small droplets of an aqueous solution of water and glycerol in the core. Polydimethylsiloxane (PDMS) capsules are generated by using water-in-oil-in-water double emulsions as templates. PDMS microcapsules can swell in deionized (DI) water by the difference in osmotic pressure between the inner and the outer phases of the complex emulsions. The swelling ratio in DI water can be controlled by the ratio of water to glycerol in the inner phases, and it is closely related to the resulting mechanical properties of the composite materials. In addition, they exhibit shape memory behavior due to inhomogeneous swelling behavior of the composites. Subsequently, the generated PDMS microcapsules are connected to each other by capillary bridging with liquid PDMS precursor for use as 3D printing inks. The composition of the outer phases (i.e., with glycerol or without glycerol, the molecular weight and the concentration of the surfactants) is varied to understand the relationship between rheological properties and printing performance. Overall, by taking advantage of controlled swelling and shape memory behavior of composite inks containing osmotically sensitive capsules, complex architectures capable of actuating can be fabricated, which opens up new opportunities in soft robotics and stimuli-responsive materials.

A tongue is a soft muscular organ which is one of the most sensitive and flexible human body parts transducing vital chemical information for the survival and health. One of the unique functions of the tongue is perceiving astringency, which is resulted from the strong association of the ingested astringent molecules and saliva proteins covering the tongue. Previously, artificial tongues are presented based on the lipid/polymer membranes, human taste receptors, and stripped epithelium cells. However, these works are hardly emulating human tongue due to the low selectivity for the target tastes, bulky and rigid structures. Here, we present a soft artificial tongue mimicking the mechanism of the human astringency perception based on the polyacrylamide hydrogel containing mucin (MUC) as secreted protein and lithium chloride as electrolyte. The thickness of soft hydrogel layer is comparable with that of actual saliva layer (70-100 μm) on the tongue, enabling efficient absorption and diffusion of astringent compounds (tannic acid, TA). Moreover, a flexible artificial tongue is fabricated by the polymerization of soft astringent hydrogel on the polyethylene-naphthalate (PEN) film, exhibiting stable sensing performances even after bending. Our resistive-type astringent sensor exhibits wider sensing range (10 g/L–0.001 g/L) and lower threshold sensing concentration (0.001 g/L) compared with the panel tests and other evaluating methods such as potentiometry, turbidity, and tribology. In addition, the astringent hydrogel shows better selectivity (ΔI/I_o) for the TA compared with the same concentrations (5 mM) of other tastants and derivatives of TA. Finally, as a proof-of-concept demonstration, we fabricate the artificial tongue sensor array which can be utilized as a portable taste sensing pad for the taste mapping and wipe-and-detection performance.

In decades, there have been many efforts to study the superb functions of unique structures in Nature. Researchers have tried to fabricate the artificial structures inspired from moth eyes, lotus leaves, gecko’s feet, wings of Morpho-butterfly and developed nano-, micro- and hierarchical structures. However, most of the features in Nature have 3D structures and they show more sophisticated functionality such as high adhesion in a wet condition of octopus and robust oleophobic surfaces inspired from springtails. In this talk, I explained a simple method to realize 3D structures by using