Symposium SM11—Design and Analysis of Bioderived and Bioinspired Multifunctional Materials

By exploiting the novel liquid–liquid equilibrium (LLE) that exists between lignin and hot, one-phase solutions of aqueous renewable solvents, crude bulk lignins can be simultaneously fractionated, cleaned, and solvated for conversion to higher-value, high-quality bioproducts. This unusual LLE phase behavior forms the basis for a fractionation process that we refer to as Aqueous Lignin Purification with Hot Agents, or ALPHA. With this recently patented technology, simultaneous control of both lignin purity and molecular weight becomes possible. Furthermore, ALPHA has also been developed for continuous operation, so it can be commercially scaled-up. Finally, the technology has the added advantage of using renewable solvents that are produced within the biorefinery itself, including acetic acid and ethanol.
Lignin is like any other polymer in that the molecular weight can have a dramatic impact on its suitability for a given application. In addition, polymer purity can also be an important requirement if the desired materials properties are to be achieved. Two large and growing markets have been identified for our “ALPHA” lignins: (1) high-performance carbon fibers for automotive applications and (2) rigid polyurethane foams for building spray insulation. In both cases, we are showing how lignin fractions isolated by ALPHA with preferred molecular weights, purities, and chemical functionalities yield decidedly superior performance vs. the starting bulk feed lignins, whether they be Kraft lignins or agriculturally based lignins derived from hybrid poplar or corn stover. In particular, ALPHA lignins exhibit superior spinnability and result in carbon fibers having improved strength and modulus. Alternatively, other ALPHA lignins tuned to have a completely different set of properties are being used to make polyurethane foams at polyol substitution rates of up to 60%, with most foam properties showing improvement over the polyol-based control.

Being significant components of woody and non-woody plants, lignocellulosic have recently found enormous applications in various fields ranging from biofuels and filtration to battery materials. We present an innovative approach to fabricate bioinspired lignocellulosic materials with tunable sorption and release profiles. We have prepared lignin-cellulose hybrid nanofibers and particles via respective electrospinning and anti-solvent precipitation of mixtures containing biodegradable cellulose and alkali lignin. We find an interesting correlation between the precursor mixture composition and the fiber/particle physical properties. When the sorption and release profile of these matrices is investigated, the matrix composition seems to monitor its capacity and kinetics to sorb and release various types of molecules. In particular, we have examined the scope of these matrices as sorbents for industrial contaminants using model dyes, while efficacy of these matrices as sustained-release media for agrochemicals is analyzed by using abamectin as the model pesticide. We have also determined the bioavailability of abamectin from various matrices using in-vitro bioassays. We believe that by manipulating the composition of the matrices, we can fine-tune their sorption and release profiles, while flexibility in fabricating the matrices in different physical forms further enhance the scope of our approach to be applied in diverse applications.

Electroconductive hydrogels are promising materials for mimicking electrophysiological environments of biological system towards cardiac/neural tissue engineering, therapeutic applications, and bioelectronics. Considering recent approaches of 3D printing technique to fabricate desirable objects for medical applications, injectability, biocompatibility and mechanical strength of those conductive hydrogels are necessarily required. However, current strategy of simple imbedding of conductive additives (e.g., carbon materials, metal nanoparticles, and conducting polymers) into the hydrogel network has challenges to achieve stable gelation, toughness, and high conductivity before and after 3D printing. Herein, we propose two types of plant-inspired phenyl chemistry, i) gallol oxidation and ii) biphenyl formation via Suzuki-miyaura coupling, for in situ fabrication of electroconductive hydrogel inks applicable to extrusion-based 3D printing. In the first topic, injectable and conductive microgels are developed for in situ deposition of silver nanoparticles on the surface of the hydrogels via redox activity of the gallol moieties - which is abundant polyphenol in plant kingdom, further applying to 3D printing and electrophysiological muscle tissue support. In the second topic, the phenylborate-triggered conductive hydrogels are formed by biphenyl coupling upon gold reduction, exhibiting high cytocompatibility and temporal injectability for printing of biotic-abiotic interfacing layers in bioelectronics. Our finding of the phenyl chemistry would provide an insight to a variety of applications where conductive materials are needed.

Since its beginning, in the early 1920’s, polymeric industry relies heavily on fossil fuel resources. Approximately 4%-8% oil, gas and their derivatives are nowadays transformed into polymeric materials. Most of them are non-recyclable and non-degradable, hence leading to serious environmental issues, detrimental to wildlife and humans. In this context, there is a need for the development of alternative polymeric products, which, starting from renewable commodities, will share the same level of complexity than current ones derived from oil industry.

Among the various biosourced raw products used to make polymeric materials, vegetable oils are promising for their low cost and intrinsic degradability, but also because their production is already optimized for the food industry. Acrylated epoxidized soybean oil (AESO) is one example of the vegetable oil derivatives that are used as e.g. plastifying additives for the formulation of PVC. Alone, AESO can be readily and rapidly polymerized to give a thermoset polymer. However, as a consequence of its high intrinsic viscosity, most of the research on AESO-based polymer so far is only focused on the bulk, coating or film properties of this material, leaving the possibility to fabricate high added value materials a blind spot.

Herein, we present the development of a simple, “one-pot” approach to manufacture monodispersed AESO microparticles, based on a microfluidic chip with a flow-focusing structure for emulsification and the serpentine zone for UV-induced reticulation. We show that the size and shape of particles can be tailored easily by precisely tuning the nature and concentration of a co-solvent, used to decrease the viscosity of the dispersed phase, and monitoring the hydrodynamics of the flow. Exploiting the presence of triglycerides structures within the thermoset, we show that the particles are degradable in alkaline conditions. In addition, we show that AESO particles are good at encapsulating model amphiphilic or hydrophobic fluorescent molecules, and at releasing them on long timescales in the external, continuous phase.

Our work is a first step towards the development of a full range of functional microspheres from biosourced raw materials.

The proliferation of single-use plastics (e.g., food packaging) has led to investigation of sustainable plant-based substitutes. We report on the immense potential of leaf-sheath from a palm tree—Areca catechu—for manufacturing of eco-friendly, single-use food ware, by direct single-step forming of the sheath material. Using microstructural analyses and different mechanical loading paths, we show that this sheath material can accommodate large forming strains of up to 200% prior to failure. The sheath’s deformation response is highly sensitive to hydration, with up to 400% increase in forming strain, so that present manufacturing techniques, largely driven by empiricism and heuristics, are far from optimal. The embodied energy for the palm products is 4-5 orders of magnitude smaller than for equivalent plastic or paper products. Our results delineate product shapes that can be formed in a single step using this material, without intermediate pulping processes, thus demonstrating its versatility. The manufacturing approach demonstrated with the palm leaf has inherent advantages over other resource-intensive, multi-step processing methods commonly used with plant materials.

Plant cell walls are highly-evolved nanocomposite materials with impressive properties and useful functionality. The macromolecular assembly of cellulose, hemicellulose, and lignin, collectively termed lignocellulose, serves multiple functions to plants including structural support, transport of water and nutrients, and biological defense. This same material has also served humanity since the beginning of civilization in applications spanning construction materials, clothing, and fuel. Advances in our understanding of the molecular-level structure/property/function relationships of lignocellulose will enable us to use this natural, renewable material to meet the technological demands of modern society, and thereby displace incumbent materials and fuels derived from fossil carbon which are the cause of increasing environmental detriment. In this presentation, I will discuss modeling approaches to understand how molecular characteristics give rise the emergent properties that ultimately govern the bulk behavior of lignocellulosic composites. Specifically, I will present a study of how the molecular structure of xylan, a hemicellulose, impacts its binding affinity to cellulose nanofibrils. Our findings indicate that xylan of degree of polymerization (DP) less than 20 will detach from the surface of cellulose fibrils in an aqueous environment, while xylan polymers with DP greater than 20 remain strongly bound. Next, I will discuss the construction of simulations of a 3-component system including multiple cellulose nanofibrils, cellulose, and lignin. The starting configuration of the polymers is informed by NMR experiments. Simulations varying the monomeric composition of the lignin polymers show that monomers that contain more methoxy groups on the aromatic rings increase the mechanical integrity of the assembly. Finally, I will present recent progress towards development of a coarse-grained dynamics modeling framework that will enable investigations biopolymer assemblies several orders of magnitude larger than those accessible to molecular dynamics simulations.

In nature, catecholamines play important and diverse roles, including neurotransmission, wet adhesion, pigmentation and photoprotection. The special combination of catechols and amines is a subject of high interest, not only for understanding the biological roles of catecholamines, but also as building blocks for synthetic materials. In the proteins that enable adhesion of marine mussels to wet surfaces, the intimate association of catechols and amines is believed to be essential to interfacial adhesion. As a result, combinations of catechols and amines have featured prominently in the design of synthetic adhesive polymers and in multifunctional ‘polydopamine’ coatings. Polydopamine coatings derived from polymerization of catecholamines can be exploited for a variety of practical applications. In this talk we will describe our recent elucidation of the macromolecular nature of polydopamine and describe our attempts to improve the mechanical performance of these coatings. In particular, we recently showed that laser thermal annealing of pDA produced further polymerization of monomeric and oligomeric species leading to fundamental changes in molecular and bulk mechanical behavior, including vast improvement in scratch resistance. Laser-annealed pDA has better scratch resistance than titania and silica, while preserving the multifunctional properties of pDA that are attractive in a variety of contexts. The results of this work suggest new opportunities for the use of PDA in mechanically demanding applications.

Diatoms are single celled microalgae which couple photosynthetic activity with the biomineralization process of conversion of inorganic silicate into complex and nanostructured biosilica. Biosilica shells (frustules) exhibit high surface area, periodic porosity, transparency and mechanical resistance. All these features of their silica shells make diatoms appealing living sources of sustainable smart materials for applications in photonics, optoelectronics, sensing and biomedicine [1].
Recently, we demonstrated an in vivo protocol which enables frustules’ silica modification by simple introduction of functional molecules into the colture medium. Many functional molecules can be introduced into the biosilica by this approach, including organic [2] and organometallic emitters [3] and also compounds of pharmacological interest [4].
We recently demonstrated that a surface adherent diatom species, Phaeodactylum tricornutum, can self-populate and propagate on transparent conductive ITO electrodes, producing photocurrents. In addition, these diatoms can uptake luminescent and optoelectronically active organometallic complexes during their growth and adhesion process. The combination of these features enables to envision microalgae as a platform which can self-assemble in optoelectronically active layers, suitable for producing living micro-devices.

[1] R. Ragni, S. R. Cicco, D. Vona and G. M. Farinola, Adv. Mater., 1704289, 1-23 (2017).
[2] R. Ragni, F. Scotognella, D. Vona, L. Moretti, E. Altamura, G. Ceccone, D. Mehn, S.-R. Cicco, F. Palumbo, G. Lanzani and G. M. Farinola, Adv. Funct. Mater., 28 (24), 1706214-1706223 (2018).
[3] G. Della Rosa, D. Vona, A. Aloisi, R. Ragni, R. Di Corato, M. Lo Presti, S. R. Cicco, E. Altamura, A. Taurino, M. Catalano, G.-M. Farinola and R. Rinaldi, ACS Sust. Chem. & Eng., 7(2), 2207-2215 (2018).
[4] S.R. Cicco, D. Vona, G. Leone, E. De Giglio, M.A. Bonifacio, S. Cometa, S. Fiore, F. Palumbo, R. Ragni, G.M. Farinola, Mat. Sci and Eng.: C, 104, (2019).

Addressing the global challenges of sustainability calls for the development of materials using bio-based constituents that can outperform conventional materials. An example of one such bio-based material is chitosan (that is derived from marine shells). However, the use of chitosan in load-bearing structural and industrial applications is limited due to its inferior mechanical properties in comparison to a variety of engineered materials such as ceramics and metals.
Interestingly, the shells of marine species – nacre, from which chitosan is extracted, is one of the strongest known natural materials. This is possible because in nacre the chitin (from which chitosan is derived) is embedded with mineral platelets of calcium carbonate, forming a brick-mortar architecture.
Based on this bio-inspiration, a nacre-mimetic composite comprising bio-based constituents (chitosan and silk) and calcium carbonate minerals is manufactured by a green bio-mineralization approach. The approach enables synthesis of mineralized (calcium carbonate) films with teeth-like patterned microstructures. The films comprising the patterned minerals are then stacked with the patterned sides facing each other and infused with silk fibroin. Subsequent drying consolidates the mineralized films into a nacre-mimetic composite where across successive layers, the films are laterally interlocked due to their patterned topography. The resultant composite exhibits nearly 85% higher tensile strength and elastic modulus at least 10 times higher than that of chitosan owing to the distinctive micro-level interlocking between the mineralized films.
Owing to its bio-based constitution, the nacre-mimetic composite also exhibits biocompatibility and mechanical properties similar to that of mammalian bone, making it potentially useful for hard-tissue regeneration applications.

Wrinkled surfaces and materials are widespread throughout the natural world and underpin the functionality of a variety of emerging modern technologies. Indeed, the implementation of wrinkles can improve the performance of controllably-wettable surfaces, conductive electrodes, photovoltaics, and dielectric elastomer actuators. However, despite tremendous progress to date, the reversible post-fabrication tuning of wrinkle sizes across multiple length scales has remained quite challenging, and the development of comprehensive relationships between structure and function for optically-active wrinkled surfaces has often been fraught with difficulties. Herein, by drawing inspiration from natural micro- or nano-structured cephalopod skin components and leveraging methodologies established for artificial adaptive infrared-reflecting and infrared-transmitting soft actuators, we engineer camouflage surfaces with dynamically-reconfigurable morphologies and concomitant tunable visible-to-infrared spectroscopic properties, while also developing an enhanced understanding of the relationship between their local surface structures and global functionalities. When mechanically actuated, our systems can reconfigure their height frequency distributions by ≈ 180-fold and root-mean-square roughnesses by ≈ 215-fold; alter their visible to near-infrared total reflectances, transmittances, and absorptances by ≈ 10 %, ≈ 20 %, and ≈ 30 % and their mid- to long-wavelength infrared total reflectances, transmittances, and absorptances by ≈ 26 %, ≈ 27 %, and ≈ 36 %; and modulate their specular-to-diffuse reflectance and transmittance ratios by ≈ 18-fold and ≈ 60-fold within the visible to near-infrared and by ≈ 5-fold and ≈ 38-fold within the mid- to long-wavelength infrared. When electrically actuated, our systems maintain their highly-desirable visible and thermal functionalities and feature competitive figures of merit, e.g., reasonable maximum areal strains of ≈ 60 %, rapid response times of ≈0.7 s, and good stabilities upon repeated actuation Overall, our findings constitute another step forward in the continued development of cephalopod-inspired light- and heat-manipulating architectures and appear well-positioned to facilitate new opportunities in areas as varied as sensing, electronics, optics, soft robotics, and thermal management.

In nature, structural organization of biopolymers at the nanoscale leads to iridescent coloration, as observed in beetle shells and bird feathers. These structural colors can be mimicked in synthetic materials derived from cellulose nanocrystals (CNCs) because CNCs organize into a helical structure (known as a chiral nematic liquid crystal). When a suspension of CNCs is dried, the resulting film has a chiral nematic structure and, if the pitch of the helical structure matches the wavelength of visible light, the film will appear iridescent.¹

Over the past decade, we have been developing new materials derived from CNCs, with a particular emphasis on creating new photonic materials. For example, we have exploited CNCs as a template to construct novel chiral nematic mesoporous materials with photonic properties.² We have succeeded in preparing silica,³ organosilica,⁴ and polymeric materials⁵ through self-assembly or templating methods.

In this presentation, I will discuss our recent progress using CNCs to create flexible photonic materials that respond to stimuli.^6,7

[1] Revol, J.-F.; Godbout, L.; Gray, D. G. J. Pulp Pap. Sci. 1998, 24, 146.
[2] Giese, M.; Blusch, L. K.; Khan, M. K.; MacLachlan, M. J. Angew. Chem. Int. Ed. 2015, 54, 2888.
[3] Shopsowitz, K. E.; Qi, H.; Hamad, W. Y.; MacLachlan, M.J. Nature 2010, 468, 422.
[4] Shopsowitz, K.E.; Hamad, W.Y.; MacLachlan, M.J. J. Am. Chem. Soc. 2012, 134, 867.
[5] Cao, Y.; Lewis, L.; Hamad, W.Y.; MacLachlan, M.J. Adv. Mater. 2019, 31, 1808186.
[6] Kose, O.; Tran, A.; Lewis, L.; Hamad, W.Y.; MacLachlan, M.J.; Nature Commun. 2019, 10, 510.
[7] Boott, C.E.; Tran, A.; Hamad, W.Y.; MacLachlan, M.J. Angew. Chem. Int. Ed. 2020, 59, 226-231.

I will give an overview of our published work on nanotechnologies using cellulose nanomaterials, with a focus on assembly and functionalization strategies of wood nanocellulose aimed at specific properties, with an eye toward high impact applications including energy, electronics, building materials and water treatment, including nanomanufacturing and light management in transparent nanopaper for optoelectronics (as a replacement of plastics); mechanical properties of densely packed nanocellulose for lightweight structural materials (replacement of steel, Nature 2018); artificial tree for high-performance water desalination and solar steam generations; mesoporous, three-dimensional carbon derived from wood for advanced batteries (replacement of metal current collectors for beyond Li-ion batteries); nano-ionic thermoelectrics (Nature Materials, 2019); radiation cooling (Science, 2019).

Superstructured colloidal materials are proposed to endow new functions to renewable nanoparticles, including chitin and cellulose which can be isolated as large axial aspect nanofibrils or shorter nanorods. Interparticle interactions and ensuing adhesive forces are used for building macroscale assemblies displaying networks with tailorable strength, cohesion, porosity and with opto-mechanical response. Here, we demonstrate that the topology of nanonetworks formed from the respective system enables robust superstructuring of diverse particles, including mineral and organic, representing a generic pathway for the fabrication of a new class of constructs. An intermixed network of fibrils with particles increases the toughness of the assemblies by up to three orders of magnitude compared, for instance, to sintering. Supramolecular cohesion is transferred from the fibrils to the constructs following a power law, with a constant decay factor. Our results are expected to expand the development of functional colloids from laboratory-scale towards their implementation in nanomanufacturing of bulk materials.

Due to its lightweight and high porosity, aerogel has been considered a promising material with great potential in thermal insulation application. Although silica aerogel demonstrates ultralow thermal conductivity of less than 15 mW/(m K), its brittleness has limited its wide application. Therefore, flexible and durable aerogel with low thermal conductivity has been actively pursued, especially those derived from natural polymers. In this presentation, we report a cellulose nanofibrils (CNF)/Pickering emulsion composite aerogel with quasi-closed internal pores with extremely low thermal conductivity. The composite CNF/emulsion aerogel was fabricated by Pickering emulsion templating and solvent exchange methods. By removing the oil phase from the emulsion, quasi-closed pores could be generated inside the aerogel, which can reduce the thermal conductivity to 15.5 mW/(m K). The presence of quasi-closed pore from emulsion templating is verified from both confocal microscopy and scanning electron microscopy images. The composite aerogel showed very low density of 11.4 mg/cm³, high mesoporosity, high specific modulus of 18.2 kPa/(mg cm³), and specific yield strength of 1.6 kPa/(mg cm³). The CNF/emulsion composite aerogel also demonstrates superb flexibility and infrared shielding performance. It is expected such all-cellulose aerogel can be used in textile and clothing, as well as building and construction for thermal insulation and management.

To date, ionic conducting hydrogel has attracted tremendous focus as an alternative to the conventional rigid metallic conductors in fabricating flexible and soft electronics, owing to their intrinsic characteristics of high stretchablility, transparency, tunable mechanical property, consistent conductive phase, and biocompatibility. However, the current ionic conductive hydrogels still suffer from two long-standing dilemmas, which is between the strength and toughness, as well as between the mechanical strength and ionic conductivity. In addition, ionic conductive (organo)hydrogel with freezing tolerance has not been widely reported, and the current anti-freezing ionic conductive (organo)hydrogel showed unsatisfactorily low ionic conductivity at subzero temperature. Therefore, simultaneous realization of high strength, stretchability, toughness, ionic conductivity, and freezing tolerance through a simple approach is still a challenge.

In this work, a novel polyvinyl alcohol (PVA)- cellulose nanofibrils (CNF) ionic conducting organohydrogel with integrated characteristics, including superb mechanical performance (stress up to 2.1MPa, strain up to 660%), high conductivity (3.2 S/m at room temperature), transparency (90%), freezing tolerance (-70 °C), and long-term solvent retention, was facilely fabricated through a simple sol-gel transition method. Owing to the existence of DMSO/H2O binary solvent system, the organohydrogel maintains flexible and conductive (1.1 S/m) even at -70 °C. This material design verifies the synergistic effect of CNF in enhancing both mechanical properties and ionic conductivity, providing a facile solution to address the long-standing dilemma among strength, toughness, and ionic conductivity for the ionic conducting hydrogel. In addition, the ionic conductive organohydrogel exhibits excellent sensing performance and can be rationally assembled into multi-functional sensors to detect full-range human body movement with high sensitivity, stability, and durability. Attributed to these characteristics, this PVA-CNF ionic conducting organohydrogel is believed to function as a versatile and adaptive platform for future manufacturing of multi-functional sensors in extensive applications such as health monitoring, electronic skin, and wearable electronics.

Nanocellulose research has addressed increased attention in the bioprocessing community, especially the utility of these materials in different fields including biomedical and materials applications. However, the major concern in today’s nanocellulose research is not about production but matters a lot to find a better application where its structural characteristics could be tailored by different methods. In this presentation, a scalable method for the assembly of oriented bacterial nanocellulose (BC) films is presented, based on using wrinkled thin silicone substrates of meter square size as templates during BC biotechnological synthesis. Control samples, including flat templated and template-free oriented bacterial cellulose, along with the oriented BC, are morphologically characterized using scanning electron microscopy (SEM). Multiple functional properties including wettability, birefringence, mechanical strength, crystallinity, water retention, thermal stability, etc., are being characterized for the BC samples, where the wrinkling induced in-situ BC alignment not only significantly improved material mechanical properties (both strength and toughness) but also endowed unique material surface characteristics such as wettability, crystallinity and thermal stability. Owing to the enhanced properties observed, potential applications of wrinkle templated BC in printing and cell culture is being demonstrated as a proof of concept. The excellent improved mechanical properties and respectable printability of wrinkle templated BC also opens the door for various cellulose-based wearable and printable electronic devices and sensors application.

Inspired by nature’s biopolymers, we engineer artificial protein materials on the genetic and chemical level leading to new properties and function. We employ synthetic and chemical biology to construct our materials and endow them with stimuli-responsiveness. In particular, we have fabricated protein-derived nanomaterials: coiled-coil fibers and helix-elastin block polymers. We investigate the fundamental self-assembly and molecular recognition capabilities of these systems. More importantly, we are able to harness these structure as well as others to interface with small molecule therapeutics and cells. Our studies lead to insights in how we can program self-assembling protein biomaterials to be sensed and respond to external stimuli.

Silk fibroins are naturally occurring proteins that can exhibit a combination of strength and toughness far exceeding those achieved by man-made polymers. For example, the dragline silk of the European garden spider has higher tensile strength and stiffness than nylon 6/6, with three times the toughness of Kevlar. The exemplary properties of silk fibroins arise from their chemical architecture, in which rigid hydrophobic and flexible hydrophilic peptide segments linearly alternate. Supramolecular assembly of silk fibroins yield a nanostructured material with crystalline beta-sheet domains, which provide strength and stiffness, dispersed in an amorphous matrix, which provides toughness. Interestingly, silk fibroins bear structural resemblance to synthetic segmented copolymers such as poly(ether-block-amide) (PEBA), yet man-made PEBA are vastly inferior in mechanical properties compared to many natural silk fibroins. Thus, mimicking silk fibroin architecture in synthetic polymers can unlock the path to synthesizing exceptionally strong and robust next-generation polymers. Unfortunately, rational design of silk-mimetic polymers is hindered by: 1) the challenges faced in rapid synthesis of well-defined segmented polymers bearing multiple aggregation-prone "blocks", and 2) the lack of knowledge in predicting how chemical structure and sequence dictates supramolecular structure and mechanical properties. This talk will present our recent work in developing a new route towards efficient synthesis of silk-mimetic polymers. In particular, we discuss a two-stage modular approach based on microwave-assisted chemistry that is capable of generating silk-mimetic polymers with well-defined beta-sheet forming peptide segments and improved molecular weights. This work is the first to demonstrate Cu(I)-mediated click chemistry as a new approach toward efficient step-growth polymerization of silk-mimetic polymers. Notably, this synthetic approach can reach molecular weights within 20 min that far surpass those obtained by traditional peptide coupling reagents, and the resulting polymers readily form silk-like supramolecular structures. The speed and modularity of this synthetic approach offers possibility for creating libraries of silk-mimetic polymers for systematic study of structure-property relationships. Furthermore, this talk will also briefly discuss a new computational model for predicting materials properties based on chemical structure in silk-mimetic polymers. This computational model can reveal fundamental mechanisms in the mechanical behavior of silk-mimetic polymers in relation to molecular and supramolecular structure. Thus, these experimental and computational tools are crucial steps towards enabling rational design and synthesis of silk-mimetic polymers.

Spider silk that mechanically swells and shrinks in response to changes in relative humidity or water gradient has shown capability to exert higher energy than conventional actuators and artificial muscles, and thus holds potential to be used as high-energy actuating components for various engineering applications, including robotics, shape morphing, and smart structures. However, spider silk’s low availability largely limits these potential applications. We found that water-responsiveness of Bombyx (B.) mori silk, which possesses a similar supramolecular structure to that of spider silk, could be dramatically increased, and even surpasses that of spider silk, by simply adding silica nanoparticles. Mechanical and microstructural analyses using FTIR and AFM, together with our previous studies on water-responsiveness of regenerated silk with various β-sheet crystallinity, suggest that stiff silica nanoparticles could dramatically reduce energy dissipation within silk’s supramolecular network, and increase energy conversion efficiency during silk’s water-responsive actuation. We also demonstrate that a large-scale actuator of B. mori silk/silica nanoparticles composites that reversibly lift a weight powered by humidity changes, showing the possibility of using silk with lower-cost and wider availability as building blocks for high-energy water-responsive structures.

Silk fibroin fibers (FFs), produced from natural silk by removing their sericin coating layer, have been used as a biomedical suture material for centuries. Both physical and chemical methods have been used to enhance the strength of silk fibroin. However, the current methods have limitations. For example, the physical methods lead to the brittle nature of silk fibroin due to the increasing of β-sheet content. The chemical crosslink methods show better nature, but they may be time-consuming or lead to cytotoxicity under certain conditions, limiting the fields, especially in biomedical. Therefore, a rapid and mild chemical crosslink method is necessary to develop.

In this study, silk fibroin fibers were crosslinked by employing photoredox catalysis. The chemical crosslink through dityrosine connection was confirmed, and further evaluated by the crosslink density. Further applying tension stretch to the fibers, the break stress and modulus of stretched photo-crosslinked FFs increased by nearly 70% and 50% than that of original FFs. This approach constitutes an easy and straightforward strategy for the strengthening of FFs, promotes the FF applications in broad engineering fields.

Cell-free systems have growing importance as a way to use synthetic biology tools in resource-poor environments. Lysates may be dried for storage, delivering biochemical activity for sensing or producing molecules on-demand upon rehydration at the point of need. Up to now, cell-free protein synthesis (CFPS) reactions have been studied as aqueous solutions in test tubes or absorbed onto paper or cloth. Embedding biological functionality into broadly-used materials, such as plastic polymers, has long been an attractive goal. Unfortunately, this goal has for the most part remained out of reach, often due to the fragility of biological systems outside of aqueous environments. In this work, we describe and utilize a surprising and useful feature of lyophilized cell-free lysate systems: tolerance to casting methods involving exposure to organic solvents or heat up to 90°C. To explore this newly discovered feature, a variety of solvents were tested and CFPS reaction components were screened for protective properties. CFPS is compatible with several polymer types. Tolerance to polymer casting enables the delivery of dry cell-free reactions in the form of coatings or fibers, among other processing possibilities.

Biobased Cellulose NanoFibrils (CNFs) constitute a highly anisotropic nanomaterial with excellent mechanical properties with a well defined surface chemistry and outstanding durability in harsh environments. During the last two decades CNFs have been used in numerous applications ranging from antibacterial, composite, energy storage, display and fire proofing applications , to mention a few, where different aspects of their inherent apllications have been utilized. The Youngs modulus of the fibrils is around 130 GPa and it should hence be possible to create outstandig materials of these materials provided that the nanostructure of the prepared materials could be controlled. Since materials from CNFs are almost exclusively formed from water it is essential to control their colloidal interactions in dispersion to create an ideal structure for a certain end-purpose. In the present contribution two different strategies will be handled in detail. In the first appoach anionically modified CNFs were well dispersed at low concentrations together with small amounts of high molecular mass sodium alginate before dewatering of the dispersion to a solid gel before drying. The so prepared materials were then re-swollen in aqueous solutions containing different di-valent or tri-valent counterions resulting in wet films with excellent mechanical properties. A wet film of these materials with 50 % water was shown to have modulus, strength and stress at break comparabel and even better than HD polyethylene. The reason to this extraordinary behaviour is that the fibrils form a volume spanning arrested state (VAS) as the concentration is increased during dewatering and this creates a lamellar structure in the concentrated wet film with an intertwined network of alginate polymers. As the dry films are re-swollen this network basically expands in one direction and by using multivalent ions the alginate molecules are able to lock the structure creating a type of interpenetrated network of CNF and alginate. In the second approach the CNFs are converted to end-less filaments using a flow-focusing methodology. In this approach the well dispersed fibrils are oriented in an elongational flow in a flow-focusing device and by using an acidic solution to create this flow the fibrils are locked in an oriented structure where their excellent mechanical properties can be fully utilized to create strong and thin filaments. This concept can also be developed by using coaxial arrangements where different types of interactive filaments can be prepared.

Polymer matrix cellulose biocomposites are widely used in the form of molded components in industry exemplified by automotive applications. Improved control of the nanostructure makes it possible to significantly widen the range of properties and potential applications. Top-down approaches are particularly interesting, since the nanostructure can be controlled both in terms of spatial nanocellulose fibril distribution and its orientation. One can also prepare optically transparent materials by selection of an appropriate polymer matrix. By the addition of functional components in the form of nanoparticles or dyes, the photonics functionality can be extended further for applications such as smart windows, wood for solid state lasing and heat storage.
Molecular and nanoscale understanding of processing for nanostructural control is essential, as well as the effect of nanostructure on physical properties. Materials design in terms of wood substrate modification, chemical treatment and polymer impregnation strategies will be discussed. This includes methods for nanostructural characterization, mechanisms for light transmission, reduction of moisture sensitivity and effects from refractive index matching between the polymer and the wood substrate.
An important argument for cellulosic materials is their role in sustainable development, and this topic will be analyzed. There is a tendency to emphasize the renewable resource origin of cellulose, but this may not always be sufficient to justify the replacement of established materials.

Other than its superior mechanical strength and thermal stability, bacterial cellulose (BC)-derived thin sheet could also provide other crucial functions as an excellent separator candidate used in emerging battery technologies. Particularly, for lithium sulfur batteries (LSBs), polysulfide shuttling effect and lithium dendrites are two tough issues that cause numerous problems including low cell efficiencies, fast battery decay and safety concerns. To attack these two problems simultaneously, this study presents a functionalized BC separator by manipulating its oxygen-containing functional groups. With enhanced repulsive force between polysulfides and the carboxyl-altered BC film, the polysulfide shuttling can be effectively suppressed on the cathode side. Correspondingly, the tendence of lithium ion absorption to the oxygen functional groups is capable of generating uniform lithium ion diffusion at the interface of the lithium anode and the BC separator, resulting in stable lithium stripping/plating processes by inhibiting lithium dendrite growth. As a result, the LSB cell with a BC separator, at a sulfur load of 4 mg cm^-2, delivers a specific capacity of 1450 mAh g^-1 at 0.1C, or 1000 mAh g^-1 at 0.3C over 100 cycles, suggesting the superior performance of BC separators in LSB.

Growing interest in using cellulose nanofibrils (CNFs) to reinforce polymers is attributable to CNFs’ unique properties such as high aspect ratio, high specific strength, light weight, low cost, and renewability. However, drying CNFs effectively with less agglomeration at low cost is a main challenge for enabling use of CNFs in biocomposites. In the present study, CNFs derived from bleached pulps were spray-dried at six different conditions: two temperatures (~125 °C and ~110 °C) and three feed concentrations (1.3%, 1.5%, and 1.8%). The spray-dried CNFs were compounded with polylactic acid (PLA) (at 5 wt% CNF level) to form CNF/PLA biocomposites. The biocomposites obtained were characterized using techniques including tensile testing, rheological analyses, dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The tensile strengths of the CNF/PLA biocomposites varied largely from 32 to 54 MPa (69% change). When the CNFs were spray-dried at the higher temperature (~125 °C) with a feed concentration of 1.3%, the CNF/PLA biocomposite had the highest tensile strength among all composites. This indicates that the CNF spray-drying condition has a significant effect on the mechanical properties of the CNF/PLA composites. Some physicochemical treatments on CNFs will be utilized in the future to further improve the properties of CNF/PLA composites.

Dental diseases are a global health problem affecting large populations despite the widespread use of fluoride and other preventive treatments. Primarily as result of demineralization, i.e., loss of mineral from teeth, these ailments are associated with incipient caries, gum recession, hypersensitivity, and gingivitis. Current dental therapies mostly rely on replacement defective or lost tissue with synthetic restorative dental materials with limited long-term success, often causing post-therapeutic problems, e.g., gingival inflammation, secondary caries, and even tooth loss. Incorporating a functional mineral layer that can be fully integrated into underlying molecular tooth structure in repairing the tissue has been a long-standing challenge. Following lessons from biology where proteins guide tissue formation, we develop a peptide-based biomimetic remineralization methodology to restore demineralized dental hard tissues in enamel, dentin and cementum using peptides derived from biomineralizing proteins, such as amelogenin, the key protein in enamel. Dubbed as amelogenin-derived peptides, ADPs are designed through a multipronged approach including biocombinatorial selection, bioinformatics, molecular simulations, and by iteratively testing via binding and mineralization assays. The ADPs are used in guiding remineralization in vitro on artificially demineralized teeth of extracted human, rat, and porcine teeth as under simulated physiological conditions and in vivo rat model. In a variety of treatment modalities, the peptide treated test groups displayed structure and morphology with well-integrated interfaces exhibiting local mechanical properties mimicking the restored tissues, e.g., similar to dentin-enamel junction (DEJ) and dentin-cementum junction (DCJ). The highly potent materials and methods developed in this work pose to drastically alter the current dental health care by highly effective practical products and procedures in restorative and cosmetic dentistry as well as in preventive daily oral care.

An elegant way of biomaterial synthesis is through supramolecular chemistry, where functional moieties are held together via dynamic and reversible bonds. An example of such a supramolecular moiety is the ureidopyrimidinone (UPy), which dimerizes by four-fold hydrogen bonding and distinctly self-assembles into nanofibrous structures. Various polymers, functionalized with multiple UPy-motifs, can be processed into films and scaffolds, giving a wide choice of materials characteristics for numerous biomedical applications. Furthermore, because of the supramolecular nature, countless different additives modified with a UPy-motif are easily incorporated into the supramolecular materials to achieve the desired functionality for potential applications as biomedical materials.
Previously, we demonstrated the design of a UPy-functional alkyl halide initiator, including its incorporation into the UPy-functional polycaprolactone (UPy-PCL) films at different concentrations by solvent casting. Grafting of antifouling polymers by atom transfer radical polymerization (ATRP) in form of polyzwitterions in a fully aqueous medium at room temperature was described. Furthermore, we were able to successfully functionalize microporous supramolecular electrospun scaffolds prepared from telechelic UPy-PCL with polyzwitterions. Post-polymerization surface elemental composition measurements, revealed presence of two distinct signals that reflected the charged atoms of the polyzwitterions. The charges strongly affected the wettability of the grafted materials. Additionally, presence of the new polymer layer on the surfaces was characterized by differences in surface morphology and cellular adhesion pre- and post-polymerization. The amount of polymer was dependent on the concentrations of UPy-initiator incorporated into the supramolecular films, as well as polymerization times.
We have now further improved our approach by utilizing photo-induced ATRP to gain temporal control over the polymerization. Photo-induced ATRP allows us to pattern our supramolecular material surfaces with functional polymers. With recent developments in the field of radical polymerization, we now utilize enzymatically degassed ATRP, which is oxygen-tolerant and has alleviated the need for inert atmosphere. Thus, we can perform open-to-air polymerization and effortlessly upscale supramolecular material functionalization to multiple materials at a time. With catalytic amounts of glucose oxidase enzyme, we have observed excellent control over the polymerization in a fully aqueous medium at room temperature, by means of linear first-order kinetic behaviour and narrow molecular weight distributions. We have successfully synthetized hydrophilic oligo(ethylene glycol) (OEG) polymer brushes with varying brush lengths, which resulted in thermoresponsive materials. Additionally, functional OEG copolymer brushes were prepared with multiple pendant amine moieties, which were positively charged at physiological conditions. Amine moieties can act as anchors to conjugate various peptides, dyes and bioactive motifs, post-polymerization. Currently, we are continuing implementation of photo-induced oxygen-tolerant ATRP for the design of bioactive materials with carbohydrate moieties. Materials functionalized with carbohydrate moieties serve as excellent candidates for extracellular matrix mimics. We are excited to further investigate a plethora of possible applications of our functional supramolecular materials in the field of tissue engineering and regenerative medicine.

Natural biological materials often demonstrate intriguing properties that are difficult to replicate in man-made materials, such as self-repairing/-regeneration, adaptable morphological and mechanical switch, sensing and responding. One promising strategy of incorporating these living aspects into creating new materials is to genetically program microbes and use them as the major building blocks. Here we report a new Engineered Living Material (ELM) that harnesses the active properties of bacterial cells to create an ultra-stiff, regenerable, and responsive film. The material is assembled from tightly packed cells whose solid surfaces are densely crosslinked. The surface layer (S-layer) protein of C. crescentus was engineered to display SpyTag over the entire cell body. These functionalized bacterial cells crosslink into tight assemblies with close cell-cell contact mediated by nanoparticles displaying SpyCatcher and the formation of SpyCatcher-SpyTag iso-peptide bonds. We found (1) A layer of densely packed Qdots can be displayed on living bacterial surface. (2) Stiffness of the crosslinked bacterial film increases over 30 times compared to non-crosslinked biofilms. Cleavage of a disulfide bond inserted between SpyCatcher and the nanoparticles melts the crosslinked film, confirming the specific covalent linkage is responsible for the enhanced mechanical properties. (3) The engineered ultra-stiff bacterial film can harvest nutrients to both continue to manufacture new material and regenerate damaged regions due to the continuous growth of C. crescentus cells and the expression of new S-layer proteins in the presence of crosslinking agent. (4) The crosslinked living bacterial film exhibits dynamic morphological and mechanical response to environmental osmotic stressing caused by a neutral polymer macromolecule polyethylene glycol 8000. With these materials we introduce a new design principle for creating high stiffness in liquid content materials.

Microphysiological cancer systems (Cancers-on-Chips) are emerging cancer models for better cancer research. Conventional cancer models have failed in capturing the underlying mechanisms of how cancer reacts to the current anti-cancer approaches due to the lack of similarities with the original cancer of patients. The challenge is modeling a complex and heterogeneous cancer environment where every element contributes to cancer hallmarks development. Recently, biofabrication technologies have been advanced to spatially control multiple types of cells and biomaterials to mimic the native physiology of human tissue and organs. In particular, 3D cell-printing has beauty in manipulating the 3D anatomical structure of cancerous tissue through a layer-by-layer process that stacks up cells and bioinks following a precisely designed sequence. The decellularized extracellular matrix bioinks that mimic the tissue-specific environment has recapitulated the pathology and aggressiveness of cancer. In addition, 3D cell-printing has shown the possibilities in modeling various types of cancers for future cancer research.

Cryopreservation is very important in biotechnological, pharmaceutical, biochemical or food industries as the purpose of storage of protein drugs, cells, tissues and food, and ice slurries for refrigeration systems. Antifreeze protein (AFP) have been received attention with their potential as a cryopreservation agent by their ability to prevent the organisms from freezing at the subzero environment through antifreeze activity such as ice recrystallization inhibition or thermal hysteresis effect. However, it is struggling to apply the natural AFP in practical industries as cryopreservation agent because of their irreversible denaturation and the difficulty in extraction from nature. These challenges have led to developing artificial cryopreservation agents like dimethyl sulfoxide and sodium phosphates but due to the cytotoxicity and less biocompatible of them, the recovery rate of the target matter is too low when they are added. Here, the natural AFP mimetic short peptides conjugated with specific amino acids showing antifreeze activity and fibrous assembly with enhanced π-π stacking are prepared by supramolecular chemistry to increase both antifreeze activity and biocompatibility. This research might provide a useful strategy to fabricate the cryopreservation agent through the supramolecular nanomaterials and to figure out the mechanism of ice binding to antifreeze protein.

Polymer/virus based biosensors are a compelling system for medical diagnostics, environmental monitoring, and food security. The hybrid system of a biocompatible polymer with a virus bio-recognition element, results in a bio-friendly device that is solution processable. Typically, antibodies or aptamers are used as the bio-recognition element, however they can be costly and time consuming to produce, lack stability under sensing or surface functionalization conditions, and be poorly oriented during functionalization rendering a fraction of receptor sites useless. In contrast, the M13 virus, a harmless and non-toxic filamentous bacteriophage, can be manufactured in large quantities through inexpensive infection of a bacterial host and can withstand a large range of temperatures and pHs. Moreover, this combinatorial phage display workhorse can be genetically modified to display thousands of well-ordered, densely packed affinity peptide fusions with controlled orientation along its less than one micron length.
Recent work has demonstrated that electrospun polymer fibers can be utilized as optical resonator whispering gallery mode (WGM) sensors. These WGM sensors have potential as highly sensitive, label-free sensors. The high quality (Q) cavities are of particular interest as they enable light to recirculate hundreds to millions of times or more, significantly increasing interaction with an analyte and improving device sensitivity. Light propagating at the periphery of these radially symmetric resonators is confined by total internal reflection such that its evanescent field serves as a probe for analyte binding events on the resonator surface. A promising biosensor device would combine the polymer/virus bio-recognition with the WGM sensing mechanism. An ideal method would be to electrospinning polymer/M13 fibers capable of supporting WGM while still maintaining the M13 bio-recognition properties
Here, we used near-field electrospinning, a direct write fabrication method utilizing a low strength electric field, to create polyvinyl alcohol (PVA) WGM fiber resonators with incorporated M13 biorecognition elements. A streptavidin-binding phage functioned as a model bioreceptor to demonstrate the utility of the sensing platform. The surface concentration of M13 was evaluated via streptavidin-conjugated gold nanoparticle binding and x-ray photospectroscopy (XPS). Rhodamine 6G (R6G) was then incorporated into the fiber as an emitter. Sharp peaks associated with WGMs decorated the broad dye fluorescence. The resonant modes were identified using Mie theory, and Q values and free spectral range were measured. Subsequently, the fibers were used to detect streptavidin and the sensitivity of these novel PVA/M13 biosensors was determined. These studies demonstrate the potential of electrospun WGM resonators with incorporated phage-based bioreceptors as a robust platform for highly sensitive biosensing.

Layer-structured composites have broad applications in the biomedical device, tissue scaffolds, skin membranes, solar cell devices, battery and supercapacitor devices, sensors, and actuators. Here we report the biosystem-mimicking structure of layers along the thickness or radial directions. These polymer/nanoparticle composites display in different material forms, such as fibers, thin films, or laminates. The combination of the soft micromoles and hard nanoparticles have synergistic effects in mechanical robustness and functional versatility. We demonstrate via a few polymers of polyvinyl alcohol (PVA), polyacrylonitrile (PAN), and thermoplastic polyurethane (TPU). Different nanoparticles in one-dimension and two-dimension are incorporated in these polymers, for example, carbon nanotubes (CNTs), carbon nanofibers (CNFs), and graphene nanoplatelets (GNPs). The composites’ compositions and structures in each layer can be tuned via manufacturing customization and material modification. We will demonstrate how uniquely designed structures benefit mechanical enhancement, electrical conductivity, and gas sensitivity.

The growing field of printed biodegradable electronics provides the opportunity to monitor soils at a high spatial density without the risk of increased waste. A tunably degradable encapsulant is a critical component of soil-degradable electronics, as it acts to delay the ingress of water, microbes, and other agents responsible for degradation. Existing biodegradable polymers such as poly(lactic acid) tend to have limited utility due to their uptake of water which could in turn expose components underneath. Candelilla wax has been shown to be an effective encapsulating material in biomedical applications [1]. We have recently demonstrated that a blend of beeswax and soy wax is an effective encapsulant for printed biodegradable soil moisture sensors [2]. In this presentation, we elaborate on the thermal/mechanical properties of beeswax-soy wax blends to explore the conditions required for melt processing and coating substrates. In addition, we explore the tunability of degradation and introduce a novel wax-based soil degradation sensor, where time to sensor failure can be correlated to microbial or enzymatic activity.

[1] Won, S. M.; Koo, J.; Crawford, K. E.; Mickle, A. D.; Xue, Y.; Min, S.; McIlvried, L. A.; Yan, Y.; Kim, S. B.; Lee, S. M.; et al. Natural Wax for Transient Electronics. Adv. Funct. Mater. 2018, 28 (32), 1–10. https://doi.org/10.1002/adfm.201801819.
[2] Sui, Y.; Atreya, M; Dahal, S; Gopalakrishnan, A; Khosla; Whiting, G. Controlled Biodegradation of an Additively Fabricated Capacitive Soil Moisture Sensor. ACS Sustainable Chem. Eng. in press.

Nature provides soft materials, such as gels, capable of complex mechanical responses that vary with hydration level and other environmental factors such as pH and salinity. Such biological “soft” polymers often consist of nanofibers capable of aggregating further into microbundles. These biopolymers contain relatively rigid building blocks along the chain backbone, which is necessary to form hierarchical structures characteristic of fibers. The fiber forming hierarchical biopolymers exhibit a nonlinear stress-strain response – typically a ‘J-shape’ stress-strain curve that demonstrates strain-stiffening behavior. Being able to replicate this strain-stiffening behavior is critical for the success of future bio-electronic interfaces and medical devices. Systems designed to exhibit strain-stiffening responses demonstrate unfolding, deformation, and straightening of the network. Recent designs include wavy-textures induced by pre-straining, self-assembled elastomers, and kiragami-inspired systems. Yet, it remains a worthwhile goal to develop tunable strain-stiffening systems, particularly from biocompatible polymers. Here, we demonstrate a new approach to modulating the strain-stiffening response of monolithic fibrous hydrogels through application of a physical surface topography.

We fabricated periodic pillar nanostructures on a fibrous chitosan hydrogel using solvent dropcast lithography. We produced a range of regularly spaced nanopillars with periodicities of approximately 200 nm, 300 nm, and 500 nm, which is comparable to the biopolymer radius of gyration (~250 nm). We performed tensile testing in the plane of the hydrated films with and without nanopatterns to determine the effect of surface nanostructures on film stiffness. We found, surprisingly, that the elastic moduli increased in the films with nanopillar topography, and that the amount of increase was correlated to the increasing feature size of the films. Furthermore, the nanopillar topography strongly modulated the strain-stiffening response.

To determine the origin of the processing-structure-mechanical property relation, we systematically investigated the nanoscale topography deformation utilizing atomic force microscopy, and observed significant alignment of the nanofibers at deformations above the nonlinear stress-strain transition point. In this presentation, we report on our study to examine the role of interactions and ionic linkages in the hydrogels and to determine if there is a limit to the tunable mechanical properties. The simple method to fabricate a monolithic strain-stiffening system from fibrous hydrogels could be translated towards other biopolymer-based devices and materials including electronically active biopolymers.

Hydrogels are a class of water-laid crosslinked polymers with tissue-like microstructure and unique stimuli-responsive deformability, with great potential for tissue engineering, humane-machine interface, and artificial muscle for soft robots and wearable electronics. However, due to the high porosity their intrinsic mechanical weakness and low deliverable actuation force limit their applications. We have recently made progresses on developing a new generic method to construct hydrogels of (1) ultra-toughness and (2) high deliverable force and power density during actuation. First, Natural load-bearing materials like tendons are strong and tough, owing to the hierarchically assembly of anisotropic structures across multi-length-scales. We have developed a strategy to produce polymers with tendon-like hierarchical architecture. Multiple mechanisms originating from these structures at different length-scales were integrated in the water-rich polymer (70-95% water) to feature both ultra-high ultimate stress (23.5 MPa) and strain (2900%), which yields giant toughness (210 MJ/m³, 170 kJ/m²) and remarkable fatigue resistance, 10-time tougher than natural tendon, Kevlar and rubber. This research may make hydrogels capable of practical applications that requires long-term services with high-loads and abrupt-impacts, and extend to the optimization of various polymeric materials. Second, inspired by the energy conversion mechanism of many creatures during jumping, we designed an elastic-driven strong contractile hydrogel through storing and releasing elastic potential energy in polymer network. It can generate high contractile force (40 KPa) rapidly at ultra-high work density (15.3 KJ/m³), outperforming current hydrogels (~0.01 KJ/m³) and even biological muscles (~8 KJ/m³). This demonstrated elastic-energy storing and releasing method endows hydrogels with elasticity-plasticity switchability, multi-stable deformability in fully reversible and programmable manners, and anisotropic or isotropic deformation. With the high power density and programmability via this customizable modular design, these hydrogels demonstrated potential for broad applications in artificial muscles, contractile wound dressing, and high-power actuators.

Nature with the 3.8 billion years of research and development experiences can always provide us with out-of-the-box ideas for man-made materials from their superior design and functionality. Recent progresses by our group on energy harvesting (Nat. Nanotech. 2019) and energy storage (Adv. Funct. Mater. 2019; Matter 2020) materials will be presented. First, plant can turn its head following the sun, known as phototropism, to maximize the photo(thermal) energy harvesting. Engineering such a self-adaptive actuation ability in synthetic materials would be highly advantageous for advancing intelligent energy-efficient systems and enhancing the performance of optical or optoelectronic devices, avoiding computer programming or electromechanical control and external power supply. We have an artificial phototropic system based on nanostructured stimuli-responsive polymers that can aim and align to the incident light direction in the three-dimensions over a broad temperature range. Such adaptive reconfiguration is realized through a built-in feedback loop rooted in the photothermal and mechanical properties of the material. This system is termed a sunflower-like biomimetic omnidirectional tracker (SunBOT). We show that an array of SunBOTs can, in principle, be used in solar vapour generation devices, as it achieves up to a 400% solar energy-harvesting enhancement over non-tropistic materials at oblique illumination angles. The principle behind our SunBOTs is universal and can be extended to many responsive materials and a broad range of stimuli. Second, wood in nature has well-defined vertical structure with low tortuosity to facilitate the mass transport. Inspired from the wood structure, we designed anisotropic hydrogels with alignment to increase the ionic conductivity of materials. The pore size can be rationalized and reduced even smaller than natural wood to increase the specific area, while maintaining the alignment. Conducting polymer, owing to its mesoporous structure and high electrical conductivity has been widely used for supercapcitors. By incorporating the conducting polymer in hydrogel-based matrix, the all-solid-state supercapacitor with high electrochemical performance can be fabricated. Such conducting polymer-hydrogel composites exhibit unprecedented ionic conductivity, areal supercapacitance, power density, energy density, capacitance retention and cyclic stability. Besides, the hydrogel matrix also provides excellent flexibility under cyclic bending, making it possible for flexible electronics.

Fish scales serve as a natural dermal armor with remarkable flexibility and puncture resistance. Through biomimetic scales, researchers are able to acquire these properties and tune them by adjusting their design parameters. Overlapping scales, as seen in elasmoid scales, can lead to complex interactions between each scale. These interactions are able to maintain stiffness while improving flexibility. Hence, it is important to understand these interactions in order to design biomimetic fish scales. As the scaled substrate deforms and the scales start to engage, modeling the flexibility requires accounting for nonlinear relations. Current studies focus on characterizing these kinematic linear and nonlinear regions but fall short in modeling the kinematic phase shift. Here we propose an approach that will predict when the transition from linear to nonlinear will occur, allowing for more control of the substrate's overall behavior. Using a kinematic analysis of the interacting scales, we can model the flexibility at the transition point where the scales start to engage in a nonlinear manner. The validity of these kinematic predictions will be investigated through finite element analysis. The results of this investigation could allow for an efficient optimization method for scale-like designs that can be applied to various applications.

Hierarchically ordered structures can be found in a variety of biological systems ranging from microscopic to the macroscopic scale in nature. Not surprisingly, inspiration from nature has provided cues to stimulate research in materials preparation to obtain functional hierarchy. For instance, hierarchical and ordered biological structures, in many tissues such as cartilage, and cornea, are well exemplified. Extensive efforts have been made to mimic the native biological structures of a tissue on cell layers and stratification. We attempt to develop hierarchical and layered hydrogel architectures with robust design necessary for cellular encapsulation.

Research on hierarchical structured hydrogels is still in its infancy. More recently, new hierarchical hydrogel architectures have been pioneered to create multi-layered chitosan hydrogels in a concentric fashion. Pioneering efforts to develop hierarchical architectures with hydrogel have provided fundamental insights at the molecular level. Yet the strategies might not be standardized because substantial different design considerations is required due to a wide range of biochemical processes involved. In some cases, cytotoxic processes and/or chemicals to form a gel structure are utilized which results in an inevitable cell damage. Furthermore, at small scales, the fabrication of micro-size architectures requires higher reaction rates than that of macroscopic objects, which causes agglomeration between gels in a reaction bath. Due to the agglomeration issue, there has been an absence of reliably scale-down models for mass production. Only a few methods have been introduced to produce a single multi-layered capsule with diameters between 4 and 20 mm. Even with predictive mechanisms in various hydrogels, challenges exist in both mass production and scaling-down of the size of hydrogel architectures, and multi-layered techniques for cell encapsulation studies are even sparse.

We propose the fabrication of multi-layered alginate capsules to resolve the technical bottlenecks through precise control of hydrogel modalities and shell thickness at micron scale enabling scaleup for mass production. The multi-layered capsules comprise of natural alginate polymer crosslinked with Ca²⁺ ions without auxiliary crosslinking agents. To the best of our knowledge, no theoretical or empirical formulation has been suggested to describe the process underlying our hierarchical alginate structures. In addition to the materials we also suggest a hypothetical mechanism to explain how different alginate hierarchical structures can be fabricated and demonstrate its encapsulant application for heterogenous microbial spatial distribution. We believe our proposed encapsulation methodology with alginate hydrogels will be an effective avenue to organize cells into sophisticated and stratified structures to study intra and multi-cellular communication.

Biochar, a highly porous carbonaceous product of biomass pyrolysis, offers a wide array of surface functional groups and structural modalities that depend on biomass properties and pyrolysis conditions. This tunable platform promises versatility in capturing aqueous organophosphates, including malathion, a hazardous pesticide and chemical warfare agent surrogate. While some studies have elucidated the general mechanisms associated with biomass pyrolysis, the relationship between material evolution and efficacy toward a variety of emerging applications is largely unknown. In this work, we use Raman spectroscopy and Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) to probe in situ the molecular and structural changes of coir biochar at various temperatures up to 850 °C. Raman signatures from biochar reflect the complex structural changes of the amorphous carbon as it gradually transforms to larger aromatic structures, during a slow temperature ramp and subsequent 2-hr dwell. DRIFTS similarly indicates increasing aromatic character and fewer aliphatic groups as pyrolysis temperature increases, while some oxygen-containing functional groups (hydroxyl, carbonyl) are largely eliminated by 500 °C. These tunable chemical groups/carbon structures are expected to significantly impact the adsorption of aqueous malathion onto the meso and micro pore surfaces of biochar due to various non-covalent interactions. To test this hypothesis, we use high-performance liquid chromatography (HPLC) to record the concentrations of aqueous malathion containing biochar suspensions, over time. Initial work suggests that biochar is effective in adsorbing malathion, and continued studies elucidate the nature of the biochar-malathion interactions. In particular, during the course of an adsorption experiment, biochar suspensions are removed and analyzed using attenuated-reflectance FTIR. Spectra from suspensions containing the highest concentrations of malathion near equilibrium suggest the highest density of surface-adsorbed malathion, and that the malathion carbonyl groups may be responsible for this interaction.

Silica aerogels are lightweight, open-celled, porous structures that have advantageous properties such as low density and high surface area. Due to these characteristics, silica aerogels would be great candidates for aeronautical applications. Recently, there has been considerable interest in functionalizing substrates with polydopamine (PDA), a polymeric, bio-inspired synthetic analogue of melanin. Due to the catechol functionalities in PDA, PDA can easily adhere to a variety of substrates. While many studies coat two-dimensional substrates easily, very few studies exist that coat three-dimensional scaffolds with PDA while maintaining the scaffold’s original properties. Here we demonstrate an in-situ coating method for depositing PDA on silica aerogel by utilizing the amine functionalities within the aerogel. The coated PDA-aerogel maintain high porosity (> 90%) and high surface areas (around 600 m²/g). It also exhibits strong absorption of UV-light in comparison to the uncoated aerogel monolith due to UV-absorption ability of PDA. PDA- coated aerogels have promising potential to serve as radiation-mitigating materials for space exploration.

Thermoelectric devices can collect heat and convert them as electricity; thus, fabrication of composites with programmable electrical conductivity, thermal conductivity, and Seebeck coefficient parameters can enable highly efficient energy generation and storage. Our research reported the processing of polymer and nanoparticles from a molecular scale via the in-situ polymerization method. The nanoscale polymer/nanoparticle hybrid mimicked biosystems such as blood vessels or cellular structures in plants. Via the interphase formation, the thermal and electrical conductivity of the macroscale composites showed optimized properties. As compared to the simple blending of the polymer and the nanoparticles, our in-situ polymerized composites exhibited much enhanced thermoelectrical performance and shed light on manufacturing that transfer the nanoscale properties to the macroscale device performance.

The reversible binding of phenyl boronic acids (PBA) to 1,2 or 1,3 diols has been explored for over 20 years.¹ Solution based studies have used these molecules to generate measurable colorimetric, fluorescent, or electrochemical change in response to common saccharides, such as glucose and fructose. As the nature of their reversible bond formation remains relatively unspecific to the nature of the sugar present, their application has struggled to ever compete with the accuracy of enzymatic systems based on glucose oxidase. However, the potential to incorporate these materials, in a facile manner, into soft polymeric matrices can offer significant advantage in the generation of passive sampling and even self-regulating systems.
To this end, sensors and actuators based on the PBA-containing hydrogels have found application in optically, electrically, and even mechanically responsive materials. A large proportion of the research which generates binding-induced shape changes, relies on swelling or shrinkage of PBA materials, caused by modulating osmotic pressure upon bond formation with the sugar molecule, a phenomenon first exploited by Matsumoto et al. in 2004.² Volume change of PBA in hydrogel structures can be hampered by slow response times as the speed of the response relies on the volume-dependent diffusion times of analytes to receptor sites. To date, such systems have primarily been implemented in macro-sized gels which have contributed to this effect. As the kinetics of hydration process are typically proportional to the square of the linear dimension³, a reduction in hydrogel size from mm to μm (as presented herein) reduces the response time by a factor of 1 million. We present a system compatible with two photon polymerization (2PP) which allows for the fabrication of structures on the micron and sub-micron scale. The advantage of having such small structures is that the traditionally slow responses times associated with PBA based hydrogels are overcome by the fast diffusion of the analyte throughout the structure.
To study the actuation of microstructures fabricated using our novel photoresist, arrays of pillars with 20 μm diameter and 30 μm height were fabricated. When exposed to a D-fructose solution, the pillars underwent a significant swelling response. Up to a 90 % increase in area of the pillars was observed within 30 seconds of the addition of 100 mM fructose solution. It was demonstrated that this response was reversible and reproducible over multiple cycles.
Interestingly, the degree of actuation can be tailored by adjusting the laser dosage used to fabricate the structures. As expected, structures fabricated using higher laser powers were more densely crosslinked and therefore exhibit a reduced swelling response when compared to structures fabricated at lower laser powers. For example, the area of structures fabricated at a 20 mW laser power increased by almost 90 %, while structures fabricated at a 40 mW laser power only underwent a 40 % increase in area.
This work enables the realization of soft complex 3D microstructures and actuators with programmable response and fast response-time.

1. Lorand, J. P.; Edwards, J. O., Polyol Complexes and Structure of the Benzeneboronate Ion. The Journal of Organic Chemistry 1959, 24 (6), 769-774.
2. Matsumoto, A.; Kurata, T.; Shiino, D.; Kataoka, K., Swelling and Shrinking Kinetics of Totally Synthetic, Glucose-Responsive Polymer Gel Bearing Phenylborate Derivative as a Glucose-Sensing Moiety. Macromolecules 2004, 37 (4), 1502-1510.
3. Shibayama, M.; Tanaka, T., Volume phase transition and related phenomena of polymer gels. In Responsive Gels: Volume Transitions I, Springer Berlin Heidelberg: Berlin, Heidelberg, 1993; pp 1-62.

The structural variation of functional side groups and sequence structures of repeating units in oligodepsipeptides (ODPs) allows the design of matrix materials exhibiting strong physical interactions with specific drug molecules^[1,2]. In this way high drug loading can be achieved. Here teroligomers are prepared by a ring-opening polymerization of three different morpholine-2,5-diones. Dibutyl tin(II) oxide were reacted with 2-hydroxyethyl disulfide forming the catalyst / initiator system for the library of teroligomers^[3]. It was designed to potentially introduce redox sensitivity to the ter-ODPs. The optimized synthetic route enabled the presence of dihydroxy terminal groups on the ter-ODPs, and minimized the formation of macrocycles as a potential side reaction. The systematical variation of repeating units composition in ter-ODPs samples was quantitatively calculated by ¹H-NMR according to the intensity variation of the methyl/methylene signals from the different repeating units, and it was in line with the variation of comonomer ratio of the feed composition for the ROP reactions. As the repeating units in ter-ODPs have different molecular weight, the composition variation in different ter-ODPs was also reflected by MALDI-TOF-MS results. The intensity of m/z⁺ peaks assigned to telechelic ter-ODPs with high methyl-modified MD units (MMD_units) content increased accordingly as the composition of the MMD_units increased, and thus a shift of m/z⁺ peaks of telechelic structures was observed. In addition, the intensity change of the δ_s(CH₃) band at 1375 cm^-1 in the fingerprint area of the FT-IR spectra of different ter-ODPs samples, attributed to the iso-butyl modified MD units could be an additional hint for the composition variation of ter-ODPs. The good end group functionality of ter-ODPs was reflected by the further linkage with isophorone diisocyanate (IPDI) via the coupling of hydroxy ends of ter-ODPs and one of the isocyanate group of IPDI. In future, these ter-ODPs could be used as interesting candidate matrix materials for drug releasing implants such as particulate dosage forms.
References
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Unique structural and intermolecular properties found in nature for generations have inspired humanity to engineer more efficient products. Biomaterials-driven nanostructures have also shown remarkable performance improvements in electronics. The recent development of carbon-coated TiO₂ has been proved to improve the performance of TiO₂ as an anode material in Li-ion batteries (LIBs). Microbes, such as E. coli, contain a high amount of carbon, making them a promising precursor for the formation of carbon layers. In this presentation, we report a bioinspired synthesis method to fabricate a composite using microbes and anatase TiO₂ to improve the energy density and cycle life of aqueous LIBs with the water-in-salt electrolyte (WiSE), (aqueous electrolyte composed of 21m LiTFSI (lithium-bis(trifluoromethanesulfonyl)-imide)). Anatase TiO₂ synthesized by the sol-gel method can reach a high theoretical capacity (167 mAh/g) and increase batteries’ energy density. The volumetric changes in its crystalline structure during the lithiation/delithiation is less than 4%, making the anatase TiO₂ a possible anode material for stable batteries. By using two different strains at different growth stages, we were able to control the microstructure of the microbe-assisted TiO₂ (m-TiO₂) composite based on the variability of the shape of the microbes. The synthesis process involved subsequent mixing and dehydration of the microbe and TiO₂ mixture, followed by an annealing process. The microbes acted as carbon precursors and formed a carbonaceous layer on the anatase TiO₂. These carbonaceous biofilms are expected to improve the composite’s conductivity and prevent direct contact between the anode and water molecules in WiSE. With m-TiO₂ anodes, we achieved 37.2% higher specific capacity at the fortieth cycle at the C/5 rate and 49.2% higher at the C/2 rate compared to the performance of bare TiO₂ anodes.