Symposium SB08—Bioinspired and Biological Polymers—From Living Organisms to Sustainable Functional Materials in Photonics, Electronics and Biology

Structural protein is one of the key factors to realize the unique properties and functions of natural tissues and organisms. However, use of structural proteins as structural materials in human life is still challenging. One of the major drawbacks of protein/polypeptide-based materials is their limited synthesis/process method. My research group has successfully synthesized various polypeptides, such as spider silk protein-like and elastin-like multiblock polypeptides, even with unnatural amino acids or nylon units, via chemoenzymatic polymerization. Those artificial polypeptides containing unnatural units achieve several properties that cannot be done by natural polypeptides. These synthetic polypeptides with nylon units are highly biodegradable and less environmentally toxic. Thus, this enzyme-mediated polymerization of amino acid monomers provides a new insight for material design of polypeptide. My research group also reported the new finding in spider silk spinning, which is essential to clear the hierarchical structure of spider silk. The scalable and sustainable synthesis method along the clarified structure-function relationship of natural proteins provides a new insight for structural and functional material design of amino acids-based polymers.

Spider silk combines outstanding strength and toughness with biocompatibility and light weight, thus outperforming some of the best synthetic materials. Despite extensive research, fully comprehensive experimental evidence of the formation and morphology of the internal structure of spider silk is still limited and controversially discussed. We used mechanical exfoliation to completely exfoliate spider silk, which showed that the silk of the golden orb-weaver is entirely composed of parallel, 10 nm-diameter nanofibrils featuring a particular morphology. This process allowed us to mass-produce spider silk nanofibrils for the first time. Furthermore, we show that the silk protein possesses an intrinsic mechanism to form nanofibrils of the same morphology via shear-induced molecular self-assembly, which can be easily triggered in vitro. By altering the physical and chemical environment of this process, we were able to study the conditions of formation of spider silk and to reveal both physical and chemical triggers for assembly at molecular scales. This knowledge will help understand the fundamentals of this exceptional material, paving the way for the realization of silk-inspired high-performance materials.

Nanofibrils play a pivotal role in spider silk and are responsible for many of the impressive properties of this outstanding natural material. However, little is known about the internal structure of these protein fibrils. We carried out polarized Raman and polarized Fourier-transform infrared spectroscopies on native spider silk nanofibrils for the first time and determined the concentrations of six distinct protein secondary structures, including β-sheets, and two types of helical structures, for which we also determined orientation distributions. Our advancements in peak assignments are in full agreement with the published silk vibrational spectroscopy literature. We further corroborated our findings with X-ray diffraction and magic-angle spinning nuclear magnetic resonance experiments. Based on the latter and on polypeptide Raman spectra, we assessed the role of key amino acids in different secondary structures. For the recluse spider we developed a structural model with unprecedented detail, featuring seven levels of structural hierarchy. The approaches we developed are directly applicable to other proteinaceous materials.

The process of molecular imprinting allows to produce biomimetics of nanometric dimensions (nanoMIPs) by means of a template assisted synthesis [1]. NanoMIPs are gaining momentum for their outstanding recognition properties in vitro and in vivo, proving effective in cell imaging, tumor-cell targeting, drug delivery [2-5]. The expectations for nanoMIPs in medicine stake high. Yet, nanoMIPs are currently prepared starting from synthetic monomers (e.g. acrylamides), while focal point for their translation into clinical applications should be biocompatibility.
In this framework, we imagined a possible breakthrough development, based on the original idea to synthesize fully biocompatible nanoMIPs starting from the natural polymer silk fibroin, that is characterized by non-toxicity and high biocompatibility. Given the natural origin, we named the silk imprinted nanoparticles bioMIPs.
We investigated and optimized the synthesis of the bioMIPs by a three parameters (quantity of silk fibroin, pH, photoinitiator) response surface method (RSM) that enabled to model the landscape of the possible synthetic conditions. In set conditions, uniform (polydispersity index < 0.25) nanometer sized populations of bioMIPs, with Z_average ~50 nm or Z_average ~100 nm, were obtained.
The possibility to imprint recognition cavities on the bioMIP and the ability of these bioMIPs to trap a defined target molecule was also studied. Target molecules of different sizes (i.e. a peptide and a protein) were chosen as templates, so to consider the effects of the template size on the imprinting process [6,7]. Both isothermal titration nanocalorimetry and fluorescence spectroscopy proved the molecular recognition abilities of the formed bioMIPs. The estimated dissociation constants of the bioMIPs for the targets were in the nanomolar range, moreover the bioMIPs had selectivity and specificity for the target and a quasi-single binding site per nanoparticle. Additionally, the bioMIPs proved to be nontoxic for cultured mouse embryonic fibroblasts even at significantly high concentrations (2 mg/mL). Finally, we produced functional biomaterials with tailored recognition by coupling the bioMIPs to silk micro- and nano-fibers. Such bioMIP-silk specialized functional fibers proved to selectively trap the targeted molecule [6].
Hence, the unprecedented combination of silk fibroin building blocks to molecular imprinting appears as a compelling strategy to entail recognitive-functions to bio-nanoparticles. BioMIPs open for a new class of biomimetics that conjugate natural polymers to the custom design of molecular recognition abilities, with foreseen impact in precision medicine and instructive biomaterials.

References
1. Y. Hoshino, T. Kodama, Y. Okahata, K.J. Shea J. Am. Chem. Soc. 2008, 130, 15242.
2. S. Piletsky, F. Canfarotta, A. Poma, A.M. Bossi, S. Piletsky, Trends Biotechnol. 2020, 38, 368.
3. A.M. Bossi, Nat. Chem., 2020, 12, 111.
4. K. Haupt, P.X. Medina Rangel, B.T.S. Bui, Chem. Rev. 2021, 120, 9554.
5. Y. Dong, W. Li, Z. Gu, R. Xing, Y. Ma, Q. Zhang, Z. Liu, Angew. Chem. Int. Ed. 2019, 58, 10621.
6. A.M. Bossi, A. Bucciarelli, D. Maniglio, ACS Appl. Mater. Interfaces, 2021, 13, 312431.
7. A.M. Bossi, D. Maniglio, Microchem. Acta, 2022, 189, 66.

Molecular complexes that are inspired from biological enzyme-substrate interactions can be mimicked with the lock-and-key templating process. The use of functional monomers that can be electrochemically polymerized enables the formation of cross-linked polymer films with cavities that enable high binding assays of analytes: chemical and biological. There are a number of methods to improve sensitivity and selectivity in sensors but usually, this requires more elaborate instrumentation methods In this talk, we will show the effective and bio-inspired artificial enzymes for the detection of chemical and biological analytes. We will focus on the
demonstration of electropolymerized molecularly imprinted polymer (E-MIP) sensor elements and their ability to utilize transduction methods such as surface plasmon resonance (SPR) spectroscopy or quartz crystal microbalance (QCM) to enable high sensitivity and selectivity. The monomer and molecular design for optimized analyte interaction enable effective templating protocols in a conducting polymer matrix with tunable oxidative states to enable a high volume of analyte-cavity sites. Optimized electropolymerization methods are important for film deposition and surface characterization.

Spiders are unrivalled in the diversity of high-performance silk types they produce. Biomaterial studies of spider silk primarily focus on orb-weavers, renowned for their seven functionally distinct silk types, including the well-studied dragline due its ease of collection and high tensile strength. However, orb-weavers are just one of many spider lineages that have further diversified silk into materials with unusual structures and properties, modified for wide-ranging mechanical demands. In this talk I provide an overview of the rich diversity of spider silks and highlight how recent advances in genomics are revealing the greater complexity of these materials, as well as recipes to mimic or re-imagine them. In addition to reviewing the silk types investigated to date and their underlying genetics, I will highlight unexplored species and silk types that could yield roadmaps to novel biomaterials and describe the challenges to closing our knowledge gaps.

Many biological processes, including biomineralization, are modulated via condensation phenomena at the interface between biopolymer matrices and inorganic ions modulate. Despite their enormous inspiration for high-performing materials design, little is known about simultaneous behaviors of inorganic io crystallization and biopolymers assembly. In this study, we present the control of co-occurring silk fibroin assembly and inorganic nucleation at their phase front to drive the formation of microneedles with designed nano-porous and hollow microstructures. This phase front assembly approach, for the first time, enabled the one-pot manufacturing of mesostructured microneedles with hollow and nanoporous tips: different internal microneedle structures develop in one type of mold via the interaction of silk fibroins and ionic salts. These mesostructured microneedles will serve as new connecting tools between biotic-abiotic worlds. For the agricultural application, we demonstrate the transport of biomolecules and detection of early-stage bioaccumulation of environmental contaminants (e.g., cadmium and arsenic) in tomato plants.

New systems capable of precise and efficient agrochemical delivery in plants will foster precise agricultural practices and provide new tools to study plants and design crop traits, as conventional delivery practices such as standard spray suffer from a significant loss, severe environmental side effects, and limited access to remote plant tissues. We previously demonstrated that silk-based microneedles could circumvent these limitations, capable of delivering a variety of payloads ranging from small molecules to large proteins into specific loci of various plant tissues. However, the plant responses to microneedle injection and microneedles’ efficacy in deploying physiologically relevant biomolecules are unknown. Here, we show that gene expression associated with Arabidopsis thaliana wounding responses decreases within 24-hours post microneedles’ application. Microneedles-mediated gibberellic acid (GA₃) injection in A. thaliana mutant ft-10 is more effective and efficient than spray in activating GA₃ pathways and accelerating bolting. Microneedles’ efficacy in delivering GA₃ is also observed in several crop species, i.e., tomato (Solanum lycopersicum), romaine lettuce (Lactuca sativa), and carmel spinach (Spinacia oleracea), underpinning the use of this new tool in plant science and agriculture.

In nature, water diffusion is the principal driving force of all organisms for performing the homeostatic motions, so-called hydration-adaptive actuation. For instance, animals reshape their feather through the hydration-adaptive buckling, and plant seeds exhibit a twisted opening response to osmotic stimulation. The structural biopolymer, such as silk fibroin, and keratin, spontaneously demonstrate the hydration-adaptive crystallization, i.e., phase transition into β-sheet crystals. This crystallization enhances structural stability. Meanwhile, the crystallized biopolymers become inert and hardly interact with the surroundings. Hence, the inevitable biopolymeric crystallization exerts significant leverages in biomedical fields, for instance, pros in human-robot interfaces or cons in tissue adhesives. However, the underpinning chemical and physical aspects of hydration-adaptive crystallization have rarely been investigated up to date.
We have developed an unconventional silk fibroin by regulating hydration-adaptive crystallization, the mechanism of water responsivity in nature. Technically, the crystallization rate is modulated by activating a standard amino acid (Serine; Ser). Inspired by the natural activation of polar amino acid of an insect and shellfish via chelation of Ca²⁺, the silk fibroins with different activities of Ser (7.90-10.8%) are prepared through divalent cation-mediated protein modification. In detail, Ser morphs into the exposed activated status according to the interaction between the divalent cation and the hydroxyl group of Ser.
A rheological model of case II diffusion through silk fibroin is demonstrated to deeply understand the hydration-adaptive crystallization. Case II diffusion is relevant to the hydration-adaptive crystallization as it regards the water-biopolymer interaction as a decisive parameter in entire diffusion kinetics. According to the proposed model, activated Ser enables downregulating the rate of silk fibroin crystallization. Moreover, the crystallization of protein secondary structures is monitored in situ by Raman spectroscopy. Both model and empirical results exhibit the inverse relationship between Ser activity and the crystallization rate, proving the active Ser-dependent crystallization kinetics. Particularly, a 30% increased activity of Ser results in an approximately 55% decreased rate of hydration-adaptive crystallization from 0.206 to 0.0936.
The mechanism of amino acid-based regulation of hydration-adaptive crystallization is figured out based on the thermodynamic water stability. In the hydrated biopolymer, the less-stable water molecules bridge the frame amino acids and cause crystallization. The hydroxyl group of Ser is more favorable in water stabilization than the carboxyl group of Gly and Ala. Hence, the crystallization-triggering water molecules spontaneously construct the stable lattice network in the silk fibroin with highly-activated Ser. The measured results (i.e., number of hydrogen bonding of water molecule and exothermic enthalpy) indicate that the water stability is enhanced by approximately 2.5 folds by a 20% increased activity of Ser. In summary, the active Ser stabilizes the water molecules and delays the hydration-adaptive crystallization.
Finally, the active Ser-dependent crystallization regulation realizes the unconventional silk fibroin, irrelevant to the crystallization-induced inevitable loss of adhesive force. The silk fibroin with less-activated Ser losses 82% of initial adhesive force after 120 s hydration, suggesting the limited biomedical potential. Meanwhile, the silk fibroin with highly-activated Ser maintains a strong adhesiveness of 160 kJ m^-3, enabling stable adhesion on ex vivo porcine mandible tissue. In conclusion, the amino acid-based regulation technology imparts the unique mechanochemical response to the silk fibroin itself.

There is an unmet demand for ways to restore functional tissues following damage. Elastic tissues do not typically regenerate in adults because they rely on an exogenous supply of elastin’s primary building block, tropoelastin. We have developed ways to make and use tropoelastin to build a range of elastic repair materials. To our surprise, tropoelastin also promotes broader tissue repair. Powerfully, the use of tropoelastin promotes healing following surgery, including the recovery of full thickness wounds.

An emerging model for tropoelastin is that it delivers this potency by emulating extracellular matrix interactions including those needed in development and repair. This paradigm for enhanced tissue repair encompasses a novel, pure, synthetic material that promotes the repair and fixation of soft tissues. These biomimetic and bioinspired materials leverage an innate ability to promote new blood vessel formation and cell recruiting properties to accelerate healing. Utilizing our accumulated knowledge of their assembly and interactions has led to the realization of a diverse range of powerful biomaterials with tunable mechanical and self-assembly properties.

Metal-coordination interactions are promising chemical motifs for the design of bioinspired polymeric materials that mimic the mechanical performance of biogenic materials such as the arthropod fangs and mussel byssal threads. Building upon the use of such motifs for the design of associative polymer gels, we demonstrate a bioinspired strategy to introduce additional mechanical reinforcement and novel functionalities into metal-coordinate hydrogels, by using the strongly metal-coordinating ligands as templates for the mineralization of metallic nanoparticles in the hydrogels in situ. We demonstrate ability to induce significant mineralization of iron oxide nanoparticles in a catechol-based polymer network, which results in significant stiffening (surpassing that arising from metal-ion coordination alone) as well as magneto-responsivity in the hydrogel. These findings further advance our utilization of metal-coordination interactions in bioinspired soft materials, and offer promise for their use in technological areas such as soft robotics, energy harvesting, and medicine.

Dextran, a neutral bacterial exopolysaccharide made up of repeating 1-6 linked glucose subunits, has been widely recognized for its water solubility, inherent inertness and biodegradable nature. Owing to these properties and its ability to conjugate with different polymers, dextran has shown promise in several biomedical applications. Copolymers between dextran and poly(N-isopropylacrylamide)(PNIPAM) - a thermosensitive polymer with a lower critical solution temperature (LCST) of 305 K - and their star-like architectures have shown potential for creating targeted drug delivery systems. This has led to significant research in studying other soft-material architectures consisting of dextran-PNIPAM copolymers, with bottlebrush polymers (BBPs), being a particularly interesting example. BBPs, traditionally seen as worm-like cylindrical molecules, can be designed in various shapes by adjusting structural parameters such as the grafting density as well as side chain length and arrangement. Furthermore, temperature-sensitive BBPs (TS-BBPs) of PNIPAM, have shown that the shapes of these architectures significantly impact their overall conformations, leading to different properties and applications. In the present work, we perform coarse-grained (CG) molecular dynamics (MD) simulations of BBPs of dextran-PNIPAM copolymers, broadly belonging to three shapes - (i) cake-like, (ii) dumbbell-like and (iii) plus-like. We study in comparison to non-dextran conjugated BBPs, the effect of BBP shape and temperature (below and above LCST of PNIPAM) on the conformations of overall BBPs, their backbones and side chains as well as the structure of solvent around these architectures. We also investigate the effect of dextran chain length and conjugation density on these architectures by grafting dextran 10-mers and 30-mers onto the TS-BBP in different arrangements. Through conventional analyses like free volume, contact maps, asphericity, etc., we show that the lengths of conjugated dextran chains around the backbone and their immediate environments influence the compactness of overall structures while also affecting PNIPAM conformations in the core of these architectures to varying degrees. Finally, we use a recently developed convolutional neural network (CNN)-based analysis protocol to quantify the similarities and differences between conjugated and non-conjugated TS-BBPs by capturing molecular-level features that may go unnoticed using conventional analysis. Through this analysis, we attempt to unravel the relationship between the degree of dextran conjugation and its effect on PNIPAM side chains in the TS-BBP, to further provide guidance in designing novel BBPs of dextran-PNIPAM conjugates.

This work was supported by GlycoMIP, a National Science Foundation Materials Innovation Platform funded through Cooperative Agreement DMR-1933525.

Globally, rapidly aging human populations are significantly accelerating the occurrence of non-communicable diseases. Understanding the fundamental mechanisms of tissue damage due to aging can provide predictive capabilities that will inform medical treatments. Coupled with this understanding, nature-inspired dynamically responsive biomedical devices and implants can address this major health crisis due to their excellent environmental adaptability and biocompatibility. We apply multiscale molecular modelling and machine-learned metamodels to characterize aging-related diseases and engineer various candidate materials in two aspects: (1) dynamically-responsive silk and silk-elastin-like materials, and (2) customized molecular and material designs for ligands and polymers. Through this approach, we unveil the myriad material properties of chemically and physically processed silk-based materials, such as ionic conductivity. We also rapidly and efficiently determine the material parameters of constitutive models governing the time-dependent behavior of soft polymers. We further design customized ligands that potentially bind better to integrins than existing ligands for neural implants.

Genetics and exogenous factors, such as aging, diseases and injury, affecting the human body highly demand clinical repairs to restore the functions and morphologies of the damaged tissues or organs. Tissue engineering is an emerging multidisciplinary field involving biology, medicine, and engineering to modernize the ways which can improve the health and quality of life of affected people by restoring, maintaining or enhancing tissue and organ functions. A successful scaffold construction requires mimicing the native tissue both physiologically and anatomically.
Electro(static) spinning is one of the most established techniques for constructing ECM mimicking fibrous scaffolds from various biodegradable polymers/biomaterials with diverse morphologies. However, smaller pores from the inter-fiber gaps than the human cells and poor jet path controllability due to complex jet-field interactions produce cell-impermeable sheet-like 2D scaffolds. We report here a “novel autopilot polymer single jet (AJ) electrospinning” capable of self-switching between cantilever-like armed jet motion (M1) and whipping motion (M2) due to charge-retention and dissipation of pre-deposited fibers. This new operation mechanism empowers successful fabrication of cell permeable porous scaffolds with buckled fibers that exhibited gradient porosity and mechanical strength thus satisfying physiological requirements from simple, homemade electrospinning setup in one shot. In this study, we also show the AJ-electrospinning is reproducible, robust and tunable which brings consistency to electrospinning produced scaffolds for the first time.
Further, we also demonstrated the self-searched writing of AJ on various 3D templates in the attempt of fabricating 3D scaffolds mimicking human organs anatomically, in which the AJ took various 3D bending paths which follows dynamically the self-modulated optimal field lines to deposit fibers on different sides of a 3D collector. Novel writing strategies were adopted thus avoided the competitive field lines to templates having complex 3D geometries. The AJ displayed high target recognition/specificity and resolution with pattern features as small as 100 µm to 10’s cm and capable of direct writing challenging 2D and 3D scaffolds, including human-organ-scale 3D face, female breast & nipple and vascular graft, by achieving conformal fiber deposition thus produced exact 3D replicas. The physical and biological characteristics revealed as-spun scaffolds were spongy and showed exceptional shape memory through M1/M2 switching of AJ-electrospinning with multi-directional 3T3 cells attachment and proliferation. To our knowledge, this is the first study to introduce reproducibility and direct-writing 3D scaffolds with excellent shape memory to the century-old electrospinning thus pave the path of adding this technique as a new 3D scaffold fabrication method.

Hydrogel system based on enzyme-mediated mild crosslinking reaction has been a promising approach in tissue engineering. Inspired by skin melanin synthesis and marine mussel adhesion, tyrosinase-mediated hydrogel crosslinking has been exploited as cell-friendly reactions and explicit reaction mechanisms. Hydrogel prepared by tyrosinase exhibits appealing properties as a dynamic scaffold for cell delivery and as a bioink for 3D bioprinting. Recapitulating the structure of the native extracellular matrix (ECM), innovative tyrosinase-mediated hydrogel crosslinking has now shifted to the field of translational medicine. Biomimetic hydrogel with in situ tyrosinase crosslinking can be efficiently and easily applicable to the disease model for therapeutic purposes. We demonstrate that the novel enzyme-based crosslinking hydrogel has a robust potential in tissue engineering and regenerative medicine.

E. coli and S. aureus, along with many other bacteria can cause pathogenic effects. One of the most common bacteria species commonly presenting on human skin is S. epidermidis: about two-thirds of human infections and a serious threat to human life. E. coli, the gram-negative strain, is commonly found in the large intestine of humans and other warm-blooded animals that can cause various types of extraintestinal infections. Nanofibers have recently been used in fibrous materials for a wide range of applications in medicine and hygiene, including health care and coatings, medical devices, water purification systems, and air filters. Consequently, the use of antimicrobial fibers has become an attractive idea because microorganism activity in textiles are detrimental to both the user and textile itself.
Polylactic acid (PLA) is a natural biodegradable thermoplastic aliphatic polyester that can be replaced synthetic polymers in terms of environmental aspects as well as their biodegradable nature, high safety, mechanical strength, fabricability, and biocompatibility properties. Electrospinning is one of the most widely used techniques to fabricate PLA nanofiber mats in hygiene, medical, and industrial filter applications. In particular, functional PLA fibers such as core–sheath, or porous morphology have been studied to carry and control the release of antimicrobial agents. In this study, porous functional PLA fibers obtained through electrospinning techniques with the different ratios of solvents in a high-humidity environment. In this study, a variety of porous surfaces were developed using polymer-solvent systems to enhance surface physical properties with the average size and the depth of pores of PLA fibers from various electrospinning conditions and solvents formulations. These porous PLA fibers have high surface to volume ratio, small fiber average diameter, and high nanoscale porosity. These high surface to volume ratio and nanoscale porosity result in controlled release of antimicrobial agents.
The aim of this study was to fabricate various morphology of porous PLA fibers and control the release of antibacterial agents, such as chitosan, trimethyl chitosan (TMC), gentamicin, kanamycin, and amikacin. Antimicrobial agents-loaded to porous PLA fibers were evaluated antibacterial activities using three types of antibacterial assays (inhibition zone tests, live/dead bacterial cell assays and antibacterial kinetic growth assays) against E. coli and S. epidermidis. Among the samples, gentamicin-loaded PLA fibers had the most bactericidal activity, with the widest inhibition zone and the highest visible dead bacteria on the fiber. In order to analyze quantitatively antibacterial activities, chitosan and chitosan derivatives-loaded PLA fibers, growth kinetic curves were analyzed using OD₆₀₀ against E. coli and S. epidermidis. For the results, we found that antibacterial performance was as follows gentamicin > amikacin > kanamycin > TMC > chitosan and more efficient on S. epidermidis than E. coli. This is mainly attributed to the different peptidoglycan layer structures in the cell wall of E. coli and S. epidermidis. S. epidermidis has a thicker peptidoglycan layer with a higher cross-linking degree in the cell wall compared with that of E.coli. It has been found that nonporous PLA fibers exhibits the initial-burst release profile whereas porous PLA fibers with highly porosity or deep-depth pores indicate a steady release. This study offers how to develop various morphology of PLA fibers to carry antibacterial agents efficiently and how long to control the release of antimicrobial agents depending on the type of PLA fibers to protect humans from biohazards in many applications. This investigation will provide a better and comprehensive understanding of porous microfiber formation during electrospinning and the fiber morphology-antibacterial property relationship.

Over 80,000 heart valve replacements were performed in the United States in 2014 and the global need is expected to exceed 850,000 by 2050. Currently available replacements fall into two categories, mechanical valves and bioprosthetic valves. While both types of valves improve patient’s lives, they also pose significant risks to patient health. Mechanical valves are durable but require patients to take vitamin K antagonists for life-long anticoagulation therapy. Vitamin K antagonists have significant risks including but not limited to risk of death from minor trauma, significant fetal loss for pregnant women, and major dietary restrictions. Bioprosthetic valves have significant reoperation rates ranging up to 20% within 10 years of implantation when they are implanted via open heart surgery. However, when implanted via catheter, failure rates for bioprosthetic valves are even higher. 50% of these valves have structural deterioration within 7 years of implantation. A paradigm shift is needed to address the growing need for artificial heart valves. An ideal valve would operate in a non-thrombogenic manner preventing the need for anticoagulants, provide longevity seen from mechanical valves, could be placed via catheter preventing the surgical risks associated with open heart procedures, and would be made from low-cost materials. Furthermore, designing a radiopacified valve that could be monitored in-vivo using computed tomography could help prevent irregular deployment, monitor for leaflet deterioration, and prevent poor placement leading to coronary artery overlap. Finally current valves are evaluated using echocardiograms which identifies issues only once valve function has been reduced. Direct imaging with CT scans has the potential to shift the paradigm from waiting on a reduction in function to active monitoring of valve behavior.
In this work we describe a method to incorporate radiopaque materials (tungsten and bismuth trioxide) into linear low-density polyethylene (LLDPE) so that the material can be imaged via x-ray. The radiopacified LLDPE is then treated with hyaluronic acid to form an interpenetrating polymer network that has been previously shown to increase blood compatibility. This final material is structurally complex consisting of radiopaque filler embedded in LLDPE with an interpenetrating polymer network between the LLDPE and hyaluronic acid. The material is demonstrated to be radiopaque when imaged using an EPX-F2800 x ray source and a Universal Imaging MyRad digital radiography machine. Next the material was evaluated for the presence of hyaluronic acid using captive bubble contact angle goniometry and toluidine blue O staining. The captive bubble contact angle goniometry shows a significant increase in hydrophilicity (a hallmark of hyaluronic acid), while the toluidine blue O strains carboxyl groups found in HA. Control samples were not hydrophilic, nor did they stain with toluidine blue O. Uniaxial tensile testing demonstrated the radiopaque materials had no significant reduction in yield strength or yield strain compared to control materials and only slight reductions in toughness, elongation at break, and ultimate tensile strength. Finally, the material was demonstrated to be non-cytotoxic when cultured with red blood cells. This work demonstrates significant progress toward developing a structurally complex heart valve leaflet material that addresses the major shortcomings of currently available replacements while providing an additional diagnostic tool for physicians and patients to evaluate the health of the replacement valve.

Connective tissues and organs of high tensile strength, like lung, heart and skin, extensively express elastin. Elastin is a key extracellular matrix protein responsible for elasticity, resilience, and mechanical strength in these tissues; on this basis, elastin-based materials have been widely applied in various fields such as tissue regeneration and drug delivery. During elastogenesis, the hierarchical elastic fiber assembly process, elastin is subject to a less-studied post-translational modification, prolyl hydroxylation, where, mediated by prolyl-4-hydroxylase, a hydroxyl group replaces one of the hydrogen atoms at the C-gamma position in proline residues. The structural stability of other connective tissue proteins, such as collagen, is thought to be mediated in part through hydroxylation of proline residues. This calls into question the role of prolyl hydroxylation in elastin. According to recent experimental studies, elastin-like peptides with hydroxyproline modifications are more resistant to enzymatic digestion, and subject to an abnormal behavior in elastogenesis. We hypothesize that hydroxylation alters elastin’s biological behavior via protein-solvent interactions. To substantiate our hypothesis, we used existing mass spectrometry data of elastin samples obtained from humans to build representative molecular models and perform extensive molecular dynamics simulations. As a starting point, we employ our recently developed fully atomistic model of elastin’s precursor, tropoelastin. Our findings suggest that in comparison to prolines, hydroxyprolines exhibit an increase in hydrogen bonding with water and a rise in surrounding hydrophilic hydration. Such enhanced protein-solvent interactions rearrange the residue’s local configurations, reducing elastin’s global dynamics required for essential biological process, thereby preventing it from targeted degradation and hierarchical assembly. Overall, our investigation provides insights into functions of prolyl hydroxylation in elastin at a nanoscopic scale. We propose that strategically-placed hydroxyproline residues may be useful for tuning the sustainability of engineered elastin-based materials.

Stretchable pressure sensors are important components of multimodal electronic skin needed for potentializing numerous Internet of Things applications. In particular, to use pressure sensors in various wearable/skin-attachable electronics, both high deformability and strain-independent sensitivity must be realized. However, previously reported stretchable pressure sensors cannot meet these standards because they exhibit limited stretchability and nonuniform sensitivity under deformation. Herein, inspired by the unique sensory organ of a crocodile, we developed an omnidirectionally stretchable piezoresistive pressure sensor made of polydimethylsiloxane (PDMS)/silver nanowires (AgNWs) composites with microdomes and wrinkled surfaces. Our stretchable pressure sensor exhibits high sensitivity that changes negligibly even under uniaxial and biaxial tensile strains of 100% and 50%, respectively. This behavior is attributed to the microdomes responsible for detecting applied pressures being weakly affected by tensile strains while the isotropic wrinkles between the microdomes deform to effectively reduce the external stress. In addition, because our device comprises all-PDMS-based structures, it exhibits outstanding robustness under repeated mechanical stimuli. Our device shows strong potential as a wearable pressure sensor and an artificial crocodile sensing organ, successfully detecting applied pressures in various scenarios. Therefore, our pressure sensor is expected to find applications in electronic skin for prosthetics and human–machine interface systems.

The versatility and consistency of tissue engineering scaffolds could be vastly enhanced by converging different 3D printing, biofabrication, and data-driven techniques into a single process flow. Here, we report additive manufacturing of three-dimensional fibrous devices via integrating fused filament deposition and low-voltage electrospinning patterning. Polylactic acid scaffolds and gelatin fibres (with 3-5 um diameter and 150 um inter-fibre pitch) were printed automatically without manual stacking. Fibroblast cell line and brain cancer cell line were seeded onto the three-dimensional fibres. Cell attachment and proliferation experiments demonstrated good biocompatibility of the culture devices manufactured. We subsequently applied a machine learning model to find the correlations between operating parameters and fibre device quality. Future work involving multi-functional fibres deposition is proposed to accelerate the application of fibrous devices in tissue engineering and drug discovery applications.

Three-dimensional culture of cells, allowing cells to interact with their surroundings in all dimensions, provides a more in vivo like microenvironment than traditional two dimensional cell culture. Organoids and artificial tissues or organs made by three dimensional cell culture are promising in both in vivo transplantation and in vitro experiments such as disease modeling and drug screening. However, existing three dimensional culture methods are always dependent on specific substrates or equipment, such as round-bottom culture plate, cell spinner and cell rotator. In addition, cell spheroids with uniform and controlled size are still difficult to make while are highly required in various applications to ensure the reliable and reproducible results.
In this study, we developed a universal coating for three dimensional cell culture. The coating was made with chitosan-gallol (CHI-G), and both somatic cells and stem cells automatically self-assemble into spheroids on it. CHI-G coating could be universally coated onto any materials in any shapes simply by immersing and shaking in the CHI-G solution for 48 hours. As a result, any materials coated with CHI-G coating could be substrates for spheroid culturing. We coated CHI-G onto the surface of regular two-dimensional cell culture platform (eg. cell culture plate with flat bottom and glassware for confocal) and inner-surface of three dimensional materials (eg. porous scaffolds and silicon tubes), and cell spheroids were cultured inside. Interestingly, cell spheroids cultured on substrates with different shapes could be applied in different scenarios. Porous scaffolds with spheroids cultured and imbedded inside is promising to be used as tissue engineering scaffolds. Silicon tubes with CHI-G coated on the inner-surface could be used as the device for continuous generation of spheroids. With the continuous injection of cell suspension solution and cell culture medium into the CHI-G coated silicon tube, spheroids could be generated and collected at the another end of the long silicon tube. The size of cell spheroids generated in silicon tubes is much more uniform than those generated on the two dimensional culture plate, which is mainly because of the restriction of round shape in tube. Furthermore, by changing the cell density of the cell suspension solution injected, spheroids with controlled size ranging from 60 um - 300 um could be generated, thus realizing fabricating spheroids with controlled size in a continuous and high-throughput way.

Introduction: Alginate hydrogels have unique mechanical properties that can be used to control biological responses in tissue engineering applications. Stiffness, for instance, has been shown to influence cell adhesion, differentiation, morphology, etc. in both 2D and 3D culture. The advancement of designing tissue-specific biomaterials therefore depends on our ability to chemically or physically tune these mechanical properties. In this study, we characterized how changes in calcium concentration influence the initial elastic modulus of ionically crosslinked alginate hydrogels independent of their varying stress relaxation rates. In addition, we observed that overmixing resulted in a reduced elastic modulus.
Materials and Methods: Alginate hydrogels (15 mm diameter, 2 mm thick) were formed by ionically crosslinking LF20/40 alginate with CaSO4. Alginate polymers of four different molecular weights were used to make hydrogels with four different rates of stress relaxation; lower molecular weight results in faster stress relaxation. The crosslinker concentration was adjusted (13.4 mM-54.9 mM) to tune the elastic moduli of the hydrogels to achieve the same modulus (7 kPa) independent of the various stress relaxation rates. After incubating the gels in medium for 2-3 days, compression testing was used to measure their elastic moduli.
The effect the amount of mixing has on the elastic modulus was evaluated on the fastest stress relaxing hydrogels. They were mixed five, seven, and eleven times before their moduli were characterized.
Results and Discussion: From the slowest to the fastest stress relaxing hydrogels, crosslinker concentrations of 13.4 mM, 26.8 mM, 37.8 mM, and 47.6 mM, respectively, were initially used. The two fastest relaxing hydrogels were much softer than 7 kPa; the fastest relaxing gels had an average elastic modulus of 2.1 kPa, and the second fastest relaxing gels had an average elastic modulus of 4.4 kPa, so the calcium concentration was increased for those two conditions. From slowest to fastest stress relaxation rates, the hydrogels had final average elastic moduli of 8.5 kPa, 7.2 kPa, 7.8 kPa, and 6.2 kPa with crosslinker concentrations of 13.4 mM, 26.8 mM, 42.7 mM, and 54.9 mM, respectively. While all four conditions had average moduli near 7 kPa, the target value, the second slowest relaxing hydrogels had the closest average elastic modulus to 7 kPa. The second fastest relaxing hydrogel had the lowest variability followed by the second slowest relaxing condition. This result may be explained by the fact that these two conditions had alginate solutions with intermediate viscosity (due to their intermediate molecular weights) and intermediate calcium concentrations compared to the slowest and fastest relaxing conditions. The slowest relaxing gels are made with alginate solution that is highly viscous, so it is difficult to combine the alginate solution with the crosslinking solution quickly enough to evenly mix the two, resulting in considerable variability. The fastest relaxing hydrogels are made with a high crosslinker concentration, which causes the alginate solution to crosslink quickly, again making it difficult to achieve more homogeneous mixing.
The effects of the amount of mixing of the alginate and crosslinker solutions were studied using the fastest stress relaxing hydrogels. They had average elastic moduli of 10.3 kPa, 6.2 kPa, and 5.8 kPa when mixed five, seven, and eleven times, respectively. There was a significant difference between the hydrogels that were mixed five times and seven times as well as the hydrogels that were mixed five times and eleven times. These preliminary results suggest that increased mixing results in lower elastic moduli. While enough mixing is desired to evenly distribute the crosslinks, overmixing can result in damaging the gel after crosslinks have formed, causing some to rearrange. Such rearrangement can give rise to an inhomogeneous gel with reduced elastic modulus.

Introduction: Paper-based bioelectronics, papertronics is an emerging technology for next-generation sensing and energy storage due to its significant material properties; including high surface-to-volume ratio, porous structure, biocompatibility, biodegradability, low-cost availability, foldability, and lightweight composition ^[1]. However, due to the intrinsic mechanical properties of cellulose, these stiff mechanics create undesirable substrates for stretchable bioelectronics. As a result, papertronics demonstrate limited conformability to the complex microarchitecture of skin and fail to exhibit deformation mechanics required to address the mechanical mismatch between rigid electronics and skin. To bridge the gap between papertronics and electronics skin (e-skin), herein we studied engineering strategies to exploit the material, chemical, and physical properties of paper (cellulose acetate or cellulose) amalgamated with the soft mechanics of a silicone elastomer (e.g., Dupont Liveo Soft Skin Adhesives) through coaxial electrospinning. The core-sheath silicone elastomer-cellulose acetate fibers mimic the extracellular matrix of human skin while maintaining the chemical surface properties of paper, enabling the integration of electronic components with existing manufacturing and printing techniques.
Materials and Methods: Cellulose acetate (CA) (MW = 30,000) and organic solvents (e.g., THF, DMF, Acetone) were purchased from Sigma Aldrich. The 7-9700 soft skin silicone adhesive (SSA) was gifted from DuPont. We used a coaxial needle with an electrospinning unit (MSK-NFES-3; MTI Corporation, CA) to create the fibrous mats while systematically testing operational parameters (e.g., feed rate, applied voltage, polymer concentration, etc.). Scanning electron microscopy (SEM) and confocal microscopy was used to analyze fiber alignment and core-sheath structure. Fiber diameter was measured with the utilization of ImageJ. Mechanical properties of the engineered fiber mat were evaluated by tensile testing with a 5 N load cell at a 5.10 mm sec^-1 strain rate. Fourier transform infrared (FTIR) spectroscopy and Electron Dispersive Spectroscopy (EDS) determined the chemical and elemental characteristics of the fabricated stretchable papers.
Results and Discussion: SEM confirmed a fibrous structure of the fiber mat with an average fiber diameter of 1.38 ± 0.37 µm (n=250). Confocal microscopy revealed the core-sheath structure of the SSA core (blue) and CA sheath (red) via coaxial electrospinning. Energy dispersive spectroscopy (EDS) identified elemental peaks that reflect a core-sheath structure of an individual SSA-CA fiber. Using this stretchable paper, we were able to develop a microbial fuel cell by stacking three stretchable papers as an anode, membrane, and cathode material, which generated a max power output of 10.5 µW in PBS.
Conclusions: The coaxial structure of cellulose acetate and soft skin adhesive improves the stretchability of paper substrates up to 45% strain which is greater than the stretchability of conventional paper substrates (< 2%). Fabricating an MFC device using our stretchable paper demonstrates fabrication processing compatibility of these materials and thus shows the potential for future application in various ranges of papertronics while also sharing characteristics from soft bioelectronics.
Acknowledgments: This research is supported by the National Science Foundation (NSF; ECCS#2020486). We thank DuPont for donating the SSA elastomer.
Reference: [1] Martinez, A, W et al. Angewandte Chemie (2007) 46 (8), 1318-20.

Rare earth elements (REEs) are described as the vitamins of modern industry owing to their use in high-tech and clean-energy industries. Growing concerns of the unpredictable supply, possible health risks, and unsustainable extraction practices demand the development of green technologies for the selective extraction and recovery of REEs. Protein based polymers called elastin-like polypeptides (ELP) were genetically engineered for the selective and repeated recovery of REEs. ELP exhibits a fully reversible thermal coacervation behavior over multiple cycles of cooling and heating and was exploited to enable easy recovery of the bound REEs for repeated use. A lanmodulin protein which exhibits an unusually high affinity and selectivity for REEs was fused to the ELP to provide the highly selective nature to the biopolymers in the presence of higher concentrations of competing non-REEs. Selective binding of REEs was demonstrated at an expected ratio of 2 REE/biopolymer, and minimal binding of competing heavy metals (magnesium and zinc), even at a 300-fold excess, was observed. The REEs were extracted and recovered easily, enabling continuous reuse of the biopolymers. Utility of the biopolymers for REEs recovery from real world samples such as steel slag leachate (≈0.13 mol% REEs) was demonstrated with no decrease in recovery efficiency, the recovery efficiencies of non-REEs were minimal. Results establish the potential of engineered thermoresponsive protein-based polymeric materials as biotechnological tools for environmentally friendly extraction and recovery of REEs with a minimum carbon footprint, which is essential for the sustainability of metal life cycles, from mining to end-of-life to recycling.

The COVID-19 global crisis shows that preparedness plans need to be developed, including methodologies enabling the early stage detection and identification of potential health threats, in order to contrast effectively future pandemics [1]. In particular, new technologies enabling the identification of the “latency period”, in which the virus is circulating among small communities but it is not yet recognized, are sought. Despite many efforts, current technologies for virus detection based on PCR or immuno-recognition show significant limitations. In particular, PCR cannot resolve the latency period, as it requires typically 24 to 48 hours to analyse the samples. On the other hand, immune assays show much lower sensitivity, giving rise to a significant amount of false negatives.
In this project, we developed a new bio-inspired surface allowing highly sensitive, real-time virus detection in air samples. This system is a label-free virus detection platform, with single viral particle sensitivity. Its concept, inspired by biology, could give rise to a new generation of lab-on-chip devices for studying many different viral infections, not only related to the respiratory system.

[1] Cevik, M. et al. Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Transmission Dynamics Should Inform Policy, Clinical Infectious Diseases 73(S2), S170–6 (2021).

In reptiles and birds, the claws, scales, feathers, and beaks are composed of beta keratin with exceptional material properties and outstanding performance. The beta keratin protein is a hierarchical structure, and a four-antiparallel-beta-sheet of 34 amino acids forms a monomer, the basic unit of materials. We focus on a bottom-up atomistic model of the beta keratin to study the molecular structure and the mechanics of the different hierarchical assemblies, including monomer, dimer, and fibril. For the monomer and dimer systems, the unfolding force in the dimer is larger than the monomer. Moreover, beta strands unfold at the monomer's pulling end for the dimer when the dimeric-sandwich structure remains intact in the peak force regime. For the fibril model, the unfolding peak force in shear loading is larger than in tensile loading. In shear and tensile loading, the initial unfolding of the fibril occurs in the interface of the interdimer, and the dimer structure remains when the fibril fails, suggesting that the dimer serves as a more stable building block of the beta keratin. We further compare our results with the mechanical properties of other proteins with similar beta-sheet structures and discuss how the hydrogen bond formation affects the mechanics between the materials. Our study provides insight into the quantitative comparison to the hierarchical structure of beta keratin at the atomistic level. The results could be further applied to designing bioinspired materials for the specific functions from a bottom-up perspective.

Composite materials with bioinspired microstructures are of high interest in numerous engineering applications. Indeed, thanks to their unique microstructure where inorganic particles are distributed in hierarchical patterns, unusual combinations of properties can be achieved, such as strength and toughness in nacre-like composites. However, contrary to many synthetic composites, nature produces its materials in a 'one pot' fashion where inorganic and organic components are assembled simultaneously. Also, water plays a great role in natural composites and is often absent in synthetic materials. Although examples of nacre-like hydrogels exist, they often contain a low concentration of reinforcing inorganic particles and more complex microstructures have not been realized. To address this issue, we developed a one pot synthesis approach where complex microstructures are built while the concentration of inorganic particles is getting concentrated. We study the capabilities and limits of the method and carry out mechanical testing to illustrate how the microstructure and presence of water can be leveraged to increase strength and toughness. To do so, we used an established method called magnetically assisted slip-casting (MASC) and adapted it to interpenetrated hydrogel matrices. MASC uses an external magnetic field that controls the orientation of magnetically responsive anisotropic particles in a water-based suspension, which is being removed through a porous mold. MASC therefore offers the capability of building complex bioinspired microstructures. Here, we used MASC to assemble Al₂O₃ microplatelets while polymerizing an interpenetrating network hydrogel made of poly-acrylamide (PAM) and poly(N-isopropylacrylamide) (PNIPAM). The resulting composites, containing around 40 vol% of Al₂O₃, show tunable alignment of microplatelets with polymer strands in-between when observed under SEM. From compression tests, aligned samples containing the hydrogel show higher strength and toughness than aligned samples without the hydrogel and randomly aligned samples, which were 6.5 MPa and 1000 kJ/m³, respectively. Interestingly, thanks to the presence of hydrogel inside, the dried samples absorb moisture from air and show small recovery under compression. These results highlight the potential of MASC as a processing method to create reinforced hydrogels for development of novel materials.

Extracellular vesicles are known as an important mediator for signaling in cell-cell communication and cellular processes including immune response and antigen presentation. Since extracellular vesicles contain therapeutic proteins, a variety of cell therapeutic strategies are developing while avoiding side effects such as low survival rate and immune rejection response associated with direct use of cells as a therapeutic agent. Most of the exosome studies conducted so far are based on animal-originated cells. Recently, there are challenging attempts to extract extracellular vesicles from other types of raw materials such as plant cells and microalgae. The approach to obtain extracellular vesicles from microalgae is of special interest because they have abundant biomolecules such as proteins, vitamins, minerals, and amino acids. This study proposes using microalgae containing carbohydrate bioactives, an Euglena gracilis–derived extracellular microvesicle (EMV_EG) system, for enhanced skin regeneration. The critical deformation ratio, 1.67, during cell extrusion enables us to tune the particle size of the EMV_EG at approximately 1 μm, thus satisfying the encapsulation yield of b-1,3-glucan and the cellular delivery performance. In vitro 5-bromo-2’-deoxyuridine and cell scratch assays revealed that the EMV_EG promoted the proliferation and migration of skin cells, thereby increasing both collagen synthesis and the expressions of proliferation-associated proteins. An ex vivo wound healing test using both artificial and porcine skin revealed that similar to that seen using b-1,3-glucan, the EMV_EG could substantially increase the cell population, expressing the proliferation-related protein, termed proliferating cell nuclear antigen. These results demonstrate that our EMV_EG system shows considerable potential in the field of skin regeneration. This technique is expected to design new types of extracellular vesicles that are applicable for skin regeneration in the pharmaceutical and cosmetic industries.

Amyloids are highly ordered, self-assembled protein aggregates most commonly associated with neurological diseases such as Alzheimer’s and Parkinson’s. However, their structural self-assembly into highly stable aggregates or fibrils has been shown to enhance cellular functions such as cell growth, bio-adhesion, and mechanical strength in various organisms. Synthetic biomaterial films or gels (inspired by natural amyloids) with tunable properties can be designed through peptide sequence changes that promote specific intermolecular interactions to form fibrils and strongly adhere to a variety of surfaces. Although synthetic amyloid-based materials have shown promise, there is still a lack of understanding of the influence peptide structure has on adhesive and mechanical properties. For this work, a library of amyloid peptides was synthesized and their self-assembly was investigated under varying environmental conditions. The structural and nano-mechanical properties were characterized using circular dichroism (CD) spectroscopy and atomic force microscopy (AFM) in quantitative nanomechanical mapping (QNM) mode.

Functionally graded materials (FGMs) are the materials with varying composition and structure gradually over volume, resulting in corresponding changes in the properties of the materials. Unlike traditional composites of homogeneous materials, FGMs can compromise between the desirable properties of the component materials in the desirable places in the materials. The exoskeleton of insects is a notable example of FGMs in nature. Cuticle, the constituent material of insect exoskeleton, is characterized by a wide range of elastic moduli, which can be as high as metals and as low as rubbers, are integrated without boundaries to achieve high strength, lightweight, and multifunctions.
The purpose of this study is to analyze the correlation between the composition and functionality of exoskeletons developed through evolution and to apply the insights to the engineering of novel biomimetic FGMs.
Honeybee (Apis mellifera) was selected as a model organism in this study. The antennae of honeybees have many sensors like the five human senses, and when the antennae become contaminated, dirt accumulates on the surface sensors and interferes with the sensing function. Therefore, in order to maintain their sensing function, honeybees clean their antennae using antenna cleaners on their forelegs. We focused on antennae and its specific body parts, antenna cleaners, to investigate the correlation of its material composition and functionality.
A confocal laser scanning microscope (CLSM) was used to analyze the morphology and composition of antennae and antenna cleaners. The CLSM images showed that both antennae and antenna cleaners were not homogeneous in composition, but had a combination of soft and hard parts. The antenna cleaner was also found to have a sandwich structure with soft parts sandwiched between hard parts by observation at high magnification.
We analyzed the correlation between composition and functionality by quantitatively analyzing the efficiency of the antenna cleaners in removing contaminants from the antennae. The results showed that most of the contaminants were removed in a single cleaning and that contaminants were more easily removed closer to the tip than at the base of the antennae. Based on these results, we thought that the high removal rate of antenna cleaners can be attributed to the sandwich structure, and will try to fabricate biomimetic FGMs based on these structures. In this study, we attempted to develop the FGMs with a sandwich structure having a soft and a hard layer by using vitrimers which are a special type of cross-linked material with associative dynamic covalent bonded cross-links. Vitrimers can enhance interfacial adhesion and help fabricate FGMs because the bond exchanges are occurred by heat treatment. At last, we evaluated the interfacial adhesion of the fabricated materials by atomic force microscope (AFM) and the cleaning efficiency of the fabricated materials by independent test.

In recent years, many studies have been conducted to improve the antifouling properties of surfaces in water and to reduce the fluid resistance, and it needs to elucidate the essence of the structural shape and surface composition that provide optimal properties. For example, fish scales are hydrophilic surfaces with riblet structures, and it is known that these structures produce a water layer in water flows to prevent adhesion of dirt and exhibit excellent self-cleaning ability. It is also believed that the microstructures of the scale surface are responsible for further improvement of antifouling properties and reduction of fluid resistance.
The purpose of this study is to evaluate the properties of shark mimetic surfaces that could lead to the elucidation of the unexplained mechanism of shark fluid resistance reduction. Measurement method of dynamic wetting in a liquid atmosphere that established in our laboratory was used to evaluate the antifouling properties and reduction of fluid resistance ability of microstructured surfaces in a water atmosphere.
In the past, surface properties under a water atmosphere were mostly evaluated only from static contact angles. However, surface properties under an air atmosphere are evaluated by combining static and dynamic wettabilities. The reason is dynamic wettability shows functional behavior that cannot be predicted from static wettability. Therefore, we have created a new experimental method to measure the dynamic wettability under a water atmosphere. The dynamic contact angles of air bubbles and oil droplets on the surface with tilting were measured in a water atmosphere.
Experimental substrates were a commodity polymer resin with a riblet structure mimicking shark scales. Hydrophilicity and hydrophobicity of the polymer surfaces were changed by fabricating a self-assembled monolayer after gold-ion sputtering. 10mL of ethanol solutions including hydrophilic and hydrophobic molecules with thiol groups were prepared and the gold-coated polymer substrates were immersed in each ethanol solutions for 3 hours. After immersion, the substrate was washed thoroughly with ethanol and dried naturally. 5 kinds of surface-modified substrates having various ratio of hydrophilic and hydrophobic molecules in outermost surfaces were fabricated and measured by the dynamic wettability analyze system in air or water atmospheres. In an air atmosphere, 15μL of water or 6μL of n-hexadecane was attached and the substrate was tilted. In a water atmosphere, 11μL of an air bubble or 20μL of n-hexadecane was attached and tilted.
As a result, the value of the contact angle when air bubbles were attached in a water atmosphere was larger than that expected from the contact angle when water was attached in an air atmosphere. In addition, the tilt angle required for the bubbles to leave the substrate was smaller. This is thought to be because of product of a water layer on the substrate surface by the shark's microstructure. This result suggests that the shark's scale surface prevents bubbles from attaching to the substrate and reduces fluid resistance by not creating surface irregularities.
Next, the contact angle value when n-hexadecane was attached in a water atmosphere was significantly larger than the value expected from the contact angle when hexadecane was attached in an air atmosphere. However, the tilt angle required for the n-hexadecane to leave the substrate was also large. This is thought to be because of the difference in the height of the microstructure on the shark-mimetic surface. This is thought to this difference in height cause a petal effect, which prevents the oil droplets from leaving the substrate surface even when the substrate is tilted up to 90°. These results strongly emphasize the necessity of measuring dynamic wetting behavior in water atmosphere and indicate the possibility of creating new functional surfaces through further clarification of the functions of organisms existing in water.

Despite being gill-breathing organisms, Ligia exotica are unable to swim. They breathe to use transported water without external energy caused by using capillary action of microscopic protrusion structures on the surface of their legs. Energy-less liquid-control surfaces not to require the external energy will be possible to create in mimicking of the structure of legs. In previous studies, it has been found that fabrication of microscopic protrusion structures on the polymer surface enables spontaneous liquid transport. However, while polymers are easy to form, there is a fear of deformation and softening above the glass transition temperature. Therefore, the goal of this research is to replace the material of the mimic substrate from polymer to metal. For this purpose, we fabricated a metal film on the surface of a polymer substrate with a mimic structure and checked shapes of droplets on the surface to verify whether the substrate material could be replaced from polymer to metal. Next, a new metallization method was examined, in which a metal substrate is formed by thick plating on a porous polymer mold.
Polymer substrates with mimic structures were fabricated by pouring polydimethylsiloxane (PDMS) into polyethylene (PE) molds. Conical and triangular pyramidal protrusions were fabricated and arranged evenly spaced grid. We also examined whether the behavior of the droplets differed depending on the kinds of metal, such as gold and nickel, and the method of the metal coatings, such as gold vapor deposition and electroless plating. A 1.5 µL drop of water was dropped onto each prepared substrate and spreading of the droplet was observed. As a result, the spaces between the protrusions functioned as flow paths, and the droplets spread vertically and horizontally. Further, the droplet shape on the metal surface was like that on the polymer surface, with the droplet shape being nearly square on each substrate with conical structures, and nearly rectangular on each substrate with triangular pyramids. The aspect ratio was calculated from the wetting shapes of droplet at the point when wetting stopped. The aspect ratio was about 1.0 for cones and about 1.5 for triangular cones. The difference in wetting shape is closely related to the capillary pressure caused by the structure shape. In the case of conical protrusions, the distance between adjacent protrusions is equal from vertical to horizontal, and the strength of capillary pressure does not vary from vertical to horizontal. On the other hand, in the case of triangular pyramidal protrusions, the distance between adjacent protrusions is not constant, which causes a difference in the strength of capillary pressure. Even if the surface is coated with metal, the projection shape without any change, so the capillary pressure gradient is the same as on the polymer surface and the droplets have the same shape.
From the above, it was confirmed that the structure inspired by the legs of ligia exotica can be applied to metal surfaces. As the next step, we tried to fabricate a metal substrate with the mimic structure by the thick plating method. A thin metal film was fabricated on the surface of the mold, and electrolytic plating was utilized to obtain the metal substrate. To facilitate detachment of the mold after molding the metal substrate, the mold was made of flexible PDMS, but PDMS substrates have a very weak durability of the metal thin film fabricated on their surface. Therefore, the PDMS molds were immersed in a polydopamine solution to form a hydrophilic dopamine film on the surface of the molds, and metal films were fabricated on the dopamine film. As a result, the durability of the metal film against peeling increased and electrolytic plating became possible for thicker plating.

Since mussel-inspired polydopamine (PDA) was introduced in 2007, dopamine chemistry has attracted huge attention due to the surface-independent coating capability in mild alkaline conditions. Based on the unique binding property, PDA and its related analogues (i.e. phenolic polymers) have been adopted in various fields such as cell culture, composites, microfluidics, drug delivery membrane, and others. However, a comprehensive understanding of PDA is still limited owing to the abundant reactive sites of dopamine monomer. Due to the polymerization in multiple regions, PDA has various building blocks, which are composed of 5,6-dihydroxyindole (DHI) and dopamine units in various oxidation states. This complex structure restricts the systematic analysis of PDA.
Here, we rationally designed the series of PDA derivatives (DA1, DA2, DA3, DA4, DA5, DA6, and DA7) and synthesized its corresponding polymers to investigate the role of each building block as well as bonding mechanisms on different substrates. The chemical structures of each polymer are logically controlled by blocking or removing reactive sites that enable the successful isolation of building blocks of PDA. Therefore, a series of polymers is characterized to disclose a secret of PDA. First, molecular structures are confirmed by Nuclear Magnetic Resonance (NMR), Mass spectrometry, Fourier-transform infrared spectroscopy (FTIR), and X-ray Photoelectron Spectroscopy (XPS). Then we focused on the adhesion and cohesion mechanism of PDA derivatives that determine various coating modes on metal, silicon, polymers, etc. Based on the comparison among DA1, DA2, and DA4, we found both catechol and amine play a pivotal role in surface-independent adhesion regardless of the presence of DHI unit. In contrast, DA5, a catechol-only polymer, exhibits limited adhesion. Meanwhile, film and particle morphologies were examined by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) to reveal the aggregation mechanism that determines the surface roughness and the coating thickness. Finally, the optical properties of PDA are analyzed by UV-vis spectroscopy. We successfully figured out the origin of the dark brown color of PDA that is attributed to the combination of various oxidized modes of catechol quinone and DHI units.

Optical methods represent a powerful and non-invasive tool to stimulate and probe biological matter. In particular, conjugated molecules and macromolecules have been demonstrated a great platform to interface with cells and living organisms.^1,2 This interaction has been promoted by materials high optical absorption/emission cross sections, versatility in chemical synthesis and low toxicity. Even though the efficiency of this approach has been demonstrated in neurosciences and cardiology,^3–5 the visible light absorption and the relative low penetration inside human body is still a critical point.

In this work, we evaluate the use of a novel NIR-absorbing organic bulk heterojunction (composed by a conjugated polymer and a small molecule) for living cells photostimulation. We initially developed a fabrication method to produce a diffuse interface shaping the material in the form of nanoparticles. Furthermore, we evaluate biocompatibility and photostimulation ability of the proposed blend.


References

1. Di Maria, F., Lodola, F., Zucchetti, E., Benfenati, F. & Lanzani, G. The evolution of artificial light actuators in living systems: from planar to nanostructured interfaces. Chem. Soc. Rev. 47, 4757–4780 (2018).
2. Hopkins, J. et al. Photoactive Organic Substrates for Cell Stimulation: Progress and Perspectives. Adv. Mater. Technol. 4, 1800744 (2019).
3. Maya-Vetencourt, J. F. et al. A fully organic retinal prosthesis restores vision in a rat model of degenerative blindness. Nat. Mater. 16, 681–689 (2017).
4. Lodola, F., Vurro, V., Crasto, S., Di Pasquale, E. & Lanzani, G. Optical Pacing of Human Induced Pluripotent Stem Cell Derived Cardiomyocytes Mediated by a Conjugated Polymer Interface. Adv. Healthc. Mater. 8, 1900198 (2019).
5. Vurro, V. et al. A Polymer Blend Substrate for Skeletal Muscle Cells Alignment and Photostimulation. Adv. Photonics Res. 2, 2000103 (2021).

Many wild animals that are active at night have evolved to have layered eye structures that include thin reflectors to improve night vision. Light incident on the eyes of these wild animals is primarily absorbed by the retina, but some transmission loss is unavoidable. A naturally occurring biological reflector located behind the retina provides an opportunity for the retina to absorb residual light. In this presentation, we introduce a new type of diffuse reflector with excellent scattering properties by applying the optical amplification mechanism resulting from the layered structure to the scattering behavior. The newly developed diffuse reflector has a biologically inspired layered structure of an ordered nanoporous medium serving as a scattering layer and a metallic thin film serving as a reflective layer. The secondary scattering caused by the reflector enables an exceptionally homogeneous diffuse reflection close to the Lambertian distribution, which is predicted through optical simulations (FDTD or FEM) and verified experimentally. Finally, we present several advanced optics, including smart contact lenses, by utilizing miniaturized diffuse reflectors through photopatterning.

Since the 2000s, various types of dry adhesives have been proposed that mimic the hierarchical ciliary structure of gecko lizard’s paws. Recently, deviating from the research paradigm of simply mimicking the adhesive function, conductive dry adhesives made of nanocomposites in which conductive nanomaterials (e.g., CNTs and AgNWs) are dispersed in an elastomeric matrix have been developed. Attempts have been made to acquire various bio-signals by using them as skin-mountable dry electrodes, but their sensitivity is still limited due to the inherent trade-off relationship between electrical conductivity and adhesion in typical nanocomposites. Here, we propose a functionally layered, highly conductive, dry adhesive patch through rational design of spray coating and molding processes. Lateral collapse of the high aspect ratio ciliary structures, which frequently occur during spray coating of conductive dispersions, can be avoided through optimization of the process sequence. The dry adhesion and electrical conductivity of the patch are independently controlled by the aspect ratio of the ciliary structure and the amount of spray-coated AgNWs. We have finally succeeded in realizing a large-area (4 in²), defect-free dry adhesive patch that exhibits high electrical conductivity (< 100 ohms) and favorable normal adhesion (> 1.3 N/cm²) to human skin. Several proof-of-concepts utilizing the developed highly conductive dry adhesive patch will be presented.

The self-assembly of highly branched Janus dendrimers (JD) into Janus dendrimersomes (JDS) comprised of a hydrophilic/hydrophobic bilayer has shown promise for drug encapsulation and delivery. However, at higher concentrations and degrees of generation, the hydrophilic portions of traditional JDs have proved to be cytotoxic. To improve biocompatibility, JDs have been decorated with saccharide groups which assisted in the self-assembly of non-toxic Janus glyco-dendrimersomes (JGDS). It has been seen that, due to distinct peptide/polymer hydrogen bonding interactions, saccharide stereochemistry plays an important role in carbohydrate functions such as biological recognition, protein binding, and peptide aggregation pathways. This work explores using synthetic glycopolymers as the hydrophilic layer to amplify the structures’ hydrogen bonding ability, potentially enhancing the self-assembly of JGDS. The stereospecific arrangements of the pendant saccharide groups may be used for cell targeting, lectin specific binding in the body, and to mimic the biological glyco-clustering effect. Linear glycopolymers were synthesized through reversible addition fragmentation chain transfer (RAFT) at different target molecular weights and coupled to polylactic acid (PLA) branched dendrons. While maintaining a constant molecular weight of the hydrophobic dendron and altering the hydrophilic segment, a multitude of nanostructures may be seen. Coupled conjugates and nanostructures were characterized through nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), dynamic light scattering (DLS), transmission electron microscopy (TEM), and atomic force microscopy (AFM).

Bioengineered chloroplast has great potentials in carbon sequestration as well as production of biological molecules. Although plants are preferred in chloroplast engineering, isolated chloroplasts provide benefits in terms of environmental friendliness, abundant resource in nature, and cost effectiveness. For example, the isolated chloroplasts are more efficient than plant in carbon dioxide absorption, because they did not discharge carbon dioxide unlike plants. However, isolated chloroplasts lose their photosynthetic activity quickly. It requires a novel platform for chloroplast incubation as maintaining intactness of chloroplast. Chloroplast encapsulation in biopolymers or synthetic materials has been proposed to prolong the photosynthetic activity. Nevertheless, sufficient photosynthetic activity of encapsulated was not achieved in these attempts. In this study, we fabricated pectin hydrogels as a novel matrix, which mimicked plant cytosol for preservation chloroplast photosynthetic activity. Chloroplast-laden pectin hydrogels were formed via thiol-ene photo-crosslinking with pectin-norbornene and dithiothreitol. As a result of modulus measurement, the network integrity was maintained in incubation medium for 14 days. In pectin hydrogel, the encapsulated chloroplasts showed photosynthetic activity for 7 days, while the depletion of the photosynthetic activity of the chloroplasts suspended in the medium was relatively quick. The use of antioxidant even improved the photosynthetic activity in pectin hydrogel. Importantly, caffeic acid was most effective in preventing chloroplast damage by reactive oxygen species during photosynthesis. In conclusion, photo-crosslinked pectin hydrogel provided a suitable microenvironment for encapsulated chloroplasts, resulting in extended photosynthetic activity.

There is an increasing need for biocompatible neuronal cell proliferation and regeneration scaffolds as regeneration of the neurite structures is slow and complex, which results in permanent nerve cell damage. Non-invasive electrical stimulation could potentially enhance neural cell proliferation and differentiation. Interfacing cells with biocompatible materials with electrical properties could be harnessed to introduce potential gradients across the cell membrane for neurological activation and repairs. The ability to stimulate individual neurons can impact the development of neural networks, and enhanced motor rehabilitation. The influence of voltage stimulation on human neural progenitor cells will be studied in-vitro using a high-density array of peptide-based nanotubes deposited via plasma-enhanced chemical vapor deposition (PECVD). Peptide-based building blocks containing aromatic amino acids that can self-assemble to form highly organized nanoscale structures with key functional properties such as biocompatibility, high aspect ratios, semi-conductivity, and stiffness will be used as the scaffold in this study. Tryptophan and tyrosine are aromatic amino acids known for their redox properties and roles in neurotransmitter synthesis. These structures have the ability to “carry” cells, which should result in functional modifications and an altercation in protein behavior, which can lead to highly polarized cells. Following the analysis of physicochemical properties of these peptide nanostructures, we studied the biological interactions and influence these scaffolds on human bone marrow neuroblasts and neural progenitor cells and subjected to an electrical stimulation. Prior studies have used carbon nanotubes scaffolds for subsequent electrical stimulation protocols, but their cytotoxicity makes their use in many biological systems undesirable. Electrical stimulation can induce the depolarization of the plasma membrane, as well as affect the function of membrane proteins, including enzyme activity and ion-transporting channels. These processes are most likely generated via the increased presence of reactive oxygen species (ROS), which are highly reactive molecules that have also been found to potentially act as an intermediate signal transducer between neural cells for the purpose of cell differentiation. To test the same, MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) cytotoxicity studies, morphological cellular interaction imaging through SEM and confocal imaging, dopamine-enzyme linked immunosorbent assay, immunostaining for neuronal markers, and real-time polymerase chain reaction (q-PCR) for gene expression were carried out on the neuronal cells cultured on the synthesized peptide bioscaffolds.

The ability to accurately model RNA in computer simulations is important as potential applications are increasing with the mRNA vaccine platform. Various length and shape of RNA chains as well as their interactions with the environment, play an important role in medicine, origin of life and homochirality studies. The extensive experimental research on short RNA strings provide an excellent opportunity to utilize those structures as benchmarks for nucleic acids force-fields[1], and increase our understanding of structural and dynamic properties RNA strings. In recent years, all-atom molecular dynamics was used to show accurate RNA folding[2], dynamic protein-RNA binding[3] and plasticity of dsRNA duplexes[4] among others.
We have studied a series of RNA dinucleotides, tetranucleotides and hairpin loops, GAGA (IZIG) and UUCG (2KOC), with respect to structural stability in vacuum, and in presence of implicit- and explicit water, for AMBER-OL3, OPLS-AA/M, and CHARM-36. The results of J3 coefficients from dihedral angles were compared with experimental NMR data. For these models, AMBER recreated the structures with best agreement with experimental data, compared to OPLS and CHARMM. Based on results stretching-folding experiments were conducted on selected nucleotides in AMBER-OL3/bsc0 force field with explicit water and vacuum. The dynamic and mechanical properties of RNA chains were shown as a function of chain length and investigated further for size effects.

[1] J. Zhao et al. “Nuclear Magnetic Resonance of Single-Stranded RNAs and DNAs of CAAU and UCAAUC as Benchmarks for Molecular Dynamics Simulations”. In: J. Chem. Theory Comput. 16.3 (2020), pp. 1968–1984. doi:10.1021/acs.jctc.9b00912.
[2] A. M. Yu et al. “Computationally reconstructing co-transcriptional RNA folding from experimental data reveals rearrangement of non-native folding intermediates”. In: Nat. Comput. Sci. 81.4 (2021), pp. 870–883. doi:10.1016/j.molcel.2020.12.017.
[3] M. Krepl et al. “MD simulations reveal the basis for dynamic assembly of Hfq RNA complexes”. In: J. Biol. Chem. 296.100656 (2021), pp. 1–15. doi:10.1016/j.jbc.2021.100656.
[4] W. He et al. “The structural plasticity of nucleic acid duplexes revealed by WAXS and MD”. In: Sci. Adc. 7.17 (2021), pp. 1–15. doi:10.11126/sciadv.abf6106.

Black-legged ticks (I. scapularis) are vectors for a number of pathogenic bacteria, parasites, and viruses that affect both humans and livestock. Reducing the expression of key tick proteins, such as Selenoprotein K (SelK), through RNA interference is a promising approach to reduce pathogen transmission, but efficient delivery of nucleic acids to arthropods has proven challenging. Cationic glycopolymers have shown great promise with human cells as non-viral gene delivery vehicles to protect RNA and enhance delivery while also mitigating polymer cytotoxicity. Previous work established that glucose- and galactose-based glycopolymers exhibited variations in hydrogen bonding patterns in solution and resulted in different polymer-protein aggregation behavior. In this study, statistical acrylamide-based cationic glycopolymers with glucose or galactose pendent groups were synthesized by RAFT polymerization and the effects of saccharide pendent group and cationic monomer loading on polymer cytotoxicity, RNA complexation, and SelK gene knockdown in ISE6 cells were evaluated. All polymers exhibited low cytotoxicity, yet RNA/copolymer complex cell uptake and gene knockdown were highly dependent on saccharide structure and N:P (amino to phosphate groups) ratio.

With the onset of climate change, there is increasing concern about its effects on soil erosion. Microorganisms produce extracellular polymeric substances (EPS) that have shown potential in lessening the impact of environmental stressors. Specifically, a Rhizobium tropici (R. tropici) derived biopolymer has been reported to effectively strengthen the soil and mitigate soil erosion. Another study suggests that this biopolymer enhances the plant growth, proliferates leaf production and develops a compact root structure. To probe the mechanism behind EPS and its role in compacting soil and stimulating plant growth, we studied water retention and water-biopolymer, soil-biopolymer interactions.
EPS produced from Rhizobium tropici bacteria were ethanol precipitated into EPM(ethanol precipitated materials). 5%, 10%, 20% EPM biopolymers rehydrated with different kaolinite (EPK) concentrations were prepared. For each concentration of biopolymer and water mixture, four samples were made, containing clay that are 0%, 5%, 10%, and 20% by mass. The hydrated water molecules in polymer can be divided into three classes: free water, intermediate water (weakly bonded), and non-freezing water (tightly bonded). Differential Scanning Calorimetry (DSC) was carried out on EPS/EPK hydrated samples by a cooling scan from 25°C to -50°C followed by a heating scan to 25°C at 10 °C/min rate. The proportion of the freezable water (free water), non-freezable water was calculated based on the enthalpy of the melting peaks. The calculated non-freezable water in rehydrated EPS increased from 5% to 21% with higher EPS concentrations. This indicates a possible formation of a more compact structure when EPS is at high concentration. In the EPS/EPK system, the presence of a secondary melting peak at -8°C which is not observed in EPK/water mixture indicates that kaolinite in EPS induces a weakly bounded water layer. On the other hand, the percentage of non-freezable decreases as more EPK is introduced in EPS. A possible explanation of this is that the surface of kaolinite contact water diminishes the surface where water is enclosed by entangled biopolymer EPS. A model of nacre-like structure of EPS-EPK-EPS is supported by cryo-SEM images, and postulated to be the mechanism of EPS stabilizing the soil.
Next, the water retention behavior of EPS was investigated by two means. A low concentration of 1% rehydrated EPS water solution droplet ~ 5 μL was dropped on untreated silicon wafer. Subsequently, the droplet width and height versus time were measured at 3-minute intervals using the goniometer. Using water contact angle analysis, the rate of evaporation was determined for each sample at pH 5, 6, 7, 8, and 9 to simulate performance in real environmental soil conditions. Lastly, the water retention ability of biopolymer EPS was also assessed by taking one droplet~10 mg on a mass balance to record the rate of evaporation by mass over time.
Calorimetry data indicated that higher concentrations of biopolymer and percent of non-freezable water were positively correlated. Also, the addition of kaolinite changes the surface chemistry of EPS biopolymer. Droplet analysis of all three solutions revealed that the biopolymer evaporated height-wise, while water evaporated equally in height and width. Biopolymer solutions from varying pH all evaporated height-wise, with greater height change in solutions further from the original 7 pH solution. The formation of a complex from the EPS/EPK may explain its soil strengthening ability. These suggest possible applications such as maintaining crop-soil moisture and aiding soil compaction during freeze-thaw cycles. Future goals are to solidify our understanding of the interaction between EPS and nanoclay with field tests, and properties that promote soil health, paving the way to an environmentally friendly future.

Work supported by the ERDC (W912HZ-20-2-0054) and the Morin Charitable Trust.

Due to their complex network of distinct physical structures at different length scales, bones are responsible for body support, structure, motion, and several other functions for many different life forms. At the nanoscale scale, bones can be characterized as a fiber composite, i.e., a bundle of mineralized collagen fibrils surrounded by a matrix of water and calcium minerals. Different fractions of these constituents lead to different bone mechanical properties, making each bone unique, thus patient-specific.
It is well established in the literature that a higher concentration of mineral content leads to superior mechanical properties, i.e., stiffer bones. Moreover, most of the mineral content in bones, about 80%, is found in the matrix surrounding the fibrils, also labeled the extra-fibrillar volume (EFV). However, the literature presents models that include minerals in the intra-fibrillar volume (IFV) only, models that resemble mineralized collagen fibrils.
In this study, we investigate the structural and mechanical properties of all-atom bone molecular models constituted of type-I collagen, hydroxyapatite, and water through molecular dynamics (MD) simulations. Our models resemble fibers in bones, they encompass an EFV, explore different degrees of mineralization, and consider mineral content in both the EFV and the IFV, consistent with experimental observations presented in the literature. An analysis of the radial distribution function reveals that the local tetrahedral order of water is lost in similar ways in the EFV and IFV regions for all mineralized models, as calcium and phosphate ions are strongly coordinated with water molecules. By performing MD simulations using LAMMPS, we subject our models to uniaxial tensile loads and analyze their mechanical response. An analysis of the spatial stress distribution shows that the EFV plays a crucial role in the mechanical response of bone fibers. Both mineral and water content concentrate higher stresses when located in the EFV. Our results also corroborate the well-established finding that high mineral content makes bone stiffer. Our study reveals the EFV, which has been only recently contemplated in all-atom models, as an essential region to be considered when studying the mechanical properties of bones at the nanoscale. The mechanical properties of bones at such small scales can directly affect the properties at higher length scales, making bone more or less prone to fracture. Further development and studies on such elaborate all-atom models can give us additional insight into deformation and failure processes in bone, leading to a better understanding of bone diseases like osteoporosis.

In recent years, next-generation sequencing (NGS) has significantly advanced high-throughput sequencing. However, the NGS library preparation process can result in the loss of information regarding spatial organization, making reassembly difficult [1]. This study examines the application of depositing DNA onto flat polydimethylsiloxane (PDMS) samples that are then contact-printed onto PMMA-coated thin film gratings to suspend the DNA (bridging) and provide steric clearance for the Tn 5 transposase to simultaneously cut and label the DNA strands, a process termed tagmentation.

Samples of PDMS were dipped into solutions of λ DNA (NEB) in either DNase I reaction buffer (NEB) or Tris-EDTA (TE) buffer with sodium chloride to promote DNA adsorption to PDMS. Glycerol was also added to some solutions at a 1% (v/v) concentration to encourage the DNA to transfer from the PDMS to the Si grating. The samples were then imaged with a LEICA fluorescence microscope at 10x and 63x magnification. Samples with linearly stretched DNA were stamped onto a PMMA-coated Si wafer for various lengths of time up to 180 seconds using various weights up to 70 g. Results indicated that PDMS cured in a 60°C oven for 48 hours increased the adhesion of DNA onto the PDMS. However, this made it too difficult for the DNA to be stamped and transferred onto the Si wafer. PDMS that was cured for less time (4 hours) resulted in improved separation of adsorbed strands. Additionally, the NaCl made it difficult to transfer the DNA, causing the DNA to tear and not bridge. To address this problem, glycerol was added instead of salt to aid transfer. Furthermore, it was found that finer gratings were preferable because the DNA did not need to stretch as far to bridge. A solution with a concentration of 2.5 ng λ DNA per µL of DNase I reaction buffer with 1% (v/v) added glycerol deposited on PDMS and stamped across an 8.6 µm linear grating for 15 seconds and no weight yielded the best results thus far. Further development of this method will allow NGS to be analyzed with minimal risk of losing important genome information.

We acknowledge the Morin Charitable Trust for funding.

[1] Cho, NaHyun & Goodwin, Sara & Budassi, Julia & Zhu, Ke & Mccombie, W. & Sokolov, Jonathan. (2017). Fragmentation of Surface Adsorbed and Aligned DNA Molecules using Soft Lithography for Next-Generation Sequencing. Journal of Biosensors & Bioelectronics. 08. 10.4172/2155-6210.1000247.

Implantable biomedical devices require an anti-biofouling, mechanically robust, low friction surface for a prolonged lifespan and improved performance. However, there exist no methods that could provide uniform and effective coatings for medical devices with complex shapes and materials to prevent immune-related side effects and thrombosis when they encounter biological tissues. Herein, we developed a facile method to fabricate a robust lubricant-infused surface for biomedical devices which can be applied to any materials regardless of their size, shape, and composition. The application of the robust lubricant-infused surface to the materials was facilitated by a bio-inspired adhesive polymer, polydopamine (PDA) that activates the substrate surface to form stable covalent bonds with an engineered fluorinated polymer. The bio-inspired adhesive layer makes the application of the fluorinated polymer suitable for any type of surface with different material compositions and shapes. The resultant fluorinated polymer forms a very thin layer with a controllable thickness which exhibits swelling behavior in fluorinated lubricant forming lubricant-infused skin (L-skin). This allows the surface to maintain an adequate amount of lubricant even without the hierarchical structures of conventional liquid-infused surfaces. The smooth surface of L-skin provides superior anti-biofouling properties against viscoelastic fluids (blood, saliva, bacterial suspension) and solids (feces, biological tissues) which make L-skin suitable for biomedical applications. Unlike conventional self-assembled monolayer (SAM) based lubricant-infused surfaces, L-skin is both mechanically and chemically robust that maintains its functionality following swabbing, scratching, and sterilizations. To further investigate the wide adaptability of the L-skin, various applications in which complex structure requires anti-biofouling properties were demonstrated in small diameter bioprinting needle (Inner diameter = 53 μm), microfluidic channels (Channel height 150 μm), and long narrow silicone tubing (2 meters long).

Biomineralization is a mineral precipitation process occurring in the presence of organic molecules and used by various organisms to serve a structural and/or a functional role. Many biomineralization processes occur in the presence of extracellular matrices that are composed of proteins and polysaccharides.
There is growing evidence that bacterial biofilms induce calcium carbonate mineralization, giving the system enhanced mechanical properties and that this process may be related with their extracellular matrix (ECM). In addition, recently, it has been suggested that bacteria and biofilms may play a role in calcium oxalate kidney stones genesis and development. Therefore, we explored, in vitro, the effect of the ECM components, the exopolysaccharide EPS, and the protein TasA on calcium carbonate and calcium oxalate crystallization. Moreover, the protein TapA was also tested on calcium carbonate.
By characterizing the crystals using SEM, micro-Raman spectroscopy, FTIR, XRD, FIB-SEM and SAED we showed that: In both the calcium carbonate and calcium oxalate, the biopolymers had an effect on the morphology of the crystals by the interaction of the polymers with specific planes. In the presence of the proteins the calcium carbonate crystals were composed of single crystalline domains that assemble together into spherulites (in the presence of TapA) or dumbbell-like shapes (in the presence of TasA). The TasA produced rounded microstructure crystals of calcium oxalate. The EPS, in addition, affected the structure of the crystals, producing less thermodynamically stable crystals, vaterite and calcium oxalate dihydrate.
Our results suggest the EPS affects the nucleation of calcium minerals unlike the proteins that seem to affect only the crystal growth. Biomineralization processes induced by bacterial ECM macromolecules make biofilms more robust and difficult to remove when they form, for example, on pipes and filters in water desalination systems or on ship hulls. Understanding the formation conditions and mechanism of formation of calcium carbonate and calcium oxalate in the presence of bacterial biopolymers may lead to the design of suitable mineralization inhibitors as well as better approaches for kidney stones treatments.

The application of small self-organized molecular systems for the formation of soft and in situ electrodes with combined electrical and biochemical signals leads to new means of bridging the biology-technology gap. Such systems have seen increased attention over the past few years with their promise of entirely novel pathways for monitoring and augmenting biological function. In parallel, organic electrochemical transistors (OECTs) have become a standard tool in the field of organic bioelectronics as they can take full advantage of ion (biomolecule) injection from an electrolyte (or physiological system) to modulate the volumetric conductivity of an organic semiconductor channel. In addition, overall biocompatibility and synthetic tunability of the organic conductive polymers make OECTs ideal for interfacing with biological systems. In this work we have combined the burgeoning field of in situ formed organic electronic materials into an OECT platform by using light-assisted photocatalysis. Specifically, we used direct light excitation, as well as excitation of porphyrins, for the in situ photoinduced polymerization of conjugated oligomers. The conjugated oligomers, bis[3,4ethylenedioxythiophene]3thiophene sulfonic acid (ETE-S, i.e., an EDOT-thiophene-EDOT trimer with a sulfonate ligand) and a variety of derivatives (ETE-CooNa and EEE-CooNa) were implemented, and the photoinduced polymer films were assessed by cyclic voltammetry as well as transistor output and transfer characteristics. The resulting OECTs exhibited excellent figures of merit (Transconductance, on/off ratio) with performance approaching PEDOT:PSS but with several advantages. We believe that these results pave the way for expanded in situ bioelectronics and even OECTs and similar component fully formed/fabricated in vivo.

DNA sequencing technology has been evolving throughout the past century, however, in the past 10 years, new approaches to sequencing technology, namely Next Generation Sequencing (NGS), have been emerging to make this process more streamlined. With current technology, sequencing reads are limited to the order of 10,000 base pairs or less. Therefore, cutting the DNA into sequenceable portions is vital [2]. After cutting, the spatial ordering of the DNA fragments is usually lost, requiring a complex computational method for reassembly. One novel solution to this problem is using soft lithography and hydrophobic surfaces instead of solution-based cutting [1]. This allows for preservation of DNA order.
In our experiment, Transposase (Tn5), an enzyme that cuts and moves DNA strands, was tested at its ability to fragment surface-immobilized DNA on a PMMA surface. Tn5 solution was made by mixing transposase solution, Tagmantase buffer, and water of varying concentrations. Silicon wafers were cut into 6 mm wide and 15 mm long samples to be spun cast with 70 nm thick films of PMMA. The wafers were dipped into DNA solution and later in Tn5 solution for the DNA-cutting reaction. Using a Leica Fluorescent microscope, images of the SyBr Gold labeled DNA strands were taken and then used for data analysis. To test the efficacy of using SDS and Proteinase K as a Tn5 removal agent, this experimental procedure was repeated with different concentrations of Tn5 solutions (0.0008 mg Tn5/mL, 0.0016 mg Tn5/mL, and 0.0032 mg Tn5/mL) for both SDS and Proteinase K reactions. Additionally, Proteinase K reactions were repeated at both room temperature as well as 55 degrees C.
The results indicate that after Proteinase K removed Tn5, DNA strands were cut into linear segments with ordering preserved; while with SDS, the DNA strands were curled up and in disorder. The trials with Proteinase K were analyzed using ImageJ. It was found that DNA strands were fragmented after the Tn5 reaction. At 0.0016 mg Tn5/mL, room temperature and heated, the strand length averaged 1.87 µm and 0.91 µm respectively after the Tn5 reaction. Before the Tn5 reaction, the strand lengths averaged 16.20 µm and 16.29 µm respectively. At 0.0032 mg Tn5/mL, room temperature and heated, the strand length averaged 0.71 µm and 1.05 µm respectively after the Tn5 reaction. Before the Tn5 reaction, the strand lengths averaged 17.91 µm and 12.28 µm respectively. This indicates that Tn5 can effectively fragment DNA on surfaces when the transposase is pre-loaded onto the DNA in solution before surface adsorption.

We would like to acknowledge the Morin Charitable Trust for funding.

[1] Cho, N. H., Goodwin, S., Budassi, J., Zhu, K., McCombie, W. R., & Sokolov, J. (2017). Fragmentation of surface adsorbed and aligned DNA molecules using soft lithography for next-generation sequencing. Journal of Biosensors & Bioelectronics, 08(04). https://doi.org/10.4172/2155-6210.1000247
[2] Goodwin, S., McPherson, J. D., & McCombie, W. R. (2016). Coming of age: Ten Years of next-generation Sequencing Technologies. Nature Reviews Genetics, 17(6), 333–351. https://doi.org/10.1038/nrg.2016.49

Polyphenols are a class of biologically active compounds that are derived from plant-based natural products such as fruits, vegetables, coffee, and tea. Polydopamine, dopamelanin, gallic acid, pyrogallol, and tannic acid contain the representative chemical features of polyphenols which can form coordination bonding with protons, ions, or electrons via redox reaction. Due to their physical, chemical, and electrochemical properties, polyphenols have attracted significant interest in various research areas, including charge storage, heavy metal ions removal, or drug delivery. Recent studies have shown that phenol-based polymeric particles can inhibit bacterial growth and prevent biofilm formation by releasing the reactive oxygen species in aqueous environment. However, the surface disruption of polymers in complex surroundings and the poor efficiency due to the low surface area to volume ratio of the coating remain the potential challenges that shorten the long-term stability.
Herein we report the facile synthesis of a free-standing poly(pyrogallol) (1,2,3-trihydroxybenzene, PPG) polymer that can be used as an environmental friendly and efficient antibacterial agent. PPG consists of homogeneous nanofibrous microstructure containing the chemical moieties that allow the reversible redox reaction via catechol or gallol groups. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy corroborated the formation of the ether functional groups that are induced by the polymerization between the hydroxyl group and the carbons of the benzene. The antibacterial activity of PPG was examined using the gram-negative Escherichia coli. The antibacterial activity was quantitatively evaluated by a colony count method after incubating the E. coli with the concentration of 1.5 X 10⁵ CFU mL^-1. The survival rates were compared with the natural melanins extracted from Sepia Officinalis that contains the catechol groups. PPG achieved 63.1% and 99.9% E. coli inhibition within 30 min and 4 h of incubation, which is approximately 50% higher than the catechol-containing melanins. This is mainly due to the higher density of phenolic compounds available in PPG to produce ROS in the aqueous environment. The results herein suggest that PPG exhibits potential to be utilized as functional antibacterial agents for a variety of applications in biomedical and environmental engineering.

The use of Tn5 transposases is essential to Next Generation Sequencing (NGS) as it is required to cut DNA into shorter and more manageable lengths while also labeling the shortened strands to be later rearranged into the original sequence[1]. However, Tn5 transposases have to wrap around DNA in order to cut, posing an issue for surface-adsorbed DNA samples[2]. In recent transposon experiments, evidence suggests that sodium dodecyl sulfate (SDS), which is already used to remove the Tn5 transposases from DNA molecules after cutting is complete, could desorb the DNA from a flat surface, specifically polymethyl methacrylate (PMMA) spun-cast on silicon. Finding a method of desorbing DNA from a flat surface remains important because it provides an opportunity to increase the efficiency and decrease the cost of NGS in fields such as medical diagnoses and forensic science. Although there are already existing methods of desorbing DNA, they are cumbersome and time-consuming. In this study, we aimed to investigate whether or not SDS could desorb surface-adsorbed DNA. To do this, 0.286% DNA in DNAse buffer dyed with SYBR Gold was prepared and machine-dipped onto PMMA spun-cast onto silicon. After doing so, the DNA sample was imaged under a fluorescence microscope under 63x magnification to determine the quality of the sample. Once the quality was confirmed, the sample was placed into a well containing 350 μL of varying concentrations of SDS in water. This way, half of the wafer would have been treated with SDS while the other side would serve as a control. The wafer, still in the well, was then placed into a column heater and heated at 55°C for 20 minutes. Once finished, the wafer was once again placed under the microscope for analysis. Initially, it was thought that the SDS did in fact desorb the DNA from the surface as no DNA could be seen on the SDS-treated side. Microscope images showed a distinct border between the SDS-treated side, where no DNA was visible, and the non-SDS side, where DNA was clearly visible. However, after re-dyeing the SDS-treated side in SYBR Gold, DNA was once again shown on the surface. This implied that SDS could not desorb surface-adsorbed DNA but could remove SYBR Gold dye from DNA. Although SDS likely cannot desorb surface-adsorbed DNA, future experiments will be done on Triton X-100 instead in an effort to find an easier method of desorbing DNA from flat surfaces.

[1] Feng, Kuan. "Comprehensive Sequencing with Surface Tagmentation Based Technology." (2018). https://digitalrepository.unm.edu/ biom_etds/188
[2] Cho N, Goodwin S, Budassi J, Zhu K, McCombie WR, et al. (2017) Fragmentation of Surface Adsorbed and Aligned DNA Molecules using Soft Lithography for Next-Generation Sequencing. J Biosens Bioelectron 8: 247. doi: 10.4172/2155-6210.1000247

We thank the Morin Charitable Trust for funding.

Soil erosion is a significant issue costing the U.S. economy forty-four billion dollars per year and increasing water pollution (Sulaeman & Westhoff, 2020). Typical erosion treatments use toxic, non-biodegradable petrochemicals that pose threats to surrounding ecosystems and agricultural efforts. An alternative may come from symbiotic Rhizobium tropici bacteria which secrete gel-like biopolymers known as EPS that can then be ethanol precipitated into EPM (non-dialyzed EPS) (Maróti & Kondorosi, 2014). EPS soil treatments have been tested by the ERDC and results indicate that the soil was strengthened substantially, reducing erosion. REF Analysis of the vegetation showed that plant root systems were larger, which was postulated to be a contributing factor to the soil stability increase. The role of bacterial infection and nitrogen sequestration in root development has been extensively studied, but less is known about the role of bacterial EPS in strengthening the soil via gelation or other interactions with the soil particles. In order to study the possible mechanisms through which the EPS can strengthen soil, we performed a series of experiments where the biopolymer was precipitated in alcohol and subsequently rehydrated. In this manner no bacteria was present and only the material properties of the EPS are probed.
The rehydrated EPM’s rheology behavior with various concentrations was tested on DHR-2 rheometer oscillation-amplitude and oscillation-frequency mode. The results show that upon rehydration the polymer formed a gel at concentrations of 2% with a modulus G’=20Pa. The modulus increases approx. linearly with concentration to a value of G’=300Pa at a concentration of 20%. In each case a distinct yield point was observed, at 20-170Pa between the lowest and highest concentrations measured, where G’ approached zero. The systems were rested for 30 min without an applied force and the amplitude scan was repeated. The gels completely recovered in each case after at least three cycles, indicating that in each case physical gels were formed and then reformed when the forces were removed. Measurement of the gels in the frequency mode indicated shear thinning behavior in all cases at room temperature. The chemical structure of the gels was investigated using Raman spectroscopy and TGA. RAMAN spectroscopy indicated that the EPM was composed of polysaccharides with a high content of potassium dihydrogen phosphate. TGA showed that ~50% of the gel was removed at T<100C, and another 10% was removed at T<257C. This is consistent of a gel with large water content, while the additional 20% indicated strongly adsorbed water and a high degree of water retention. A surprisingly high fraction, ~30% of the gel was stable to temperatures of at least 800C. This temperature is higher than organic polymers, and was attributed to the dihydrogen phosphate salts. RAMAN spectroscopy of this residue confirmed this where one large and narrow peak was observed consistent with a crystalline compound formation. Auxiliary testing for the antibacterial, antiviral, and cytotoxic effects of the EPM were performed to determine the safety of EPM application into soil. Results indicated that EPM is neither antiviral nor antibacterial. Application of EPM into human fibroblast cultures indicated no adverse effects on the doubling time nor any other function of the tissue.
Work supported by the ERDC (W912HZ-20-2-0054) and the Morin Charitable Trust.
E. M. G. K. (2014, June). Nitrogen-fixing rhizobium-legume symbiosis: Are polyploidy and host peptide-governed symbiont differentiation general principles of endosymbiosis? Frontiers in Microbiology.
Larson, S., Nijak Jr, G., Corcoran, M., Lord, E., & Nestler, C. (2016, June). Evaluation of Rhizobium tropici-derived Biopolymer for Erosion Control of Protective Berms. US ERDC.
Sulaeman, D., & Westhoff, T. (2020, Feb.). The causes and effects of soil erosion, and how to prevent it. World Resources Institute.

The mutable collagenous tissue (MCT) of echinoderms has been extensively studied because of its mechanism that allows rapid change in its stiffness and extensibility. Collagen is also the most abundant protein in the extracellular matrix and provides its main structural component. Thus, research on its physicochemical and mechanical properties will be useful for identifying its potential for cosmeceutical and biomedical applications. Moreover, the unique properties of MCTs can also be an inspiration for the design of new smart functional biomaterials. Sea cucumbers, like other echinoderms, also have MCTs that respond according to different environmental stress conditions. There are many sea cucumber species found in the Philippines, but only a few are studied well. Among the less studied ones is the Stichopus cf. horrens, which is also commonly found in other Southeast Asian countries. In this study, we have extracted the collagen from S. horrens and characterized its physicochemical properties. Pepsin-solubilized collagen (PSC) was prepared, and using SDS-PAGE we observed the presence of the ß, α1, α2, and α(1)3 chains at 75 to 250 kDa, typical for Type I collagen. Protein identification and sequence analysis were also performed. Protein blast search showed the presence of sequences commonly found in Type VII and XII collagen. This suggests that S. horrens collagen is heterotypic, consistent with related proteomic studies of collagen from other species. The maximum absorbance of PSC was also measured at 212 nm using UV-Visible spectrometry, attributed to the presence of multiple peptide chains of collagen. The susceptibility of collagen to heat is another way of determining its potential application. We identified a higher maximum transition temperature (T_m = 56 °C) for the PSC extracted from S. horrens using differential scanning calorimetry (DSC) as compared to other sea cucumber species. The T_m of collagen correlates to its stability and durability, suggesting that S. horrens PSC has higher thermal stability—uncharacteristic of marine-derived collagen. After the physicochemical characterization, the extracted collagen was used for the facile preparation of collagen-based films through the solvent casting method using phosphate-buffered saline at pH 7.4 as the solvent. The FTIR spectra of the films showed the characteristic peaks of collagen—Amide A (3341 cm^-1), I (1657 cm^-1), II (1553 cm^-1), and III (1241 cm^-1). AFM imaging also showed that the collagen fibers making up the films have a diameter of 145 ± 31 nm. Due to the high thermal stability of S. horrens PSC based on the DSC findings, the thermal response of the films was also analyzed using thermomechanical analysis (TMA) at a constant applied force of 0.1 N. Here, we observed that thermal degradation only starts at a temperature of >190 °C. Meanwhile, at lower temperatures of 100 and 150 °C, the films changed from translucent and soft into an opaque and brittle physical state due to the removal of moisture. Subsequent AFM images showed that the collagen fibers are still present and intact after TMA. Upon exposure to ambient temperature (25 °C) for 10 min, the collagen-based films returned to their original translucent and soft state due to the reabsorption of moisture. TMA analysis at lower temperatures was repeated at least three times before the films started degrading based on apparent discoloration. This study shows that Stichopus cf. horrens is a potential source of collagen that can be prepared into useful smart biomaterials, such as collagen-based films stable at higher temperatures, for food and biomedical applications.

Polymer contact electrification (a.k.a. triboelectrification) is crucial for mechanical energy harvesting in triboelectric nanogenerators (TENG), droplet generators, and ferroelectrets [1]. Polymer triboelectrification can be enhanced in several ways, including surface functionalization, adjustment of the electronic and physicochemical properties or by increasing the specific contact area via nanostructuring.
Contact electrification can be observed also in nature. Spider ballooning is one of the most exciting natural phenomena. Using electrified strands of silk, spiders can travel in the airstream for distances of hundreds of kilometers [2]. Spider silk is electrified due to contact and friction with airborne particles or during the spinning process. A strong surface charge is required to ensure the electrostatic flight, holding the weight of a spider even in the absence of any air stream.
This work presents triboelectric polymer composites with structure inspired by the macromolecule ordering in spider-silk leading to strongly enhanced contact electrification. The ordering in polyether block amide (PEBA) is induced by the addition of inorganic goethite (α-FeOOH) nanowires that form hydrogen bonds with the elastomeric matrix. The addition of as little as 0.1 vol% of α-FeOOH into PEBA increases the surface charge by more than order of magnitude. Hydrogen bonds between α-FeOOH and PEBA promote the formation of inclusions with higher degree of macromolecular ordering, analogous to the structure of spider silk. The formation of these inclusions is proven via nanoindentation hardness measurements, and correlated with H-bond induced changes in structure shown by fourier transform infra-red spectroscopy, and direct scanning calorimetry. Theoretical studies reveal that the irregularity in hardness provides stress accumulation on the polymer surface during contact-separation. Subsequent molecular dynamic studies demonstrate that stress accumulation promotes the mass-transfer during contact electrification. The proposed macromolecular structure design provides a new paradigm for developing materials for applications in mechanical energy harvesting.

References
[1] B. -Y. Lee, D. H. Kim, J. Park, K. -I. Park, K. J. Lee, C. K. Jeong, Sci. Technol. Adv. Mater. 2019, 20, 758.
[2] E. L. Morley, P. W. Gorham, Phys. Rev. E 2020, 102, 012403.

Fibrinogen is a plasma-soluble glycoprotein that is responsible for thrombogenesis, the formation of blood clots. While thrombogenesis is an important process, excessive blood coagulation can cause serious health conditions such as strokes, heart attacks, and embolisms. Viruses such as SARS-CoV-2 and H1N1 can cause thrombosis in host vascular systems, despite endothelial cells lacking the necessary receptors for SARS-CoV-2. Epithelial cells surrounding blood vessels are susceptible to viral infection, and once infected, produce lipids in and around cells. When blood vessels are damaged, infected cells and conditioned media enter the bloodstream, and provide ample hydrophobic surfaces for fibrinogen to polymerize onto and for thrombosis to occur. Here a model is proposed to explain the correlation between virus-induced lipid secretion and fibrinogen fiber formation.
To study the formation of fibrinogen fibers on hydrophobic surfaces, solutions of polybutadiene, polystyrene, and polylactic acid were spuncast onto silicon wafers for their thrombogenic and biocompatible nature. Fibrinogen was added to the films, imaged through AFM, and analyzed for morphological properties. To test lipid production, Madin-Darby canine kidney (MDCK-2) cells and human umbilical vein endothelial cells (HUVEC) were plated and infected with the H1N1 virus. Human gingival keratinocytes as models of epithelial cells were also infected with H1N1 through direct infection and conditioned media taken from previous MDCK-2 cultures. After fixing, cultures were stained for actin, lipids, and DNA, and imaged using EVOS microscopy. The images showed multiple lipid droplets concentrated within the MDCK-2 and the gingival keratinocyte cells following infection. Conditioned media and infection in MDCK-2 and HUVEC cultures yielded increases in lipid droplets of 35.13% and 15.02%, respectively. On the HUVEC cultures no brightly stained droplets were visible following direct infection. Only large diffuse regions of green stain were visible following exposure to the conditioned media. Some of these large domains were also found in the epithelial cell cultures following infection, and were likely formed when the lipid droplets were released into the media following the disintegration of infected cells. These diffuse lipid rich regions were then carried from the conditioned media onto the surface of the endothelial tissue after exposure to the conditioned media, demonstrating that the hydrophobic secretions of an infected culture spreads to nearby tissue at the systemic scale.
Polyvinylpyrrolidone (PVP), a hydrophilic surface, will be treated with conditioned media taken from control and H1N1-infected MDCK-2 cultures. According to the model, the non-infected sample should remain relatively hydrophilic, while the infected sample should become more hydrophobic, as measured through contact angle analysis. It is hypothesized that fibrinogen fibers will form on the infected hydrophobic polymer surface and not form on non-infected hydrophilic surfaces. This project reveals that fibrinogen fibers after viral infection are due to the lipid showers in epithelial tissue that make the environment suitable for blood coagulation, which provides insights into the treatment of COVID.

Acknowledgements:
The authors gratefully acknowledge and thank the Morin Charitable Trust for support, as well as Dr. Miriam Rafailovich for mentorship and technical guidance.

Over twenty million people in the United States have so far benefitted from implantable medical devices (IMDs) intended for different purposes; therapeutic, diagnostic and rehabilitation. Efforts to improve IMDs have seen the development and use of transient materials, which dissolve in the body after a programmed lifetime, therefore, eliminating the need for secondary surgery to remove the IMD. However, the conventional lithium-ion batteries are non-transient, therefore limiting the use of transient IMDs. Recent advances in energy harvesting technologies have provided transient materials based options with great potential to power transient IMDs. Photovoltaic and thermoelectric in vivo energy harvesters were introduced as sources of power for transient electronics, but their use is limited by lack of light sources, and constant body temperature, respectively. On the other hand, the biodegradability of piezoelectric catalysts is unverified limiting the use piezoelectric nanogenerators in transient electronics. Triboelectric nanogenerators (TENGs) are an emerging technology with great potential for powering transient IMDs, offering a number of advantages including wide material selection and minimizable system scale. Conventional transient TENGs exploit passive operation, referring the circumstances in which their transience starts when implanted and deployed inside the body. Due to the long timescale from the loss of energy generation to the complete transience, undesirable burdens and potential hazards can be induced to the patients.
Here, we demonstrate a new protocol by establishing a remotely stimulated transience mechanism using biologically certified ultrasound sources. To demonstrate the feasibility of ultrasound-triggered TENGs, we developed a fully biodegradable and implantable TENG (FBI-TENG) consisting of a magnesium (Mg) electrode layer, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) membranes, and a poly(ethylene glycol)-based polymeric composite (PHBV/PEG) layer. We aimed to determine the efficiency of the FBI-TENG by solely altering the degree of ultrasound intensity. The ultrasound-triggered transient process which originated from high ultrasound intensity, was initiated by the microporous structure of the PHBV encapsulation layer developed using finite element method (FEM) simulation that facilitates the distribution of intensified acoustic pressure inside the micropores. When the FBI-TENG was inserted into a porcine tissue, we observed a significant reduction in electrical output 20 minutes after applying high ultrasound intensity. Our findings support that ultrasound, a verified non-invasive and reliable power source, can be used for powering IMDs and for provoking device dissolution after a programmed lifetime.

De novo-designed peptides emerged to form nano-fibrils in solution and exhibited chemical reactions with activities comparable to natural enzymes.¹ These materials are often referred to as catalytic amyloids.² Their versatility in productive accommodation of various cofactors,³ highly designable sequences, and simple molecular structures that can be produced in large amounts at low cost offers an exciting possibility for creating highly efficient hybrid materials for different electrochemical applications. Although all the currently reported applications of these catalytic peptide amyloids were demonstrated in solution, there are no attempts to incorporate these into complex assembled structures on solid surfaces for electrochemical applications.
We hypothesized that assembling catalytic peptides on a graphitic surface would fully harness the catalytic potential of peptide assemblies in an electrochemical manner and create a highly functional interface capable of efficiently catalyzing practical chemical reactions. There have been multiple reports demonstrating peptide self-assembly on graphite surfaces.^4,5 These catalytic amyloids may have the ability to form self-assembled structures on the surface. In a proof-of-concept study, we focused on peroxidation reactions due to their potential applications in various processes ranging from cancer therapy, and wastewater purification, to polymer production. Especially, the enhanced capability of accelerating the reduction of H₂O₂ is essential for constructing the electrocatalysts of various peroxidation applications due to its role as an electron acceptor in most peroxidase reactions. Furthermore, peroxidase activity in natural enzymatic and model systems has been extensively studied, providing important activity and stability benchmarks.
To test our hypothesis, we employed several peptides found to self-assemble in the presence of hemin into catalytic amyloids with high peroxidation activities in solution. Among them, we selected highly active (LMLHLFL, LILHLFL) and moderately active (LHLHLFL, VHVHVYV) peptides in this work.⁶ First, we investigated their ability to form highly ordered nanostructures on graphite surfaces. Atomic force microscope images revealed that all peptides could form monomolecular-thick peptide self-assembled thin film on graphite surfaces. Hemin molecules were successfully immobilized on the peptide thin film on the graphite surfaces. The immobilized hemins on peptides exhibited their catalytic activities under electrochemical measurements over H₂O₂.
Additionally, we introduced 3,3’,5,5’-tetramethylbenzidine (TMB) to demonstrate the model of peroxidase reactions for multiple substrates and analyze the efficiency during the electron transfer process. In both catalytic reactions, the highly ordered nanostructures of peptides with hemins promoted peroxidation with kinetic parameters approaching the natural enzymes in the same reaction at a fraction of the cost. The robust structure, ease of production, and high peroxidation activities of our hybrid system make them notable interfaces for electrocatalysis.

References
1. C. M. Rufo, Y. S. Moroz, O. V Moroz, J. Stohr, T. A. Smith, X. Hu, W. F. DeGrado and I. V Korendovych, Nat Chem, 2014, 6, 303–309.
2. O. V Makhlynets, P. M. Gosavi and I. V Korendovych, Angew Chem Int Ed Engl, 2016, 55, 9017–9020.
3. O. Zozulia and I. V Korendovych, Angew Chem Int Ed Engl, 2020, 59, 8108–8112.
4. Y. Hayamizu, C. R. So, S. Dag, T. R. Page, D. Starkebaum and M. Sarikaya, Sci. Rep., 2016, 6, 33778.
5. P. Li, K. Sakuma, S. Tsuchiya, L. Sun and Y. Hayamizu, ACS Appl. Mater. Interfaces, 2019, 11, 20670 – 20677.
6. W. Luo, H. Noguchi, C. Chen, Y. Nakamura, C. Homma, O. Zozulia, I. Korendovych, and Y. Hayamizu, Nanoscale, 2022,14, 8326-8331.

Squids have developed predatory teethed structures in their suction cups that are composed of structural proteins. Unlike other hard tissue in cephalopods, these biological materials are stabilized by β-sheet nanocrystalline structures that give rise to high-strength materials without mineralization. Here, we introduce cephalopod-inspired polypeptides with a repetitive diblock design (alanine-rich and glycine-rich blocks) that self-assemble into β-sheet nanocrystalline structures. These β-sheet nanocrystals act as physical and reversible hydrogen-bonded crosslinks in supramolecular protein networks, where β-sheet size and network topology regulate the physical properties. We demonstrate the dynamic properties of squid-inspired polypeptides in self-healing networks with healing strength and kinetics (~25 MPa strength after 1 second of healing) surpassing those typically found in other natural and synthetic soft polymers. This family of proteins and their biosynthetic derivatives open new opportunities in bioinspired design for adaptive functional materials, and we demonstrate their potential in actuator prototypes for applications in soft robotics and wearable technology.

Surfaces contaminated with infectious bacteria and viruses contribute to transmission and pose a significant threat to global public health. Common liquid spray disinfectants kill microbes in seconds to minutes, yet they require reapplication often. Surfaces that rely on heavy metals or metallic nanoparticles for antimicrobial efficacy remain antimicrobial over a long period of time but take hours to kill pathogens leaving time for disease transmission. There is currently no surface that can provide instant and persistent antimicrobial efficacy against a broad spectrum of bacteria and viruses. Inspired by the naturally antimicrobial secondary metabolites secreted by plants, we created a new class of highly durable polyurethane surfaces capable of rapid disinfection (>4-log reduction in minutes) of various pathogens, including Escherichia coli, Pseudomonas aeruginosa, methicillin-resistant Staphylococcus aureus, and SARS-CoV-2. These surfaces maintain this efficacy over several months and under significant environmental duress due to the chemical stabilization of the natural antimicrobial components within the polyurethane. Additionally, we show that the surfaces can be applied to surfaces using various commercial techniques such as spray-, flow-, or brush-coating allowing for a wide range of potential applications.

As the global population rises alongside a worsening climate outlook, alternative proteins such as plant and cell-based meat provide exciting avenues for meeting the increasing demand for meat sourced from animals and have implications for planetary and human health. While food science is a well-established field with a rich history, inclusion of methods and research paradigms from the materials community can accelerate the development of promising food technologies. In this work, we review the complex and interesting structure and functionality of cephalopods, the landscape of existing materials advances towards replicating these creatures, and extensions towards food and edible materials. In doing so, we bridge the rich culinary traditions around cuttlefish, octopus, and squid¹ with advancements in tissue engineering and bio-inspired design.

Few creatures generate as much wonder and curiosity as cephalopods. Renowned for their protective and communicative capabilities (camouflage, texture and shape change), they also demonstrate fascinating behavioral and cognitive abilities².Researchers have looked to cephalopods for inspiration in designing systems as varied as displays³, programmable coloration⁴, self-healing coatings⁵, mechanochromic windows⁶, and bioelectronics⁷. Here, we look to their unique structure and properties to inspire a new domain of compelling alternative food materials.

References:
1. Mouritsen, Ole G., and Klavs Styrbæk. "Cephalopod gastronomy—a promise for the future." Frontiers in Communication 3 (2018): 38.
2. Schnell, Alexandra K., and Nicola S. Clayton. "Cephalopod cognition." Current Biology 29.15 (2019): R726-R732.
3. Wilson, Daniel J., and Leila F. Deravi. "Artificial cephalopod organs for bio-inspired display: progress in emulating nature." Matter 4.8 (2021): 2639-2642.
4. Wang, Yu, et al. "Generation of Complex Tunable Multispectral Signatures with Reconfigurable Protein-Based, Plasmonic-Photonic Crystal Hybrid Nanostructures." Small (2022): 2201036.
5. Manabe, Kengo, Emiko Koyama, and Yasuo Norikane. "Cephalopods-Inspired Rapid Self-Healing Nanoclay Composite Coatings with Oxygen Barrier and Super-Bubble-Phobic Properties." ACS Applied Materials & Interfaces 13.30 (2021): 36341-36349.
6. Ke, Yujie, et al. "Cephalopod-inspired versatile design based on plasmonic VO2 nanoparticle for energy-efficient mechano-thermochromic windows." Nano Energy 73 (2020): 104785.
7. Kautz, R.; Gorodetsky, A. A. Revisiting A Classic Inspiration Source: Cephalopod-Derived Materials for Bioelectronics In Roadmap on Semiconductor-Cell Biointerfaces. Phys. Biol. 2018, 15, 031002.

Functionally graded materials (FGMs) are novel composite materials with gradual variations in their structures and chemical compositions throughout their bodies, so that FGMs possess locally tailored properties. Since FGMs consist of continuous structures without borders of physical property changes, conflicting physical properties within a material can be maintain not to break in their bodies. In contrast to isotropic bulk materials, the structures and chemical compositions of FGMs can be accurately designed to create tailored multifunctional properties. Noted to the natural world, there are many kinds of FGMs such as bones, teeth, bamboos, shells, and crustacean shells. They continuously change their microstructures and chemical compositions, with corresponding smooth changes in mechanical properties such as hardness, stiffness, and toughness. These natural materials mentioned above are composed of elements lighter than iron, such as carbon, silicon, and calcium. They are both lightweight and strong with limited resources by placing these elements in the necessary quantities and in the necessary places. In recent years, much research has been conducted to mimic these natural materials to reduce the weight and increase the strength of materials. In this study, we focused on the grass species, Job’s tears (Coix lacryma-jobi). The seeds of Job’s tears are covered with the involucre, a thin, lightweight, hard shell containing a high amount of silica. This shell is only about 740 μm thick, but is strong enough to withstand a load of about 280 N. We analyzed the spatial distribution of porosity, chemical composition, and hardness of these shells to investigate the factors that contribute to their lightweight and high-strength. Then, FGMs mimicking the shells of Job’s tears were fabricated based on the analysis results. We used scanning electron microscopy (SEM) to observe the cross-sectional microstructures of the shell of Job’s tears and energy dispersive X-ray spectroscopy (EDX) to analyze their chemical compositions. The inner layer of the shell was composed of tubular plant cells with a diameter of approximately 2 μm. The plant cells became smaller and more isotropic toward the outer layer and were densely distributed. The outermost layer of the shell was deposited with fine particles less than 100 nm in diameter. Therefore, the porosity of the shell decreased toward the outer layer. EDX analysis showed that the shells contained more silica toward the outer layers.
We measured the change in hardness from outer to inner layer in the cross-section of the shell by Vickers hardness test and nanoindentation test. The Vickers hardness test revealed that the outer layer of the shell was about four times harder than the inner layer, and the nanoindentation test showed a gradual decrease in elastic modulus from the outer to the inner layer of the shell. In addition, we analyzed the stiffness characteristics of the shells by performing three-point bending tests in different loading directions. The shells withstood three times more strain and twice as much load when bent from the outer layer of the shell compared to when bent from the inner layer.
These results indicate that the outer layer of the shell is harder and the inner layer softer due to spatial gradients in both shell porosity and chemical composition. This material property would allow the shell to withstand loads from outside the shell.
Based on our analyses, we fabricated FGMs mimicking the shells of Job’s tears. We printed porous materials with a spatial gradient of porosity using fused deposition modeling 3D printer and polyurethane filaments whose extent of foaming and hardness changes with heating temperature. By impregnating the porous materials with glass or silicone resin, we expressed the spatial gradient in chemical compositions and hardness. This study may provide design guidelines for lightweight, high-strength organic/inorganic hybrid FGMs.

The remarkable underwater adhesion of mussel foot proteins has long been an inspiration in the design of peptidomimetic materials. Although the synergistic wet adhesion of catechol and lysine has been recently highlighted, the critical role of the polymeric backbone has remained largely underexplored. Here, we present a peptidomimetic approach using poly(ethylene glycol) (PEG) as a platform to evaluate the synergistic compositional relation between the key amino acid residues (i.e., DOPA and lysine), as well as the role of the polyether backbone in interfacial adhesive interactions. A series of PEG-based peptides (PEGtides) were synthesized using functional epoxide monomers corresponding to catechol and lysine via anionic ringopening polymerization. Using a surface force apparatus, highly synergistic surface interactions among these PEGtides with respect to the relative compositional ratio were revealed. Furthermore, the critical role of the catechol−amine synergy and diverse hydrogen bonding within the PEGtides in the superior adhesive interactions was verified by molecular dynamics simulations. Our study sheds light on the design of peptidomimetic polymers with reduced complexity within the framework of a polyether backbone.

Current methods of surgical joinery look as though they were devised in a medieval torture chamber. Sutures concentrate mechanical stresses, punch holes into healthy tissue, and create sites for infection. Patient outcomes will improve when we can devise alternate means of connecting tissues. Adhesives are appealing here. However, we do not yet have any materials that are simultaneously able to set in a wet environment, create strong bonds between tissues, and exhibit no toxicity. Further properties that are desirable include cure times compatible with surgeries, an ability to degrade, and having moduli (i.e., flexibility or stiffness) matched to the surrounding substrates. Our research team has developed sea-mussel inspired synthetic adhesives by taking cues from the way they attach themselves strongly onto surfaces in the ocean and synthesizing glues that mimic their chemistry. We have recently shifted our focus from synthetic to natural materials and developed inexpensive, bio-derived and non-toxic bioadhesives from corn protein (Zein )and Tannic acid (TA). Zein being a by-product of ethanol production from corn has been used as a wood adhesive. Tannic acid is a plant-based polyphenol and also one of the cheapest sources to impart sea-mussel inspired chemistry to any adhesive. We studied the in vitro burst pressures of these bioadhesives on several tissue substrates including sausage casings, porcine skin, heart, liver, lungs, aorta, dura and stomach. Our studies found these natural bioadhesives really promising with the ability to withstand pressures greater than the normal physiological pressures experienced in most of these organs. Moreover, we successfully conducted ex vivo studies on multiple tissue substrates to demonstrate the ability of our bioadhesives to plug body fluid leakages. We envision the potential application of our bioadhesives to seal surgical incisions and wounds under wet condictions.

Aerogels, featuring low density (< 0.5 g/cm³), high porosity (>90%), and high specific surface area (SSA) (> 100 m²/g), show vital roles in various areas such as super thermal insulation, separation, catalyst, etc. Cellulose stands out ascribing to the abundant and fossil-free resources and the favorable mechanical properties. The mainstream fabrications of cellulose aerogels are from a bottom-up approach, the energy consumption and hierarchical porous structure reconstruction are challenging for cost-effective and scalable production. A top-down approach directly from wood was reported recently through delignification and sometimes followed by hemicellulose extraction. However, the SSA is low and meso/micro pores are limited. Here, we propose an approach to fabricate hierarchical wood aerogel through cell wall partial dissolution and regeneration in the lumen space. The aerogel combines high SSA (up to 250 m²/g) with good mechanical strength (1.2 MPa) and abundant of meso/micro pores. The aerogel could be further modified for advanced applications such as thermal insulation, energy harvesting, etc.

Bio-phosphors have emerged as an alternative to rare-earth color down-converting filters in light-emitting diodes (LEDs). They are mainly produced with biogenic emitters, like Fluorescent Proteins (FPs), embedded in polymer matrices.^1–3 The first biohybrid LED (Bio-HLED) with FP-phosphors featured a loss <10% of the emission intensity after 100 h.¹ This performance was recently enhanced using zero-thermal quenching PMMA-FP phosphors, reaching >150 days and 5 min of stability at low and high powers.⁴ However, the ideal combination of highly efficient and stable fully biogenic phosphors is still in its infancy.⁵ Here, we disclose the optimization of a bio-derived biodegradable polymer hosting and stabilizing a natural red FP – mCherry, as red-emitting phosphor in Bio-HLEDs. The photoluminescent properties of the bio-phosphors - PLQY> 20% with λ_em = 630 nm - led to Bio-HLEDs with excellent photostabilities > 2000 h operating, representing 2 orders of magnitude enhancement. We are strongly convinced that our work represents a crucial breakthrough in the development of red emitting bio-phosphors and in the stabilization of further natural FPs.
1. Weber, M. D. et al. Bioinspired Hybrid White Light-Emitting Diodes. Adv. Mater. 27, 5493–5498 (2015).
2. Fernández Luna, V. et al. Deciphering Limitations to Meet Highly Stable Biohybrid Light Emitting Diodes. Adv. Funct. Mater. 29, 1904356 (2019).
3. Aguino, C. F. et al. Single-Component Biohybrid Light-Emitting Diodes Using a White-Emitting Fused Protein. ACS Omega 3, 15829–15836 (2018).
4. Espasa, A. et al. Long-living and Highly Efficient Biohybrid Light Emitting Diodes with Zero-thermal-Quenching Biophosphors. Nat. Commun. 11, 1–10 (2020).
5. Fernández-Luna, V. et al. Biogenic Fluorescent Protein-silk Fibroin Phosphors for High Performing Light Emitting Diodes. Mater. Horizons 7, 1790–1800 (2020).

Applications of robotics and sensing technologies, big data analysis and biotechnology in farming, plant and food science are highly sought to guarantee global food security while mitigating the environmental impact of agriculture. In this scenario, the potential benefit of applying biomaterials science and drug delivery principles to enhance food security remains underexplored when compared to material- based research efforts in biomedicine, energy and optoelectronics. In this seminar, we highlight recent development in the nanomanufacturing of structural proteins to engineer a new generation of advanced materials that can be interfaced with food and plants. We will present newly developed techniques to direct the assembly of structural proteins into nanostructured, hierarchical materials that can serve as: edible coatings to prolong the shelf-life of perishable food, microenvironments to boost seed germination in marginal land and injectors to precisely deliver payloads in plant vasculature. These examples will provide an opportunity to discuss how the establishment of a successful interface between biomaterials and plants tissues requires the development of a basic scientific knowledge on: mechanics of disorder to order transitions in proteinaceous materials during condensation phenomena, fluid mechanics and transport phenomena in plants vasculature, and swelling of porous materials exposed to plant fluids.

Recombinant nanoworms are promising candidates for materials and biomedical applications ranging from templated synthesis of nanomaterials to multivalent display of bioactive peptides and targeted delivery of theranostic agents. However, the molecular design principles to synthesize these assemblies (which are thermodynamically favorable only in a narrow region of the phase diagram) remains unclear. To advance the identification of design principles for programmable assembly of proteins into well-defined nanoworms and to broaden their stability regimes, we were inspired by well-documented findings of topological engineering for accessing rare mesophases formed by synthetic macromolecules. To test this design principle in biomacromolecular assemblies, we used posttranslational modifications (PTMs) to generate lipidated proteins with precise topological and compositional asymmetry. Using an integrated experimental and computational approach, we show that the material properties (thermoresponse and nanoscale assembly) of these hybrid amphiphiles are modulated by their amphiphilic architecture. Importantly, we demonstrate that the judicious choice of amphiphilic architecture can be used to program the assembly of proteins into adaptive nanoworms, that undergo a morphological transition (sphere-to-nanoworms) in response to temperature stimuli. Due to their amphiphilicity, these nanoworms can easily solubilize hydrophobic chemotherapeutics without resorting to complex, inefficient, and time-consuming conjugation/purification protocols. The recombinant nature of this system enables the fusion of genetically encoded bioactive or targeting peptides, which can be used to optimize the delivery and efficacy of these nanoplatforms. We anticipate that these methods will be generalizable to other classes of proteins and PTMs. Thus, this work advances the study and design other hybrid systems, such as proteins modified with other classes of lipids or charged PTMs such as phosphorylation.

Polymeric microparticles are widely used in agriculture, food processing, biomedical and electronic industries. Their structures and surface patterns are critical in specific applications. However, assembling intricate polymeric microstructures in a simple, repeatable, and at-scale manner is challenging compared with inorganic counterparts. To address this issue, we will describe a universal, template-free approach to fabricating spiny biopolymer microspheres. Silk fibroin – a natural protein with outstanding mechanical properties, biodegradability, and biocompatibility – is selected as an example here. Silk fibroin spiny microspheres are prepared with different sizes, spine numbers, and payloads. The mechanically robust spines are analyzed and tested. The enhanced adhesion performance in agriculture and micro-robotic applications will be demonstrated.

Here we present how the ionic strength and effective charge density affect the final structural organization of cellulose nanocrystals (CNCs) after drying suspensions with different ionic strengths in terms of quantitative characteristics of the orientation order. We demonstrated that electrolyte’s introduction into CNCs dispersion results in dramatic changes in electrical double layer thickness and subsequently, the effective charge density, measured experimentally, as well as the interparticle interaction energy calculated from the DLVO theory. The question of whether electrostatic interactions by themselves can control the nanocrystals' chiral organization is frequently debatable. We showed with high-resolution AFM that the reduction of the Debye charge screening length below a critical value of 3 nm results in the loss of the long-range helicoidal order and the transition to a disordered morphology with random packing of nanocrystals within thin films’ layers. Subsequently, very high local orientation ordering with the 2D orientation factor, S, obtained by applying image analysis software that was within 0.8–0.9, gradually decreased to a random order with the final value S = 0.1–0.2. The effect of Coulombic interaction on CNCs chiral assembly is clearly supported by the measured shrinking of the helical pitch length and shifting the photonic band gap from 400 to 250 nm, and increase in helical twisting power from 4 to 6 μm^–1 and doubling of the twisting angle between neighboring monolayers from 5.5 to 9°. Thus, we conducted quantitative characterization of the CNCs molecular organization down to the level of individual nanocrystals and their orientational organization at nanoscale and microscale levels. Simultaneously with these comprehensive molecular characteristics, we measured optical appearance, chiral activity, and evaluated their charged state, offering unique comprehensive and quantitative characterization of the molecular orientational order of the CNCs.

Problem:
Electrospun nanofibers should have higher strength then their larger scale counterparts, however, due to the difficulty in drawing the fibers, a critical processing step that creates high molecular alignment in the fiber, their promise of high strength remains unkept. Individual nanofibers have been drawn using a parallel based track collection and drawing system, but this has only been done at ambient temperatures. The proper application of heat will allow for the fibers to be drawn to much higher draw ratios, and allow for the release of chain entanglements and imperfect crystal structures so that the resultant fibers can have optimal chain alignment and straight chain crystals.
Solution:
We aim to apply the technique of laser zone drawing to track electrospun nanofibers. Laser zone drawing heats up just a small portion of the fiber at a time, allowing for precise thermal control over the fiber, both spatially and temporally. This technique has been applied to larger fibers with incredible results but has yet to be applied to nanofibers. We believe that by combining the techniques of track electrospinning and laser zone drawing, we can create nanofibers with near ideal macromolecular properties, which may result in polymer nanofibers with the highest tensile strength to date. Additionally, this method is scalable and flexible, and should be applicable to any thermoplastic polymer that can be spun into nanofibers.
Methods:
Track electrospinning and Laser Processing: Polylactic acid (PLA) nanofibers are electrospun onto a parallel track collection system, which allows to the collection of aligned nanofibers. The fibers are then transferred onto a robotic stage which passes the fibers through a 9.3 micron wavelength laser beam.
Raman Spectroscopy:
Single fiber Raman spectroscopy is used to measure changes in the molecular alignment and crystallinity of the fibers.
Scanning Electron Microscopy (SEM):
SEM is used to evaluate the diameters and morphology of the fibers.
Mechanical Properties:
Dynamic Mechanical Analysis is used to determine the modulus off fiber mats, because individual fibers do not produce a large enough load.
Results:
We have demonstrated that PLA fibers of different diameters can be predictably thinned to diameters of less than 20% of the original diameter with low variability simply by increasing the power density of the processing laser. This allows for the nanofibers’ diameters to be precisely controlled after the spinning process. We have also established that this effect is not dependent on the duration of laser exposure, indicating that the fibers reach thermal equilibrium during the process, despite being exposed to very high laser power densities. This is explained by their enormous surface area to volume ratio, which only increases as they thin, which keeps them from melting even under extreme laser exposure. We have also demonstrated that the fibers can be thinned in a single step, as there was no difference in diameter compared to fibers that were treated multiple times at incrementally increasing powers. By comparing the power density of the laser to the diameter, using Newtons law of cooling, and assuming thermal equilibrium, we can calculate the convective heat transfer coefficient of the nanofibers. Knowing this will allow us to predictably raise the fibers’ temperature using the laser, which will aid in the zone drawing process, by allowing us to heat just above Tg, which has been shown to be the optimal temperature for zone-drawing.

In nature, simple molecular building blocks self-assemble into complex structures to achieve outstanding functionality. For example, proteins are made up of amino acids and DNA (deoxyribonucleic acid) is made up of nucleotides. Proteins and DNA are involved in most processes in life, from genetic encoding of information to enzyme catalysis. The large sequence space and the variation of the physicochemical properties of biomolecules leads to their functional diversity. Inspired by the superior properties of such self-assembled systems, materials with unique properties can be designed. The base pair complementarity of DNA and the origami method laid the foundation for the field of DNA nanotechnology and synthesis of 2D and 3D nanostructures of desired geometry. Bioconjugate chemistry enables the modification of DNA strands with functional molecules that can be designed with optimized spacings and orientations within the DNA backbone, leading to applications in energy transfer, vaccine development, or enzyme catalysis.

In this work, we present the design of DNA origami for the development of functional nanostructures. Modeling and simulation have been used to better understand the molecular structure of functional DNA structures and to guide new designs. The 2D and 3D DNA structures were first generated using the ATHENA software package, followed by coarse-grained oxDNA simulations to investigate the structural integrity of the DNA nanostructures. As an example, hybrids of DNA wireframe structures decorated with fluorescent molecules have been tailored to achieve the desired spectroscopic properties. The goal was to mimic and engineer the outstanding efficiency of fluorophores in large protein complexes such as the light-harvesting antenna complex. Fully atomistic molecular dynamics (MD) simulations provided further insights. This approach enables the design of hybrid systems with functional properties for applications where molecules need to be arranged on the nanometer scale.

References
X. Wang^#, S. Li^#, H. Jun^#, T. John, K. Zhang, H. Fowler, J.P.K. Doye, W. Chiu*, M. Bathe*, Planar 2D Wireframe DNA Origami, Sci. Adv. 8 (2022) eabn0039.

H. Jun, X. Wang, M.F. Parsons, W.P. Bricker, T. John, S. Li, S. Jackson, W. Chiu, M. Bathe*, Rapid prototyping of arbitrary 2D and 3D wireframe DNA origami, Nucleic Acids Res. 49 (2021) 10265–10274.

Many biomacromolecules are known to undergo thermoresponsive assembly into various morphologies, making them promising candidates for temperature-modulated applications such as drug delivery and tissue engineering. As two examples, methylcellulose (MC) chains self-assemble to form fibrillar structure in aqueous solutions at elevated temperature [Schmidt et al. Macromolecules, 2018, 51, 7767-7775]; elastin-like peptide-collagen-like pepetide (ELP-CLP) conjugates self-assemble to form vesicles at physiological temperatures [Luo and Kiick, J. Am. Chem. Soc. 2015, 137, 15362-15365]. Understanding the assembled macromolecular structure - domain shapes and dimensions - is key to precise control of the behaviors of such biomacromolecular materials in commercial applications. Small-angle scattering (SAS) is a useful experimental technique to characterize the structure of polymer assembly in solutions. However, interpretation of the SAS output - a scattering profile of averaged intensity (I(q)) at various wave factors (q) - often relies on analytical models only available for several conventional structures. Interpretation of I(q) vs. q plots for unconventional/non-equilibrium assembled structures with simple/complex polymer conformations remains challenging as relevant analytical models are not always available for such cases. In this talk, we present our recently developed computational method, CREASE, to analyze SAS results obtained from structures with high dispersity in dimensions formed upon assembly of complex polymer chemistries. Using genetic algorithm (GA) as the optimizer, CREASE takes as input I(q) vs. q plot and a general category of assembly morphology (e.g., “semiflexible fibril” or “bilayer vesicle”) and provides as output the relevant dimensions of the structure and dispersity in the dimensions whose computed scattering profile most closely matches input scattering profile. We test the performance of CREASE on both scattering profiles of methylcellulose fibrils and ELP-CLP vesicles and compare the predicted dimensions with those obtained from fitting analytical models. We also show how CREASE can be accelerated by incorporating neural network (NN) models. This talk will demonstrate CREASE’s potential to extract useful information about microscopic structure from SAS outputs without being limited by off-the-shelf scattering models and greatly improve the interpretability of small-angle scattering as a method to characterize polymer structures.

The structure-based tuneability of the electronic and optical properties of conjugated polymers has enabled their application across a range of fields, including energy harvesting and optoelectronics. However, in the context of biological sensing, the use of conjugated polymers has thus far incorporated little specificity in terms of covalent modification.¹ Previously, we demonstrated a crown ether-functionalised PEDOT which displayed improved adhesion and electrochromic behaviors compared to unmodified PEDOT.² Now, we move towards an expanded landscape of materials investigating copolymers, deposition parameters, and alternative functional groups which enable the precise fine-tuning of material characteristics and functionalities.

Developing robust, highly selective, biologically compatible sensing platforms is of critical importance because the measurement of analyte concentrations in biological samples is crucial for the management or detection of many diseases.³ Currently, many devices which function for this purpose are complex, multi-component systems. However, directed synthetic strategy with conjugated polymers enables the fine-tuning of analyte specificity, electroactive or optical functionality, and physical and morphological properties, within a single multi-purpose material. In addition, these entirely organic systems offer affordability, biocompatibility, and simple design and fabrication.

Here, we present a novel covalently modified EDOT monomer featuring pendant analyte-binding groups which, when electropolymerised in the presence of a glucose template, forms a porous molecularly imprinted matrix which is shown to be electrochemically responsive to glucose. Supported by in-depth topographical, electrochemical, QCM, and OECT analysis, we will discuss how this new design platform can be used to introduce sensing capability in an enzyme-free, single polymeric material, for next-generation device fabrication.

1. J. Borges-González, C. J. Kousseff, C. B. Nielsen, J. Mater. Chem. C., 2019, 7, 1111-1130
2. C. J. Kousseff, F. E. Taifakou, W. G. Neal, M. Palma, C. B. Nielsen, J. Polym. Sci., 2022, 60, 504-516
3. S. Wustoni, A. Savva, R. Sun, E. Bihar, S. Inal, Adv. Mater. Interfaces, 2019, 6, 1800928

Here, a photonic bio-organic multiphase structure is proposed for thin-film electronic nets integrated with multilevel logic elements for multilevel computing via reconfigurable photonic band gaps in chiral biomaterials. Inspired by an artificial intelligence system having efficient information integration and computing capabilities, the photon active dielectric layer of the chiral nematic cellulose nanocrystal is coupled to a printed p-type and n-type organic semiconductor as a bifunctional logic element. These adaptive logic elements can trigger customized quantized electrical output signals under light having different photon energies and with different photonic band gaps in active dielectric layers. A bifunctional structure enables complex memory operations due to repeated changes in photonic band gaps controlled by expansion and contraction of chiral nematic pitches and photon energy controlled by light absorption of complementary organic semiconductor layers. This conceptual demonstration of a multivalued logic structure facilitates an optical calculation system for low-power optical information processing integrated into an interface between a human and a machine.

Plant processes such as photosynthesis, production of biomaterials and environmental sensing and adaptation, can be used in technology via integration of functional materials and devices. We demonstrated that plants can be functionalized with electronic materials by leveraging their biocatalytic machinery. Specifically, conjugated oligomers based on thiophene and EDOT polymerize in-vivo forming conductors within the plant structure. We showed that the polymerization is enzymatically catalyzed by endogenous peroxidases that are present in the plant cell walls, resulting in conducting polymers integrated within the plant cell wall structure. The plant is not only catalyzing the polymerization but also templates the polymer in a favorable manner. Recently we demonstrated intact plants with electronic roots that continue to grow and develop enabling plant-biohybrid systems that maintain fully their biological processes. The electronic roots were used to build supercapacitors that outperformed previous plant biohybrid charge storage demonstrations. Here I will also present our latest results on developing plant based biohybrid circuits for enhanced energy storage in plants and a demonstration in powering an electrochromic display. Furthermore, extending the concept to trees I will present our results on functionalizing wood in-vivo prior to harvest.

Photosynthetic microorganisms represent attractive tools for the harvesting and the conversion of solar light in bioelectronic devices [1, 2]. The optimization of the interfaces of poorly conductive bacteria with electronic components can be achieved via biocompatible polymers that encapsulate the bacterial cells and allow the intimate contact between the outer cell membrane and the electron acceptor surface, required for an efficient electron transfer in biohybrid systems.
The outer membrane of the metabolically active photosynthetic purple non sulfur bacterium Rhodobacter (R.) sphaeroides was coated with polydopamine (PDA), a bioinspired polymer produced by the self-polymerization of dopamine. Although the presence of oxygen is an essential requirement for dopamine polymerization [3], the PDA coting formation around the cell membrane occurred also in anaerobic condition.
Laccases, enzymes belonging to multi-copper oxidases family, have been reported to oxidize a wide range of phenolic compounds and aromatic amines, including dopamine. Using laccase, the polymerization rate of the dopamine monomer was greatly increased, and the polymer film resulted more uniform compared to traditional self-polymerization and uncontrolled mechanism [4].
Laccases have a wide taxonomic distribution in Nature but with few or little evidence of their presence in anaerobes, since these enzymes use oxygen as an electron acceptor [5]. Here we investigate the process of anaerobic polymerization of dopamine in the growth medium of R. sphaeroides.

Similarly, laccase from T. versicolor was also used to improve dopamine polymerization around the photosynthetic organisms belonging to diatom microalgae, with the goal of wastewater treatment and their bioremediation.

[1] F. Milano, A. Punzi, R. Ragni, M. Trotta, G. M. Farinola, Adv. Funct. Mater., 29, 1805521, (2019)
[2] a. M. Di Lauro, S. la Gatta, C. A. Bortolotti, V. Beni, V. Parkula, S. Drakopoulou, M. Giordani, M. Berto, F. Milano, T. Cramer, M. Murgia, A. Agostiano, G. M. Farinola, M. Trotta, F. Biscarini, Adv. Electron. Mater., 6, 1900888, (2020)
b. M. Di Lauro, G. Buscemi, M. Bianchi, et al., MRS Advances 5, 985–990 (2020)
[3] H. Lee, S.M. Dellatore, W.M. Miller, P.B. Messersmith, Science 318(5849):426-30 (2007)
[4] Q. Zhou, W. Wu, T. Xing, RSC Adv., 12, 3763-3773 (2022)
[5] F. Berini, M. Verce, L. Ausec, et al., Appl Microbiol Biotechnol 102, 2425–2439 (2018)

Bioinspired microrobots capable of actively moving in versatile biological fluids and environmental surroundings have attracted considerable attention for biomedical and environmental applications because of their unique dynamic features that are otherwise difficult to achieve by their static counterparts. Herein, algae-based biohybrid microrobots are fabricated via click chemistry to functionalize algae with different agents from small molecules to nanoparticles (eg. angiotensin-converting enzyme 2 (ACE2) receptor and antibiotics-loaded cell membrane-coated nanoparticles). The resulting biohybrid microrobot displays fast (>100 μm/s) and long-lasting self-propulsion in diverse simulated biofluid and aquatic media, obviating the need for external fuels. In a mouse model of acute pneumonia, the resulting antibiotics-loaded biohybrid algae-based microrobots achieve significant therapeutic efficacy in reducing the bacterial burden and effective treatment of bacterial infection, while showing negligible in vivo toxicity. In another example, the ACE2-modified algae microrobots display effective “on-the-fly” removal of SARS-CoV-2 pseudovirus in many contaminated water matrices.

During photosynthesis, plants use light energy to transform carbon dioxide and water into carbohydrates for their own growth. The photosynthetic process comprises many steps that can in principle be optimized to have higher efficiency. RuBisCO (Ribulose 1,5-bisphosphate carboxylase/oxygenase) catalyzes the carboxylation reaction that is the initial reaction for carbon fixation and conversion of CO₂ to sugars. The reaction occurs in organelles called chloroplasts present in leaf cells. However, RuBisCO has naturally a poor affinity for CO₂ and the transfer of the atmospheric CO₂ to the RuBisCO enzyme is highly limited by the diffusion of CO₂ through the stomata and the intercellular space which ultimately considerably reduces the photosynthesis rate. Polyamines have been shown in-vitro to be able to transfer carbon dioxide to RuBisCO for the carboxylation reaction. In this work, we present biocompatible fluorescent polyethylenimine nanoparticles for enhancing the CO₂ transfer to the RuBisCO enzyme. With in vitro and in vivo studies, we evaluated the nanoparticles uptake of atmospheric CO₂ and transfer kinetics to RuBisCO for the carboxylation reaction. Then, we introduced the nanoparticles into the plant apoplast via localized infiltration. First, we studied the toxicity of the nanoparticles and results showed no evidence of a direct harmful impact. We then investigated their distribution within the plant leaf with confocal microscopy and showed that the nanoparticles not only are present in the intercellular space but also in the direct centers of photosynthetic activity: the chloroplasts, which indicate the possibility of a pathway to increase the diffusion of CO₂ in the plant tissue.

Bacterial photosynthesis has huge applicative potential when it comes to have small, metabolic active and versatile living catalysts. The use of photosynthetic bacteria in non-conventional or in polluted environments to catalyze light transduction is very promising in bioelectronics. The strategy to connect these light converting bacteria to external, non-biological wiring will be presented, along with some recent results that will illustrate the advancements of the interfacing between electrodes and living microorganisms.

Photosynthetic bacteria in self-assembled biocompatible coatings for the transduction. Phosbury. (Fonds Nationale Suisse, CRSII5_205925)

Chloroplasts absorb atmospheric carbon dioxide in the plants, which play an important role in converting global carbon into a chemical energy source by light. Since isolated chloroplasts quickly lose their photosynthetic activities once isolated from plants, extending their viability is essential in engineering chloroplasts for sustainable carbon sequestration. Here, we suggest a plant cytosol-mimicking matrix to extend the photosynthetic activities of isolated chloroplasts. Encapsulation of chloroplasts within photo-clickable pectin hydrogels enabled uniform distribution of chloroplasts within the hydrogel and securely entrapped chloroplasts to maintain the mechanical properties. Antioxidants were introduced to protect chloroplasts from photooxidative damage. We evaluated the comprehensive in vitro photosynthetic activities by monitoring chlorophyll concentration, O₂ evolution, electron transfer rate, ATP synthesis, and glucose export. As a result, we found that antioxidants alone prolonged the isolated chloroplasts’ lifespan by 48 hours, and encapsulation within the pectin hydrogel extended their lifespan by 168 hours. In 96 hours of incubation, the chloroplast-laden pectin hydrogel with antioxidants showed a 3-fold O₂ concentration and 8-fold electron transfer rate compared to encapsulated chloroplasts without antioxidants. In addition, the ATP synthesis and glucose export were increased by 1.6-fold and 1.2-fold, respectively. These results will provide the potential perspective on the generation of carbon-fixing materials, the manipulation of biological functions, and the production of therapeutics using chloroplast culture in designing environmentally sustainable materials.

Vision loss due to the degeneration of photoreceptor cells in the retina occurs in millions of people every year worldwide through diseases such as retinitis pigmentosa and age-related macular degeneration. The development of a photosensitive organic semiconductor device that can function in a way to replace lost or damaged photoreceptor cells may be a possible treatment for those suffering with these diseases. We demonstrate that natural dyes extracted from various berries and vegetables are excellent chromophore candidates for colour-specific organic devices with similar absorption spectra to those produced by human rod and cone cells. Using fabrication methods resembling those used in the development of dye-sensitised solar cells, bio-derived chromophores have been investigated and the production of active devices interfaced with electrolyte, phosphate buffered silane, have been demonstrated. Devices produce photo-current and photo-voltage spectra in the spectral regions corresponding to the activity of cones and rods. . Our results show the chromophores can respond to pulsed light in a similar way to photoreceptor cells and produce a rising photovoltage. In summary, we discuss if natural dyes can lead us to devices capable of stimulating neuronal circuitry in human eye.

For the realization of sustainable development goals, regional ecosystems must develop and use universal sustainable technologies, and the widespread use of renewable energy is essential for this purpose. Thus, there is an urgent need to develop renewable energy production and storage devices. A wood-derived carbon is a promising electrode as an energy device because its high porosity improves the carbon's surface area Recently, we have reported a highly active wood-derived electrochemical catalyst for oxygen reduction reaction which occurs on the cathode of metal-air batteries and fuel cells (1). The pyrolyzed wood performed high porosity and high catalytic activity. Pyrolysis is required to control the atmosphere at high temperatures and under inert gas, resulting in being expensive and cumbersome. Herein, we report the direct laser-pyrolysis of wood chips for an anode and cathode with a commercial blue laser and establish a three-in-one zinc-air battery.
Paulownia was used as a wood carbon source. Wood chips were pyrolyzed with the blue laser under the ambient atmosphere. The irradiated area became black and metallic. The obtained carbon had macro-scale pores confirmed by an optical microscope and showed the graphitic peaks confirmed by Raman spectra. The electric resistance was improved by increasing the intensity of the blue laser, and the obtained carbon performed highly active electrocatalytic activity by adding metal sources as catalysts.
We confirmed the electrocatalytic activity of the cathode for the oxygen reduction reaction. In this study, the Fe(NO3)3 was used as a metal source and added to the wood before the pyrolysis (wood-Fe). In addition, iron phthalocyanine was modified on the obtained carbon material using the organic solvent as a molecular catalyst (wood-FePc). The molecular catalysts are promising materials since they show superior oxygen reduction activity without any pyrolysis processes (2). The oxygen reduction properties were evaluated in 0.1 M KOH, and the catalytic activity was found to increase in the order of wood, wood-Fe, and wood-FePc. From these results, the wood-derived laser-induced graphene for the electrocatalysts of the oxygen reduction reaction was successfully obtained from wood using the blue laser under the ambient atmosphere.
Finally, we established the three-in-one zinc-air battery. The wood chips have porous structures, resulting in the solvent and electrolyte can be absorbed into their structure. We irradiated the laser at double sides on the wood chip to form the cathode and anode without a connection between each electrode. The FePc and zinc powder loaded onto the cathode and anode, respectively. The open-circuit potential was observed by adding the electrolyte (0.1 M KOH) into the wood chip. The woody battery showed over 10 mA/cm2 and 5 mW/cm2. The wood chip irradiated with the laser at double sides acted as the three-in-one zinc-air battery consisting of the cathode, anode, and separator without an assembly process.
References: 1) Y. Goto, Y. Nakayasu, H Abe, Yuto Katsuyama, T. Itoh and M. Watanabe, Phil. Trans. R. Soc. A (2021) 379: 20200348. 2) H. Abe et al., NPG Asia Materials 11, Article number: 57 (2019)

Diatoms are the most widespread organisms in our planet’s aquatic environments and among the most ecologically important. Indeed, the tens of thousands of existing species of these microalgae produce about half of the oxygen we breathe and are an extraordinary example of how Nature is capable of cyclically adapting biological systems to the natural environment by playing with the universality-diversity dualism. In diatoms, in particular, this binomial is determined by the multiscale architecture of their biosiliceous exoskeleton known as the “frustule”. This biological material, in addition to being a marvelous and sophisticated physical barrier against predators, through its hierarchical porous structure allows diatoms to acquire nutrients through filtration, exploit buoyancy phenomena for photosynthesis processes, and thermally regulate the organism. Given the amazing multifunctionality of the frustule, diatoms are still widely studied for applications in filtration, drug delivery, biosensing, energy harvesting, and scaffolding. Yet, little is known regarding their mechanical properties. To extend the knowledge of the present relationship between the morphology of diatom frustules and their structural performance, in this work we focused on the mechanical analysis of the frustule of the diatom Coscinodiscus sp. Starting from the analysis of the multilayer structure that characterizes the microscale, we built biomimetic models on a macroscopic scale using CAD tools and studied their deformational behavior, both through numerical finite element simulations and through experimental tests performed on samples fabricated through additive manufacturing. In particular, we focused on the effect produced by variation in the morphological details that distinguish the natural sandwich-like structure of the frustule on its energy absorption properties. Through predictive techniques, we then researched the optimal topology and analyzed the potential benefits of using bioinspired design for the architected materials. Nature’s design principles used to make biological materials and, in particular, the use of functional gradients and structural heterogeneity are a formidable source of ideas for increasing the efficiency and performance of man-made materials, and this research is evidence of that. To reinforce this, as a possible application, we propose in addition a new bioinspired prototype protective helmet designed for micromobility and outdoor activities that combines lightweight and the energy-absorbing capacity from impacts with breathability, waterproofing, and aesthetics.

The alginate hydrogel is a natural polysaccharide that has high biocompatibility and is used for drug delivery, dressing for wound healing, scaffold for 3D bioprinting, etc. It can be readily prepared by mixing sodium alginate with divalent cations such as Ca2+ in solution to crosslink the alginate polymer chains. The most common method to facilitate the crosslinking of sodium alginate is to add a small amount of solution of sodium alginate into a bulk solution of CaCl2 slowly or in a dropwise manner. CaCl2 permeates into a blob of the alginate solution to immediately crosslink the alginate and form a hydrogel. Morphologies of the alginate solution being added (droplet or a stream of liquid, droplet size, etc.) affect the morphologies and properties of the resulting hydrogel, which are important for different applications. Since CaCl2 solution is normally of a bulk volume, if this reaction was conducted in a setting where both reactants are in microdroplets, it may lead to unique characteristics. However, it is difficult to facilitate efficient reactions between microdroplets by conventional techniques.

In this study, crosslinking reactions between sodium alginate and CaCl₂ were conducted by spraying them on the substrate surface with wettability patterning that collects and mixes microdroplets on the surface. We fabricated highly-branched “open microfluidic channels” [1,2,3] by patterning different wetting properties such as hydrophilic and hydrophobic ones. When aqueous microdroplets are sprayed on the open microfluidic channels, they are captured and transported along a hydrophilic channel surrounded by a hydrophobic surface, driven by capillary action. Superhydrophobic coating of TiO₂ and Capstone (R) ST-100 turns to be superhydrophilic upon irradiation with UV light, which makes complex patterning possible by simple photolithography. This photo-patternable surface was used to fabricate a highly branched tree-like microfluidic channels to collect microdroplets and facilitate mixing of solution at a large number of branching points that exists throughout the surface.

On the fabricated microfluidic surface, aqueous solution of 20 g/L sodium alginate (500-600 cP at 10g/L, 20 °C) and that of 20 g/L CaCl₂ were prepared. Droplets of different aqueous solutions were sprayed onto the unused channels using a spray nozzle with a controlled rate: (1) sodium alginate solution, (2) CaCl₂ solution, (3) both using two spray bottles containing each of them. The positions of liquid blobs after spraying were recorded by a digital camera. When droplets of CaCl₂ solution, which has low viscosity, were sprayed on the channels, they were transported through the channels to form a large liquid blob at the focal point (the root of the tree structure) within 1 s. When droplets of sodium alginate solution were sprayed on the unused channels, they were also transported to the focal point despite their high viscosity (estimated viscosity is 1 × 10³ cP). On the other hand, when the two kinds of droplets were simultaneously sprayed on the channels, the transport of droplets to the focal point was apparently hindered. This hindered transport can be attributed to crosslinking of alginate by Ca²⁺ upon merging of fine droplets of sodium alginate and those of CaCl₂ at the branching points, which turned the fluid droplet to a non-fluid hydrogel.

In conclusion, we demonstrated mixing and reactions of microdroplets of sodium alginate and CaCl₂ to form hydrogel on the microfluidic surface. More detailed investigation of the reaction dynamics between droplets as well as properties of the resulting alginate hydrogel is in progress.

[1] H. Kai, R. Toyosato, M. Nishizawa, RSC Adv., 8, 15985-15990, 2018.
[2] H. Kai, µTAS 2020.
[3] H. Kai, 2021 MRS Fall Meeting & Exhibit.

Peptoid (N-substituted glycines), as one of the unique sequence-defined synthetic “foldamers that mimic proteins and peptides for functions, - have recently received increasing attention for the design and synthesis of biomimetic nanomaterials with hierarchical structures. ¹ Due to the unique proteinase-resistance, chemical and thermal stabilities of peptoids, peptoid-based nanomaterials are promising candidates for applications in photonics, ^{2, 3} flexible electronics, ⁴ and biological systems. ^{2, 3, 5} Recently, by designing amphiphilic peptoids that contain aromatic hydrophobic domains, our group recently reported their self-assembly into highly crystalline membrane-mimetic 2D nanosheets^{2, 6} and 1D nanotubes, ⁷ we demonstrated that these peptoid-based nanomaterials are highly stable and a wide range of functional groups can be precisely placed within these materials to achieve programmable functions. To gain a better understanding of their formation mechanisms of these biomimetic materials, herein, I will report my group’s recent discovery of designing short peptoid oligomers, including tetramers, for controlled assembly into twisted nanoribbons, helices, along with nanosheets and nanotubes. Mechanistic studies using X-ray diffraction, AFM, TEM combined with computational simulations indicate the asymmetric packing of amphiphilic peptoids is the main driving force that leads to the formation of twisted nanoribbons and nanohelices. Tuning hydrophilic side chain chemistry and the number of hydrophobic side chains can significantly influence the peptoid assembly pathways and dynamics for the formation of hierarchical materials with designed morphologies.

References:
(1) Li et al., Chem. Rev. 2021, 14031. Cai et al., Acc. Chem. Res. 2021, 81. Yang et al., Chem. Mater. 2021, 3047.
(2) Song et al., ACS Mater. Lett.2021, 420.
(3) Wang et al., ACS Applied Bio Materials 2020, 6039.
(4) Li et al., Macromol. Rapid Commun. 2022, 2100639.
(5) Cai et al., Research 2021, 9861384. Song et al., Small 2018, 1803544.
(6) Jin et al., Nat. Commun. 2016, 12252.
(7) Jian et al., Nat. Commun. 2022, 3025. Jin et al., Nat. Commun. 2018, 270.

The growing demand of disposable electronics raises serious concerns for the corresponding increase in the amount of electronic waste (e-waste), with severe environmental impact. Organic electronics has been proposed long ago as a sustainable and energy efficient technological platform. Yet, such technology is inevitably leading to a drastic increase of plastic waste if common approaches for flexible substrates are followed. In this scenario, biodegradable electronics is an incipient need in order to mitigate the above mentioned issues. Flexibility, solution processability, low capital expenditure and energy-efficient processes, which are distinctive features of organic electronics, have to be complemented by a sustainable end-of-life of materials employed. This requirement calls for solutions where materials, especially substrates that represent the largest volume, can be biodegraded in the environment with no harm, yet assuring that no precious resources are dispersed. In this work, we succesfully employed a bioderived and biodegradable biopolymer as a substrate for an all-organic field effect transistor (OFET) based on an inkjet printed polymer semiconductor. The OFETs showed good reproducibility, a proper current modulation and extremely low leakage, which remained almost unaltered also after intensive mechanical stresses as bending and rolling. Such mechanical stability and flexibility, together with the biodegradability and bioderivation, make this approach an appealing candidate for the development of sustainable printed electronics, with widespread future applications in the biomedical and food packaging sector.

Silver, in the form of nanostructures, is widely employed as an antimicrobial agent. Despite the large body of work addressing the effects of silver on the antibacterial mechanism and on the (bio)physical chemistry pathways that drive bacterial eradication, little effort has been devoted to the investigation of nanostructured silver plasmon response upon interaction with bacteria. We investigate the bacteria-induced changes of the plasmonic response of silver nanoplates after exposure to the bacterial model Escherichia coli (E. coli). Ultrafast pump-probe measurements indicate that the dramatic changes on particle size/shape and crystallinity, likely stemming from a bacteria-induced oxidative dissolution process, translate into a clear modification of the plasmonic response.¹ Finally, we exploit such an effect to build up photonic crystals embedding silver nanostructures, which have the potential to reveal colorimetrically the presence of bacteria.^2–5 This study opens innovative avenues in the bio- physics of bio-responsive materials.
References
1. Paternò, G. M. et al. The impact of bacteria exposure on the plasmonic response of silver nanostructured surfaces. Chem. Phys. Rev. 2, 021401 (2021).
2. Paternò, G. M. et al. Hybrid One-Dimensional Plasmonic–Photonic Crystals for Optical Detection of Bacterial Contaminants. J. Phys. Chem. Lett. 10, 4980–4986 (2019).
3. Paternò, G. M. et al. Integration of bio-responsive silver in 1D photonic crystals: towards the colorimetric detection of bacteria. Faraday Discuss. 223, 125–135 (2020).
4. Normani et al., Design of 1D photonic crystals for colorimetric and ratiometric refractive index sensing. Opt. Mater. X 8, 100058 (2020).
5. Paternò et al., Distributed Bragg reflectors for the colorimetric detection of bacterial contaminants and pollutants for food quality control. APL Photonics 5, 080901 (2020).

Colors of avian feathers can be produced by pigmentation and/or structural coloration. Interestingly, avian plumage colors, where optical nanostructures are present, only produce the color “blue”. The reason why nature uses structural coloration instead of pigmentation to produce blue in the short wavelength regions of the visible spectrum is poorly understood, despite its fundamental significance to physiology and potential to spark advances in biomimetic applications. We may postulate that natural blue pigments are chemically less stable than red pigments due to their molecular complexity so that evolutionary process has led birds to use structural ways to produce diverse array of blue colors. Here, we discuss nature’s strategy to produce color “blue” with structural ways by elucidating various cases of avian feathers using optical measurement, electron microscopy, numerical modeling, and biomimicry.
We show that how birds produce and enhance appearance from photonic crystal or photonic glass nanostructures by addressing ingenious biological designs. To understand the various color-showing mechanisms in avian feathers, the correlations between the avian nanostructures and colorations were analyzed quantitatively, and the avian structural colors were mimicked with synthetic pathways to verify our understanding. For the case of common pheasant, we find that the photonic crystal nanostructures in their feathers can further modulate color in combination with the surrounding thin-film-like cortex layer to produce brilliant colors from blue to green. For Eurasian jay displaying periodic array of blue and white colors in their feathers, our analysis indicates that they vary colors by controlling only the thickness of color-producing optical nanostructures using multiple scattering effects. On the other hand, Kingfisher modulates plumage colors from blue to cyan by changing channel width of optical nanostructures. All these findings suggest that birds have various efficient way to produce blue colors with structural coloration. Inspired by nature’s strategy to color “blue”, we also demonstrate biomimetic “green” fabrication methods to display brilliant blue colors using synthetic nanoparticles and controlling the conditions similar to the cases in avian optical nanostructures.
This study was funded by the National Institute of Ecology through the grant number (NIE-C-2021-18) and Human Frontier Science Program through the grant number (RFP0047/2019).

Biomaterials and biopolymer materials such as biopigments (melanin, xanthommatin, etc.) have fascinating optical properties, such as bright and structural color and advanced camouflage. These material properties are explored in basic research to learn about how the skin of cephalopods (e.g., squid, octopus) functions optically, based on pigment, texture, and photon-scattering granules (~50-500 nm in size). Natural pigment molecules and bio-polymers are attractive for photonics applications: displays, adaptive lenses, underwater optical communications, etc.
Small-molecule biopigments readily dissolve in polymer hosts, resist ultraviolet light, are toxicologically benign, and can be fabricated using large-scale chemical methods. Over 500 mg was synthesized and dried in our laboratory for toxicological analysis. Because of their small-molecule nature, their ability to combine with polymers such as polyvinyl alcohol (PVA), their manufacturability (biological and chemical synthesis), their high refractive index (RI), and their sustainability (they're eaten by animals), the bio-pigments and associated bio-polymers are useful for photonically functional thin films, anti-reflective coatings, photonic scattering for color, etc. Large-scale environmentally friendly synthesis may enable new designs of lightweight optical systems that can adapt and change shape, have a high numerical aperture, and aid in underwater detection or imaging.
The chromatophores in squid skin change from an expanded, pancake-like shape to a punctate, spherical shape and back again to influence photonic scattering and color; they are colored yellow, red, and brown, and are responsible for the bulk color changes. Underneath the chromatophore lie less-obvious iridocyte cells - multilayered Bragg reflectors that reflect color iridescently. The chromatophore cell, in its expanded state, contains multiple layer of sub-monolayers of photon-scattering granules.
Our group discovered that the cephalopod’s Xa pigment has a high RI (n > 1.55), at 589 nm and at 532 nm. For the latter experiment, n may have been artificially low. Recently, we have carried out more comprehensive broadband (300 nm – 3200 nm) ellipsometric spectroscopy to determine the optical indices (n and absorption coefficient k) of Xa, extracting natural Xa pigment from the squid’s chromatophores and forming smooth, high-quality films with concentrations of Xa as much as 90% in polyvinyl alcohol (PVA). Many samples containing natural Xa, and some with artificial Xa, show the same trends, providing a more complete description of Xa’s optical properties (n, k) across the entire wavelength range of interest. We have observed an unreported infrared absorption peak and associated reduction in n, and explain possible origins.
Armed with ellipsometric data, we model optical properties (e.g., reflectivity) using a four-flux model (forward and backwards-propagating specular and diffuse light), to gain a more complete and quantitative understanding of squid skin optics, improving on an analytical model of light scattering and absorption developed in 2008 that made important breakthroughs, but lacked separate experimental data on fundamentals for the Xa, and did not comprehensively treat the full optical problem. Here, we update this model analytically, taking better account of the optical coupling between chromatophore and underlying iridocyte. Our 4-flux optical model of the chromatophore will not ignore the background reflectivity and scattering.
The to-be-reported physics modeling and theory, with experimental characterization, will enable new bio-pigment and bio-polymer materials and applications. By understanding how the color of the chromatophores changes, another important step can be taken to harnessing artificial and novel material platforms for more efficient control of light at the nanoscale. We discuss possible new functional nanophotonic systems, based on the bio-pigments, and possible applications.

Upconversion materials (UCMs) have been developed to convert tissue-penetrating near-infrared (NIR) light into visible light. However, the low energy conversion efficiency of UCMs have limited their further biophotonic applications. Here, we developed controlled afterglow luminescent particles (ALPs) of ZnS:Ag,Co with strong and persistent green luminescence for photochemical tissue bonding (PTB). The co-doping of Ag⁺ and Co²⁺ ions into ZnS:Ag,Co particles with the proper vacancy formation of host ions resulted in high luminescence intensity and long-term afterglow. In addition, the ALPs of ZnS:Ag,Co could be recharged rapidly under short ultraviolet (UV) irradiation, which effectively activated rose bengal (RB) in hyaluronate – RB (HA-RB) conjugates for the crosslinking of dissected collagen layers without additional light irradiation. The remarkable PTB of ZnS:Ag,Co particles with HA-RB conjugates was confirmed by in vitro collagen fibrillogenesis assay, in vivo animal wound closure rate analysis, and in vivo tensile strength evaluation of incised skin tissues. Taken together, we could confirm the feasibility of controlled ALPs for various biophotonic applications.

This talk will desribe recent advances in the use of gelatin-based bioelectronics to interrogate the structure and function of organs. Materials processing and device fabrication strategies will be presented. Device demonstrations to interrogate gastro-enterological and cardiac organ systems will be presented.

Dynamic optical appearance plays a critical role for many animals that rely on adaptive camouflage or bright and varying color displays for their survival. The materials employed by these organisms have inspired scientific and engineering efforts to emulate their dynamic optical behavior in synthetic material analogues, such as mechanochromic photonic materials, which change their optical properties in response to mechanical forces. Mechanochromic materials provide a versatile platform for colorimetric force sensing in a variety of different research and technology fields, including healthcare, robotics, and human-computer interaction. We have developed a roll-to-roll manufacturing technique based on combining Lippmann photography with holographic recording materials, providing a fast, scalable, low-cost method of producing mechanochromic photonic sheets. The benefits of this technique include high-resolution spatial patterning across the entire RGB color space, printing in the near-infrared region to create hidden patterns that appear when stretched, control of the angular distribution of reflected light, and tuning of the mechanical properties of the material to map color variations to different force ranges.

RNA oligonucleotides and their biophysics are an essential part of therapeutics, sensing, and forensics applications. They have gained importance in the research focus in recent years for several reasons. Not only do several pathogens (e.g., SARS-CoV2) have RNA genomes, but many therapeutic¹, biotechnological², and modern molecular technologies (e.g., Gene editing³, gene silencing⁴) use RNA oligonucleotides at their core.
Single-molecule electrical techniques have allowed studying the charge transfer process in biomolecules with unprecedented resolution in the last decade⁵. In the biomolecular electronics discipline, the electronic and charge-transport (CT) properties of short oligonucleotides (dsDNA &DNA: RNA hybrid) have been reported extensively⁶. But despite its biophysical and biological importance, the single-molecule electronic properties of double-stranded(ds)RNA and single-stranded (ss) RNA have not been studied to that extent.
Biomolecular electronics, the discipline studying the charge transfer process in biomolecules, has the potential to describe the interaction between electronic materials and biological systems (RNAs) at molecular interfaces. We use the Scanning tunneling microscope-assisted break junction method (STM-BJ)⁷ to study charge transport in short oligonucleotides by reproducible conductance histograms related to their biomolecular structure and conformations. Each biomolecule will be confined within a nanometric gap at a well-defined molecular orientation to measure its electrical properties. Herein, we measured, for the first time, the conductance of individual dsRNA molecules and compared it with the conductance of DNA: RNA hybrids⁸. The average conductance values are similar for both biomolecules, but the distribution of conductance values shows an order of magnitude higher variability for dsRNA, indicating higher molecular flexibility of dsRNA. In our next study, we have demonstrated base-mediated charge transport in specific single-stranded 5 and 10 base pairs(bp) RNA oligonucleotide sequences. We found base stacking is the main factor for getting a probable conductance value for those spontaneously formed RNA oligonucleotide junctions. By comparing with their DNA counterpart, we have found that single-stranded DNA for both 5 and 10 bp sequences are less conductive than RNA due to a lack of base stacking in them.
These results pave the way for measuring various biomolecular interactions at a single-molecule level. In the future, we will measure the conductance of a protein (Argonaute)– RNA complex. This can give us a better understanding of the formation of the RISC(RNA-induced silencing complex) complex and allow the study of the thermodynamics and kinetics of gene expression at the individual complex level. Lastly, we can use these fundamental results for designing next-generation smart biomaterials and biosensors that may address improved biological performances and advanced health monitoring.

References:
1. C. F. Bennett and E. E. Swayze, Annu. Rev. Pharmacol. Toxicol., 2010, 50, 259–293.
2. J. A. Doudna and E. Charpentier, Science, 2014, 346, 6213.
3. D. B. T. Cox, R. J. Platt, and F. Zhang, Nat. Med., 2015, 21, 121–131.
4. Zhang, Y., W. Dubitzky, et al., RNA-induced Silencing Complex (RISC), in Encyclopedia of Systems Biology, Editors. 2013, Springer New York: New York, NY. p.1876-1876.
5. K. G. G. P. Arachchillage, S. Chandra, A. Piso, T. Qattan and J. M. A. Vivancos, J. Mater. Chem. B, 2021, 9(35), 6994–7006
6. Li, Yuanhui, et al. "Comparing charge transport in oligonucleotides: RNA: DNA hybrids and DNA duplexes." The journal of physical chemistry letters 7.10 (2016): 1888-1894.
7. B. Xu and N. J. Tao, Science, 2003, 301, 1221–1223.
8. Chandra, Subrata, et al. "Single-molecule conductance of double-stranded RNA oligonucleotides." Nanoscale 14.7 (2022): 2572-2577.

Poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonate (PEDOT:PSS) is the most common organic semiconductor in OECTs. The comparably high transconductance compared to OFETs, combined with easy circuit integration, makes them good candidates for biosensors. While metabolites and neurotransmitters have been successfully sensed with OECTs, reports on other inflammatory proteins and especially cytokines are few.^1–3

Here, we demonstrate a modification strategy using a small linker molecule to attach to the sulfonates on PSS, which then allows EDC/NHS coupling to bind a recognition element. In this study, we choose aptamers as the recognition elements to demonstrate the concept. Aptamers are synthetic oligonucleotides that exhibit high specificity, low production costs, good shelf-life, and can be modified for various immobilization strategies,⁴ making this a versatile, cheap, up-scalable approach. While first investigations focus on cytokine sensing with aptamers, the approach is easily adaptable to bind other elements of interest (e.g., antibodies, enzymes, …).

1. Kergoat, L. et al. Detection of glutamate and acetylcholine with organic electrochemical transistors based on conducting polymer/platinum nanoparticle composites. Adv. Mater. 26, 5658–5664 (2014).
2. Tang, H., Lin, P., Chan, H. L. W. & Yan, F. Highly sensitive dopamine biosensors based on organic electrochemical transistors. Biosens. Bioelectron. 26, 4559–4563 (2011).
3. Burtscher, B. et al. Sensing Inflammation Biomarkers with Electrolyte–Gated Organic Electronic Transistors. Adv. Healthc. Mater. 10, 2100955 (2021).
4. Maehashi, K. et al. Label-Free Protein Biosensor Based on Aptamer–Modified Carbon Nanotube Field–Effect Transistors. Anal. Chem. 79, (2007).

Biological materials such as amino acids are attractive due to their smaller environmental footprint, ease of functionalization, and potential for creating biocompatible surfaces for devices. Here, we report facile self-assembly and characterization of highly conductive films of composites of phenylalanine, an aromatic amino acid, and PEDOT:PSS, a commonly used conducting polymer, which has been shown to have increased conductivity when doped with polar organic compounds. However, the behavior observed with Phenylalanine is significant because it is non-polar in nature and is biologically derived. We have observed that the composite films formed by introducing aromatic amino acid phenylalanine in PEDOT:PSS can improve the conductivity of the film to about 594 S/cm, a 400% increment compared to the conductivity of a pristine PEDOT:PSS film of about 1.5 S/cm. In addition, the conductivity remains high even with a 10 vol% PEDOT:PSS solution. These conductive properties show a clear trend with changed proportions and the composites appear physically distinct. Using DC and AC measurement techniques, we have determined that the conduction in the highly conductive composites is purely due to efficient electron transport compared to pure PEDOT:PSS films. As observed from SEM and AFM, this is likely due to the phase separation of PSS chains from PEDOT:PSS globules which has previously been shown to increase conductivity since PSS regions impede charge transport. Fabricating composites of bioderived simple amino acids with conducting polymers using facile techniques such as the one we report here opens up opportunities for the development of low-cost biocompatible and biodegradable electronic materials with desired electronic properties.

In-vitro neuroscience makes use of dissociated neural networks of iPSC derived or animal origin, grown on the surface of microelectrode arrays (MEA) for electrical access. Upon exposure of neurons to a MEA surface, neurons adhere and connect to each other at random, creating highly complex systems. The complexity of neural networks can be reduced by various surface patterning methods, which render part of the surface cell adhesive and other parts cell repellant [1]. Alternatively, the use of biocompatible microstructures is a popular method to confine the neural adhesion and guide the growth of their axons. In the past, polydimethylsiloxane-based microstructures were used with great success to pattern precise neural networks in vitro on low-density glass MEAs with an electrode pitch of 500 µm [2,3] and more recently on high density complementary metal-oxide-semiconductor (CMOS) MEAs [4], that offer up to 26’400 electrodes at a pitch of 17.5 µm.
Here, we demonstrate an alternative patterning method that aims to establish neural guidance structures directly on the surface of the CMOS MEA with a spatial resolution only limited by the electrode pitch of the MEA. By inducing hydrolysis locally on user-defined electrode sets, the pH can be selectively altered in the vicinity of the selected electrodes. This mechanism allows for the local formation of polymers that show a pH-dependent formation, such as transglutaminase crosslinked hydrogel which assembles close to neutral pH [5] or the nature-inspired biopolymer polydopamine that forms in slightly basic (pH > 8) environments [6]. We demonstrate that we can alter the pH with single-electrode precision and can quantify the induced pH change optically using the pH reporter 5-(and-6)-carboxy SNARF-1. Using CMOS MEAs with platinum black coated microelectrodes, we are able to inject large enough currents to shift the local pH of the precursor solutions precisely from 6.6 to 8.4 for dopamine polymerization and 5.8 to 7.5 to form hydrogel. We observe constant pH elevations without precision loss for up to 35 min, which is enough time for local polymer formation. Finally, we provide preliminary results that show that the formed hydrogel guides the growth of primary rat cortical neurons and that the observed effects are dependent on the polymerization time of the hydrogel.

[1] Aebersold et al. “Brains on a chip”: Towards engineered neural networks. Trends in Analytical Chemistry (2016)
[2] Ihle et al. An experimental paradigm to investigate stimulation dependent activity in topologically constrained neuronal networks. Biosensors and Bioelectronics (2022)
[3] Girardin et al. Topologically controlled circuits of human iPSC-derived neurons for electrophysiology recordings. Lab on a Chip (2022)
[4] Duru et al. Engineered Biological Neural Networks on High Density CMOS Microelectrode Arrays. Frontiers in Neuroscience (2022)
[5] Milleret et al. Electrochemical Control of the Enzymatic Polymerization of PEG Hydrogels: Formation of Spatially Controlled Biological Microenvironments. Advanced Healthcare Materials (2013)
[6] Lee et al. Mussel-Inspired Surface Chemistry for Multifunctional Coatings, Science (2007)

There is a growing demand for transitioning electronic circuitry and components from stiff and rigid substrates to compliant and flexible platforms, such as thin plastics, textiles, and foams. In parallel, the push for replacing expensive metals-based inks with cost-effective conductive inks has led to the development of formulations with novel nanomaterials and binders.[1,2] Among the nanomaterials, 2D materials, and in particular graphene-related materials (GRMs), have drawn attention due to their increasingly facile and scalable production, high electrical conductivity, and compatibility with industrial manufacturing methods.[3] The resulting conformable electronic materials are poised to unlock thrilling applications in the wearable, healthcare, and Internet of Things sectors. Nevertheless, the substrates, the binders, and the solvents employed are so far often selected without considering the outcome in terms of material sustainability.

We developed electrically conductive composite coatings based on GRMs and biobased and/or biodegradable binders.[2,4] The fabrication is simple and exploits green solvents such as alcohol and/or water. Sustainable binders, ranging from biopolymers and natural waxes such as polyvinyl alcohol and beeswax to proteins from the waste stream such as keratin extracted from wool/feather wastes, were preferred depending on the selected sustainable substrates (i.e., cellulose-/biopolymer-based). The as-obtained materials display a low sheet resistance of about 10 Ohm/sq and excellent stability to tens of folding events, hundreds of abrasions, and thousands of bending cycles. Thus, they can be applied as deformable conductors or strain sensors, depending on the material formulation (i.e., 2D-1D nanofiller hybridization and binder:nanofiller ratio) and the consequent electrical percolation preservation/disruption after mechanical stress. These materials are multifunctional since they exhibit enhanced thermal conductivities. As such, they can be applied simultaneously for thermal dissipation and electromagnetic interference shielding. Due to their flexibility, multifunctionality, and reduced footprint, such versatile electrically conductive coatings have the potential to enable applications in the wearables and conformable electronics field, reducing the environmental impact of the conductive materials for electronics simultaneously.

References:
[1] Ergoktas M. S. et al., 2020, Nano Letters, DOI:10.1021/acs.nanolett.0c01694.
[2] Cataldi P. et al., 2020, Advanced Functional Materials, DOI:10.1002/adfm.201907301.
[3] a) Kovtun A., 2019, 2D Materials, DOI:10.1088/2053-1583/aafc6e; b) Cataldi et al., 2018, Applied Sciences, DOI:10.3390/app8091438.
[4] a) Wu et al., 2020, Advanced Electronics Materials, DOI: 10.1002/aelm.202000232; b) Cataldi et al., 2019, ACS Sustainable Chemistry and Engineering, DOI: acssuschemeng.9b02415.

Human beings are facing severe problems related with the global climate change. There have been international efforts to replace carbon-based energy system with carbon-free/hydrogen-based energy one. Solar hydrogen conversion techniques gains attention as they can produce hydrogen using sunlight and water without emission of greenhouse gas. Photoelectrochemical (PEC) water splitting is considered as one of the promising solar hydrogel conversion techniques because it can be realized using low-cost thin-film materials. However, current low-cost thin-film based PEC devices have a relatively short lifespan due to its low structural stability. Light-absorbing semiconductor of the PEC device severely suffer from photocorrosion by electrolyte. Although amorphous TiO₂ is deposited via atomic layer deposition on the device to provide physical separation between the semiconductor and electrolyte, photoelectrons accumulated near the device surface induce the reduction and dissolution of the TiO₂ layer. In addition, platinum (Pt), which is the best hydrogen evolution reaction (HER) catalyst, can be easily agglomerated and detached from the PEC device.
Although various strategies including insertion of functional layer under the catalyst have been introduced, still there is a need to develop a versatile protection strategy which can prevent both co-catalyst detachment and photocorrosion for practical operation of PEC devices. We hypothesize that device-on-top protector made of nanoporous polymeric network may prevent the dissociation of components of the PEC device. A protector with a high transparency and water content can be preferred in order not to disturb light transmission and electrolyte transfer to the device. We are inspired by ocean plants where algae cells are covered by ‘hydrogel’ which has a transparent and nanoporous polymer network structure having high water content.
In this study, we demonstrate that the hydrogel protector on the PEC device enhances the structural stability of the PEC devices. As a hydrogel protector, we selected low cost polyacrylamide which has high chemical inertness in electrolyte solution. The hydrogel was coated on a reference Pt/TiO₂/Sb₂Se₃ photocathode via a mold casting method. Dynamics of hydrogen bubbles in the hydrogel and their escape can depend on the mechanical and structural properties of the hydrogel. We demonstrate that trapped bubbles cause the fracture of the protector in the case of high concentration of hydrogel. When the hydrogel protector is relatively thick, hydrogen bubbles are trapped inside the protector leading to reduction in photocurrent. With the protector having the optimal properties, bubbles can effectively escape from the protector through micro gas tunnels which are formed in the hydrogel at the initial stage of the PEC operation. The hydrogel protector coated on the PEC device can prevent detachment of Pt catalyst and dissolution of TiO₂ layer. Compared to without protector, the lifetime of the Pt/TiO₂/Sb₂Se₃ photocathode covered by the hydrogel protector was increased by 100 folds. Furthermore, we showed the hydrogel protection strategy can be applied to various types of PEC devices including SnS photocathode and BiVO₄ photoanode. We expect that further engineering of the hydrogel in terms of microstructure, poroelastic property, and chemical property can help to develop a semi-permanent hydrogen production system.

Organoids are three-dimensional, multi-cellular constructs with emergent structural properties that mimic organizational features found in natural tissue. Individual organoids can fuse together to form tissue-like structures, termed “assembloids,” that can serve as in vitro models of human development and disease. A key requirement for assembloid fabrication is the spatial positioning of individual organoids, which is currently performed manually. To automate and scale-up this biofabrication process, we have developed a family of biopolymers that work together with a custom-built electromagnetic bioprinter. Here, we demonstrate the capacity for an iron-oxide nanoparticle-laden hydrogel to mediate the spatial patterning and subsequent fusion of human induced pluripotent stem cell (iPSC) derived neural organoids within a support hydrogel. The support material is shear-thinning and self-healing to accommodate the motion of the electromagnetic printer, promote organoid hydration, and achieve stable placement within three-dimensional space while organoid fusion occurs. Unlike aspiration-mediated biofabrication approaches that can lead to irreversible plastic deformation of cellular aggregates, magnetic lifting was well tolerated by the organoids. We leveraged this system to create precisely arranged neural assembloids with excellent viability and maintenance of the internal cytoarchitecture of individual organoids. In summary, this platform represents a significant advance in the emulation of large, compositionally diverse neural tissues to enable high-throughput studies of neural development and disease.

Synthetic DNA, as small functional molecules or in large self-assembled structures, provides exquisite addressability, functionality, and fidelity. As a poly-electrolyte with repeating negative charge DNA mimics poly-anionic proteins found in enamel, bone, and marine organisms. DNA aptamers have been selected to influence calcium phosphate mineral formation using a novel precipitation SELEX method. These aptamers have been demonstrated to slow mineralization kinetics while altering materials morphology depending on pH and the presence of G-quadruplex secondary structures. Current research efforts have been in applying DNA aptamers to calcium phosphate mineralization of collagen and to calcium carbonate mineralization. Using DNA aptamers in coordination with DNA self-assembled materials, such as DNA origami, is currently being explored as a means for building and mimicking hierarchical structures.

Hydrogels have emerged as a promising platform for three-dimensional (3D) in vitro models of disease progression. However, widely utilized animal-derived matrices (e.g. Matrigel/Cultrex) are highly variable and do not allow for tuning of biophysical and biochemical cues. Additionally, such matrices do not capture the dynamic features of the in vivo extracellular matrix (ECM), which is remodeled during disease progression and causes further dysregulation of cell behavior. Here, we present an engineered matrix crosslinked by dynamic covalent bonds that enable on-demand tuning of material mechanics to model the stiffening of the liver during fibrosis.

During disease progression of fibrosis, there is an associated increase in the deposition of elastin, fibronectin (FN), and hyaluronan (HA), resulting in an increase in stiffness. We have established a liver-mimetic environment by incorporating HA modified with benzaldehyde functional groups and a recombinant elastin-like protein (ELP) modified with hydrazine functional groups to create a HA-ELP (HELP) matrix. The engineered elastin-like protein (ELP) contains a cell-adhesion motif from fibronectin and a peptide sequence derived from elastin. When mixed, the benzaldehyde and hydrazine functional groups form dynamic hydrazone bonds, which can break and reform at physiological conditions, creating a dynamic microenvironment. By altering the wt% of HA and ELP, we have assembled a suite of HELP gels whose stiffnesses (0.5 – 6 kPa) reflect that of normal liver through those with advanced stages of fibrosis. To regulate HELP stiffness during culture, we have introduced a small molecule competitor that competes for crosslinking sites, which can decrease the crosslink density and stiffness of HELP. Over time these competitors diffuse out of the hydrogel, which leads to an increase in crosslink density that mimics the stiffening environment that occurs during the progression of fibrosis.

Using a library of competitors, we demonstrate that HELP stiffness can be reduced by an order of magnitude in a dose-dependent manner. By altering the chemical functionality of the competitor, we can tune the time-scale of modulus recovery, ranging from < 1 day to over three weeks. This enables us to examine the effect of acute stiffening and the effect of gradual stiffening occurring over a >2 week period. Using this chemically defined, adaptable hydrogel platform, we developed a model of liver fibrosis progression using human hepatic organoids (HO). We combine HELP with laminin-111 to promote the formation and culture of HO, and demonstrate long-term growth of HO across a variety of stiffnesses. Finally, we demonstrate that incorporation of competitors does not impact HO growth and morphology. Human HO grown in HELP matrices are viable, proliferative, and metabolically active, and they continue to express markers of differentiated hepatic tissue and accumulate lipids in a stiffness-dependent manner. We are currently evaluating the altered metabolic profile and lipid accumulation in these gradually stiffening materials.

Overall, we have developed of a dynamic HELP hydrogel with on-demand control of mechanical properties using crosslinking competitors. We demonstrated formation and growth of HO in dynamic HELP with liver-mimetic stiffnesses to model liver fibrosis progression.

We report 3D-bioprinted skin-mimicking phantoms with skin colors ranging across the Fitzpatrick scale. These tools can help understand the impact of skin phototypes on biomedical optics. Synthetic melanin nanoparticles of different sizes (70–500 nm) and clusters were fabricated to mimic the optical behavior of melanosome. The absorption coefficient and reduced scattering coefficient of the phantoms are comparable to real human skin. We further validated the melanin content and distribution in the phantoms versus real human skins via photoacoustic (PA) imaging. The PA signal of the phantom could be improved by (i) increasing melanin size (>1,000-fold), (ii) increasing clustering (2–10.5-fold), and (iii) increasing concentration (1.3–8-fold). We then used multiple biomedical optics tools (e.g., PA, fluorescence imaging and photothermal therapy) to understand the impact of skin tone on these modalities. These well-defined 3D-bioprinted phantoms may have value in translating biomedical optics and reducing racial bias.

Complex networks of polymer linked nanoparticles have potential applications in chemical separation, biomedicine and nanophononics. Inspired by Cajal’s picture of a single neuron [Gomez-Marin, Science, 2022, vol 375, issue 6586, p 1237], the tree-like single neuron structure could be the key to developing new brain-like computing materials. In this work, we have designed computational models of binary tree networks using polymers and gold nanoparticles (AuNP) to mimic a neuron structure. The tree structure and thermal transport properties in polymer-AuNP networks are uncovered using all-atom molecular dynamics simulations. We vary the height of the binary tree structure from 1 to 5 levels corresponding to a total number of 2 to 32 leaves. The heat flux in both directions, from leaves to the root and from the root to leaves, are reported. Two polymer types of similar branch chain length with different backbone stiffness are compared, viz. polyethylene (PE) and poly(p-phenylene) (PPP). We also compared tree networks with different branch chain length using 12 and 50 carbon length PE. The results from our simulations provide useful guidance for developing new bioinspired materials and devices.

Non-invasive manipulation of cell signaling is critical in basic neuroscience research and in developing therapies for neurological disorders and new tissue engineering and regenerative medicine approaches. Current techniques for drug-free, selective, and deep stimulation of the nervous system present major drawbacks such as low spatial resolution, limited target depth or the requirement of highly invasive neurosurgical procedures. To overcome these limitations, nanotechnology approaches are being developed to allow for wireless and cell-type specific neuronal stimulation. Though it is known that electric fields modulate several biological processes and that neurons are electrogenic cells, electrical stimulation and conductive cues have been disregarded in tissue engineering and regenerative medicine approaches until recently. In this work, biomimetically synthesized conductive copolymer 3,4-ethylenedioxythiophene (EDOT)-Pyrrole nanoparticles (RB02 NPs) were used for enhancing neuronal differentiation and for wireless and localized neurostimulation.

Biomimetic synthesis of EDOT-Pyrrole copolymers doped with PSS was carried out using hematin as catalyst. The obtained RB02 NPs were characterized by means of Raman spectroscopy, Fourier transform infrared spectroscopy, electron microscopy and dynamic light scattering. The electrochemical properties were characterized by galvanostatic charge discharge, voltammetry, and electrochemical impedance spectroscopy. For electrical stimulation of neurons, NPs were charged by applying 3V using platinum electrodes, obtaining C-RB02 NPs. NPs effect on ND7/23 neuron hybrid cell line viability was assessed by live/dead staining using flow cytometry. ND7/23 differentiation was evaluated by cell cytoskeleton staining and quantification of morphological parameters such as dendrite number and length. Primary cortex neuronal stimulation was studied by calcium ion influx detectable through the dynamic fluorescence changes of Fluo-4.

The NPs presented a pseudocapacitive behavior and large specific capacitance, allowing their use as nanocapacitors by charging them through electrical current exposure, obtaining C-RB02 NPs. The live/dead assay showed that RB02 NPs presented no toxicity towards ND7/23 cells. Furthermore, charged NPs enhanced cell differentiation at short times after addition (<6 hours), evidenced in cells with more and longer dendrites. Charged RB02 NPs largely increased cortex neuronal activity assessed by intracellular calcium dynamics.

In conclusion, biomimetic synthesized conductive RB02 NPs were used for the localized stimulation of neurons. Biomimetic synthesis was utilized to avoid cytotoxicity of the nanomaterials associated with traditional wet chemistry protocols. RB02 NPs displayed similar charge-transfer velocity and larger specific capacitance than PEDOT:PSS, benchmark in electroconductive material for bioengineering. Electroconductive RB02 NPs were shown to enhance ND7/23 differentiation within 3 hours of co-culturing. The differentiation effect was more pronounced when charged nanoparticles were employed. Charged RB02 NPs largely increased neuronal activity in primary rat cortical networks assessed by calcium imaging. Overall, biocompatible RB02 NPs fabricated here have a great potential for the remote control of biological signaling, which is anticipated to contribute to the progress of basic neuroscience research and for developing neurological therapies.

Hydrogels that can be injected into the body using standard needles or catheters enable a minimally invasive strategy to prolong local delivery of therapeutic drug and cellular cargo. In particular, physically crosslinked hydrogels exhibit shear-thinning and self-healing behaviors enabling facile injectability and depot formation upon administration. While prior efforts to characterize these systems have focused on injectability and cargo release behaviors, prediction of cargo release in the body often assumes the materials form a depot rather than spreading out upon administration. Here, we evaluate how hydrogel rheology correlates with depot formation and persistence following subcutaneous administration in mice with two physiochemically-distinct, physically crosslinked hydrogel systems. We evaluate calcium-alginate and polymer-nanoparticle hydrogel systems exhibiting variable mechanical behaviors across several rheological properties (stiffness, viscoelasticity, yield stress, and creep). By relating measured rheological properties to depot formation and persistence time following subcutaneous administration, for these two gel systems we identify that yield stress is predictive of initial depot formation while creep is predictive of depot persistence. Indeed, only materials with yield stresses greater than 25 Pa form robust depots, and reduced creep correlates with longer depot persistence. These findings provide predictive insights into design considerations for hydrogel technologies capable of extended controlled release of therapeutic cargo.

For cell physiology, the microenvironment can play an important role, and hydrogels can provide a three–dimensional microenvironment to allow native cell growth in vitro. Hydrogels, a crosslinked hydrophilic polymer that does not dissolve in water, have been widely studied as an artificial extracellular matrix (ECM) that can mimic the ECM of various tissues due to its high water retention capacity, permeability to cellular nutrients and metabolites, excellent mechanical properties and biocompatibility. The mechanical properties of the extracellular matrix (ECM) contribute to the regulation of various cellular behaviors, and controlling the mechanical properties of hydrogels is of key importance in enabling various cell-hydrogel interactions. However conventional hydrogels have a homogeneous environment with an isotropic distribution limiting complete mimicking of the complex architectures of native tissues and pathological gradients found in tumors, scars, and wounds. In this work, we report hydrogel with gradient mechanical properties using hyaluronic acid which is a natural polymer and an excellent candidate for use in tissue engineering due to its excellent biocompatibility and bio–functions. Hyaluronic acid was conjugated with methacrylate and ¹H NMR spectrum confirmed the successful synthesis of methacrylated hyaluronic acid. We successfully prepared the gradient hydrogel via photocrosslinking method, and the studies were performed with syringe pumps for gradient generation and a fluidic mixer for homogenous mixing of hydrogel precursors with different crosslinker concentrations. The gradient hydrogel was characterized and assessed the feasibility of tissue engineering application. The successful formation of the gradient in crosslinking density is confirmed by NMR spectrum and the viscoelastic properties of the hydrogels were tested on a rheometric fluid spectrometer. Scanning electron microscopy confirmed the different cross–sectional morphology and the pore size in our hydrogel system. For in vitro test, L929 fibroblasts were encapsulated in gradient hydrogel and stiffness–dependent cellular behaviors are monitored using a confocal microscope. In all samples, cells are highly active and spread well along the hydrogel substrate, and enhanced cell spreading was confirmed as the degree of crosslinking decreases. We further investigated the hydrogels’ cell differentiation ability by culturing human adipose tissue–derived mesenchymal stem cells (hAD–MSCs) and stiffness–dependent hAD–MSCs morphology, migration, and differentiation were studied. In vitro drug release analysis was conducted to evaluate the drug release profile of gradient hydrogel and a gradual release of the model drug was observed. Taken together, this gradient hydrogel will be exploited in a tissue engineering platform to mimic variable mechanical gradient tissues.

A non-invasive glucose monitoring system is ideal for measuring glucose levels. However, most diabetic patients still rely on the traditional invasive finger-prick measurements due to the cost issue. We developed a disposable contact lens-based colorimetric glucose sensing platform. A plant-derived polyphenolic polymer called poly(tannic acid) having substantial molecular adhesion was used as a functional coating layer for conjugating a nucleophilic molecule, 4-mercaptophenylboronic acid. The boronic acid-functionalized contact lenses showed a strong and reversible binding affinity for glucose depending on pH conditions. The bound glucose can be released by immersing the contact lens in an acidic enzymatic cocktail, resulting in an immediate color change. This allows a facile colorimetric determination of glucose levels. The glucose concentration dependent color change was quantified by UV-vis studies. The successive chemical modifications of the contact lens surface were characterized by XPS analysis and contact angle measurements. An in-vitro cytotoxicity test (i.e., CCK-8 assay) confirmed the biocompatibility of the system. Taken together, our glucose-sensing contact lens is expected to successfully replace the conventional glucose measurement methods; this will be especially beneficial for low-income people.

Disruption of cell plasma membranes, a crucial component of cells, is fatal for cellular functions. Poloxamer 188 (P188), a poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (PEO–PPO–PEO) triblock copolymer, is known to protect cell membranes against various external stresses and injuries, demonstrating its potential to treat diseases such as Duchenne muscular dystrophy or ischemia-reperfusion injury. However, the mechanism by which the polymer protects the cell membrane is poorly understood. Here, I present several systematic approaches to exploring how amphiphilic block copolymers interact with cell membranes and model lipid bilayers. First, we probed how block copolymer architecture affects cell membrane protection using a cellular membrane integrity assay and precisely synthesized PEO–PPO diblock copolymers. To gain a more quantitative assessment of the interactions at the molecular level, we employed supported lipid bilayers as model cell membranes. Binding kinetics and surface coverage of similar molecular weight P188 and a PEO homopolymer were examined using surface plasmon resonance spectroscopy. Distribution of P188 and PEO within the bilayer was studied using neutron reflectivity and atomic force microscopy. We discovered that P188 and PEO both adhere to the lipid bilayer with slow binding kinetics, and surprisingly, both penetrate into the inner lipid leaflet, suggesting that PEO plays a significant role in driving the block copolymer interactions with cell plasma membranes. Study with fluorescent dye-labeled polymers translates these finding to living tissue. Collectively, these results provide important clues regarding how block copolymers protect cell membranes.

Long acting injectables aim to improve the current standard of care for various infectious diseases and neurological disorders, by eliminating the oral dose. As a result, decreasing dosing frequency with highly active, well-tolerated medications offers an avenue by which the challenges of pill/treatment fatigue, and desire for anonymity can be addressed, while also improving outcomes. To further simplify the dosing schedule and improve adherence, we aim to develop a pulsatile release formulation that enables long-acting delivery of API through either a subcutaneous or intramuscular administration.
A microfluidic approach is proposed to fabricate biodegradable, biocompatible PLGA drug loaded microparticles to enable high drug loading, sustained-release formulations. A glass focus-flow microfluidic design was used to form single oil-in-water emulsions and fabricate PLGA drug loaded microparticles. The dispersion, or oil phase, consists of the drug, organic solvents, and polymer. The continuous, or water phase, consists of a water miscible surfactant. The drug loaded (API_A), single emulsions formed droplets ranging from 150 um to 300 um. The size of the diameter has been shown to be tunable to a desired value based on the capillary number and the relative fluid velocities ratio.
A solvent evaporation step is incorporated to remove two organic solvents. As a result, a 73% reduction in drug loaded (API_A) microparticle size is observed after a timeframe of two days. Gas chromatography confirmed there to be no residual organic solvents detected in washing steps or in dissolved drug loaded (API_A) microparticles. SEM images showed a spherical shape maintained after mixing and washing steps. However, some large pores were captured on the microparticles based on the SEM images, perhaps due to one of the organic solvents, which is also miscible in water, leaving the PLGA polymer upon droplet formation.
A lyophilization step was incorporated after the washing step of the microparticles, to improve drug loading efficiency assessment using UV spectrometry. Furthermore, drug loading efficiency increased, from 3% to 10%, by increasing the polymer to API_A ratio. Due to one of the organic solvents forming a stream upon droplet formation on a chip, as the possible root cause to our low drug loading efficiency, a different API (API_B) was assessed. Furthermore, prodrugs of API_A, are also currently being investigated to improve its hydrophobicity and therefore increase its drug loading efficiency.
API_B, with its lower solubility in water, was also investigated and showed significant improvement to drug loading efficiency, in comparison to API_A, and eliminated the need of one of the organic solvents. The control release functionality of API_B, using a USP-4 apparatus is currently being investigated. An exploratory PK/PD study will also be conducted to test the microfluidic technology.

Dynamic behaviours driven by intracellular cytoskeleton such as migration, division and endocytosis are mainly regulated by the contraction of cytoskeleton network consisting of cytoskeleton and motor proteins. Depending on the functional demand in each cell function, various structures and contraction characteristics of cytoskeleton networks are observed. For example, in the early phase of cytokinesis, chromosome segregation is progressed by the radial-directional contraction of the linear assembly of microtubules and motor protein dynein. During cleavage furrow ingression, the ring-shaped actin-myosin structure attached to the inner surface of cellular membrane shrinks at a constant speed by the circumferential-directional contraction of the ring.
Many have studied how the contractile behaviours of cytoskeleton-motor protein networks depend on protein concentrations, chemical environments and geometric boundaries. In vitro experiments found that concentrations of motor protein and network crosslinkers play a crucial role in modulating contraction speed of the cytoskeleton-motor network. KCl concentration is critical for the global and synchronized contraction of actin-myosin network. The speed and length scale of the network contraction were significantly affected by the network shape such as square and circle. Nonetheless, it remains unclear how the mechanical boundary condition of the motor protein determines the dynamics characteristics of cytoskeleton-motor protein network contraction.
Here, we analysed the contractile behaviours of actin-myosin network in two different mechanical boundary conditions of motor protein, myosin. We prepared “immobilized motor” (IMM) condition by firmly attaching myosin thick filaments to a glass surface. In “mobile motor” (MM) condition, actin network cross-linked with actin binding proteins (ABPs) were prepared on a glass surface coated with cellular lipid membrane allowing movement of motor proteins. Contraction of actin-myosin network in IMM and MM conditions were visualized using fluorescence-conjugated actin. We found that the relative concentration of actin and ABP which defines a network connectivity determines the contraction shape and speed. While contracting actin-myosin networks exhibited radial patterns in IMM condition, a global and isotropic contraction was observed in MM condition. Contraction speed increased with the network connectivity in MM but decreased with it in IMM condition.
To elucidate the mechanism of the actin contraction depending on the boundary condition of motor protein, we developed a computational model tracking each component of network such as actin, ABP and myosin during contraction. The radial contractile pattern of actin network was exhibited in IMM condition similar to the experimental results. The computational simulation found that local actin-myosin clusters gathered into a larger one leading to a global contraction in MM condition.
In summary, we showed how the characteristics of actin-myosin network contraction depend on the mechanical boundary condition of myosin motor protein. Changes of contraction behaviours in terms of contraction pattern and speed by the network connectivity depends on the mobility condition of motor protein. While the contraction speed increased proportional to network connectivity in MM, it decreased in IMM condition. Our study provides an intuition into not only the mechanism of cell dynamics but also the design of biomimetic systems. By modulating the mechanical boundary condition of motor protein, a dynamic molecular system transporting substances to a target destination can be designed.

Large bone defects have attracted attention as a remain major challenge in bone tissue engineering. In bone tissue, the mineralized collagen fibril is an important basic building block which collagen molecules are hierarchically assembled into fibrils and mineralized with the formation of hydroxyapatite (HAp) nanocrystals. Due to the uniformly distribution HAp in collagen fibrils and together built up hierarchically from nano to macrostructures in bone tissue, mineralized collagen fibril is regards as the important level for the mechanical properties. Collagen based scaffolds have been increasing used in tissue engineering due to its excellent biocompatibility. However, the insufficient mechanical strength and structural support limit it wider in bone regeneration application. Many attempts have been devoted to improve collagen-HAp based scaffolds’ properties by understanding the process of bone mineralization to fabricate bone mimicking scaffolds. The mineralization pathway of HAp has been suggested as non-classical crystallization as reported, but the physical and chemical mechanism is still poorly understood with a difficult challenge, especially in collagen fibril’s structure. In this work, with the presence of polydopamine (PDA) to promote the biomineralization process, the structure of intrafibrillar mineralized collagen-PDA fibrils in modified-simulated body fluid (m-SBF) solution was studied at the nano scale by STEM-EDS techniques to investigate a detail hydroxyapatite intrafibrillar mineralization pathway. Collagen-amorphous calcium phosphate (ACP) fibrils was obtained by assembling Collagen-PDA fibrils in SBF solution with the present of Mg²⁺ and polyaspartic acid as a precursor stabilizer. Then later the phase transformation of ACP to HAp was determined by tuning the phosphate concentrations in m-SBF. It was found, in this work, that the phase transformation of ACP to HAp in Collagen fibrils can be accelerated even in 12 hr-mineralization with the m-SBF solution of calcium and phosphate ratio of 1:10, higher phosphate ratio produces a monodentate Ca-P geometry and evolved directly to HAp, while the lower 1:5 would affect in slower phase transformation kinetic, and for 1:1 the crystallization of HAp cannot be initiated even up to 7 days of mineralization. The finding suggests that an elevated concentration of phosphate is crucial for initiate phase transformation of ACP to HAp. From these studies and strategy, we adopted to fabricate mechanically self-sustained Collagen-PDA-HAp hydrogels. By controlling the mineralization, it is beneficial for collagen-based scaffolds’ fabrication design. A synergistic effect was also investigated and observed in the Collagen-PDA-ACP and Collagen-PDA-HAp for both in vitro osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). Thus, the results presented in this work could serve a better understanding the mechanism of the HAp mineralization in collagen fibrils, which may provide approaches to effective, and materials design for efficient osteogenesis bone tissue engineering.

Black phosphorus (BP) has been widely investigated for various biomedical applications with the unique characteristics of 2D nanomaterials including its high photothermal conversion efficiency, biocompatibility, biodegradability and ultraviolet (UV)-meditated reactive oxygen species (ROS) generation. However, the finite depth of light penetration has limited further development of BP-based photomedicines. Here, we developed hyaluronate-BP-upconversion nanoparticle (HA-BP-UCNP) complex for near-infrared (NIR) light mediated multimodal theranosis of skin cancer with photoacoustic (PA) bioimaging, photodynamic therapy (PDT), and photothermal therapy (PTT). In contrast to the conventional BP-based skin cancer theranosis systems, HA-BP-UCNP complex could be non-invasively delivered into the tumor site to induce the cancer cell apoptosis upon NIR light irradiation. HA in the complex facilitated the transdermal delivery of BP into the tumor tissue under the skin. Upon 980 nm NIR light irradiation, UCNP converted the light to UV-blue light to generate ROS by sensitizing BP in the HA-BP-UCNP complex for PDT. Remarkably, 808 nm NIR triggered PTT for the apoptosis of tumor cells. The photoacoustic imaging of BP successfully visualized the non-invasive transdermal delivery of HA-BP-UCNP complex into the mice skin. The cell viability test revealed the low cytotoxicity of HA-BP-UCNP complex in fibroblast cells. On the other hand, the complex showed high cytotoxicity to tumor cells under NIR light irradiation by PDT and PTT. The combination therapy of PDT and PTT by 980 + 808 nm NIR light irradiation drastically reduced tumor growth compared to only single NIR light irradiation for up to 7 days in skin cancer model mice. The antitumor effect of HA-BP-UCNP complex with NIR light irradiation was also confirmed by immunohistochemical TUNEL assay. Taken together, we could demonstrate the feasibility of HA-BP-UCNP complex as a non-invasive theranostic nanoplatform for skin cancer.

The breast precancer stage will not necessarily develop into invasive breast cancer and theoretically does not always require treatment. However, it is impossible to predict whether precancers will become invasive cancer. More than 90% of breast precancer cases contain pathological minerals called microcalcifications. Most microcalcifications are calcium phosphate in the form of apatite, and their composition and crystal properties correlate with malignancy in clinical samples and may have a prognostic value. In clinical samples, apatite crystals with high and low carbonate content are associated with benign and malignant lesions, respectively, and calcium oxalate dihydrate (COD) is always found in benign lesions. Recent in vitro and in vivo studies show that specific changes in the properties of apatite crystals can trigger precancer progression.
Here, we developed a breast tumor in vitro model consisting of synthetic microcalcification analogs embedded in precancer multicellular spheroids that mimic the 3D microenvironment of mammary ducts. As microcalcification analogs, we use various synthetic mineral types that are physiologically relevant: apatite with high and low carbonate content and COD. Our methodology includes micro-CT for 3D imaging of mineral particles within soft tissues and scanning electron microscopy and vibrational spectroscopy for mineral characterization.
We show that cell proliferation and the expression of proteins associated with cancer change with the properties of the embedded mineral in our in vitro model. Low carbonate apatite promotes precancer malignancy compared to other types of minerals or conditions of no added mineral. Surprisingly, COD suppresses precancer malignancy compared to apatite or conditions of no added mineral. This finding suggests that microcalcifications can affect precancer cells by either triggering them to proliferate or inhibiting their proliferation, even compared to conditions of no minerals. Possibly, the presence of COD crystals only in benign clinical tissues is not random but is a result of its tumor-suppressing qualities. Insights from this study may suggest in the future ways of affecting disease progression by manipulating the crystal properties of breast microcalcifications in situ.

Hydrogels have found widespread utility in many research areas including controlled therapeutic delivery and tissue engineering. Many gel systems have been developed that mimic properties of the extracellular matrix (ECM), providing biocompatibility and enabling 3D cell culture. Traditionally, hydrogels have been formed from polymeric precursors that are either naturally occurring or synthetic. Natural gels are derived from naturally occurring biomolecules, often extracted from tissues. As such, many of these hydrogels mimic the ECM at a chemical and/or structural level, making them a top choice for biomedical applications, but lack in their tunability, providing researchers with few options to control these systems in a defined manner. They also frequently suffer from batch-to-batch variation, creating technical challenges in their implementation. In contrast, hydrogels formed from synthetic polymers retain batch-to-batch similarity and provide significantly more tunability through incorporation of diverse chemistries during synthesis or crosslinking. However, many of these materials are dissimilar to the chemical and/or structural makeup of the ECM. On top of this, both synthetic and natural hydrogels are intrinsically polydisperse. This results in networks with an ill-defined inter-crosslink distance, impacting material elasticity and contributing to overall heterogeneity in these ideally homogenous systems. To unite the advantages of synthetic and natural hydrogels, there has been growing interest in engineering materials from recombinant proteins. These efforts remain nascent but promise perfectly monodisperse, customizable gel networks, with molecular tunability achieved through engineering at the amino acid and fusion protein levels, while also mimicking the proteinaceous nature of the ECM and conferring high biocompatibility. Our work is focused on further enabling external tunability of recombinant hydrogels by installing stimuli-responsivity, which has often been limited to synthetic polymers.

We have developed and characterized a novel, stimuli-responsive recombinant gel platform named PhoCoil. This material is injectable, photodegradable, and formed from a single protein. PhoCoil is crosslinked through homopentameric, physical coiled-coil interactions, resulting in a reversible gel-sol transition in response to applied shear force. Coil domain pairs are connected by an intrinsically disordered protein, originally engineered for high expression and low immunogenicity, providing intra-protein mobility and enabling intermolecular interactions without steric restriction. At the center of the protein is PhoCl, a photolabile green-fluorescent protein which undergoes irreversible cleavage of the polypeptide backbone in response to visible light. The resultant PhoCoil protein hydrogel is shear thinning and self-healing due to its physical crosslinking, enabling easy injection, as well as degradable on-demand in response to cytocompatible light. PhoCoil degradation can be spatiotemporally triggered through conventional mask-based and laser-scanning photolithography. Controlled hydrogel softening can also be achieved by modulating the light dosage, or through co-formulation with a non-light-responsive coiled-coil protein network. PhoCoil is the first fully recombinant protein hydrogel to utilize PhoCl as a cleavable linker and is differentiated from other previously developed photoresponsive recombinant hydrogels by its stability in ambient light and its simple single-component formulation, which does not require any small molecule or metal additives. PhoCoil hydrogels have applications in in vitro cell culture, as they show high cytocompatibility and enable bioorthogonal post-encapsulation release for single-cell analysis. Of particular interest is the use of PhoCoil for controlled, localized drug or cell delivery via post-injection photodegradation, which has been demonstrated in proof-of-concept ex vivo studies.

The neurovascular unit (NVU) is an essential component of the central nervous system with a vital role in maintaining brain homeostasis. The early onset of several neurological disorders has been associated with alterations in the blood-brain barrier (BBB), a component of the NVU that protects the brain microenvironment from potentially harmful substances circulating in the bloodstream (e.g., small molecule drugs, bacteria).¹ Despite recent advances in the study of neuro-pathologies, at present there are very limited effective treatments against neurological disorders and amongst others, the lack of appropriate research tools is a major limitation. In vivo animal models have high costs, are time-consuming, and carry uncertainties in the translation to human biology. Therefore, there is a compelling need to explore technologies capable of better resembling the human brain milieu in health and disease. 3D in vitro models, such as 3D gels and scaffolds integrating human cells are excellent inert supports prompting in vivo-like tissue generation.²
Here, we used a composite electroactive scaffold integrating biomolecules of the human brain extracellular matrix (ECM) as a biomimetic substrate for hosting vascular endothelial and neural cells representative of the NVU. We reconstructed the neural tissue microenvironment using a tri-culture cell model, whose barrier formation, integrity, and neural-glia compartment were characterized via Confocal and Two-Photon Microscopy, showing the development of a multicellular neurovascular unit-like structure. Electrochemical Impedance Spectroscopy (EIS) was also used as a sensitive tool to provide a continuous and non-invasive readout of cell properties and tissue generation real-time. This NVU model has great potential as test bed for screening neurological drugs and disease modelling.

References
[1] Bhalerao, A. et al. In vitro modeling of the neurovascular unit: advances in the field. Fluids and barriers of the CNS 17, 22 (2020).
[2] Moysidou, C. M., Barberio, C. & Owens, R. M. Advances in Engineering Human Tissue Models. Front. Bioeng. Biotechnol. 8, 620962 (2021).

Through its appealing avenues of processing the component devices at room temperature and from low-cost precursor materials, organic electronics has a tremendous potential for the development of products able to achieve the goals of production sustainability as well as environmental and human friendliness for electronics.

In an effort to stave off the e-waste growth, the presenter and his research group went further down the path opened by organic electronics research and investigated a large number of biomaterials as substrates, dielectrics, semiconductors and smoothening layers for the fabrication of organic field effect transistors, integrated circuits and organic solar cells. The presentation will focus on the highlights of our recent research, especially with respect to materials investigated, devices fabricated and the immense potential for follow up research:
-Flexible natural and biodegradable substrates
-Natural dielectrics
-Bioorigin, H-bonded semiconductors in the families of indigos, anthraquinones and acridones
-Biodegradation protocols for organic semiconductors

These highlights will be placed in the context of the mountain that one has to climb in order to reach the coveted “green” connotation for electronics, sensors and integrated circuits:
-Biocompatibility issue
-Biodegradability issue
-Compostability issue
-Cost of production / energy expanded in production issue
-Materials choice issue (carbon foot print)
-Toxicity and the environmental impact of the synthetic avenue for component materials

The potential of follow-up research in the green electronics field is immense, with large area electronics fabrication, biomedical implants, bio-sensing and smart labeling, representing only the tip of the iceberg of many more immediate possibilities of high interest for our group. Natural and nature-inspired materials have the unrivalled capability to create “safe-first” electronic markets for human and environment, with minimal or even neutral carbon footprint.

Skin wearable piezoelectric nanogenerators (WPENGs) have recently drawn significant attention owing to their unique properties, like flexibility, sensitivity, and self-powered nature. Barium Titanate (BaTiO₃) is one of the eco-friendly piezoelectric ceramics. In recent days, BaTiO₃-based piezo-fillers use in WPENGs has attracted broad concern. Herein, bio-inspired microcracks, skin wearable, cost-effective, highly sensitive, and flexible PENGs were developed using functionalized multi-walled carbon nanotubes (f-MWCNTs) doped barium titanate (BaTiO₃)/poly(dimethylsiloxane) (PDMS) film. f-MWCNTs/BaTiO₃@PDMS was prepared by mixing of f-MWCNTs/BaTiO₃ and PDMS polymer solution by the overnight vacuum drying process. The sensor film was prepared by sandwiching f-MWCNTs/BaTiO₃@PDMS film between two PDMS films, followed by making electrical connections with two copper wires to form the WPENG. The as-prepared composite and PENG film were characterized by powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy-dispersive X-ray analysis (EDX), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The composite PXRD data revealed the degree of crystallinity is 63%. FE-SEM and TEM results clearly showed that BaTiO₃ in-situ coupled with f-MWCNTs with the addition of BaTiO₃ with f-MWCNTs. The real-time application of the developed sensor was carried out by attaching the sensor to the throat to detect the minute oscillations produced during speaking. Monosyllabic, disyllabic, and polysyllabic words were spoken by the reader and their corresponding waveforms are recorded to show the ability of the sensor to clearly differentiate between these words. The sensor is also equally sensitive to male and female voices. A disyllabic word was spoken by a male and a female, and the recorded waveforms have a similar trend with different amplitudes. These results indicate the potential of the fabricated sensor to detect the human vocal cord vibrations efficiently, and paving a path to design a system for a wider range of applications in the next generation of noise detection and skin wearable sensors.

Colloidal arrays create structural colors originating from the constructive interference by the periodicity of the nanostructures. They are highly bright and angle-dependent when the colloids are periodically stacked. There have been several strategies to crystallize colloids in a film format; dip-coating, doctor-blading, infiltration, and roll-to-roll process. However, these methods cannot induce regioselective crystallization in the first place, but rather require additional processes for the patterning. Recently, many researchers exploit the secondary assembly of photonic spheres to construct a photonic surface. However, the spherical compartments have low reflectivity because of the lack of a planar region for backward reflection. Furthermore, several layers of spheres are needed because their monolayer inevitably leaves vacancy due to the interstices between roundish morphologies.
Here, we induce polyhedral deformation of photonic emulsions with built-in crystalline colloidal arrays to create planar surfaces with no voids even with a monolayer of emulsions. We use a microfluidic device to create monodisperse emulsions in fluorocarbon oil of which fast evaporation deforms emulsions with the surfactant-stabilized interface even in the air. Inside the emulsions are silica particles dispersed in acrylate polymer and crystallized by interparticle repulsion, where the crystallization is enhanced by a shear force from the interface. The emulsions are extruded using a nozzle, assembled into a monolayer, and deformed to polyhedrons. As a result, the iridescent rainbow colors are developed on the particles, which are enhanced by thermal energy before curing. The surface is perfectly flat and it is UV-crosslinked to create fixed structural colors, leading to a more reflective photonic surface than a monolayer of photonic spheres.
The colloidal arrays are rearranged during the deformation of emulsions from spheres to polyhedrons and they follow the shear force that is larger on the polyhedron side than top or bottom because of larger curvature change and larger relocation of the fluid inside the emulsions. A large portion of colloids are crystallized from the side wall of the polyhedrons, but there are polycrystalline arrays inside the compartment because not all the regions are rearranged from a sideward shear force. (10-11) planes of hcp lattice are dominant at the center of the polyhedron, while (111) planes of fcc lattice are at the edge. (10-11) planes of hcp lattice stem from the combination of two shear forces from the top and side of polyhedrons, the latter of which is stronger so that they outnumber (111) planes of fcc lattice even at the center; the center part is close to top/bottom, but far from side. In contrast, the occurrence of (10-11) planes of hcp lattice is exceeded by that of (200) planes of fcc lattice which is slanted more compared to (111) planes of fcc lattice growing from the top.
As the colloidal arrangement is polycrystalline with two dominant planes, the structural colors from the film assembled by emulsions are both iridescent and less angle-dependent. The accurate control of crystallization is not needed during the film formation because the colloidal arrays are crystallized in emulsions in advance; hand-assisted placement of emulsions in a mold rapidly forms a photonic surface. Most importantly, emulsions can be assembled and fixed on a three-dimensional surface which forms structurally-colored 3D objects such as a beetle and turtle. The advantage of this strategy is that the as-formed film can be diversely colored by deforming differently colored emulsions together or stacking the different groups layer by layer. It proposes a new way of regioselective manual formation of structural-color films and patterns both on 2D and 3D objects, of which the printed results have highly uniform color and height. Also, it unveils a new mechanism of colloidal crystal formation in polyhedral photonic compartments.

Continuous development and advancement in modern detection technologies have increased demand for multi-band (e.g. visual, infrared) compatible camouflage. However, challenges exist in the requirements of incompatible structure resulting from the adaptation to different camouflage effects. This study is inspired by the light absorption structure of butterfly wing scales and demonstrates porous anodic alumina/ aluminum flake powder material, prepared by microscopic powder anodic oxidation technique for visual and infrared camouflage. The fabricated structures manipulate compromise condition for visual camouflage by low reflectance (R(400~800 nm)=0.32) and dual-band infrared camouflage by low emission (ε(3~5 μm)=0.081 and ε(8~14 μm)=0.085). Further, the characteristic of short-range disorder in these bio-inspired structure allows maintenance of the camouflage performance under omni-directional detection (0~60°). This study provides new insight and feasible method for coordinated manipulation of electromagnetic waves via bio-inspired structural design and improved fabrication.

Intravascular catheters (IC) are indispensable medical devices that allow diagnostics of heart conditions, dranage or injection of drug fluids and delivery of other surgical devices. However, IC has the potential to cause serious complications that put the patient at risk of death. The major critical issues with insertion of ICs are blood stream infections, thrombosis and damage of blood vessel[1, 2, 3].
Therefore, Antimicrobial, antithrombotic activity and low-friction functions are essential for the surface of intravascular catheters (ICs). One of the strategy for the multi-functionalization of ICs includes coating with hydrogel embedding antimicrobial and antithrombotic agents. Although catheters with hydrogel coating that contain antimicrobial agents contently prevent these issues, undesired side effects of cytotoxicity and tolerance can be caused. Moreover, hydrogel coated ICs showed unsatisfactory performance because of progressive loss of there functions owing to the leaching of functional agents from the coating layer[4].
O-carboxymethyl chitosan (CMC), could be a particularly promising material for functionalization of ICs owing to its outstanding functions including non-toxicity, biodegradability, biocompatibility, antimicrobial and antithrombosis properties. Although CMC has a sufficienct hemocompatibility, the antithrombotic activity is questionable due to its incomplete performance of thrombosis reduction and lack of clinical use cases[5]. Furthermore, there are only a few studies related to the multi-functionalization of IC by introducing chitosan derivatives such as CMC. Therefore, verification of such multi-functional performance, including antithrombotic activity, is still an unresolved challenge in the introduction of chitosan derivatives such as CMC to ICs.
Here, we introduce a novel strategy for biocompatible and eco-friendly surface multi-functionalization of the ICs with CMC. In order to improve the intrinsic performance of CMC, we fabricated the surface of coating layer to be rough. Nanoscale porous CMC (pCMC) coating layer of pre-treated IC was simply fabricated through a selective leaching of the water-soluble polyethylene glycol (PEG) from heterogeneous CMC-PEG composite. The pCMC layer surface exhibited superhydrophilicity due to the increase in roughness. Especially, the antifouling effect by superhydrophilicity showed excellent anti-adhesion of Escherichia coli and platelets, and it gave a synergistic effect along with the intrinsic functions of CMC. Meanwhile, despite the rough surface of the pCMC layer, it showed adequate low frictions property under continuous wet friction conditions. Furthermore, we demonstrated that the practical pCMC coated IC tube provides superior trackability in a curved artificial blood vessel. The potential of the proposed coating strategy can be offered not only ICs, but also wide range of polymer-based vascular devices such as vascular filters, grafts, pacemakers and soft robots.

References
[1] L. Liu, et. al., Biomater. Sci. 2020, 8, 4074.
[2] I. H. Jaffer, et. al., J. Thromb. Haemost. 2015, 13, S72.
[3] R. I. Mehta, et. al., Am. J. Med. 2017, 130, e287.
[4] D. C. Leslie, et. al., Nat. Biotechnol. 2014, 32, 1134.
[5] S. K. Park, et. al., Chem. Eng. J. 2022, 433, 134565.

Acknowledgements
This work was supported by the Korea Medical Device Development Fund grant funded by the Korea government (the Ministry of Science and ICT, the Ministry of Trade, Industry and Energy, the Ministry of Health & Welfare, the Ministry of Food and Drug Safety) (Project Number: KMDF_PR_20200901_0081, 1711138107)

Corresponding author
Dong Yun Choi, E-mail: [email protected]

Three-dimensional (3D) bioprinting has emerged as a promising tool for constructing in vitro cancer models with tumor microenvironments (TME) in a rapid and reproducible manner. To realize the translational impacts of 3D bioprinting in a wider cancer research community, innovations in bioprinting workflows still required to integrate affordability, user-friendliness, and biological relevance. Here, we developed ‘Bioarm’, a simple, yet highly effective extrusion bioprinting platform, which can be folded into a carry-on pack, and rapidly deployed between facilities. Bioarm enabled TME reconstruction by printing 3D core-shell tumoroids with cancer-associated fibroblasts (CAFs) deposited as the shell. The population of CAFs showed heterogeneity in tumoroids and produced de novo synthesized extracellular matrices, demonstrating more in vivo-like characteristics compared to traditional 2D co-culture models. Embedding the 3D printed tumoroids in an immune cell laden collagen matrix permitted tracking of the cancer-immune interactions, and subsequent immune perturbation under immunotherapy treatments. Our deployable extrusion bioprinting workflow could significantly widen the accessibility of 3D bioprinting for replicating TME with complex multi-compartmental architectures, and for developing personalized cancer drug screening strategies.

Many microorganisms produce specific protection structures, known as spores or cysts, exploited to increase their resistance to adverse environmental conditions. Scientists started to produce biomimetic materials inspired by these natural membranes, especially for industrial and biomedical applications.[1] Diatoms, for instance, are marine organisms able to uptake inorganic silicates from the ocean in order to build highly porous biosilica shells, called frustules, at mild environmental conditions. Diatoms shells, exploited for years for producing biohybrid materials for applications in photonics, optoelectronics and biomaterial science, can be chemically decorated via the common surface silanization reactions or the in vivo incorporation of functional organic molecules.[2] Our group has managed to obtain, via green processing, phosphorescent nanoparticles and fluorescent biosilica with specific optical features starting from simple feeding of diatoms with new synthesis fluorescent dyes [3-5]. We also produced 2D diatoms-based scaffolds for tissue engineering applications, after in vivo functionalization of living algae with pharmacological molecules like bisphosphonates, active towards osteogenic promotion and against osteo-resorption and bone degradation. [6-7] In this abstract we present biological data on the biocompatibility of a polydopamine-based artificial coating with diatom cells. Here living Thalassiosira weissflogii [8] cells were individually encapsulated with soft, artificial and easily functionalizable polydopamine layers with adhesive properties similar to feet proteins found in mussels. Polydopamine did not strongly interfere with diatom cells growth kinetics, and it can be exploited for entrapping detoxifying agents, like natural enzymes, and magnetic nanoparticles useful for living cells recovery after the decontamination process. These outcomes pave the way to the use of living diatom cells in the area of biomedicine, cell-based sensors and natural, and living devices for bioremediation. Polydopamine does not only confer certain sorption properties towards pollutants to surfaces [9], but it can encapsulate degrading functions, like catalytically active nanoparticles or enzymes, which bio-transform pollutants into small non toxic organic molecules.

Aknowledgements: D.V. acknowledges the financial support from Fondo Sociale Europeo “Research for Innovation (REFIN)”; project n°87429C9C - Alghe vive per la bonifica dell’ambiente marino (AlgAmbiente).

References

[1] Lo Presti, M., Vona, D., Ragni, R., Cicco, S.R., Farinola, G.M. MRS Comm. 11, 213–225 (2021).
[2] Ragni, R., Cicco, S.R., Vona, D. and Farinola, G.M. Adv. Mater. 1704289,1-23 (2017).
[3] Leone, G., De la Cruz Valbuena, G., Cicco, S. R., Vona, D., Altamura, E., Ragni, R., Molotokaite, E., Cecchin, M., Cazzaniga, S., Ballottari, M., D'Andrea, C., Lanzani, G. Sci. Rep. 11 (1), 5209 (2021).
[4] Ragni, R., Scotognella, F., Vona, D., Moretti, L., Altamura, E., Ceccone, G., Mehn, D., Cicco, S.R., Palumbo, F., Lanzani, G., Farinola, G.M. Adv. Funct. Mater., 28 (24), 1706214 (2018).
[5] Della Rosa, G., Vona, D., Aloisi, A., Ragni, R., Di Corato, R., Lo Presti, M., Cicco, S. R., Altamura, E., Taurino, A., Catalano, M. and Farinola, G. M. ACS Sustain Chem Eng, 7, 2, 2207–2215 (2018).
[6] Cicco, S.R., Vona, D., De Giglio, E., Cometa, S., Mattioli Belmonte, M., Palumbo, F., Ragni, R. and Farinola, G.M., Chem Plus Chem, 80, 1104–1112 (2015).
[7] Cicco, S.R., Vona, D., Leone, G., De Giglio, E, Bonifacio M., Cometa, S, Fiore, S. Palumbo, F, Ragni, R., Farinola, G.M., Materials Science & Engineering C 104 109897 (2019).
[8] Vona, D., Cicco, S.R., Ragni, R., Vicente-Garcia, C., Leone, G., Giangregorio, M.M., Palumbo, F., Altamura, E., Farinola, G.M. Photochem. Photobiol. Sci. 21, 949–958 (2022).
[9] Aresta, A., Cicco, S.R., Vona, D., Farinola, G.M., Zambonin, C. Separations, 9(8), 194 (2022).

Nature’s exquisite designs are a constant source of inspiration for materials scientists, yet our ability to replicate biological interactions on the macroscale in engineered systems is often severely limited. Biological systems exist in perfectly balanced environmental conditions that regulate the functionality of the processes within the system. Thus, a major obstacle in exploiting biological interactions in macroscale materials is a lack of understanding of how the changing chemical environment - from the molecular to the macroscale - affects the intrinsic molecular functionality of the biological unit, ultimately impacting macroscale behaviour.
From a material design standpoint bacterial adhesins are particularly interesting proteins. These proteins are expressed on bacterial cell surfaces to allow them to bind to, and colonise, a host. Many of these bacterial adhesins exhibit so-called ‘catch bond’ behaviour. Essentially, the adhesive force of these receptor-ligand complexes increases when subjected to high shear, in contrast to traditional ‘slip’ bonds, which decrease/rupture under high shear. On reaching a maximum applied force, the catch bond then reverts to slip bond behaviour resulting in a catch-and-roll type action that bacterial cells use to move in a targeted fashion along a surface. This behaviour also allows pathogens to continue to colonise host organisms despite aggressive actions from the host to remove colonies.
Transplanting catch bond-forming protein receptors and ligands onto polysaccharide chains opens up the possibility of creating bio-based hydrogel networks with unique tensile properties. Specifically, networks that display both shear-thinning and shear-thickening properties depending on the applied force, which also have the potential to self-heal as complexes rupture and reform. However, the complexity of intermolecular interactions in both catch-bond forming adhesin complexes and bio-based polymers mean the road to macroscale materials is less than straightforward.
Focusing on adhesins isolated from Staphylococcus epidermidis (serine-aspartate repeat protein G (sdrG)) and Staphylococcus aureus (serine-aspartate repeat protein E (sdrE), clumping factor A (clfA) and clumping factor B (clfB)), we use single molecule force spectroscopy to probe the fundamental interactions between these adhesins and their specific ligands to understand the impact of orientation, substrate, mutations and environmental composition on the stability of the catch bond behaviour. Expressing adhesins on yeast cells and probing substrate interactions with spinning disk microscopy, a deeper understanding of cooperative interactions as a function of environmental complexity is gained. Finally, functionalisation of polymer chains with adhesins and their corresponding ligands creates the building blocks for the catch bond cross-linked hydrogel networks, whose macroscale mechanical properties are probed using rheological measurements, completing the molecular to macroscale transition.
This multi-length scale approach to the design of catch bond cross-linked materials provides fundamental understanding of the impact of protein orientation, mutations and environment as we transition from the cell to a synthetically designed macroscale matrix. Examining how protein behaviour and macroscale materials properties change as a function of protein composition and environmental complexity allows more accurate development and manipulation of adhesin-derived responsive biomimetic materials. Thus, leading to a greater understanding of the nano-macroscale relationships in complex multiphase systems and enhanced strategies for the translation of biological interactions into macroscale materials.

As a renewable biopolymer, high-amylose starch due to its higher content of linearly structured chains is more interesting to realise enhanced material properties and new functionality. However, the full dissolution of the compact granule structure of high-amylose starch is challenging under moderate conditions, which limits its applications. In this work, we have revealed that high-amylose maize starch (HAMS) granules can be easily destructed by certain concentrations of ZnCl₂, MgCl₂ and CaCl₂ solutions (43 wt%, 34 wt% and 31 wt%, respectively) at a moderate temperature (under 50 °C) without chemical derivatization. In particular, the ZnCl₂ and CaCl₂ solutions resulted in complete dissolution of HAS granules and the regenerated starch from the CaCl₂ solution was completely amorphous.
We found by simple mixing of the HAMS with a CaCl₂ solution followed by heating the mixture at 80 °C for 5 min, a flexible and ionically conductive starch-based hydrogel can be obtained. By varying the starch/CaCl₂ dry mass ratio, the materials exhibited tuneable mechanical strength (500–1300 kPa), elongation at break (15–32%), Young’s modulus (4–9 MPa) and toughness (0.05–0.26 MJ/m³), suitable electrical resistivity (3.7–9.2 Ω m), and strain-responsiveness. With plasticisation, a more flexible starch-based hydrogel was obtained, which can be easily reprocessed and has self-healing ability. The hydrogel was then developed into a galvanic cell-type battery, with an output voltage of 0.81 V, and a self-powered (SP) wearable sensor, which had high sensitivity (1.5371 kPa⁻¹) even under weak compression stress. This SP sensor can be used to detect human activities involving small strain such as wrist pulse and throat vibration. Considering the easy processability, cost-effectiveness, high strain-sensitivity, robustness, and greenness of the starch-based hydrogel and electronics, their brilliant application prospect is foreseen.

Bioelectronics needs to continuously monitor mechanical and electrophysiological signals for patients. However, the signals always include artifacts by patients’ unexpected movement (e.g. walking and respiration under ~30 Hz). The current method to remove them is a signal process using a bandpass filter which may cause signal loss. We present an unconventional bandpass filter material, viscoelastic gelatin/chitosan hydrogel damper inspired by the viscoelastic cuticular pad in a spider to remove dynamic mechanical noise artifacts selectively [1]. The hydrogel exhibits frequency-dependent phase transition that results in a rubbery state that damps low-frequency noise and a glassy state that transmits the desired high-frequency signals. It serves as an adaptable passfilter that enables to the acquisition of high-quality signals from patients even with minimizing signal process for advanced bioelectronics.

[1] B. Park et al. "Cuticular pad–inspired selective frequency damper for nearly dynamic noise–free bioelectronics." Science 376, 624-629 (2022).

Haptic devices have wide ranging applications, from entertainment in virtual reality, to accessibility aids, and even to advance basic knowledge in sensory biology. Here, show approaches from materials chemistry could be used to improve the quality, range, or portability of haptic devices. We highlight some of our work which show that humans are sensitive by touch to molecular scale changes in surfaces and also examine opportunities for materials innovation from the stimuli responsive and wearables community. We also introduce goals and research overlaps for the symposium to connect members of the materials research community to the haptics community.

Our ability to assess and discriminate a vast variety of surface textures relies on densely packed mechanoreceptors embedded in our fingertips, which are exquisitely attuned to both temporal and spatial changes in skin deformation. Texture perception is critical for our ability to identify and evaluate the quality and material of every surface we touch, and dynamic changes in texture can also serve as an intuitive way to haptically communicate information such as finger location or changing dial settings. This range of utility suggests diverse and realistic texture rendering is an important modality to consider for any haptic display. Yet what exactly constitutes “diverse and realistic enough,” balancing ability to render a wide breadth of realistic textures using a given haptic display while maintaining efficient signal representation and accommodating actuator limitations?
My recent research focuses on texture rendering for a diverse set of displays, from friction-modulated touchscreens to wearable vibrotactile rings and watches. These devices differ broadly in site of actuation, actuator bandwidth, and concurrent visual displays, but all rely on a vibration applied to the hand during movement as the primary method of texture rendering. We explored various methods of designing new vibration patterns, such as increasing the amount of spectral content or scaling different aspects of the vibration as a function of finger speed.
The impact of these texture design choices were evaluated via psychophysical ratings of both perceived haptic texture differences and similarity to real textures. Results indicate that for higher frequency vibrations, people can differentiate only a very limited amount of spectral complexity, and are also increasingly less sensitive to speed-dependent shifts in frequency. This suggests the set of fine texture sensations achievable via applied vibration alone can be composed using a manageably small set of design parameters and rendered with a few narrow bandwidth actuators.

Haptics is the field that deals with technology that stimulates the sense of touch and motion. Haptic researchers are working to create the same level of fidelity in touch-based recording and display that we currently have in audio and video. Why is this so complicated? One of the many reasons is the complexity of the finger-device interaction and the role that this plays in the generation of touch perception in humans. The finger-device interface is complex and variations with environment and person-to-person can cause finger material property changes that impact device performance and human perception of it. Multiphysics modeling of interfacial phenomena such as capillary forces and surface tension, electrowetting, electrophoresis, multiphase flow, and soft tissue contact mechanics can help predict friction under various conditions and enable purposeful design for consistent or enhanced performance. Examples of design for consistent performance with humidity, design for consumer preference, and consideration and use of temperature will be explored. Additionally, we will consider how human finger property changes can be used as bioinspiration for material design for active friction modulation in clutches and robotic grasping.

Human skin regulates tactile perception of the world around us through interplay of the tissue’s material properties and a system of cutaneous mechanoreceptors. However, the relationship between these properties, influenced by skin’s hierarchical structure, and how we perceive sensations remains unclear. In this work, we establish a fundamental link between mechanical stresses in the top layer of skin, the stratum corneum (SC), and feelings of skin tightness [1]. We further show that these sensations can be dampened or enhanced via application of various cosmetic formulations [2].

Biomechanical changes in the stratum corneum (~20 m) stimulate cutaneous mechanoreceptors and sensory neurons in softer, underlying layers. Activated afferent neurons send signals to the central nervous system that are interpreted as perceptions. Dehydration of the SC is particularly relevant since water loss results in stiffening (from ~2 MPa to ~100-200 MPa) and contraction (by ~1.5%) of the SC, propagating strain fields into lower layers where they trigger sensations of tightness. Topical skin treatments can either augment tightness by driving more water loss (such as with cleansers), or reduce tightness by helping retain water in the SC (such as with moisturizers). Thin film characterization can measure SC mechanical stresses in vitro. Finite element simulations can model the resulting strain fields in full-thickness skin, and predict neuronal firing rates in silico. Results can then be compared to consumer perception scores gathered in vivo. We show a linear correlation between scores reported by volunteers up to 12 hours post application of cleansing and moisturizing formulations, and SC stresses measured in the lab. Predicted firing rates also correlate remarkably well with consumer scores. This framework can now aid in the development of novel formulations that carefully tune SC stresses for a desired sensation.

In this study, we establish a fundamental link between the SC’s biomechanical state and tactile perception, and use this to quantitatively understand the mechanism underlying sensorial perception of our skin in response to topical treatments. This psychophysical framework can be extended to a full range of stimulations provided by haptic devices including wearable actuators and sensors. It also provides a novel way to study the body’s sensing system which could serve as inspiration for the design of soft robotics and stimuli responsive materials.

[1]. Sebastian Hendrickx Rodriguez, Sophie Connetable, Barbara Lynch, Joseph Pace, Ross Bennett Kennett, Gustavo S Luengo, Reinhold Dauskardt, Anne Potter, "From decoding the perception of tightness to a clinical proof of soothing effects derived from natural ingredients in a moisturizer", International Journal of Cosmetic Science, 2022.

[2] Ross Bennett Kennett, Joseph Pace, Barbara Lynch, Yegor Domanov, Gustavo S. Luengo, Anne Potter, Reinhold Dauskardt, “Sensory Neuron Activation from Topical Treatments Modulates the Sensorial Perception of our Skin”, In preparation.

Designing conductive materials for human-machine interfaces, robotics, and/or haptics requires materials with good electronic properties and mechanical properties close to that of biological tissues. Electronically-conductive hydrogels, composites of crosslinked and water-swollen polymers with a conducting material (polymer or inorganic nanoparticles), can address these requirements. But, two common issues arise from the traditional synthesis of conductive hydrogels. First, the elastic modulus of the hydrogels is increased at the high loadings necessary to achieve electronic conduction. Second, the crosslinking process is irreversible, making it difficult to process the materials in different form factors, inject them for implantable electronics, or remove the hydrogels after use. To address these issues, we have developed conducting polymers that undergo a sol-gel transition close to physiological temperatures: thermo-responsive conducting polymers. We focused on the polyelectrolyte complex of poly(3,4-ethylene dioxythiophene) and poly(styrene sulfonate) (PEDOT:PSS) as our conducting polymer for its high conductivity, low impedance, low toxicity, and dispersibility in water. To achieve thermally-gellable PEDOT:PSS, we used controlled radical polymerizations to create block copolymers of PSS with a thermo-responsive polymer, poly(N-isopropylacrylamide) (PNIPAm), and complex it with PEDOT. At the adequate ratio of each component, the PEDOT:PSS-b-PNIPAm block polyelectrolyte complex thereby synthesized gels in water at 37 °C. The gel displays both ionic and electronic conductivity of 0.13 mS cm⁻¹ and 0.05 mS cm⁻¹, respectively. The thermal gelation process is completely reversible, providing exciting new opportunities in actuation for robotics or haptics, or injectable conductive hydrogels.

Haptic surfaces are a flourishing research topic at the intersection of electronics, robotics, and biomedical sciences, aimed at the development of thin and flexible devices that mimic human-environment interactions. Liquid crystal elastomers (LCEs) have great potential to drive this innovation, thanks to their unique ability to reversibly actuate to high strains with light or heat exposure. Here, an electrically driven LCE actuator matrix with the potential to be scaled up to large area production is developed. The device functions by LCE thermal actuation driven by the Joule heating of a resistive element. The multilayer actuator array consists of series of active LCE elements coupled with an electronic layer used to interconnect the elements and operate the device. These two layers are then embedded within a flexible substrate which shields them from the external environment and simultaneously amplifies out-of-plane actuation. Such a device can produce local on-demand deformation with no foreseen limitation on the overall size of the matrix. The presented concept shows great potential for applications in texture-changing surfaces or surface-driven object motion, examples of which include self-cleaning surfaces or soft touch massage mats.

Liquid crystalline elastomers (LCEs) are functional materials capable of undergoing large, complex deformations in response to stimulus. These deformations are attributed to order disruption between liquid crystalline mesogens incorporated within the polymer network. By controlling the orientation of mesogens during material fabrication, 3D shapes can be programmed into these actuating materials. This talk will detail our strategies for locally programming mesogen orientation to realize complex 3D shapes and topographical surfaces in LCEs.

In order to program mesogen orientation, the liquid crystalline moieties can be oriented before crosslinking the polymer network. One approach that we have taken in this respect is the use of photopatterned substrates as command surfaces for the liquid crystalline monomers. This method enables high resolution programming of local mesogen orientation, enabling a broad range of targeted 3D actuations to be patterned.

In addition to investigating routes to programming orientation during network synthesis, we have also recently explored opportunities for reprogramming the crosslinked materials using dynamic covalent chemistry. Using these LCEs with dynamic bonds, we demonstrate multi-stage programming that combines surface patterning with dynamic bond reconfiguration to realize additional levels of complexity in 3D actuated shapes.

Fine touch sensation is a critical source of information, especially for those with low vision or blindness. Tactile aids (e.g. braille reader) and surface-haptic interfaces typically produce fine touch sensation by using physical features, such as surface patterned bumps and pins, to alter frictional forces on the user’s finger. However, when interacting with everyday objects, frictional and adhesion forces arise not only from surface topography but also from the chemical properties of a material itself. This work aimed to generate tactile sensations by altering the materials chemistry and microstructure of thin film polymer surfaces with minimized variations in physical roughness. We demonstrated that humans are sensitive to the microstructure of chemically-similar, semi-crystalline polystyrene films due to the influence on mesoscale friction. Through dynamic friction testing with a custom mock finger mechanical test set-up, custom signals analysis, and human psychophysical testing, we demonstrated how materials phenomenon alone may be used to influence fine touch. These material phenomena may extend to broader classes of materials for design of higher graphic haptic technologies and tactile aids.

Imagine an interface device that can be programmed to feel like burlap or velvet in much the same way that pixels on a screen can be arranged to look like one of those fabrics. Extending this analogy, we might reasonably ask what information a tactile pixel would need to encode, what pixel density is needed, how an “image” of a texture might be recorded, and of course how the tactile pixels (“taxels”) could be designed and made to work. In this talk, I’ll review the progress that our group has made in answering these questions.

Our work has been done in the context of “surface haptics.” Here, a fingertip – either bare or outfitted with a wearable device – is swept across a physical surface. Virtual textures are created by using electroadhesion (i.e., electrostatic attraction) to modulate the friction at the sliding interface. I will present a simple model of electroadhesion and explain how it can be used to modulate friction at a very high rate, in excess of 50kHz.

Until recently, most of our haptic devices might be considered “single taxel”: electroadhesion, although high-bandwidth, occurred in synchrony over the entire finger-surface contact patch. There is a logic to the single-taxel approach: almost a century ago, David Katz proposed the “duplex theory” of tactile perception, suggesting that texture depends upon a “spatial sense” for coarse textures and a “vibration sense” for fine textures, and modern neuroscience has supported the idea that fine textures are encoded temporally, not spatially. In other words, it is reasonable to expect that high-bandwidth control of a single tactile taxel would suffice to recreate realistic fine textures. Unfortunately, this turns out to be wrong. A recent study performed in our lab demonstrated that recording of the skin vibrations caused by sliding over a fine texture followed by precise electroadhesive playback, did not result in realism. Texture playback was perceived to be much weaker and qualitatively different.

In that study, vibrations on the side of the finger were carefully matched, but the mechanics of contact patch interaction may have been quite different between the physical and virtual cases. In particular, some degree of spatial inhomogeneity almost surely occurred during contact with physical textures, even though they were fine. If this is the source of the perceptual discrepancy, then it sheds some doubt on the duplex theory (to be fair, the theory is qualitative in nature and does not establish strict conditions for either fine or coarse texture). A follow-up study performed with a high-bandwidth pin array showed that inhomogeneity does, in fact, play a significant role in subjective experience: greater inhomogeneity leads to greater subjective intensity. Simulations further suggest that two different mechanoreceptor populations are involved: Meissner corpuscles respond strongly to spatiotemporal variation within the contact patch, while Pacinian corpuscles respond to surface waves that propagate up the side of the finger. Single taxel electroadhesion would address only the Pacinian population while physical textures would excite both.

The path to texture realism therefore, appears to require more taxels, even in the case of fine texture. While development of a rigorous specification is ongoing, we are currently targeting 2.5mm taxel spacing and a bandwidth of 300Hz. To realize this in a compact device, we are developing a wearable array of electroadhesive taxels (also known as “pucks”). A 4x4 array has been built on a latex backing with printed silver ink electrodes addressing each taxel. The taxels themselves are made from a commercially available conductive finger cot material, which is a nitrile doped with carbon nanotubes. Puck and fingertip behavior can be imaged through a transparent countersurface (glass with and ITO electrode, coated with SiO2). I will report on preliminary physical and psychophysical results.

Emerging applications in soft robotics and haptic devices demand strong adhesives which can be easily removed on-demand and subsequently reused. This requires new paradigms in adhesive science and engineering to create new classes of multifunctional switchable adhesives. Nature can provide inspiration for these challenging adhesion scenarios. For example, the octopus couples controllable adhesives with intricately embedded sensing, processing, and control to manipulate underwater objects. Current synthetic adhesive–based manipulators are typically manually operated without sensing or control and can be slow to activate and release adhesion, which limits system-level manipulation. Here, we couple switchable, octopus-inspired adhesives with embedded sensing, processing, and control for robust underwater manipulation. Adhesion strength is switched over 450× from the ON to OFF state in <50 ms over many cycles with an actively controlled membrane. Systematic design of adhesive geometry enables adherence to nonideal surfaces with low preload and independent control of adhesive strength and adhesive toughness for strong and reliable attachment and easy release. Our bio-inspired nervous system detects objects and autonomously triggers the switchable adhesives. This is implemented into a wearable glove where an array of adhesives and sensors creates a biomimetic adhesive skin to manipulate diverse underwater objects.

Minimally invasive surgical (MIS) procedures suffer from limited haptic feedback to the surgeon and manufacturing limitations for embedded sensing capabilities on surgical instruments. The lack of sensing and haptic feedback results in the application of excessive forces on the tissue. This is exacerbated in instruments such as endoscopes where the tool’s flexibility affects transmissions of friction forces, resulting in severe adverse advents (SAEs), such as bleeding, perforation, or splenic injury. Multimodal sensing, such as force monitoring or bleeding detection, combined with direct haptic feedback could be useful in reducing SAEs in colonoscopy. Similarly, haptic feedback combined with multimodal soft sensing could be beneficial in other MIS scenarios such as remote palpation or robot-assisted laparoscopies.

Previously, we created a force sensing soft robotic sleeve to mitigate excessive forces exerted on the colon wall. The sleeve contains optical waveguides and can be mounted directly onto the colonoscope. We further extended our work to develop biosensors that can detect bleeding in the colon. This is particularly important because the surgeon is often unable to detect bleeding as their field of view is limited to the endoscope’s distal end camera. It is crucial that these sensors are integrated in a seamless manner that does not impede the functioning of the colonoscope or alter the clinical workflow. Thus, these sensors are designed to be soft and flexible with a low vertical profile (~1 mm). The sensor can easily be mounted onto the colonoscope at multiple points to provide bleeding detection. The sensor is manufactured by molding PDMS onto photolithographically patterned silicon wafers. The sensor contains micron scale soft optical waveguides that interface with a microfluidic channel allowing intake of blood. Presence of blood in the channel causes attenuation of the incident light thereby allowing detection.

To improve MIS, it is important to convey sensing modalities to the surgeon in an intuitive manner. It is essential to develop a comprehensive system that can accurately sense forces and other physical phenomena on the surgical tool, and then directly alert the surgeon through haptic feedback. Thus, we augmented the force sensing capabilities of the soft robotic sleeve by interfacing it with a pneumatic haptic feedback glove. The pneumatic actuators of the glove inflate proportionally to the incident forces on the soft robotic sleeve. Thus, the haptic feedback glove allows the endoscopist to feel the magnitude of forces exerted by the colonoscope onto the colon wall. Additionally, a comprehensive sensing and haptic feedback system can be beneficial in other MIS scenarios. Currently, we are developing a soft sensing and haptic feedback system for robotic palpation of tissue. Since the operator cannot physically feel the palpated tissue, it is difficult to detect the presence of tumors. The palpation sensor can be mounted onto a robot arm, which presses on tissue to detect tumors. The sensor consists of silicone layers of varying hardness embedded with waveguides. As the sensor presses onto tissue, the layers deform around harder areas that may be tumorous. The deformation of the layers causes a change in the waveguide signal. The sensor interfaces with a haptic glove consisting of silicone actuators mounted onto the fingertips. The sensation of tissue palpation can be translated to the user via actuator inflation.

The safety and efficacy of MIS must be improved by not only embedding sensors on the surgical tools but also developing solutions to convey the complex sensing data to the surgeon in an intuitive manner. This highlights the need for haptic feedback to enable the surgeon to process multimodal sensing cues in a manner that complements the clinical workflow. Future works that seek to embed sensing on robotic tools must evaluate optimal methods by which the sensing data is best relayed to the surgeon.

Electroadhesive clutches (EAclutches) in which frictional blocking forces can be modulated by an applied potential have recently enabled lightweight, compact wearable devices such as haptic clothing, soft exoskeletons, and controllable prosthetics. However, typical EAclutches based on electronic conductors with insulating dielectric layers suffer from low force capacities (1-25 N/cm^2) and operate using large working potentials (> 100 V), requiring tethers to specialized high-voltage circuitry. These performance limitations, along with safety concerns regarding the use of high voltages, have limited the practical implementation of EAclutches for untethered wearable devices. Previous work has sought to reduce EAclutch operating voltage by decreasing the thickness of the dielectric (< 10 µm), however, these devices are challenging to fabricate and are prone to short circuits due to defects or damage. Recently, our group developed a novel class of low-voltage electroadhesives based on oppositely charged polymerized ionic liquid elastomers (termed “ionoelastomers”). The large electric field developed across a nm-scale ionic double layer (IDL) allows for robust and reversible adhesion between two ionoelastomers at comparatively low working potentials (~ 1 V) even with overall layer thicknesses of ~ 100 µm. Despite this promise, high off-state adhesion and poor environmental stability have so far prevented the integration of ionoelastomers into practical EAclutch devices. In this work, a low-voltage, environmentally stable EAclutch based on ionoelastomer electroadhesives is demonstrated. Here, the integration of a perfluorinated comonomer enables enhanced delamination in the off-state by reducing the surface energy of the junction without significantly affecting the capacitive behavior of the IDL. Ionoelastomer EAclutches exhibiting high force capacities (60-80 N/cm^2) at low voltages (5-9 V) are fabricated. The ionoelastomer EAclutch is combined with a soft elastomer, allowing for electroprogrammable stiffness in an untethered kinesthetic haptic device. These findings provide a fundamental understanding of the mechanism of electroadhesion in ionoelastomer adhesives and broaden the scope of EAclutch integration into untethered wearable devices.

Dielectric elastomer actuators (DEA) have commonly been used as haptic devices because of their high actuation strain, quick response, large energy densities and low weight. However, the driving electric field is high, which leads to danger to users and incompatibility with portable power sources. In this work, a soft, stretchable, adhesive, transparent and all-solid-state poly(ionic liquid) (PIL) is introduced as filler into VHB to fabricate DEA. As a result, the dielectric constant increases from 4.8 to ~15 at 1 kHz and Young's modulus decreases to 0.11 MPa. Unlike liquid fillers, possibility of filler leakage reduces, minimizing short circuit which is dangerous to users. DEA with PIL filler delivers high area strain of 137% at 17 V/μm, exceeding that of most DEAs at similar electric field. The unimorph DEA with PIL filler shows a bending angle change of 38.6° under an electric field of 12.6 V/μm, which is over twice the value of the DEA without PIL. Finally, an unimorph DEA integrated with alternating-current electroluminescent layer is demonstrated. This work provides a promising strategy for building a high-performance and safer DEA for haptics.

The design, control, and functionality of soft robotic manipulators and grippers are a growing area of research interest. Recent advancements are pushing toward closed-loop control via embedding proprioceptive and exteroceptive sensing into these soft platforms. Different soft sensing technologies have been explored, i.e., resistive, capacitive, and magnetic. Fully soft optical sensors are useful for both shape sensing and contact force recognition and have been utilized for a variety of soft gripper applications. However, these grippers are often attached to rigid robotic arms, which highlights the need for soft continuum robots with embedded sensing. Soft continuum robots can benefit from the integration of tunable soft optical sensors that provide the systems with real-time 3D shape sensing. The combination of shape sensing soft continuum robots and contact sensitive soft robotic grippers presents exciting application scenarios in minimally invasive surgery (MIS) and high-precision pick-and-place tasks.

Recently, we have developed a roughness tuning strategy for the fabrication of soft optical waveguide sensors (WG) to achieve shape sensing and contact recognition within a single multi-modal sensor. We integrated the sensors into a fully soft continuum robot consisting of a multi-directional bending module and a gripper. The robot module integrates two WGs for 3D shape sensing and three soft pneumatic actuators to steer the robot in all directions. The gripper embeds two soft pneumatic actuators to deploy itself, two soft pneumatic actuators to control grasping, and two WGs, one in each jaw of the gripper, with tuned roughness to monitor both gripper tip positions and subsequent occurrence of contact with an object. The deployment and grasping motions of the gripper cause measurable losses in optical power through the WGs. These losses are utilized to track the tip position of the gripper. Alternatively, when an object is contacted, we observe a distinct increase in the output power of the WG through the system, which allows us to distinguish the tip position tracking from contact recognition and thus create a multi-modal sensor. The proposed system simultaneously tracks the real-time shape of the robot body and the tip positions of the gripper via a graphical user interface (GUI). Furthermore, upon contact with an object, the GUI alerts the user of the successful grasping of an object. The robot module is calibrated so that the shape of the robot is mapped with an electromagnetic tracker throughout its entire workspace. This data is used to determine the true shape of the robot by using a constant curvature model, and then the WG signals are fit to a surface based on the data collected to predict the shape of the system in subsequent testing and controls. The surface fits implemented to use the WGs to predict the robot module shape had an average error of the tip position of less than 4 mm.

Our soft continuum robot can be utilized in a variety of pick-and-place applications where the integration of soft optical sensors can improve the accuracy of the control of soft robotic arms. Further, we have determined that proper tuning of the sensors can result in increased sensitivity across a large range of curvatures and enable a multi-modal sensor response, which allows for a reduced number of total sensors in the robot. These advancements in the tunability of soft optical sensors pave the way toward miniaturized devices and better closed-loop control of soft robots. Providing contact force recognition to continuum robots also pushes toward improving the capabilities of haptic feedback systems that can be integrated with soft sensors and soft continuum robots. Lastly, the low cost and scalable nature of the system presents opportunities for incorporation into a variety of MIS procedures where enhanced dexterity and sensor feedback is valuable for surgeons.

Soft sensors have been widely accepted and used in many fields. However, a technological breakthrough is still needed to gain a wider sensing range, faster response speed, and longer durability. In this work, we successfully fabricated an MXene-sliver ink-based interdigitated electrode via direct-ink-writing (DIW) 3D printing technology and assemble it into robotic gloves. Test results have shown the following advantages: (1) ultrafast response time (within several seconds) for surrounding detection at the macro level; (2) extremely accurate detection and object recognition; (3) ultrasensitive detection of omicron virus up to 110^-22 molar at the micro level; (4) remarkable extension of the sensing range and targets. The 3D printed interdigitated MXene-sliver electrode could work as a figure tip sensor, as a result of being able to feedback continuously output impedance changes for any approaching objects. When functionalized with single-strand probe DNA, it can also work as a virus sensor and captures the target DNA in the environment by collecting signal changes through electrochemical response. This successful demonstration elucidates the broad prospects of MXene-based soft sensors for soft robotic devices.

Triboelectric sensors has been widely used for tactile sensing due to its self-powered attribute, low cost, and facile fabrication process. High-resolution tactile devices relying on densely arranged sensing units impose significant challenges to fabrication and signal readout for practical applications. Here we demonstrated a new touch-sensing mechanism for triboelectric tactile sensors. A trackpad with 9 sensing units was fabricated using an additive manufacturing method. The device can continuously track 25 touch locations on the panel based on a machine-learning algorithm. We also demonstrated the potential application of such device for user identification based on keystroke dynamics with random touch other than a predefined input sequence. The proposed new triboelectric sensor provide a new direction for TENG-based tactile sensing development leveraging artificial intelligence to boost the sensing performance.

Interest in soft robotics is rapidly growing in large part due to the ability to safely interact with humans. The use of soft materials allows for scalable fabrication processes that can combine various degrees of freedom into monolithic structures. Miniaturization enables soft robots to navigate in tortuous, narrow, and difficult-to-reach areas, allowing for broad applications ranging from exploration to minimally invasive surgery. However, force output scales with the robot’s cross-sectional area, thus hampering significant robotic tasks and interactions with the surrounding environment at smaller scales.
Here, we present a 3.5 mm diameter soft robot that increases force transmission and, consequently, broadens the potential interactions that may be achieved within similarly scaled environments. These capabilities are accomplished by designing three fluidic-actuated, independent degrees of freedom. The proposed robot consists of a continuum body constructed out of two polymers with differing elasticity and an attached 3 mm linear bellows actuator. The continuum body contains actuation mechanisms for steering via a bending degree of freedom and for stabilization via a radially-expansive actuator. Fabrication of the continuum body is performed through a series of molding processes in which the stiffer of the two polymers, DragonSkin 10, forms the base of the body. Dowel pins run axially along the body for alignment and masking the cross-sectional off-center bending chamber. A 3D masking technique combined with the molded shape of the base are utilized for the creation of the radial stabilization actuator through the over-molding of the less stiff polymer, Ecoflex 00-30. The linear bellows actuator utilizes a layer-by-layer fabrication technology in which the application of heat and pressure bonds each bellow at predetermined locations. The bellows actuator is adhered to the tip of the continuum body to act as an end-effector deployment mechanism enabling the robot to utilize any increase in force transmission provided by the anchoring of the stabilization mechanism.
The increase in force transmission is measured through mechanical characterizations of the robot in states with stabilization activated and unactivated. An increase in the effective stiffness of the system of about five times is measured as a result of stabilization, demonstrating that, for displacements less than 2 mm, the robot can transmit up to 0.75 N of force to the deployment mechanism located at its tip. Characterization of the deployment mechanism further confirms the need for stabilization with blocked forces measuring up to 1.1 N. Results of both stabilization and deployment force measurements validate models that guided the robot design. To characterize dexterity of the robot, bending of the continuum body is measured displaying full retroflexion with a maximum bending angle of 196 degrees. Linear expansion of the deployment mechanism is also measured showing a range of 9.3 mm. The deployment mechanism is assembled with a needle to demonstrate the feasibility of the robot to be used as a platform for minimally invasive tissue biopsy in bronchoscopy procedures. Compared with typical surgical forces, characterizations of the robot verify its ability to puncture stiffer tumor tissues while maintaining safe levels of force on healthy tissue. An in-vitro setup places the robot within a lung model to demonstrate its ability to steer into a desired lung branch, stabilize within the chosen branch, and deploy a needle for tissue biopsy. The proposed soft robot demonstrates the potential benefits of more forceful interactions between miniaturized soft robots and their environments paving the way for the creation of soft robots as advanced surgical tools.

Soft actuators can be driven via environmental humidity and provide biomimetic adaptation to environments. Humidity may serve as a passive stimulus, i.e., the desired actuation may be caused by uncontrolled changes in the humidity of the environment, or active stimuli, i.e., promoting an actuation response by controlling the humidity. Here, we report a humidity-responsive axial actuator and walking robot of sulfonated polyether ether ketone (SPEEK), which shows greatly tailorable actuation performance upon embedding graphene nanoplatelets (GNP). Three cases of SPEEK with no GNP, SPEEK with 0.5 wt.% GNP and 1 wt.% GNP was tested. Adding only 0.5wt% GNP increases the actuation by 50% and provides a maximum actuation stroke of 24% and work capacity of 230 J/kg. In addition, 0.5wt% GNP promotes faster actuation, with significantly enhanced rates of both contraction and expansion. However, the addition of 1wt% GNP slightly decreases the actuation magnitude and rates. The non-monotonic actuation tunability by GNP was correlated to changes in ion exchange capacity (IEC), water uptake, and GNP dispersion. By utilizing actuation magnitude dissimilarity, the axial actuators were converted into a walking robot stacked of two active layers consisting of fibers of the same material system. The bilayer robot demonstrated self-crawling and locomotion ability in response to humidity changes. This study shows a uniquely tailorable humidity actuator that demonstrates both linear and bending actuation.

Development of mechanically and electrically robust electrode that can be completely folded and crumpled without fatigue degradation in substrate and electrode material has been demanded as a core component of next-generation foldable electronics and soft robot. Here, we report a nanocomposite electrode that can be completely folded in half, crumpled, and endure tensile load (3 N/mm) without changing electrical resistance using a simple composite structure consisting of Elastomer, Kevlar, PET film and silver nanowires (Ag NWs). We performed rigorous experimental and theoretical investigations based on the neutral axis and strain engineering, suppressed the plastic deformation causing crease pattern by an unprecedented method encapsulating a plastic substrate with elastomers, and increased tensile strength of the electrode dramatically via aligned Kevlar fiber reinforced elastomer. Furthermore, by successfully applying developed nanocomposite electrodes to a foldable wrinkle-free display and multifunctional sensor, it is expected that our electrode presents a methodology and tool with vast potential for soft robotics and next-generation foldable electronics.

Hepatic-based simulation plays a key role in designing and developing sensors and soft robotics for improving human-like robot interaction and sensing. For example, there is a huge demand for electronic tongues and ears in the food and defense industries for sound or air pressure detection and chemical and flavor analysis. The lack of availability of soft robots with human-like sensory features has motivated us to investigate, design, and simulate a human tongue's complex motions, including that of a human ear.

Human anatomy was studied in detail to modify the standard designs of the human tongue and the human ear. In the tongue model, adding embedded chambers at strategic locations was used to replicate various 3D motions (rolling, groove, twist, and elongation) of the human tongue necessary for improving the bio-chemical sensing capabilities. The FEM (Finite element method) simulations using ABAQUS software showed the relation between pressure and deformation range for various motions in a human tongue, including stress vs. strain relation for investigating the mechanical properties. Similarly, a study was conducted to test the mechanical properties of the human ear, and a load was applied on the ear's outer rim in a downward direction. The behavior of the ear was simulated under various loads, both compressive and tensile testing, to determine the stress vs. strain relation.

Here, we propose versatile ionic conductors for high-performance, deformable and functional ionic sensory platforms by tailoring the mechanical properties of ionic conductors. For instance, porous ion gels simply fabricated by sugar cube can be effectively deformed by closing pores even with small pressure, a broad variation in the contact surface area of the porous ion gel and electrodes is induced, leading to a dramatic difference in electrical double layer (EDL) capacitance. More interestingly, the functionality of the porous ion gel is extended to include electrochemiluminescence (ECL), resulting in the production of emissive ECL ionoskins. Furthermore, the deformability of ionic conductors is tailored by using binary polymer blends as the co-gelators. To reduce the polymer chain entanglement of polymer gelators and induce effective dissipation of applied stresses, flexible and low glass-transition temperature(Tg) polymer is additionally doped into the relatively hard and high Tg polymer based-ionic conductors. The optimized ternary blend ionic conductors exhibit outstanding stretchability, mechanical elasticity and durability, indicating high feasibility for strain sensory systems.

Polymeric adhesives, which are thin, soft and flexible, with skin conformal interfaces are attractive for haptic interface technology capable of transmitting sophisticated mechanical stimulation. However, conventional polymeric skin adhesives cannot maintain adequate shear adhesion to the haptic interface, such as repetitive vibrations or sweaty skin. Here, we report skin adhesive patches inspired by the hybrid architectures of frog toe pads’ water-drainable hexagonal arrays and snail pedal muscles’ energy dissipation layer with interlocked structures. Hybrid frog-snail-inspired adhesive (FSIA) patch exhibits remarkable shear adhesion in both dry and sweaty conditions (max. ∼36.0 kPa in dry conditions, and max. ∼26.8 kPa in sweaty conditions). Adhesion force enhanced by the stress distribution was analyzed as a simple theory based on the capillary, elastic, and dissipation stresses, and the finite element method simulation according to the geometric and material parameters. Furthermore, we showed that the microchannels between the hexagonal arrays effectively drains the liquid in sweaty conditions. Our patch could tolerate high-frequency vibrations (∼60 Hz) while maintaining vibrational transmissibility on even sweaty skin. For potential application, we demonstrated an integrated system combining skin-attachable patches with thin vibration actuators. Our haptic adhesion interface may establish new strategies for developing VR/AR technology.

The development of human-like tactile sensation is vital to the advancement of robotic manipulation and the completion of highly nuanced tasks. A fundamental way humans understand and interact with their surroundings is the classification of touched object compliance, or the inverse of stiffness, via the activation of mechanoreceptors in the skin. Specifically, slow adapting (SA) I and II receptors, which sense pressure and skin stretch, respectively, are both needed to perceive compliance. We propose that such a functionality can be replicated with a multifunctional pressure and strain sensor fabricated from digitally printed conductive structures impregnated into an elastomer, such as styrene-ethylene-butylene-styrene thin films. Here, we design a novel device structure that combines pressure and strain sensing at the same pixel location, which has the potential to improve spatial accuracy and enable increased taxel density in an array. Although existing literature has reported object identification technologies, these devices require a known and controlled force or displacement. On the other hand, this work proves that both inputs can be sensed independently and are, thus, inherently deconvoluted. Additional advantages over the state-of-the-art include this device’s stretchability and thin form factor. When integrated with robotic systems or eSkins on prosthetics, this novel biomimetic sensor can provide sophisticated sensory feedback for force modulation, safer human-robot interactions, and natural sensation on artificial limbs.

Transformation a sensor of 2D type into 3D structure can realize a differentiated function. A sensor for 3D structure must be consisted of a thin or low-stiffness material to avoid a failure of sensor’s electrode. However, when the sensor was transformed the 3D structure, it requires additional tools to maintain the 3D structure, because the structural stiffness is not sufficient. In this study, we produced an electronic composite that can be flexibly bent and transformed into an arbitrary 3D shape and maintain the transformed shape due to sufficient structural stiffness after deformation using the principle of moving the neutral surface of Shape Memory Polymer (SMP). This sensor is a multi-layer composite in which SMP embeds a high sensitivity crack-based sensor. The SMP has low stiffness (2.2 MPa) at high temperature (60 °C), so the electrode is not broken during transformation, and has high stiffness (1200 MPa) at low temperature (25 °C), so it may maintain a 3D shape even after transformation. For this reason, the composite initially made in 2D form can be transformed into three 3D structures. Each structure is activated to detect external stimuli that are not detected in the initial form; Large strain (2 to 35%), Small pressure (1 to 30 kPa), Small bending (1 to 15 °). In addition, even after transforming to all 3D shapes and returning to the initial shape, there was also a reversibility in which the resistance didn’t change at all. Based on these results, we demonstrate that high stiffness electronic composites that can transform into arbitrary 3D shapes and maintain the transformed shape.

The application promise of soft and wearable electronics has accelerated the demand for deformable energy sources which can convert mechanical energy to electrical energy. Hydrogel has been applied for soft energy harvester but suffers from low conductivity, limited operating temperature range, and short service life. Herein, an ionogels-polymer network swollen with ionic liquids was fabricated and applied for a capacitor energy harvester. Benefited from the nonflammable and high conductive ionic liquid, such rationally designed ionogel performs a wide operating temperature range (from -20 to 200 °C), achieving a balance of excellent mechanical compliance and electrical conductance. As a soft energy harvester, it enables addressing the electrochemical reaction limition of hydrogel, increasing the output voltage of tens of mV. Moerover, the coupling of the dual mode of piezoionics and electrostatic was also revealed. Note that the output can be optimized by manipulating differences in the diffusion rate of cations and anions. This developed technology breaks the limitation of low transient signals and expands the application through this dual-mode harvester. It is also attractive to achieve self-powered, wireless, and sustainable stretchable devices.

In an immersive virtual interaction, realistic sensory devices allow users to provide richer experiences such as vision, hearing, touch, smell, and even taste. Recently, several haptic devices including tactile gloves [1], full-body haptic suits [2], and joysticks [3] are interesting and significant attention for human perception. However, most commercial haptic solutions are insufficient to fully immerse users in virtual environments due to the haptic feedback which is not similar to the real-like feeling. To enable sophisticated tangible interactions, it is essential to reproduce the realistic haptic signals using rendering technology in haptic interfaces between the sensor and actuator. In this study, we proposed a human-interactive tactile communication system using a piezoelectric multimorph actuator capable of both sensing and actuating functions simultaneously. The piezoelectric actuator was designed with multimorph structure with improved displacement (> 800 um) than the traditional PZT ceramic. Our actuator also exhibited uniform vibrations with input signals of frequencies ranging from 1Hz to 1kHz. which is within the perceivable frequency ranges of the human Pacinian corpuscle. To demonstrate the proposed system, 3 different textures are prepared to represent the smooth and rough feeling of the surface. While dragging the textures with the device attached to the fingertips, the signals obtained from the self-sensing actuator are classified by principal component analysis (PCA) with high accuracy of 96 %. Subsequently, rendered signals are generated by extracting key features such as the envelope of the waveform, main frequency, and amplitude based on the PCA. Finally, the actuator reproduces the rendered haptic feedback in real-time. The tactile sensing/actuating communication system is utilized in fields of artificial skin for robotics, and remote tactile communication in virtual reality.

References
[1] J. Perret and E. V. Poorten, "Touching virtual reality: A review of haptic gloves", Proc. Int. Conf. New Actuat., pp. 270-274, Jun. (2018).
[2] Mahmud, M. Rasel, et al. "Standing Balance Improvement Using Vibrotactile Feedback in Virtual Reality." arXiv preprint arXiv:2208.09082 (2022).
[3] Choi, Jiwook, et al. "Impedance matching control between a human arm and a haptic joystick for long-term." Robotica 40.6 (2022): 1880-1893.

Acknowledgement
This work was supported by Institute for information & Communications Technology Promotion (IITP) grant funded by the Korea government (MSIT, Grant No. 2020-0-00003, Development of high piezoelectric coefficient composite and ultra-low power multilayered piezoelectric sensor/actuator multi-functional module) and the Technology Innovation Program (RS-2022-00154781), funded By the Ministry of Trade, Industry & Energy (MOTIE, Korea).

Recently, attempts to connect the virtual reality world with the real world have been actively conducted. Haptic devices that make you feel like you are interacting with real objects are at the center of the metaverse technology because they can make virtual reality more realistic when you interact with objects in virtual space. In order to further enhance the sense of reality, it is important to transmit various sensations to the human skin. In particular, Warmth, which expresses feelings of comfort and love, is important for expressing emotions. Therefore, we developed a functional miniature heater array that changes color depending on temperature change. A miniature heater array was integrated through the patterning process of silver nanowires. A thermochromic liquid crystal film was stacked on the heater array to visually represent the change in temperature. Moreover, this device was integrated into a flexible substrate (polyimide) to attach to the human skin or gloves.

Liquid crystal elastomers are a class of shape-changing polymers capable of undergoing reversible shape changes in response to changes in temperature. Our goal is to create fibers of liquid crystal elastomers with a nematic to isotropic transition temperature that is sufficiently low to enable use in wearable, active textiles. A two-step reaction is used for the synthesis of the fibers. The first reaction is the Michael addition of a nematic diacrylate monomer with a dithiol. The resulting thiol-terminated liquid crystal oligomer can be extruded, creating long fibers on a rotating mandrel. The diameter of the fiber can be tuned from 210 um and 750 um based on the different speeds of mandrel rotation. During the printing phase, the fibers undergo a photocuring process to crosslink the aligned oligomers by a thiol-ene click reaction with a triallyl crosslinker. By varying the intensity of UV light, we can achieve different amounts of bending of the fibers. With the lower values of UV intensity, we observed that one side of the fiber contracts more than the other side resulting in bending. Fibers with 36% ± 6 reversible actuation strain between the temperatures of 25°C and 60°C have been synthesized with higher contractions ratios achieved by combining this strain with the bending of the fibers. As these fibers have significant actuation around body temperature, these fibers may be used for biomedical applications and active textiles.

Ionic electroactive polymer (EAP) actuators are promising candidates for wearable electronics, including artificial muscles and flexible haptic devices owing to their low-voltage operability and flexible form factor. Yet, major challenges remaining are the slow switching speed, low blocking force and lacks of motion control in real-time. Herein, we report haptic interface systems based on a sensing glove and sensor-integrated ionic EAP actuators, allowing the teleoperation of soft grippers. By using bifunctional polymer electrolytes and soft-conducting electrodes, fast switching speed and high mechanical strength were achieved simultaneously under 1.5V conditions. This enabled the development of efficient haptic feedbacks at the finger without the need for high external voltage. With an aim at controlling the actuation motion in real-time, a liquid metal strain sensor was integrated into both the ionic EAP actuators and sensing glove. The sensor signal was changed according to the degree of bending of fingers wearing the sensing glove, and an algorithm was generated to synchronize the resistance change with the mechanical deformation of sensor-integrated actuators. The physical contact between the object and soft gripper fabricated with sensor-integrated actuators was simultaneously estimated through the sensor signal generated from the actuators, which was delivered to the fingertip as haptic feedback. Given that the haptic feedback system can be operated with small portable batteries, this will be a platform in soft robotics, wearable haptic devices and biomimetic devices.

Liquid crystal elastomers (LCE) have gained enormous attention in the recent past because of their facile fabrication and reversible shape morphing when exposed to external stimuli such as heat, light humidity, and magnetic or electric force. Especially among these, the electrostatic force has several advantages including fast response, easy control, and low power consumption. Mostly, Maxwell's stresses have been employed to control the shape morphing of LCE, but electrode patterning is limited. Therefore, we propose a new type of stimuli to control the LCE based on electrostatic forces generated because of charge transfer between electrodes and LCE. As a result, we demonstrated various types of operations with a high degree of freedom by applying electrostatic forces. The above result could be achieved through three-dimensional control of the electric field according to the structure of the electrode and the application signal without a pre-program in the LCE samples. We believe this study will be very useful for developing LCE-based actuators for various operations using electrostatic control methods with a variety of electrode designs and field modulation.

Fingertip friction plays a key role in the stimulation of tactile perception upon sliding touch. We present psychophysical experiments with materials, whose tactile perception is dominated by their surface microstructure. Random roughness at the length scale of the finger ridge distance contributes more to the tactile perception of similarity than the resemblance of surface topography [1]. For micro-fibrillar surfaces, tactile perception follows the bending stiffness of fibrils rather than the elastic moduli or the length of fibrils [2]. The perception of frictional strength in sliding touch can be confused if the characteristic length scale of surface microstructure varies [3]. Finally, physiological characterization reveals the soft matter properties of fingertip skin and their influence on tactile perception of materials.

[1] R. Sahli, A. Prot, A. Wang, M.H. Müser, M. Piovarči, P. Didyk, R. Bennewitz, Tactile perception of randomly rough surfaces, Scientific Reports, 10 (2020) 15800.
[2] A. Gedsun, R. Sahli, X. Meng, R. Hensel, R. Bennewitz, Bending as Key Mechanism in the Tactile Perception of Fibrillar Surfaces, Advanced Materials Interfaces, 9 (2022) 2101380.
[3] M. Fehlberg, K.-S. Kim, K. Drewing, R. Hensel, R. Bennewitz, Perception of Friction in Tactile Exploration of Micro-structured Rubber Samples, in: H. Seifi, et al. (Eds.) Haptics: Science, Technology, Applications, Springer International Publishing, Cham, 2022, pp. 21-29.

Fabrics are breathable, conformable, and compactible interlaced fiber structures, which makes them the perfect material for wearables, among many other everyday applications. Given their ubiquity, the possibility of "roboticizing" fabrics could lead to smart adaptive clothing, self-deploying shelters, and lightweight, stowable, shape-changing machines. Ideally, a robotic fabric's actuation, sensing, and structural support should be provided by fiber-based components, designed to integrate seamlessly with the fabric's soft and conformable nature. Variable-stiffness mechanisms are often used for the structural elements, functioning as "bones" that can be turned on and off as needed. However, many available fiber-based variable-stiffness mechanisms are passively rigid, only allowing the fabric to become soft when powered, and others require bulky external air or power supplies, making them untenable for untethered robots. In this talk, I will present a new electrically-driven variable-stiffness fiber that can provide a rigid load-bearing structure when powered, but remains flexible otherwise. The active variable-stiffness fibers are stable enough for a robotic fabric to lift and locomote with its own battery pack and onboard electronics, enabling a fully untethered locomoting robotic fabric. I will also present new fabric capacitive sensors that exhibit high strains, cyclic stability, and high water-vapor transmission rates, the latter of which allows for sweat evaporation, an important parameter of comfort in wearable applications. Finally, I will speculate on the combination of the fabric sensors with actuated and variable-stiffness fabrics for human motion monitoring and haptic feedback.

Despite the importance of touch for humans, interactive tactile (haptic) displays can still be considered in their infancy. While several actuation techniques have been developed, all these methods still present major drawbacks either in terms of the power demanded for actuation or their large size, thereby discouraging their use in high-resolution haptic displays. Magnetorheological elastomers (MREs) constitute an ideal candidate for a low-power and compact solution to be integrated into a programmable haptic interface. MREs are smart composite materials made of a soft elastomeric matrix and magnetic micro-/nanoparticles. Few studies have focused on the actuation of MREs, and those that do, mostly report the use of relatively large magnetic microparticles inside of elastomeric matrices. In contrast, much smaller nanoparticles would be required to fabricate films on the order of hundreds of nanometers in thickness, able to actuate into sharp textures at the microscopic scale. This research project focuses on building high-resolution haptic interfaces by developing flexible magneto-responsive thin-films based on magnetic nanoparticles. In the future these materials will be integrated into a nonvolatile magnetic control system that can produce local magnetic fields to actuate the film and generate the desired resolution of three-dimensional shapes and textures.

In this study, we fabricated MREs composed of soft, low-remanence ferromagnetic iron nanoparticles with isotropic and anisotropic arrangement in an elastomeric matrix (Ecoflex 00-30) and optimized them by characterizing their magnetic and mechanical behavior. Films with nanoparticle concentrations varying between 2% and 8% by volume were fabricated. All films showed large visible deformations at the millimeter scale at small applied magnetic fields of only 100-300 mT. However, the magnetically-induced deformations increased with the nanoparticle concentration in the films up to 6 vol. % for both isotropic and anisotropic films. Furthermore, isotropic 6 vol. % films exhibited 1.6x the deformation of anisotropic films at the highest applied field (300 mT). These isotropic films were able to achieve deflections of 0.73 mm and 1.6 mm at 100 mT and 300 mT, respectively. Moreover, we characterized the morphology of magnetic particles from SEM cross section images of the optimal 6 vol.% isotropic and anisotropic films. While the isotropic films showed random dispersion of the nanoparticles in the matrix, the anisotropic ones confirmed preferential alignment of the nanoparticles along the magnetization direction. The magnetic hysteresis behavior of isotropic and anisotropic films was measured to visualize the difference in remanent magnetization between the two cases and a small but evident increase in magnetic anisotropy matched the particle arrangement of the anisotropic films.

To compare with the literature, identical MRE films were also fabricated utilizing soft iron microparticles. In comparison with the nanoparticle-based anisotropic MREs, at a field of 100 mT, the analogous microparticle-based films showed 25-30% lower deflection. The latter were only able to match the nanoparticle films’ deflection at higher fields of almost 300 mT. This performance difference between nanoparticle and microparticle films was attributed to the increased anisotropic film stiffness resulting from the larger micrometer-size particles. Finally, the optimal nanoparticle-based isotropic MRE was utilized to create an enlarged programmable braille display which can be refreshed real time by actuating the deflection of specific buttons to construct different letters and words. In conclusion, this research showed for the first time the benefits of utilizing nanoparticles to engineer MREs with enhanced magnetomechanical response, enabling the realization of a reconfigurable haptic interface prototype with the potential for scalability and the promise of enabling numerous future haptic innovations.

Advances in soft robotic technology helped to overcome many challenges in minimally invasive surgery by improving dexterity, flexibility, and safety. However, there are tradeoffs as well in using soft robots for surgical applications including complicated fabrication and assembly processes, low output force, poor controllability, and limited sensing functionality. The confined, tortuous workspace of minimally invasive surgery adds additional challenges, such as restricting the size of a robot to a millimeter scale and requiring a wide range of motion for navigation. Thus, the fabrication of these millimeter-scale soft robots becomes more delicate and convoluted, resulting in inconsistent fabrication outcomes. The manufacturing and assembly process becomes more onerous as the number of sensing and actuation elements increases. In addition, the control of these soft robots can be complicated due to the nature of their non-linear behavior, requiring computationally expensive control algorithms. Likewise, some aspects of mechanical performances (i.e., output force and torque) are limited due to the use of low elastic modulus materials. Bridging these gaps, we present the design, fabrication, and characterization of programmable composite actuators (PCAs). PCAs implement the concept of using an ionic solution as a working fluid for actuation and as a sensing medium for self-sensing. Unlike other soft robots, which require a manual assembly process to combine two discrete components, an actuator and a sensor, PCAs seamlessly integrate actuators and sensors into a single unit by embedding both self-sensing and actuation capabilities in a monolithic laminate structure. Leveraging a layer-by-layer fabrication method, PCAs are manufactured by stacking and bonding various types of films (i.e., rigid, flexible, soft, adhesive, and conductive films). PCAs include three components: 1) soft, inflatable Teflon balloons, 2) a rigid-flexible origami structure, and 3) conductive electrodes for self-sensing. The soft, inflatable balloons consist of adhesive films and Teflon films whose surface is chemically modified by using hydrogen plasma to promote adhesion. The Teflon films are selectively bonded to create multiple bellow-shaped actuation chambers. By fluidically inflating these chambers, the flat Teflon balloons can be transformed from 2D to 3D bellow shapes, producing motion. Similarly, the rigid-flexible origami structure is fabricated by selectively bonding rigid (i.e., fiber-reinforced epoxy laminate) and flexible (i.e., polyimide) films, and it surrounds the soft, inflatable Teflon balloons. Encompassing the soft, inflatable Teflon balloons, the origami structure helps to increase the output force of the actuator, and it mechanically programs the actuator to produce various types of motion and degrees of freedom in an actuator (i.e., extension, bending, and rotation). The conductive electrodes are composed of copper and graphene films embedded within the actuator to perform as a proprioceptive ionic sensor when the ionic solution is used as a working fluid. Thus, the position of the actuators can be sensed by measuring the change in impedance across the electrodes, which depends on the volume of the balloons. To further understand the performance of these PCAs, they are characterized in terms of the range of motion and output force. In addition, multiple PCAs are combined as a continuum robot to demonstrate their potential usage as a surgical robot for minimally invasive surgery.

The tactile sensor can be applied to various technical fields like electronic-skin technology, human-machine interface, prosthetics, and robotics. Particularly, the technology with feedback systems like haptic interfaces necessitates a sensitive, multimodal, flexible sensor for an actuator to give elaborate tactile sensations to the users. Pressure, one of the most important stimuli that the haptic interfaces should acquire, can be divided into two concepts: dynamic pressure and static pressure. To elaborately sense and apply the sensations of the pressure, it is crucial to detect the moment of the pressure application and whether the pressure application is continued. Like as mechanoreceptors of the human skin are divided into fast-adapting mechanoreceptors (Meissner corpuscle, Pacinian corpuscle) and slow-adapting mechanoreceptors (Merkel disc, Ruffini corpuscle), researchers integrate two sensors that detect dynamic and static pressure each into a single platform to discriminate the dynamic and static pressure. However, the integrated sensing system is inconsistent with the direction of the tactile sensing-related technology development that continues to develop as a system containing the sensing ability of various stimuli generated by the humans or external environment and the feedback control to interact with humans. While wearability and implantability of the system are developed for high compatibility with humans, a conventional integrated sensing system with batteries and signal processors is bulky, limits continuous operation with a fixed energy capacity, and restricts practical usage due to frequent charging. Accordingly, the integrated sensing system with energy issues and the volumetric problem is inadequate for human-linked technology. In this work, we propose a self-powered, single sensor with a compact structure using piezoelectricity and ionics as sensing mechanisms with mimicry of the sensory adaptation behavior of the human skin. Piezoelectricity is responsible for detecting dynamic pressure, and ionics is responsible for detecting static pressure and expressing the sensory adaptation behavior. Since the piezoelectric materials can only respond to dynamic pressure, we introduced the ions slower than the piezoelectric charges to sense the static pressure. Since the ions can hold the piezoelectric charges from moving to the electrode, they delay the charges from being measured by the instrument. The static pressure can be detected by analyzing a prolonged piezoelectric voltage output achieved from the introduction of the ions. We utilized the piezoelectric polymer, poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)), and ionic liquid, 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]) to achieve intrinsic mechanical flexibility and non-volatility of the sensing layer. Electrochemical impedance spectroscopy verified the stable sensor fabrication and the equivalent electrical circuit of the tactile sensor. Emulated systems based on EIS data proved the sensing mechanism and sensory adaptation behavior quantified by the decay constant. With sensory adaptation behavior, the sensitivity of the dynamic pressure increased about 4.4 times, and the sensitivity of the static pressure increased about 4 times. The tactile sensor with sensory adaptation behavior can detect the overlapped stimulus upon sustained pressure with higher sensitivity. The tactile sensor that can elaborately analyze the pressure and sense the overlapped stimulus is vital in a stimuli-flourishing environment where it is more important to detect newly applied stimulus than sustained one.

Seamless multimaterial construction, particularly joining soft, stretchable tissues with stiff, inextensible structures, is a common motif in animal physiology. Such continuous mechanical gradients remain challenging to reproduce in engineered systems as current resin chemistries typically result in a single fixed set of properties. As an alternative to single-property materials, we introduce a ternary sequential reaction scheme that produces multimaterials by profoundly altering the polymer microstructure from within a single resin composition. In this system, the photodosage during 3D printing sets both the shape and extent of conversion for each subsequent reaction. The different polymerization mechanisms of the subsequent stages allow our single photochemistry to exhibit a diverse range of soft (Young’s Modulus, E ~ 400 kPa; ultimate elongation, dL/L0 ~ 300%) and stiff (E ~1.6 GPa; dL/L0 ~ 3%), providing the capability to match the mechanical properties of commercial polymers and biological tissues. Further, we successfully pattern photostable and mechanically robust modulus gradients (d[Er,stiff/Er,soft]/dx > 1000 mm-1) that exceed those found in squid beaks and human knee entheses. We demonstrate the ability to 3D print intricate multimaterial architectures by fabricating a soft, wearable braille display.

Effectively transmitting haptic sensations can create life-like digital human twins for virtual universes. However, humans have an uncanny ability to differentiate real sensations versus artificial ones due to the very high speed and sensitivities of human tactile receptors. Although vision can be used in many cases, having a high-speed tactile mechanical transmissions can enable more immersive environments. Here, I will present our group’s work in enabling large force feedbacks together with vibrotactile sensations as a means to activate the ensemble of tactile receptors on human skins.

Humans are experts at using soft touch to efficiently manipulate a vast range of objects in a variety of situations. In several application domains, rigid robotic solutions such as exoskeletons and vibrotactile gloves have been designed in an attempt to tap into this human potential. In our lab, we are exploring soft robotic solutions for creating more comfortable and more compelling haptic displays. With these displays, we hope to enable a soft touch in Virtual Reality and tele-operation applications. In this talk, I will present our work on design, control and attachment strategies of these soft displays. I will also discuss our recent perceptual experiments in which we directly compare task performance of humans wearing rigid and soft haptic feedback displays.

Electrically-activated elastomeric materials hold great promise to bring alive the dream of autonomous life-like soft robots. Fast actuation of materials that match the compliance and rheology of biological materials could enable breakthroughs in realistically mimicking the rippling fin motion of a cuttlefish, the dynamic acrobatics and dexterity of the bat wing membrane during flight, and even simulate the contractions and twists of arteries and the left ventricle of the heart. There have been several soft materials proposed to date ranging from very soft hydrogels to shape memory polymers whose shape change can be triggered by heat, magnetic field, electric field, and light. Of the soft active materials investigated to date, dielectric elastomers have garnered significant interest due to their nontrivial and reversible fast deformations in response to an external stimulus. Another soft elastomer demonstrating large deformations are liquid crystal elastomers via light and thermal actuation near their phase transition temperature, and more recently via electric field when configured as a planar capacitor. We discuss programming complex three-dimensional shapes using soft electrically-active elastomeric materials by controlling the anisotropy and mode of electric activation. The programming is achieved by patterning contractile fibers and selective activation. We introduce a computational model for simulating the shape-changing phenomena. The model is based on a new constitutive formulation within a finite viscoelastic framework. Computational implementation using a finite element user-subroutine allows us to simulate the complex shape response. Several examples of the achievable 3D complex shapes are demonstrated.

Minimally invasive surgical (MIS) procedures, such as interventional flexible endoscopy, present several advantages to traditional surgery including shorter recovery time, less trauma, and lower risk of infections. However, MIS is more technically demanding for the surgeon, entailing limitations in visual (limited field of view, low spatial and chromatic resolution), motor (dexterity), and haptic (reduced perception and tactile information) functionalities.
This talk will highlight our recent work in the design, materials, manufacturing, and development of soft sensing technologies and wearable, textile-based, haptic interfaces that aim at restoring and amplifying sensor and haptic feedback directly to the surgeon’s hand to facilitate navigation and improve safety during colonoscopy.
First, a new class of soft surgical robots (i.e., soft reactive skins) will be discussed. Soft reactive skins are thin, conformable robots with distributed sensing and actuation, that can be wrapped around traditional medical instrumentation to augment their functionalities. Our research group (the Material Robotics lab at Boston University) has explored these devices to sense and react to inputs like contact force, bending, shape, and bleeding during colonoscopy.
Second, our progress on soft robotic wearable haptic interfaces will be discussed. The talk will highlight our efforts in materials and manufacturing towards an ergonomic, lightweight, flexible, and comfortable-to-wear design. Through a user study, we assessed the mental workload and benefits of the haptic interface in a simulated colonoscopy scenario. The device is transparent while performing tasks, and could be worn and removed with minimal to no assistance.
The talk will conclude by discussing potential future applications of soft surgical robots and soft haptics in other minimally invasive surgical scenarios, like interventional bronchoscopy and endoscopic brain surgery.

Haptic devices have attracted attention for application in automotive, telecommunication, braille communication, virtual reality, augmented reality, and medical healthcare. Dielectric elastomer actuators (DEAs), a kind of soft actuator based on electroactive materials, possess great potential for haptic devices because of the advantages of their lightweight, large displacement, fast response, and physical properties similar to skin. However, the force output generated by a single-layer DEA is limited, and can only be used in areas with high haptic sensitivity like the fingertips and the back of the hand. To expand the applicability, stacking multilayer DEA devices is a common approach to obtain larger actuation performance but can be tedious in preparation and are often low in device stability. Moreover, multiple actuators with various shapes and sizes are needed to be integrated into haptic devices for different applications, further extending the fabrication time and incurring difficulty in their fabrication. Hence, there is a compelling need for printing or molding processes that could address these challenges.
In our work, digital light processing (DLP) 3D printing is introduced to print the dielectric elastomer structure and realize the fast fabrication of multilayer cylinder DEAs. The printable elastomer resin is prepared by mixing epoxy aliphatic acrylate (EAA) and an aliphatic urethane diacrylate (AUD)-based material. The printed elastomer has a high dielectric constant of 7.3 and Young’s modulus of 800 kPa at 10% strain. The DEAs can be fabricated by injecting carbon grease as the compliant electrodes into the designed cylinder channels made from the resin and sealing the ends with silver paste. The final cylinder DEA has 1 cm in diameter and 1 cm in height. The freestanding multilayer DEA has a blocked force of 120 mN and a free displacement of 50 μm under a voltage of 6 kV. The DEA can also maintain about 40 % actuation performance under a 100 Hz AC voltage, enabling a vibrotactile response perceivable through different body parts other than fingertips. In addition, the DLP 3D printing process allows multiple DEA devices to be prepared at the same time, which largely shortens the manufacturing time and enables the integration of multiple haptic devices. Overall, this process offers new opportunities for the development of haptic devices based on dielectric elastomer actuators.

Intelligent systems with capabilities of sensing, actuation, and closed-loop control are promising for many applications such as augmented reality, rehabilitation, and soft robotics. In this talk, I will present our work on stimuli-responsive materials, structures, and electronics toward this effort. I will start with our study on liquid crystal elastomers (LCEs), a type of smart material that has capabilities of soft elasticity and large, reversible shape-changing behaviors due to liquid crystal-polymer network couplings. Through introducing a versatile mechanical programming technique, previously inaccessible reconfigurable three-dimensional structures made of LCEs and their magnetic composites are created and their potential applications in soft robotics are demonstrated. I will further present our facile strategy to locally tailor the stiffness and the morphing behavior of these reconfigurable LCE structures by harnessing molecular-material-structure interactions, i.e., locally controlled mesogen alignment and crosslinking densities. Selective photopolymerization of spatially aligned LCE structures yields well-controlled lightly and highly crosslinked domains of distinct stiffness and selective permanent mesogen programming, which enables various previously inaccessible stiffness-heterogeneous geometries, as demonstrated in diverse morphing LCE structures via integrated experimental and finite element analysis. Furthermore, reprogramming of the non-photopolymerized regions allows for reshaping, as shown in a sequentially shape morphing LCE rod and “face”. The heterogenous morphing LCE structures have the potential for many applications including in artificial muscles, soft robotics, and many others. In addition, a simple strategy for creating 3D thermochromic LCE structures with synchronous shape-morphing and color-changing capabilities for biomimetic robotics will also be introduced. I will conclude my talk with soft sensing devices for in situ pressure measurements, beyond the actuation capabilities enabled by LCEs. The introduced actuation and sensing strategies and concepts are promising for many intelligent platforms.

Crumpling is one of the easiest, quickest, and most efficient ways to pack sheet-like electronic devices at a high compression ratio. Today, rolling or folding of many electronic devices has been attempted for portability, whereas due to the disordered and irreversible plastic deformation that may affect the electronic functions, crumpling is not applicable to conventional electronic devices. Inspired by butterfly wings during the emergence process with variable stiffness, the heterogeneous integration of three materials (i.e., an elastomer, silver nanowires, and a shape memory polymer) in this study enables thermal modulation of the mechanical properties between soft (2 MPa) and stiff (1315 MPa) or between conditions suitable for crumpling and free-standing operation, respectively. The crease that is common for the crumpled sheet due to the inordinate folding and stretching becomes invisible after smoothing the surface via thermal treatment. The demonstration of this platform includes crumpling and packing of touch panels into capsules, while a flat and smooth surface for reliable touch sensing is obtained after unpacking. The results in this article suggest the ability to use a simplistic design to secure the function of crumpled electronics without having to compromise the electrical and mechanical characteristics.

Most clinicians would not trade their sense of touch for even the most powerful imaging tool or surgical robot. Indeed, touch has played a critical role in diagnosis and treatment since prehistory, and is central to most branches of internal medicine. Clinicians rely on touch for all procedures performed by hand, e.g., tracheotomy, venous catheterization, routine orthopedic, obstetric, and urological procedures, most surgeries, and many forms of physical therapy. Despite the ubiquity of touch in medicine, haptic technologies are underdeveloped. For example, plastic and rubber models do not come close to mimicking the feel of biological tissue, and they cannot be reconfigured dynamically in a training environment. In robot-assisted surgery, limited forms of kinesthetic feedback have so far not led to improved patient outcomes. In telehealth appointments for individuals located in urban and rural “healthcare deserts”—or for most patients during a pandemic—medical touch is completely absent. Nevertheless, if tactile interaction with a high degree of realism were possible in these scenarios, the value of the technology which enabled it would be immense.

To implement feedback of a visual and auditory nature in a medical context is a simple matter: a digital display can render nearly any image and a loudspeaker can render nearly any sound. Implementing tactile feedback, on the other hand, is far more difficult. Whereas vision and hearing are localized to the eyes and the ears, touch and proprioception involve a range of structures distributed through the body. The reason that virtual medical training and remote care do not include touch is that existing haptic systems are incapable of recapitulating the surface texture and mechanical response of biological structures. This deficiency arises because most haptic systems rely on off-the-shelf mechanical actuators, which are limited to vibration, tingling, and other percussive effects: i.e., inaccurate proxies for sensations produced by soft, hydrated objects. In other words, these devices cannot mimic the texture, softness, wetness, thermal conductivity, adhesion, tack, and other near-surface properties of biological tissue.

Here, we describe several ways in which our group has explored the ways in which materials science can be used to understand and manipulate the tactile sense for applications in healthcare, VR, AR, and assistive devices. In this talk, I will discuss our major outcomes from this area of research, including (1) the development of a new type of conductive polymer that conforms to the skin and can be used to deliver haptic cues to the wearer; (2) elucidation of how the details of contact with the fingertip to materials surfaces contribute to the sense of softness, as well as (3) design rules for haptic surfaces that survive human contact in the real world.

For many years, a strong research interest has been oriented towards soft electronics for artificial skin applications. However, one challenge with stretchable devices is the limited availability of high performance stretchable electrical conductors and semiconductors that could remained entirely stable while stretched. Moreover, examples of such electronic skin embed excess amount of wires for addressing each sensors (pressure or temperature) in the conventional matrix structure.

Here, we present a new process for fabricating artificial skin consisting of an optical waveguide architecture allowing wide range of sensitivity to pressure [0 to 1KPa - 0.2 kPa ^-1 ], strain, shear and/or temperature variation [20 to 100°C], in multi-level ultra-stretchable network. The manufacturing process allows for a simple and low cost design of 100% low Young's modulus polymer [<1GPa].
This new type of stretchable optical sensor is highly robust, transparent and present a large sensing area [10 x 10 cm²] with limited amount of wires. Thus, this optical artificial skin presents far superior mechanical properties compare to current electronic skin.

Having clickable buttons that appear and disappear at will on any surface transforms how we interact with objects using our fingertips, be they touchscreens, furniture or a pair of binoculars. We report soft, compliant electrostatically driven actuators that pop up from a flat state to a curved shape in a few milliseconds and provide an intuitive click-like response to a user’s fingerpress. The devices are completely transparent, allowing them to be mounted on an LCD or OLED display, while still using the multitouch finger position sensing of the display. The devices are HAXELs, a type of electrostatic zipping actuator that displaces fluid to a central elastomer region, creating a raised bump, when a high electric field is applied to electrodes at the devices’ periphery. For a 2 cm x 2 cm device, we have strokes of 1.8 mm, and a holding force of 3 N, providing a haptic feel very much like a mechanical keyboard. The arrays are flexible, and can this be used on curved surfaces. Optical transparency is achieved using ITO for the electrodes and transparent polymers and oil for the other layers. We will report device fabrication, scaling, and use for cutaneous haptics, as well as self-sensing, illustrating several use cases.

Acoustic and thermal energy transport is critical for a wide range of applications, including biomedical diagnostics (e.g. ultrasound), renewable energy production, and building thermal management. Improving the performance of these technologies requires precise tailoring of acoustic and thermal energy transport, which remains a fundamental challenge. Understanding how to tune these materials and study them in real-time requires methods that can be used in varied environmental conditions. Hydrogels are of interest because they are easily fabricated, tunable, and have environment specific behavior. Our research investigates using transient grating spectroscopy, a method that employs acoustic wave signatures, to mechanically characterize hydrogels and other inhomogeneous materials. We provide a systematic approach across a range of polymer groups, to decompose the effects of crosslinking, swelling, and/or entanglements on Rayleigh wave speeds, which can then be related to a material’s elastic modulus. Transient grating also presents a method for dynamic response measurements of hydrogels. Traditional characterization methods, such as indentation, result in large discrepancies in measurements, which indicates that mechanical properties of hydrogels differ significantly in dynamic and static conditions. These differences are the first step to developing models for the direct contribution of poroelasticity and viscoelasticity on hydrogel behavior. This project will show how we can model and subsequently develop hydrogels with the mechanical properties necessary for our desired applications. This work was supported by the UCSB Materials Research Science and Engineering Center (MRSEC) of the National Science Foundation under award No. DMR-1720256 (IRG-3). The development of the transient grating spectroscopy at UCSB is supported by a DURIP grant from the U.S. Army Research Office under the award number W911NF-20-1-0161. Allison Chau acknowledges support from the NSF Graduate Research Fellowship Program under Grant No. 1650114. Angela Pitenis acknowledges funding support from the NSF CAREER award (CMMI-CAREER-2048043).

Having a secured grip on an object fundamentally depends on controlling the amount of frictional force. Our sensorimotor system excels at estimating the frictional strength of the contact to anticipate the object’s slippage, which in turn enables our remarkable dexterity. But how the tactile information about the state of friction is encoded within the mechanical deformation of the fingertips? Using a new setup that can image and modify friction in real-time, we show using that the skin undergoes specific patterns of deformation from the moment the skin first enters in contact with a surface all the way to sliding. The presence of these patterns of deformations is confirmed by a parsimonious model of the skin which captures the interplay of the visco-elastic nature of the skin and the frictional boundary layer.
Our finding suggests that the perceptual system uses these patterns of deformation as matched filters to rapidly estimate the frictional state, independently of knowing whether the contact has a large or small amount of friction.