Symposium F.SM01—Lessons from Nature—From Biology to Bioinspired Materials

There is a growing need for rare earth metal ions such as lanthanides for use in electronics, fuel cells, and various other applications. These precious ions are currently derived by mining, causing major pollution and contamination in nearby water sources. As cellulose is the most abundant organic material, we derived carboxycellulose nanofibers from raw agave biomass using the simple nitro oxidation process for the removal of lanthanide ions. The nitro oxidation method converts untreated biomass to carboxycellulose nanofibers in a one step process using nitric acid and sodium nitrite. Zeta potential indicates that the fibers are highly electronegative (zeta potential -117.3 mV), and the conductometric titration method reveals that the fibers have a high carboxylate content (0.75 mmol/g). SEM measurements show that the fibers contain clearly visible fibrous structures. The TEM measurements of the fibers record fiber lengths of 55-690 nm and average fiber widths of 5-6 nm, and AFM data displayed an average thickness of 1.6 nm. The oxidation of the agave nanofibers was confirmed with ¹³C CPMAS NMR data. The lower crystallinity of the agave nitro oxidized carboxycellulose nanofibers compared to raw agave was determined by WAXD. The nitro oxidation approach also offers beneficial reductions in the consumption of water and electric energy as well as the need for multi-chemicals when compared with conventional multiple-step processes at bench scale (e.g. TEMPO oxidation). Remediation studies on lanthanide ions showed a floc formation between the ions and nanofibers. The Langmuir isotherm generated from ICP-MS studies indicated a 285.7 mg/g adsorption capacity and over a 90% adsorption efficiency for all lanthanide concentrations, which supersedes current water purification mechanisms such as iron oxide beads (123.6 mg/g adsorption capacity). These results suggest that the agave nitro oxidized carboxycellulose nanofibers are effective for the removal of lanthanide ions for drinking water purification and lanthanide ion industry.

Traditional lab-based synthesis of photocatalyst are ineligible for urgent demand of exceptional recyclability and stability in industrially large-scale application resulting from the inevitably undergo agglomeration of powder-form catalysts. Immobilizing catalyst is an appealing strategy to obtain enhanced performance for solid support provides chemical, thermal, and mechanical stabilization to the catalytic species besides facilitating catalyst recovery. Carbonaceous materials with unique microstructure obtained by pyrolyzing renewable and environment-friendly nature plants have promising applications in areas such as battery and catalyst support. However, unexpected cracks accompanied by low oxidation resistance retard further development. In this study, a thin SiC coating for strengthening purpose was in-situ deposited on biomorphic porous carbon materials fabricated by pyrolyzing wood while maintaining low density. Continuously ordered microchannel structures from carbonized nature wood with a diameter of ca. 20 μm was completely replicated after depositing SiC coating, resulting in the good anisotropy in mechanical and thermal properties. The thin SiC coating was found to greatly increase compressive strength from 26.4 to 47.4 MPa and thermal conductivity from 0.49 to 14.94 W/m K in the axial direction with improved oxidation resistance of weight loss from 78.5% to 1.51%. In the radial direction, however, the increase of the two properties was lower due to the longitudinal microchannel structure. Feasibility of the biomorphic carbon serving as catalyst support with highly developed continuous channels was evaluated by loading typical molybdenum disulfide (MoS₂). Result shows a significant improvement in both adsorption and photodegradation efficiency against the pure MoS₂, which is because of the enlarged specific surface area of the catalyst.

Abnormal protein behaviors, such as aggregation or mislabeling as antigens, are involved in a range of disorders including Alzheimer’s, Parkinson’s, and celiac disease. Water-soluble polymers with functional motifs mimicking those in naturally occurring polymers provide an avenue to interrogate binding and assembly processes and can be designed to modify protein behavior. RAFT polymerization was employed for the synthesis of two different families of polymers, designed for the study of two different protein systems, to produce polymers with desired structures, targeted molecular weight, and low dispersity. Aggregation processes were evaluated with dynamic light scattering, GPC-MALLS, and fluorescence assays. FTIR and NMR were employed to determine hydrogen bonding patterns of the systems. Gliadin, a component of gluten and a known epitope, is implicated in celiac disease (CeD) and results in an inflammatory response in CeD patients when consumed. Stimuli-responsive polyelectrolytes with varying charged groups were employed as models to determine the effect of molecular weight and pendent group on non-covalent interaction modes with gliadin in vitro. The polymers exhibited pH dependent binding and alteration of gliadin secondary structure, providing a platform for therapeutic design of specific structure/binding interactions with food proteins. Glycopolymers with stereospecific pendent groups designed to mimic saccharide clusters in the GM1 ganglioside were prepared to analyze interactions with the amyloid β peptide associated with Alzehiemer’s disease. The Aβ42 assembly process was directly impacted by the stereochemistry of the pendent saccharide. Glycopolymer-silicone hydrogels prepared with varying hydrophobic/hydrophilic content and copolymer composition showed structure dependence of diffusion, rheology, and nanomechanical properties. These findings demonstrate the potential for design of selective glycopolymers for targeted molecular interactions for biomedical and personal care applications.

Arsenic is a pervasive contaminant in drinking water, and it has ranked the first on the Substance Priority List of Agency for Toxic Substances and Disease Registry (ATSDR) for more than two decades. Exposure to low-level arsenic in early life impairs children’s cognitive development and buries the risk of developing a variety of cancers in young adulthood. To prevent the severe health effect of arsenic ingestion, materials with high arsenic removal capacity and fast treatment speed have been investigated. While these strategies are efficient for As(V), they are rendered ineffective when encountering the less abundant yet more toxic As(III), especially in the presence of competing ions. Solutions such as pretreatment or extensive removal of competing ions along with arsenic dramatically increase the operation cost and unnecessarily eliminate other benign species from water. Thus, there is a need for developing materials that can precisely capture arsenic from drinking water or even more complex beverage matrices and reduce the arsenic level below the EPA regulation (10 ppb) without altering the water chemistry.

In this work, we looked beyond the conventional physicochemical water treatment strategies and acquired insights from natural arsenic detoxification processes. The toxicity of As(III) originates from its high affinity to the cysteine residues in proteins. Natural organisms resolve this issue by expressing cysteine-rich peptides or proteins that can sequester As(III) in the cells. Inspired by this mechanism, we engineered a benign strain of E. coli to overexpress fusion proteins containing the binding pockets of two arsenic-binding proteins, ArsR and AfArsR, for improved arsenic scavenging competency. We also applied molecular biology tools to enhance the arsenic sorption capacity and accelerate the removal speed. One gram of these living sorbents can stoichiometrically immobilize milligrams of arsenic within a few hours. The high affinity of the proteins toward the substrate overcomes the selectivity barrier of inorganic sorbents like Bayoxide. For example, the living sorbents can bioaccumulate low levels of arsenic against common interfering species like phosphate, silicate, and natural organic matters, and the trapped As(III) does not leak to the water under these complicated conditions. In addition to remediating intractable matrices such as NSF challenge water, we found these living sorbents are adaptive to beverages including juice and wine, which were reported that are contaminated with arsenic but are not tightly regulated. Moreover, unlike the cumbersome inorganic material transportation, we propose that these living sorbents can be regenerated on-site after shipping the “seed material”. We explored freeze-drying the biosorbents for storage and demonstrated that the reconstituted sorbents maintained arsenic-binding ability. To prevent secondary contamination after remediation, we explored tagging the bacterial cells with magnetic nanoparticles and found that the bacteria can be removed with a handhold magnet within a few minutes. This work provides the potential of applying renewable living sorbents for selective drinking water contaminant removal, and it is beneficial for the rural households and small communities who do not have access to the expensive and energy-consuming arsenic treatment technologies.

Recent advances in synthetic membranes allow their use in fields as diverse as food and agriculture, industrial water treatment, potable water production, and bio-separation. Among the newly developed technologies, nanofiltration for liquids and more particularly for desalination of seawater or saline aquifers is the most recent one. However, limitations of current polymeric membranes call for the development of novel formulations that offer both high permeability (water flux) and ion differentiation (selectivity) usually considered antagonist features. We report the fabrication of membranes prepared from track-etched polymeric membranes as supports in which biological ion channels such as Gramicidin A, alpha-hemolysin are confined and ion-selective binding peptide motifs conjugated with graphene oxide as nanoporous hybrids. These bioinspired and biomimetic membranes are attracting widespread attention offering advantages including mechanical robustness, controlled pore dimension, and shape, modifiable surfaces for the desired efficiency. The permeability and selective ion transport are evaluated by ion diffusion kinetics, UV-Visible absorption spectroscopy, and nanofiltration while gaining insights into the role of key parameters including track-etch pore size, surface chemistry, and ion binding through solid-state nanopores or nanochannels. The proposed activity positively impacts the environment by integrating eco-friendly materials design, development, and deployment.

In human musculoskeletal system, skeletal muscles attached to spongy bones play an essential role in exerting quick and powerful movement. Herein, we present a musculoskeletal design capable of agile magnetomotility of ternary polymeric nanocomposites. Inspired by protein actin in skeletal muscle, iron particles are attached to surface of helical porous carbon nanotube yarn (CNTY) owing to polydimethylsiloxane (PDMS) elastomer providing a fascia-like connective function. Under rotating 2D quadruple electromagnetic field, soft robots achieved agile rectangular orbital magnetomotility reaching up to 162 body length per second. Upon varying the frequency of the rotating magnetic field, the individual rectangular orbit of multiple soft robots is reconfigured into magnetic-assembled circular orbits. We will discuss magnetic swimming of collectively assembled soft robots that can manipulate vortex chirality of sustaining fluid.

Under multi-component molecular conditions such as inside of living cells, fibrous proteins including actin filaments and microtubules are constructed based on orthogonal (self-sorted) self-assembling. Self-sorting enables plural supramolecular nanostructures to retain each property and function as well as their structures even under complex conditions. In artificial systems, construction of complex and discrete soft nanomaterials has received increasing attention in recent years, and only several self-sorting pairs of synthetic self-assembling (small) molecules and peptides have been reported. Meanwhile, the high-fidelity recognition based on Watson-Crick base paring and programmable sequences of DNAs allows a variety of DNA nanostructures with controlled sizes and shapes to be constructed, and hybrid nanomaterials composed of DNA nanostructures have been pursued for a wide range of applications (e.g., nanopores, scaffolds for catalytic reaction and protein assembly). However, much of these hybrid nanomaterials have been constructed based on co-assembly, and the orthogonal coexistence of DNA nanostructures with supramolecular nanostructures obtained by self-sorting with synthetic molecules has yet to be explored in detail.
To develop the hybrid nanomaterials composed of DNA nanostructures based on self-sorting phenomenon, we focused on nucleic acids and peptide derivatives as the component molecular pair. We recently constructed hybrid soft nanomaterials composed of DNA microspheres¹, which can be obtained from three short single-stranded DNAs, and three different supramolecular nanostructures of semi-artificial glycopeptides² (helical nanofibers, straight nanoribbons, and flowerlike microaggregates) in single medium by a simple thermal annealing process.³ Interestingly, both of supramolecular nanostructures exist orthogonally with only marginal impact on their morphology in single medium as a supramolecular hydrogel state. Noteworthily, to observe such self-sorted supramolecular nanostructures by fluorescence imaging, additional fluorochrome-labeled probes are required to synthesize. However, in this research, we have achieved the selective visualization of each supramolecular nanostructure by means of rational staining method focused on each selective molecular-recognition property of DNAs and glycopeptides (e.g., intercalating agent, lectins, and saccharide-binding DNA aptamer) without additional probe developments. Furthermore, we have demonstrated the sequence-controlled degradation of the individual supramolecular nanostructures in response to distinctive bio-stimuli (i.e., enzyme and ssDNA), rendering these soft nanomaterials active against such stimuli. In this presentation, I would like to discuss the detail of these newly developed hybrid soft nanomaterials and underlying mechanism to form such unique superstructures and functions.

1. K. Matsuura, T. Yamashita, Y. Igami and N. Kimizuka, Chem. Commun. 2003, 376–377.
2. T. Tsuzuki, M. Kabumoto, H. Arakawa and M. Ikeda, Org. Biomol. Chem., 2017, 15, 4595–4600.
3. S. L. Higashi, A. Shibata, Y. Kitamura, K. G. N. Suzuki, K. Matsuura and M. Ikeda, Chem. Eur. J., 2019, 25, 11955–11962.

With the help of computational design, a series of peptides with a length of 29 amino acids were designed to be self-assembled into stable, tetrahelical, anti-parallel coiled coil peptide bundles with net charges ranging from 0 to +32. In this research, +4 charged peptides (leading to +16 charged coiled coil bundles) are synthesized via solid phase peptide synthesis (SPPS) with the N-termini of single peptides modified with cysteine or a non-natural maleimide. These peptides are self-assembled into 4 x 2nm cylindrical peptide bundles by non-covalent interactions and subsequently conjugated via Thiol-Michael 'click' chemistry to form coiled coil peptide bundle chains with extreme rigidity. Transmission electron microscopy (TEM) and circular dichroism (CD) spectroscopy are applied to investigate the effect of temperature, pH and solvent composition on the structure of coiled coil bundle chains. Polarized optical microscopy (POM) is applied to study the liquid crystalline behavior of conjugated peptide bundle chains. Small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS) are utilized to characterize the size and structure of formed coiled coil peptide bundle chains. The effect of salt and pH on the solution behavior of the positively charged coiled coil chains will be also discussed. The self-assembled peptide bundles can be further used as building blocks to construct new 1-D and 2-D nanomaterials.

In this study, bamboo-achieved cellulose is functionalized and upcycled into efficient, low-cost and environmental-friendly bio-adsorbents for dye adsorption and separation. Dialdehyde cellulose (DAC) was prepared through the chemical oxidation on cellulose surface via sodium periodate oxidation. Then, cationic Girard’s reagent T (GT) was covalently crosslinked onto the backbone of cellulose molecules via the Schiff’s base reaction between the amino groups of GT and the aldehyde groups on the DAC to form the cationic aldehyde cellulose (cDAC). The chemical structure and morphology of two bio-adsorbents were characterized. The adsorption behaviors of the functionalized DAC and cDAC possessed different available active sites (including aldehyde groups and quaternary ammonium cations) towards various dyes in the aqueous solution were investigated systematically. The effects of dye concentration, contact time and pH environment in the adsorption of the anionic Congo red (CR) and cationic Bismarck brown Y (BBY) were studied. The results showed that DAC could adsorb BBY more effectively while cDAC has a much higher adsorption capacity towards CR, this is due to the adsorption was dominated by both the static electric force and the chemical reaction between dyes and adsorbents. The adsorption process was found to happen promptly (within the first 10 minutes) and follow the pseudo-second-order model. Both DAC and cDAC were proved to exhibit great adsorption behaviors under a wide pH range. Furthermore, the adsorption performance of six different dyes onto DAC and cDAC were studied, separately. Their adsorption capacities varied significantly on CR, BBY, Brilliant cresyl blue (BCB), Acid green 25 (AG25), Acid brown M (ABM) and Alizarin red S (ARS), indicating the DAC and cDAC could adsorb dyes from aqueous system selectively owing to the different reactiveness between dyes and the adsorbents’ active sites. Based on the selective adsorption behavior towards different dyes, DAC and cDAC were proved to possess strong abilities for separating dye mixtures, such as: BBY-ARS, AG25-CR and BCB-CR.

Over 2 billion people live in countries experiencing high water stress (UN, 2018) and water crisis has become one of the biggest challenges for the world. Current desalination techniques necessitate complex infrastructure and high operating pressures, making them impractical in poor and technologically underdeveloped regions. Membrane distillation (MD) is an emerging water purification technique capable of purifying highly saline or contaminated water, which can help to alleviate water stress especially for the off-grid community. It is a thermally driven separation process employing a porous hydrophobic membrane which allows the passage of vapor molecules only. Currently used polymeric membranes in water filtration techniques have a large carbon footprint which makes it imperative to find an environmental and sustainable solution without compromising performance. In this study, a composite porous nanostructured cellulose based membrane was fabricated using carboxymethylated fibers (obtained from wood and non-wood plants like jute). The top barrier layer in this composite membrane is hydrophobic (mimicking lotus leaf) which prevents liquid penetration followed by a hydrophilic layer. The carboxymethylated cellulose fibers were cross-linked with wet strength additives to improve wet-integrity and water retention properties. The hydrophobic layer was developed by introducing micro-scale roughness using minerals like precipitated calcium carbonate followed by sizing with dimer giving high contact angle exceeding 140° to prevent wetting of the membrane. The porosity of the entire membrane is in the range of 70-80%. Different characterization techniques like infra-red spectroscopy, solid state NMR, scanning electron microscopy, thermo-gravimetric analysis, and contact angle were used to study membrane properties. The performance of composite membrane was evaluated using a laboratory scale direct contact membrane distillation (DCMD) system. Water flux and salt rejection were tested under a set of feed water temperatures ranging between 40-60°C keeping the permeate water temperature same at 20°C. Moreover, the fabricated cellulosic membrane exhibited a comparable performance to that of commercial hydrophobic PTFE membranes.

De Novo design of peptides for assembly into targeted nanostructrue is being explored extensively in the self-assembly community with the help of computational methods. Various peptide structures and solution assembly behaviors have been achieved by computational design of the peptide molecule sequences. Previous work of our collaborative group has demonstrated that computationally designed anti-parallel, homotetrameric coiled-coil, or ‘bundlemers’, with N-terminal modifications can form nanomaterials ranging from 2-D materials with desired inter-bundle symmetry to polymer chain rigid rods via thiol-Michael reaction. In the case of concentrated rod solutions, birefringence was observed in concentrated rigid rod solutions which proved the presence of liquid crystal phases. In this current work, further study into controlling solution behavior of peptide rods was conducted with newly designed peptide sequences. Solution structure of highly net-charged bundlemers (-16 through -24 at pH 7) and bundlemers with parallel packing of constituent peptides were verified experimentally. Preliminary studies on liquid crystal behavior of rigid rods was investigated with these highly charged sequences due to their exterior charge repulsion, which can be controlled by ionic strength of solution and pH. Furthermore, semiflexible chains formed by conjugating coiled-coil and tetra-functional organic linkers as characterized via transmission electron microscopy and cryo-TEM. The semiflexible chains are expected to provide opportunities to achieve structures that resembles biological molecules.

Bundlemers are a series of computationally designed peptides that form monodisperse cylindrical particles through aqueous self-assembly into antiparallel homotetrameric coiled coils. Due to their robust coiled-coil-forming motif these peptidic colloids have extremely tunable surface chemistry mostly independent from their structure. Using this tunability, we have previously developed bundlemers that form predesigned 2D lattices, nanocages, and nanofibers through tailoring their surface chemistry and solution assembly conditions. Recently, we have used bundlemers as macromonomers to create stiff and extremely high aspect ratio supramolecular polymers through covalent chemistry between the neighboring bundlemer ends. As the library of bundlemers continues to grow, it is important to develop applications and processing methods to grow useful, disparate nanostructures out of these versatile building blocks. Drawing inspiration from carbon nanotubes, bundlemer brush nanoforests present an interesting potential nanostructure for the tuning of surface properties and the interaction of designed interfaces. By first templating a surface through the directed self-assembly of bundlemers onto a flat planar substrate, it should be possible to grow thin films of highly aligned supramolecular bundlemers brushes with tunable surface chemistry and packing structure. Ongoing work on the formation of the template layer has shown a dependence between deposition kinetics and electrostatic interactions between bundlemers. This presentation will overview the characterization of bundlemer monolayers on a flat planar gold substrate as well as the impact of pH, ionic strength, and bundlemer surface charge on deposition kinetics through the use of atomic force microscopy, infrared reflection adsorption spectroscopy (IRRAS) and quartz crystal microgravimetry with dissipation monitoring (QCM-D).

Electrospinning technique enables the transformation of polymers into functional fiber/mesh architectures, with the comparable length scales to the native extracellular matrix¹. Given the significant variation in local elastic properties of micro/nano fibers caused by the highly intersected and suspended architecture², here we elucidated the correlation of the local mechanical properties of a fiber meshwork to its microscale network architecture, and investigated the influence of fiber mesh elasticity on the behavior of human umbilical vein endothelial cells (HUVECs).
The multiblock copolymers polyesteretherurethane (PEEU), containing poly(ε-caprolactone) (PCL) and poly(p-dioxanone) (PPDO) segments with different ratios (40-70wt% PPDO) were used to prepare the fiber meshes via electrospinning technique. The fiber diameter was not remarkably influenced by the copolymer composition, with the diameter below 2 µm in all groups. The E-modulus of the fiber mesh at a dry state increased with the increase of PPDO percentage, according to the tensile tests. The three-point bending tests using an atomic force microscope (AFM) revealed a correlation between the local stiffness of a specific point on a single fiber and its position. HUVECs cultured on stiffer fiber meshes presented elongated F-actin filaments and spindle morphology, in comparison with their softer counterparts. The fiber mesh elasticity did not affect the initial HUVEC attachment, and a faster cell proliferation rate of HUVEC was shown on stiffer fibers. HUVEC pre-cultured on stiffer fiber meshes presented a faster migration velocity and an increased tube formation capacity than those from softer fibers, indicating a higher angiogenesis potential.
In summary, the functionality of HUVEC can be strongly regulated by the elasticity of fiber meshes. Mechanical characterization of the fibers at different scales, e.g. AFM for microscale in combination with tensile test for macroscale, could deepen our understanding on the cellular mechanosensing process and enable more meaningful substrate design towards favorable cell function.
Reference
1. Theocharis, A. D.; Skandalis, S. S.; Gialeli, C.; Karamanos, N. K., Extracellular matrix structure. Adv Drug Deliver Rev 2016, 97, 4-27.
2. Cronin-Golomb, M.; Sahin, O., High-resolution nanomechanical analysis of suspended electrospun silk fibers with the torsional harmonic atomic force microscope. Beilstein J Nanotech 2013, 4, 243-248.

Recently, superomniphobic (meaning highly water and oil-repellent) surfaces have been extensively studied both theoretically and experimentally in the materials community with several remarkable findings. Considering a notable process towards springtail-inspired omniphobic surfaces, however, a robust liquid repelling surface that is capable of inducing a selective liquid sliding property has been rarely reported, which would have many potential applications in microfluidics, mobile market, electronic devices and precision industry. Here, we present for the first time a selective liquid sliding surface using a springtail-inspired mushroom-like re-entrant structure with a novel geometry of concave tip. By implementing a simple yet sturdy silicon fabrication and lithography method, the fabricated micropillar arrays displayed high structural fidelity. We investigated a design rule for the cap of the proposed structures, which resulted in not only superomniphobicity but also a selective liquid sliding property with DI water and mineral oil. We believe that our study makes a significant contribution to the literature because it proposes a novel springtail-inspired mushroom-like re-entrant structure that can induce a selective liquid sliding property between water and oil, which has not been accomplished before.

Inverse opal photonic crystals are bioinspired structurally colored porous materials that have been utilized in many applications including sensing, catalysis, and microfluidics. By modifying the surface chemistry and geometry of inverse opal pores to improve control over surface-fluid interactions in these materials, we can achieve highly localized effects and dynamically alter the wetting point of inverse opal films. Several strategies were used to fine-tune the behavior of the inverse opal. The pore size and pore neck angle, which determine the threshold contact angle for fluid infiltration, were adjusted by atomic layer deposition. This technique provides sub-nanometer control of the pore radius and can be used in conjunction with surface chemical modification to change the wetting point of an inverse opal film. The surface chemistry of the pore, which controls the contact angle that a fluid forms with the surface, was patterned with multiple silanes. By taking advantage of the inherent disorder in self-assembled monolayers at features with a small radius of curvature, such as pore necks, controlled local patterns in surface chemistry were produced. For dynamic modulation of the contact angle, photoswitchable spiropyran and azobenzene molecules were attached to the pore surface. These molecules reversibly altered the hydrophobicity of the surface when their conformation was changed by exposure to ultraviolet or visible light. By understanding how pore geometry and surface chemistry contribute to the static and dynamic behavior of inverse opals and their interactions with fluids, we can more effectively utilize these structured materials.

It is well documented that twist axis of cellulosic fiber aligns parallel to applied magnetic field. In here, we showed change in orientation of bio-derived cholesteric phase confined to microgel using low magnetic fields (0.5 – 1.2 T). As equilibrated on commercial magnet, droplets of chitin nanocrystal and superparamagnetic nanoparticles mixture possessed homeotropic anchoring and light induced polymerization of the monomer in droplets captured the phase into microgels. The helix orientation directly affected the texture of microgels under polarized optical microscopy. The exhibited structures of microgel were nested cup configuration of lamellar planes or bipolar structure even in the high chirality regime. Moreover, the microgels are responsive to temperature, as we used N-isopropyl acrylamide as a monomer. With temperature change we could observe swelling and de-swelling of nested cup structure which allowed us to understand the structure with more information. These findings give fundamental understanding bio-derived cholesteric materials and their self-assembly under confinement. Methodology for embedding twisted structure in polymer with bottom-up fabrication will give guideline for designing and controlling multifunctional nature-inspired programmable devices or materials with sustainable use of our resources.

Moth-eye inspired structure (MIS) has been regarded as important technology to enhance efficiency of optical device in biomimetic field. Since the nanostructures of the moth-eye surface gradually changed the refractive index from the air to devices, the MIS improved the optical properties of transmittance and reflectance. Despite these developments, film-based structures were difficult to apply and surface coating might damage to the surface of optical device during additional processes. Therefore, we fabricated three different sizes of MIS, 300 nm, 500 nm and 1000 nm, followed by optimizing materials and nanostructure size supported through two theoretical phenomena which are diffraction grating equation and double-slit effect. Then, optical devices were packaged by attaching polymer-based MIS without any treating and processing. As a result, the freestanding MIS composed of PDMS were identified to enhanced optical properties with over 94% transmittance and below 3.5% reflectance, compared to the MIS composed of PUA with substrate of PET film. In addition, PDMS-MIS attached to cell phone and ITO glass, which was used as substrate of optical devices, was proved that optical devices facilitated packaging as well as enhanced optical properties.

Butterflies present a variety of brilliant colors on their wings based on pointillism. Pointillism is well-known drawing technique, however, to express colors, butterflies use very unique and diverse nanostructures such as tree-like multilayered ridges, chitin-air multilayers, photonic crystals, etc. Through investigating these photonic structures, we are able to come up with effective engineering strategies to produce vivid, durable, and eco-friendly colors. Papilio maackii, the alpine black swallowtail, is a butterfly that uses air-chitin partitioned multilayers to exhibit a blueish-green like color on its wing. Since it has scales that show various colors between blue to green, it has the advantage of studying how to control structural colors using multilayered structures.
In this work, we investigate the structural coloration of the wing scale of Papilio maackii according to its nanoscale multilayered. The color of the wing scales changes from blue to green, depending on the thickness of the chitin and air layer. We demonstrate by using finite difference time domain (FDTD) simulations that the chitin partitions in air-chitin mixed layers regulate the effective refractive index to improve the color contrast with low background intensities. Cross-sectional TEM investigations show that the thickness of the air-chitin mixed layers varies gradually, and when this gradual change is reflected in the simulation, it shows a more similar reflectance spectrum with that of the experimentally measured. We identify the presence of melanin on the colored scales, which is a light-absorbing pigment, by measuring Raman spectroscopy. FDTD simulations show that melanin can contribute to the intensity of the reflectance spectrum in the region of long wavelength. In order to realize the structural colors based on the partitioned multilayers, we use a method to coat polymeric nanoparticles and sol-gel glass thin films repeatedly. By using this method, the effects of inhomogeneity and volume fraction of air voids in the multilayered structure are experimentally examined.
This research was supported by National Research Foundation (NRF) grant funded by the Ministry of Education, under “Basic Science Research Program” (NRF-2017R1D1A1B04033182) and also supported by Research Program through the National Institute of Ecology (NIE-Basic Research-2020-18).

Freshwater invasive mussel species Dreissena polymorpha (zebra mussels) adhere themselves in underwater environments with a collection of protein-based fibers known as a byssus. The byssus of the zebra mussel is stronger, stiffer and faster to recover after deformation than those of the well-characterized marine mussels, but very little is known of its structure or composition. Here, we used a combination of Raman, FTIR and wide angle x-ray diffraction to elucidate the secondary structure of fresh and induced byssal fibres. Out data indicates that the secreted fibers are comprised of a mixture of parallel β-crystallites, similar to spider silk. Furthermore, investigation of the byssus biofabrication process indicates that the precursor proteins are stored in an α-helical structure and transition from an α-helix to β-sheet secondary structure during the formation process, similar to other structural proteins like intermediate filaments and keratin. This stress-induced transformation in secondary structure is being attributed to a coiled-coil protein predicted in the mussel transcriptome, and current efforts are aimed at extracting this protein to further understand its shear-induced phase transformation.

Bone is both a tissue, comprising cells, vasculature and extracellular matrix, and a material comprising mainly mineral, collagen and water. It is thus a challenge to characterize bone’s 3D structural organization in order to gain insights into how bone forms and functions. Focused ion beam-scanning electron microscopy (FIB SEM) can provide information at nanometer resolution to enable, for instance the identification of the collagen D-banding. At this resolution the spatial arrangement of fibrils can be assessed in volumes of thousands of microns cubed which can include tissue components. For example, examination of mineralized osteonal pig bone shows unidirectional collagen arrays oriented alternatively in different directions or changing direction progressively. These unidirectional arrays are separated by layers of collagen organized in a bidirectional patchwork motif. Earlier studies of demineralized lamellar bone showed that the layers with the patchwork motif stain heavily with osmium and Alcian Blue and have a disordered appearance.
Another example is the cryo- FIB SEM examination after cryo-fixation and under cryo-conditions, of the mineralized murine growth plate. It reveals the presence of a complex zone that includes blood vessels with mineral containing vesicles, blood vessel extremities surrounded by bone mineralizing matrix, and cartilage hypertrophic cells surrounded by ordered and disordered cartilage mineralizing matrix.
By exploiting the options for examining mineralized bone, demineralized bone matrix and the soft tissue components as well as the bone, FIB SEM can provide invaluable insights into bone organization. By combining FIB SEM in a correlative manner with 3D confocal light microscopy and microCT, it will be possible to address many fundamental questions in bone biology and mechanics.
Reznikov, N., Shahar, R. and Weiner, S. 2014. Bone hierarchical structure in three dimensions. Acta Biomaterialia 10, 3815-3826.
Haimov, H., Shimoni, E., Brumfeld, V., Shemesh, M., Varsano, N., Addadi, L. and Weiner, S. 2020. Mineralization pathways in the active murine epiphyseal growth plate. Bone 130, https://doi.org/10.1016/j.bone.2019.115086.
Raguin, E., Rechav, K., Brumfeld, V., Shahar, R. and Weiner, S. 2020. Unique three-dimensional structure of a fish mandible bone subjected to unusually high mechanical loads. J. Structural Biol. (in press).

In this presentation two case of studies involving the use of the protein wrapped β-chitin matrix from the squid pen Loligo vulgaris are presented.
In the first one we addressed how the mechanical properties of the squid pen are related to intra- and inter- interactions among chitin and proteins. Chemical treatments were applied to modify the interactions involving proteins, through unfolding and/or degradation processes. The data analysis showed that chemical treatments did not modify the multi-scale hierarchical structure of the β-chitin matrix. This allowed to derive from the mechanical test analysis the following conclusions: (i) the maximum stress (σ_max) relies on the presence of the disulfide bonds; (ii) the Young's modulus (E) relies on the overall correct folding of the proteins; (iii) the whole removal of proteins induces a decrease of E (> 90%) and σ_max (> 80%), and an increase in the maximum elongation. These observations indicate that in the chitin matrix the proteins act as a strengthener, which efficacy is controlled by the presence of disulfide bridges. This reinforcement links the chitin fibrils avoiding them to slide one on the other and maximizing their resistance and stiffness.¹
In the second case of study the multi-scale hierarchical structure of the β-chitin matrix used as substrate to prepare new materials bio-inspired. Finding inspiration from the byssus, and with the aim to mimic its peculiar mechanical properties, we chemically functionalize the chitin matrix with catechols, the main functional group of the byssus. The obtained functionalized matrix preserves its multi-scale structural organization and is able to chelate reversibly Fe(III). Thus, it behaves as the byssus, acting as a metal cross-linkable matrix that upon metalation increases the Young‘s modulus, E (> 10 times). This new material can be further cross-linked by oxidation of the catechols. This process generates an increase of the E (> 10 times) and first failure stress (> 5 times). The combination of oxidation and metalation of the functionalized matrix only slightly increases the mechanical properties. The produced stimulus responsive materials show that levels of complexity can be added to a multi-scale organized natural hierarchical matrix providing new properties.²
In conclusion we showed that the mechanical properties of the squid pen are controlled by the di-sulfide bonds and that its multi-scale organized β-chitin matrix can be chemically functionalized providing additional properties.

1. D. Montroni, F. Sparla, S. Fermani, G. Falini. (2020) Acta Biomaterialia, https://doi.org/10.1016/j.actbio.2020.04.039
2. D. Montroni, M. Palanca, K. Morellato, S. Fermani, L. Cristofolini, G. Falini. (2020) Carbohydrate Polymers, submitted

Biological extracellular tissues are based on proteins, polysaccharides and, in certain cases, minerals. Their complex multiscale structure confers them a wide range of properties in accordance with the tissues’ functions. While active functionality are usually attributed to cells, there are also examples of materials synthesized by living organisms, such as plant seeds, which fulfil an active function without living cells and work as mechanosensors and actuators. Water is an important component of all such extracellular tissues. While it is well known that the level of hydration determines the mechanical properties of many biological materials, it is less appreciated that water also plays an active role in generating forces within the materials. In particular water absorption and desorption provides actuation in a variety of plant seeds, including wild wheat, stone plant and banksia seed capsules. The shape change upon water uptake that provides the actuation is controlled by specific cellulose fibre architectures. In this way, well-controlled movements, such as bending, twisting or curling are programmed in these materials by structure of the underlying cellulose microarchitecture. The required deformation energy is provided by the absorption of water from the environment. Finally, the absorption of water to specific molecules and the resulting osmotic pressure is also providing internal stresses which control, for example, the mechanical behaviour of collagen in tendon, bone and dentin. The lecture will review general concepts for the roles of water in biological materials, both in the context of biology and of bioinspired engineering.

The encapsulation of biomacromolecules is an important area of research, particularly in the context of medicine where increasing numbers of therapeutics are protein based. One particular encapsulation strategy takes advantage of the associative liquid-liquid phase separation phenomena known as complex coacervation. The self-assembly of complex coacervates is spontaneous, driven by electrostatic attractions and the entropic gains associated with the release of small ions upon complexation. Furthermore, coacervation enables the sequestration of therapeutic proteins and other cargo at high concentrations, and without the need for organic solvents.

A number of recent studies have highlighted strong parallels between the dense, polymer-rich droplets resulting from coacervation and membraneless organelles that have been observed in cells. Of particular interest is the ability of these liquid-liquid phase separated granules to recruit specific proteins, RNAs, and other biomolecules, either for storage in times of stress, or as a hub of catalytic activity. Inspired by these biological structures, we look to understand the design rules whereby complex coacervation can be used to encapsulate and potentially stabilize cargo proteins. Our work focuses on complex coacervation involving two oppositely-charged polypeptides and a cargo protein. The use of two-polymer coacervates allows for the encapsulation of even weakly charged proteins at a variety of different conditions, even near their isoelectric point. We look to map out range of conditions where both phase separation is observed, and the degree to which proteins are incorporated into the coacervate phase as a function of the composition of the two polymers and the encapsulated protein. Preliminary results suggest the potential for using the protein itself as a majority component of the coacervate to achieve incorporation at levels that could be used for therapeutic injection. We intend to use proof-of-concept studies with model proteins as a foundation upon which further research into therapeutic proteins can be built.

Inspiration from ancient plant species that abound wherever the ground is disrupted and can grow through concrete and bitumen. What can we learn in terms of mineral usage and reproduction?
Equisetum species are primitive vascular plants that benefit from the biogenesis of silica bio-organic inclusions in their tissues and participate in the annual biosilica turnover in local eco-systems. As means of Equisetum reproduction and propagation, spores are expected to reflect the evolutionary adaptation of the plants to the climatic conditions at different times of the year. Combining methods of Raman and scanning electron microscopy and assisted with density functional theory, we conducted material spatial-spectral correlations to characterize the distribution of biopolymers and silica based structural elements that contribute to the bio-mineral content of the elater. We propose the expansion of elater tips upon germination and the form of silica including encapsulated biopolymers are designed for ready dispersion, release of the polysaccharide-arginine rich content and to facilitate silica uptake to the developing plant. This behavior would help to condition local soil chemistry to facilitate competitive rooting potential and stem propagation. Further, X-ray and analytical electron microscopy studies of plant materials show an amazing array of minerals that can be isolated for use in applications as diverse as sensing, optics and catalysis.

The black drum fish (Pogonias Cromis), being the largest durophagous sciaenid, has stiff, hard, and wear-resistant teeth on the powerful pharyngeal jaws to adapt to its almost exclusive diet on hard-shelled mollusks. With estimated biting force reaching 11,000 N at the largest body size (60 kg), the black drum fish’s teeth have one of the highest bite force quotient (BFQ) among all living species. In this work, we aim to uncover the structural origins of such remarkable performance of these teeth via systematic structural, chemical and mechanical analysis across multiple length scales. The black drum fish’s teeth consist of a stiff enameloid layer (90-110 GPa in reduced modulus E_r, and 3~7 GPa in hardness H) and a softer inner dentin layer (20-50 GPa in E_r, and ~1 GPa in H) separated by the dentin-enameloid-junction (DEJ). The gradient in microstructures from the enameloid (rods with increasing diameters and gradually twisted orientations) to the DEJ then to the dentin (parallel tubules with increasing curvy oscillation towards the interior), and the compositional gradient, i.e., doping of Zn and F in the hydroxyapatite (HA) crystals in the enameloid layer vs. the Mg substitution in HA crystals in the dentin, contribute to the intricate gradient design of the teeth. The outer enameloid resists strong loadings; the DEJ deflects cracks to avoid catastrophic failure; and the inner dentin provides enhanced toughness. At the macroscale, the 90°-locking between the inner dentin and the bony plates provides additional bonding between the individual tooth and the pharyngeal jaw. Beyond critical loading, the tooth units first detach from the bony plates, which facilitates the erupting process of the new teeth from underneath.

Actuators, also known as artificial muscles, are an integral part of daily life. From transportation means to biomedical devices, they all utilize actuators for one or more vital tasks. Cycle life, cost, output force, strain, energy density, power density, and efficiency are the key performance metrics that are used to evaluate the suitability of actuators for a specific application. The emerging field of soft actuators has been introducing new classes of stimuli-responsive materials that can mimic muscle’s properties (i.e., generating strain, changing stiffness). While these materials outperform the performance of the human muscle in one or more of the mentioned attributes, there is still no stimuli-responsive material that can beat the human muscle in all of them. In this talk, an overview of the field will be given and the current challenges and possible directions will be discussed.

Biomimetic assemblies using synthetic peptides facilitate a fabrication of nanoscale materials with desired structures, exhibiting several attractive features for biotechnological applications due to an ability to mimic structures and properties of nature. Sequence specificity in peptide building blocks allows designed nanostructures to have almost atomistic precision as in biological systems. Furthermore, higher-ordered materials with well-defined structures can be also produced through several processing methods such as sequential, hierarchical assembly or fiber spinning. The ability to precisely design and control the structure at the molecular level is crucial to construct new materials with well-designed structures at multiple length scales. This ability allows one to target desired properties such as the mechanical properties of the materials. Herein, peptide building blocks are employed to construct a hierarchically organized fiber material at macroscopic scale. The basic peptide building blocks are computationally designed to assemble into a cylindrical shape comprised of homotetrameric coiled coil bundles with an anti-parallel arrangement giving rise to a pair of reactive sites at each end of the bundles for further chemical reactivity. The bundles with complementary chemical functionality serve as supermonomer units and are directly connected to each other, resulting in hybrid physical/chemical peptide-based polymers. The polymeric chains exhibit highly rigid rod structure owing to a rigidity of constituent bundles and direct linkages between them through covalent interactions. Moreover, due to the unique physical characteristics, the rod chains in concentration solution exhibit liquid crystalline behavior. The resultant rigid rod-like polymers can further be assembled into a hierarchical organization on macroscopic scales via electrospinning processing, while preserving their unique rod-like structural characteristics. The organization of rods in concentrated liquid crystal solutions was characterized via polarized optical microscopy, x-ray and neutron scattering, and rheology in order to understand the control of liquid crystal behavior for the processing of concentrated solutions into fiber materials.

The inherent tradeoff between strength and toughness inspires new design approaches to structural materials with high damage tolerance. Optimizing mechanical properties for predictable and non-catastrophic failure motivates novel design of modern high-performance structural materials. Among the diverse set of structural biominerals that straddle the gap between strength and toughness, nacre is the prototypical supermaterial. Nacre forms in many mollusk shells and is the primary structure of lustrous pearls. In nacre of both pearls and shells, we show a nanostructure that optimizes structural resilience. The biomineralization precisely controls secretion of organic and inorganic ingredients and hierarchically designs the combination of soft nanoscale organic components with inorganic nanograins that govern the formation of pearls and shells. After crack initiation, bulk nacre shows a 40-fold higher fracture toughness than the monolithic/single crystal calcium carbonate from which it is constructed. Thus, a central focus has been placed on understanding the principle mechanisms of nacre’s excellent mechanical properties to inspire new designs of next-generation high-performance structural materials. However, nacre’s ability to undergo limited deformation and dissipate critical stresses before fracture has not yet been quantified nor correlated with nanomechanical processes. Understanding nanomechanical responses across the 3D hierarchical architectures is critical to understanding how the individual nacre components work together to create properties greater than the sum of their parts (i.e. far exceeding the rule of mixtures).
Our investigation of toughening strategies in nacre reveals nanomechanical deformation of organic interfaces, nanocrystallites, and organic inclusions as key to the increased damage-tolerance of nacre. High-resolution scanning / transmission electron microscopy (S/TEM) combined with in-situ nano-indentation has been adapted to biomineral systems to allow sub-nanometer resolution imaging of the nanomechanical deformation processes and provide precise assessment of when and where fracture occurs. We show that during compressive indentation nacre undergoes non-destructive locking where inorganic tablets come into contact across organic interfaces. Remarkably, the completely locked interface recovers its original morphology without any deformation after releasing compression and retains its full mechanical strength. During compression, the aragonite grains and organic inclusions reversibly rotate and deform indicating nanoscale resilience of the nacre tablets. Prior to tablet locking, strain attenuates up to 80% between the decoupled tablets. However, by 3% engineering strain of the first tablet, the tablets have locked to redistribute stress continuously across the organic interface and the strain attenuation decreases. When fracture occurs, we show the organic components restrict crack propagation both within and between tablets, sustaining the overall macroscale architecture through multiple fractures to allow further structural loading. This allows nacre to absorb significantly greater mechanical energy than monolithic aragonite. This extends the damage tolerance of the superstructure beyond a single fracture. The present in situ S/TEM nanoindentation study illuminates nacre’s distinct non-linear elastic deformation processes that provide high resilience.

Biological cellular materials, such as trabecular bone, sponge, and wood, typically exhibit disordered arrangements of pores that are neither fully random, nor perfectly ordered (hexagonal honeycomb). In fact, this degree of order/disorder has not been systematically quantified before. We have used equivalent Voronoi patterning to quantify the disorder (variation in cell size) for a wide range of biological and engineered cellular materials, through thresholds in cell nuclei spacing. We have identified a common range of disorder (pseudo-hexagonal in 2D) for biological materials (δ of 0.5 to 0.8). Using 3D printed honeycomb models with systematically increasing disorder, we demonstrate that this range of ‘pseudo-order’ in 2D stochastic cellular solids exhibits a >30% increase in fracture toughness and equivalent strength compared to ordered (hexagonal) solids of the same density. This work demonstrates that there are significant improvements in defect tolerance for architected cellular solids having a certain degree of disorder. Highly ordered (hexaongal) arrays result in straight, catastrophic crack propagation, while too much disorder has highly branched cracks, but low strength. FEA models confirm a delocalization of damage during fracture. We suggest that the disorder in these biological materials may be optimal for the ‘survivability’ of fracture. We hypothesize that the delocalization of damage (cracks) limits their absolute size to that which is repairable through primary repair mechanisms, and provides an advantage for natural selection. We suggest that 'tailored disorder' in cellular solids represents a new design principle for the digital design of architected materials in general, to improve damage tolerance.

Bulk materials with remarkable mechanical properties have been developed by incorporating design principles of biological nacre into synthetic composites. However, this potential has not yet been fully leveraged for the fabrication of tough and strong materials that are also optically transparent. ^[1] In this work, a manufacturing route that enables the formation of nacre-like mineral bridges in a bioinspired composite consisting of glass platelets infiltrated with an index-matching polymer matrix is developed. By varying the pressure applied during compaction of the glass platelets, composites with tunable levels of mineral bridges and platelet interconnectivity can be easily fabricated. ^[2] The effect of platelet interconnectivity on the mechanical strength and fracture behavior of the bioinspired composites is investigated by performing state-of-the-art fracture experiments combined with in situ electron microscopy. The results show that the formation of interconnections between platelets leads to bulk transparent materials with an unprecedented combination of strength and fracture toughness. This unusual set of properties can potentially fulfil currently unmet demands in electronic displays and related technologies.

^[1] T. Magrini et al., Nature Communications 2019, 10, 2794
^[2] T. Magrini et al., Advanced Functional Materials 2020, 2002149

Composite materials offer a unique opportunity to achieve novel (improved) material properties without the need for the development of new components. Sometimes, synergistic mechanics can be achieved, i.e. the mechanical properties of the composite are even better than the sum of the individual components. This synergy has been demonstrated within many material classes and on many length scales, from reinforced concrete to molecular polymeric composites [1,2,3] to the extracellular matrix supporting our tissues [4]. Here I will present our effort to rationalize the synergy observed in the non-linear mechanics of biopolymer composites [4] and in the fracture behaviour of generic elastic double networks [1], both containing a stiff polymer network embedded in a soft polymer matrix. We will show that the entanglement of these networks at the microscopic level is the key to the synergistic mechanics.

We look for mechanical synergy in composite biopolymer networks, inspired by the tuneable nonlinear mechanics of the extracellular matrix (ECM). In the ECM collagen is the main-component responsible for the nonlinear strain-stiffening response [5,6]. However, we show that hyaluronic acid (HA), the second most abundant biopolymer in the extracellular matrix, can significantly delay the strain-stiffening if the stiff collagen network is embedded in a much softer HA matrix [4]. Similarly, we show that the HA network enhances the linear elastic response of the collagen-HA composite. In both regimes the synergistic response is governed by mechanisms occurring at the microscopic level, but have a drastic effect on the macroscopic stress-strain response.

Experiments on synthetic double networks [2,3] show that a soft elastic matrix can not only have a significant effect on the elastic response of a stiff network, but also on the failure behaviour, shifting the failure response from brittle to ductile. By implementing bond breaking in a coarse-grained network simulation [1] we can demonstrate that the brittle-to-ductile transition can be captured by a simple force-balance between the two networks. Furthermore, our model predicts four mechanical regimes that are also observed in experiment. In particular, the simulations reveal that the four regimes are associated to differences in the microscopic failure response as well. Understanding these phenomena allows a better control over the synergistic failure response of double network materials.

Our findings not only elucidate how biology combines polymers with complementary properties to finely-tune the mechanics of living tissues, but also provide a new avenue for the design of synthetic elastic materials tuning their stress-strain response from the linear-regime until global failure.

References
[1] J. Tauber, S. Dussi, J. van der Gucht, Microscopic insights into the failure of elastic double networks, Phys. Rev. Materials, 4, 063603 (2020).
[2] P. Millereau et al., Mechanics of elastomeric molecular composites, PNAS, 115, 9110-9115 (2018).
[3] S. Ahmed et al., Brittle-ductile transition of double network hydrogels: Mechanical balance of two networks as the key factor, Polymer, 55, 914-923 (2014).
[4] F. Burla/J. Tauber, S. Dussi, J. van der Gucht, G. H. Koenderink, Stress management in composite biopolymer networks, Nat. Phys., 15, 549-553 (2019).
[5] A. J. Licup et al., Stress controls the mechanics of collagen networks, PNAS, 112, 9573-9578 (2015).
[6] A. Sharma et al., Strain-controlled criticality governs the nonlinear mechanics of fibre networks., Nat. Phys., 12, 584–587 (2016).

The air-water interface is expected to play an important role in establishing a universal model of dissipative structures in nature. Viscous fingering, as an example of fluidic flow, is an unstable situation that is widely known as tears of wine. This has been explained through the Marangoni effect, coffee ring effect, Saffman-Taylor instability, etc. However, due to the transitional nature of these phenomena, there are few strategies for immobilizing such fluidically regulated interfaces. Recently, such phenomena have been applied successfully to an immobilized structure by controlling the evaporation of a mixture of polymer and water.¹
In this study, we present a brief discussion of “meniscus splitting phenomenon”. More precisely, an air-liquid interface is divided into multiple interfaces to partition a space. In particular, by using a mixture of polysaccharides and water, a macroscopic pattern following a specific rule could be confirmed. When the mixture is dried from a top open cell, the polymer forms deposits at specific positions to split the meniscus by bridging a millimeter-scale gap. Because water irreversibly evaporates from the liquid phase to the air phase through a gap, the air-liquid interface is in a nonequilibrium state between polymer deposition and water evaporation. The interfacial instability is comparable to the mechanical instability of gels at the phase transition or to the skin layer of gel surfaces during shrinking. Furthermore, the deposited polymer film acts as vapor-sensitive materials. Here, the phenomenon and the material’s behavior would be discussed from physicochemical viewpoints: polymer science, interface science, and colloidal science.
1. Sci. Rep. 2017, 7, 5615; J. Colloid Interface Sci. 2019, 546, 184; Small, in press; Polymer J, in press.

Acantharia (Acantharea) are wide-spread marine protozoa, presenting one of the rare examples of strontium sulfate (SrSO₄, celestite) mineralization in the biosphere. The unicellular organisms produce complex star-shaped skeletons with 20 spicules that radiate from the center according to a unique geometric pattern. Specifically, two quartets of polar spicules alternate with two quartets of tropical spicules and one quartet of equatorial spicules. It has been speculated that the crystallographic arrangement of the spicules stems from an interplay between crystallochemical and biological control, reconciling an optimum use of space at the spicular joint with the crystallographic requirements of an orthorhombic crystal lattice. The Acantharia class encompasses approximately 150 species with highly diverse, taxon-specific skeletal morphology, suggesting exquisite genetic regulation of the mineral deposition. Their sizes range from roughly 50μm to 1mm, depending on their developmental stage and origin. Exploring the three-dimensional skeletal architecture of the Acantharia is essential for understanding the underlying principles of biomineralization.
Synchrotron-based X-ray micro-computed tomography is a powerful method for visualizing nano-scale features without major sample preparation artefacts. Here, we used synchrotron-based nanotomography at the P05 imaging beamline (PETRA III, DESY, Hamburg, Germany) to resolve the complex internal morphology of Acantharian endoskeletons. Our analysis revealed pronounced morphological differences between taxa, suggesting species-specific crystal growth mechanisms. The study focused on how the spicules emanate from the central junction, as it might be the key to understanding inorganic morphogenesis. We used a correlative imaging approach, combining nanotomography with electron-optical investigations and Atomic Force Microscopy. Based on the experimental results, we hope to gain a deeper understanding of the skeletal development from rod-shaped, diametral crystals in juvenile Acantharia to well-developed skeletons in the adult organism. Interesting parallels might be drawn to smoothly curved, fenestrated spicules in subtropical sea urchins and marine sponges, whose skeletons are based on far more common biomineral systems. We will further discuss how bio-inspired model systems mimic the SrSO₄ crystallization in uncultured protists.

Natural materials such as mussel byssal threads serve as inspiration for the design of new sustainable polymers. Byssal threads consist of proteins forming a complex hierarchical structure closely linked to the impressive mechanical properties including underwater adhesion, high toughness and self-healing. Each fiber forms within 5 min as a secretion of several proteins which self-assemble and crosslink into a rigid, yet extensible fiber. Interestingly, all proteins contain between 1 and 30 mol% of the post-translationally modified amino acid 3,4-dihydroxylphenylalanine (DOPA). The complex chemistry of DOPA enables a range of different interactions including metal coordination, oxidative crosslinking and hydrogen bonding. Evidence indicates that DOPA plays a key role in the post-secretion curing of the fibers though the details are still unclear.
Here, we investigated the spatiotemporal regulation of DOPA cross-linking during thread assembly, using histological staining in combination with confocal Raman microspectroscopy. These methods were combined with induced thread formation to follow cross-linking at different stages of the formation process and in different parts of the thread. Results show that different parts of the thread utilize different DOPA interactions for crosslinking. Furthermore, these DOPA interactions are likely regulated by controlling their redox environment facilitating covalent crosslinking over DOPA-metal coordination or vice versa. These insights provide relevant physicochemical pathways for the design of mussel-inspired catechol-based polymers and could lead to the development of new sustainable materials with industrial and biomedical applications.

Bio-enabled nanocomposites represent a novel class of functional bioderived materials, which uses principles of bioinspiration and biomimetic to design hierarchically organized hybrid materials with co-assembled biological and synthetic components to bring best of synthetic and biological worlds: versatile functions with responses to mechanical, optical, chemical, and light stimuli and mechanical strength, flexibility, biocompatibility, and environmental robustness [1, 2]. In first set of examples, we discuss uniformly aligned chiral bio-photonic films from a liquid crystal phase formed by a cellulose nanocrystal solution placed in a thin capillary [3]. This spatial and fluidic flow confinement facilitates homogeneous growth of chiral pseudo-layers parallel to the interface in contrast to the highly heterogeneous assembly of random tactoids. The resulting iridescence films show a narrower optical reflectance band and uniform birefringence over larger macroscopic regions than heterogeneous conventional drop-cast films. In another example, enhanced chiral properties of organized helical patterned films with high asymmetry of circular polarization have been template-assembled via preferential orientation of high-aspect cellulose nanocrystals onto optical microgrids [4]. Bright chiral emission has been co-assembled in organized biopolymer photonic films from core-shell nanorods of cellulose nanocrystals and co-assembled carbon quantum dots mediated by polymer linkers [5]. Finally, co-assembly of cellulose nanocrystals with amorphous polysaccharides resulted in the formation of robust and flexible films with the preservation of the original structural photonic and fine control of the pitch length due to intimate intercalation of macromolecular backbones into the interstitial nanoscale pores of neighboring nematic monolayers [6].

[1] R. Xiong, J. Luan, S. Kang, S. Singamaneni, V. V. Tsukruk, Natural Biopolymers for Organized Photonic Structures, Chem. Soc. Review, 2020, 49, 983.
[2] R. Xiong, A. M. Grant, R. Ma, S. Zhang, V. V. Tsukruk, Naturally-derived biopolymer nanocomposite: interfacial design, properties and emerging applications, Mat. Sci. & Eng. Reports, 2018, 125, 1.
[3] V. Cherpak, V.F. Korolovych, T. Turiv, D. Nepal, J. Kelly, T.J. Bunning, O.D. Lavrentovich, V.V. Tsukruk, Robust Chiral Organization of Cellulose Nanocrystals in Capillary Confinement, Nano Lett., 2018, 118, 6770.
[4] R. Xiong, S. Yu, S. Kang, K. M. Adstedt, D. Nepal, T. J. Bunning, V. V. Tsukruk, Integration of Optical Surface Structures with Chiral Nanocelluloses for Enhanced Chiroptical Properties, Adv. Mater., 2019, 1905600.
[5] R. Xiong, S. Yu, M. J. Smith, J. Zhou, M. Krecker, L. Zhang, D. Nepal, T. J. Bunning, V. V. Tsukruk, Assembling Carbon Quantum Dots on Cellulose Nanocrystals for Chiral Luminescent Biophotonic Materials, ACS Nano, 2019,13, 9074.
[6] K. Adstedt, E. A. Popenov, K. J. Pierce, R. Xiong, R. Geryak, V. Cherpak, D. Nepal, T. J. Bunning, V. V. Tsukruk, Broad iridescence of natural polymer nanocomposites: chiral nanocrystals intercalated with amorphous polysaccharides, 2020, in press.

Hierarchical porous materials are attractive structures for a variety of applications due to their enhanced mechanical efficiency and their high surface area with minimum permeability loss. Nature showcases remarkable examples of hierarchical porous materials that benefit from such unusual set of properties, including bamboo, bone, marine sponges and wood. However, synthetic porous materials have yet to reach the elaborate architectural design found in their biological counterparts. To fill this gap, processing routes that enable deliberate control over the material’s porous structure at multiple length scales are highly demanded. In this talk, I will show how 3D printing technologies can be exploited to fabricate hierarchical porous materials with unprecedented mechanical efficiency and architectural control. The key feature of our approach is to design inks with an internal structure that serves as a template for the formation of tailored pores within the printed object. Using oil droplets, air bubbles or phase-separating mixtures as templating structures, this methodology enables independent tuning of porosity and pore sizes at multiple length scales. To demonstrate the potential of the process, we 3D printed complex-shaped parts with bioinspired multiscale porosity and enhanced mechanical efficiency that cannot be achieved through conventional fabrication technologies.

Supramolecular interactions may hold the key to the development of network systems with tunable mechanics and modulated architecture, such as observed in the muscle protein titin. It is the dynamic nature of these physical associations that we have exploited in the design of tough supramolecular materials that super-impose covalent and non-covalent interactions to tailor tensile response. We have developed supramolecular elastomers and interpenetrating network (IPN) systems that probe the interplay of non-covalent and covalent interactions in structural organization and mechanical response. By tailoring physical associations via control of self-assembly and composition, we have demonstrated enhanced supramolecular dynamics driven by architecture and toughness enhancements due to phase behavior. Recently, non-covalent interaction strength, network regularity, and chemoresponsiveness have been utilized as handles to derive gradient materials and to induce actuation behavior. New insights into supramolecular nanoscomposites are also highlighted.

A variety of materials developed in recent years have featured artificial water repellent surface structure inspired from organisms. However, an optical microscope cannot observe interfacial structural relationship with water droplet accurately due to problems of resolution and depth of focus. Therefore, we have applied the Scanning Electron Microscope (SEM) that can be used to observe the surface of specimen accurately. Traditionally, water droplets cannot be observed by SEM due to strict vacuum requirements for electron beam based imaging. Therefore, we have been developed a unique method called Aqua Cover method that allows observation of water directly in SEM [1].
SEM has a Low Vacuum (LV) mode that can facilitate imaging of water containing specimen. The chamber pressure of LV mode is able to reach several hundred Pa, but this pressure is insufficient to keep liquid water. There is also a method called Environmental SEM (ESEM). This method can maintain water droplets on a specimen by dew condensation. This is achieved by introducing the water vapor into the specimen chamber and cooling a specimen stage in LV mode. Although this method can make many tiny water droplets on the specimen surface, it cannot drop a water droplet directly at a specific site on the specimen surface. Unfortunately, tiny water droplets are also formed in crevices of uneven structures, so the Wenzel state is created even under the conditions that should be Cassie-Baxter state [2, 3]. From this reason, it is difficult to observe a behavior of sub mm to mm order water droplet, like a raindrop, on the specimen surface accurately, but it is important for development of fine structures and quality control in artificial water repellent materials.
As a method to solve this problem, Aqua Cover method that can keep the size of a water droplet from atmospheric pressure to pressure of LV mode and be observed by SEM is developed. Using this method, the interface relationship between water droplet dropped at atmospheric pressure and the specimen surface is observed by SEM and determined whether the water repellent state was Cassie-Baxter or Wenzel.
The experimental method is as follows: approximately 10 mm x 10 mm of lotus leaf was fixed on a 45 ° tilt specimen stub and installed on a cooling stage set at 0°C. 1 mL water droplet was then dropped onto the specimen surface. The Aqua Cover method was used for SEM observation at a specimen chamber pressure of 650 Pa and an accelerating voltage of 25 kV.
As a result of SEM Aqua Cover observation, air pockets were observed at the interface between surface unevenness structure and water droplet, so the state of this condition was determined to be Cassie-Baxter.

References
1. Inoue N, Takashima Y, Suga M, Suzuki T, Nemoto Y, and Takai O (2018). Observation of wet specimens sensitive to evaporation using scanning electron microscopy. Microscopy. 67: 356-366.
2. Jung Y C, and Bhushan B (2008). Wetting behaviour during evaporation and condensation of water microdroplets on superhydrophobic patterned surfaces. J. Microsc. 229: 127–140.
3. Darmanin T, and Guittars F (2015). Superhydrophobic and superoleophobic properties in nature. Mater. Today 18: 273-285.

Bioinspired by the tardigrade and bombyx mori we engineer the seed microenvironment to encapsulate, preserve and deliver Rhizobium tropici. Scientific discoveries in agriculture and sustainability are at the crossroads of material science, biochemistry, agriculture and biology. They underpin the innovative technological solutions that will impact water, energy and food security (WEFS). These new technologies can then be implemented to address major societal problems that are linked to climate change, soil degradation and soil salinization. In particular, our objective is to augment agricultural outputs (i.e. crop yield and production) while decreasing inputs (e.g. water, energy, fertilizers, land, pesticides) by deploying plant-growth-promoting-bacteria (PGPBs) in the soil to alleviate plant stressors to be specific soil salinity. Using PGPBs as a substitute to synthetic fertilizer our design approach engineers the seed microenvironment by coating the seeds with PGPB laden biopolymers. PGPBs are well known to enhance crop production and protect plants from biotic and abiotic stresses, while decreasing the need for water and fertilizers. However, the bacteria’s delicate nature has hindered their use in current agricultural practices. We use a silk and trehalose mixture that is able to encapsulate, protect, preserve and deliver Rhizobium tropici to Phaseolus Vulgaris. The coated Phaseolus Vulgaris seed are shown to be able to significantly alleviate soil salinity stress in Moroccan soil when compared with uncoated (control) Phaseolus Vulgaris seeds.

Worldwide 350 to 400 million metric tons of synthetic polymers are produced every year and it is estimated that 5 to 13 million metric tons of plastic will enter the ocean every year. This leads to negative consequences for various ecosystems and the human and animal health. For the removal of plastic, enzymes have come into focus of recent research due to their high selectivity and catalytic efficiency under mild conditions and their sustainable alternative to toxic catalysts. Esterases and hydrolases such as lipase and cutinase, respectively, catalyze the hydrolysis of lipids and cutin, a complex hydrophobic polyester the main component of the plant cuticle.
Nevertheless, enzymes constitute an expensive catalyst making a reusable system where the enzymes are attached on the surface of magnetic particles a cost-efficient platform. Therefore, magnetic ellipsoidal-shaped SiO₂@Fe₃O₄ particles were synthesized by coating ellipsoidal shaped α-Fe₂O₃ particles in a two-step sol-gel process with SiO₂. Afterwards the α-Fe₂O₃ core is reduced to magnetic Fe₃O₄ in a H₂/argon atmosphere. Covalent immobilization of the enzyme was achieved by first modifying the particles with 3-(aminopropyl)triethoxysilane to obtain terminal amino groups which upon addition of glutaraldehyde formed a stable bond to the enzyme. The successful attachment of the enzyme was proven via Zeta potential, IR and CHNS measurements. Moreover, the activity of the enzyme was demonstrated using the optical conversion of 4-nitrophenyl acetate to 4-nitrophenol. This approach was extended to polymeric materials using polycaprolactone fiber mats which were analyzed regarding morphology changes upon enzymatic degradation.

Some calcitic biominerals have been shown to be formed through the crystallization of a Mg-rich amorphous calcium carbonate (Mg-ACC) precursor. Formation mechanisms of multiscale biogenic single crystal structures at ambient temperatures, in conditions of limited solid phase diffusion, remain largely incomprehensible. Based on experimental results, we develop a model describing the formation of the brittle star Mg-calcite nanostructure from an amorphous Mg-ACC precursor to a Mg-calcite nanostructure containing periodic layers with varying concentrations of coherent Mg-rich nano-inclusions. The formation route is rationalized in a two-step model: the first step involves spinodal decomposition of a liquid or gel-like Mg-ACC precursor into Mg-rich nanoparticles and a Mg-depleted amorphous matrix. The second step is the crystallization of the decomposed Mg-ACC precursor. The crystallization of Mg-depleted ACC matrix is accompanied by the exclusion of Mg ions into a diffusion zone adjacent to the crystallization front; after crystallization of a certain layer, the Mg concentration ahead of the layer exceeds the critical value above which the Mg-ACC matrix becomes unstable against spinodal decomposition. A secondary spinodal decomposition will then start and result in the formation of additional Mg-rich nano-domains. As a result, the density of Mg-rich nano-domains changes periodically and forms periodic layered structure inside magnesium calcite single crystals. The model was supported by our experimental results in synthetic Mg-calcite, which suggest a spinodal decomposition in the amorphous precursor. These new insights have significant implications for fundamental understanding of the biogenic layered structures formation.

Living systems regulate the disorder to order transition of biomacromolecules to achieve complex materials with a variety of functionality and structural hierarchy, which has long been an inspiration for similar endeavors in synthetic materials. In particular, materials generation in nature often involves the use of templates to direct the assembly pathway and subsequent hierarchical organization of nanoscale building blocks, with the most prominent example being biomineralization that is ubiquitous in the natural world. The same principle underpins amyloid fibrils formation through pathogen (such as prions and misfolded Aβ oligomers) templating, which follows a nucleation-elongation model. In this presentation, we introduce templated crystallization of structural biopolymers as a process to nanofabricate hierarchically structured materials up to centimeter scale, using silk fibroin as an example. The process involves the use of ordered peptide supramolecular assemblies as templates to drive a phase transformation of silk fibroin from unordered to ordered conformations, thereby enabling further assembly of the silk fibroin chains into nanostructured materials (i.e. β-sheeted nanofibrils). Multiple parameters including the relative concentration between silk fibroin and peptide seeds, silk fibroin molecular weight, pH and peptide conformation are investigated to fine tune the assembly kinetics and silk polymorphs. Combining the templated crystallization with various top-down fabrication such as soft lithography and printing enables (i) formation of different silk polymorphs at selected areas, generating free-standing patterned silk films, where the different molecular structures can be used to store or encrypt information; (ii) surface functionalization with topographical control over silk nanofibrils growth on pre-deposited peptide seeds; and (iii) three-dimensional manipulation of silk nanofibrils into macroscopic structures with customized shapes and controlled anisotropy. Together, these results pave the way for nanofabrication of a new generation of smart and adaptive materials built from the bottom up.

Converting abundant sunlight as storable heat within phase change materials (PCMs) is an attractive way to harness solar energy for a broad range of heating-related applications. Current PCMs, however, generally suffer from a low thermal conductivity, which seriously limits the solar-thermal energy harvesting (STEH) process. In nature, STEH is also vital for normal functioning of biological species, but they have developed different strategies. For example, butterflies rely on spreading their wings towards sunlight to absorb solar photons to quickly warm the body and dynamically folding their wings to mediate the body temperature. Inspired by such unique mechanism, we demonstrate dynamic movement of the solar-thermal converters along the melting solid/liquid interface as an effective strategy to accelerate transportation of solar photons within PCMs thereby achieving fast STEH. By magnetically tuning the distribution of Fe₃O₄@graphene nanoparticles within the paraffin composite the STEH rate was increased by ~3 times. The low loading concentration requirement also enables the composites to fully retain and even slightly increase the fusion enthalpy of the PCMs. We further demonstrate rapid roll-to-roll STEH through illuminating the thin flexible form-stable composite PCM sheets while being continuously rolled. Due to shortened heat-diffusion distance and rollability of the composites, it achieves fast and uniform STEH within the bulk PCMs. The flexibility of charged composites also enables broad tuning of the discharging behavior, and provides the possibility to explore wearable thermotherapy and other flexible solar-thermal applications.

Brushite is one of the most important polymorphs of calcium phosphate in the context of bio-inspired mineralization. It has been used as reconstruction materials, dental cements and in formulation chemistry. It is also a precursor of hydroxyapatite which is a common component of bones and teeth. Due to its wide application as a functional material and a precursor of other bioceramics, the control of its crystal morphology is important. The performance of a functional material significantly depends on its shape and surface properties. Fundamentally, carboxylates are known modifiers of crystal growth. One example is hydroxycitrate (HCA) which have effectively curbed and controlled calcium oxalate mineralization. Here we reported the effect of HCA in the crystal shape, aspect ratio and number density. The bulk crystallization was coupled with interfacial studies using atomic force microscopy to further evaluate its impact on the surface of brushite. Analysis shows a 50% reduction in the number of crystals formed and a change in brushite’s morphology event at a very small inhibitor concentration (Ca/inhibitor=25000). Amplitude and Frequency Modulated AFM studies show that surface roughness increased through time in the presence of the HCA. Changes in the periodic features at near atomic resolution was also observed in the presence of HCA implying possible modifier-hydration layer interactions. Results obtained in this study may serve as a step in understanding the HCA’s effect on brushite and in designing bio-inspired calcium phosphate materials and precursors.

Life is an “emergent” property – i.e., one exhibited by living systems as a whole, but not by any of their individual parts. In a single eukaryotic cell, there exist internal compartments called organelles, such as the nucleus and mitochondria. While the organelles each have distinct functions, it is the overall cell that has the property of life – i.e., the whole is greater than the sum of the parts. Here, we describe our attempts to create millimeter-scale polymer capsules that exhibit emergent properties. In particular, we have created multicompartment capsules (MCCs) that have many internal compartments, each with distinct contents. We have also found ways to perfectly encapsulate (hermetically seal) aqueous solutes in a capsule core until an external stimulus is applied. The key to this property is to utilize hydrophobic shells that are impermeable to aqueous solutes. However, the shells can be degraded or made permeable by external triggers – either by heat or by oxidants that generate reactive oxygen species (ROS).

Using these concepts, we have activated multi-step or cascade reactions within MCCs. In one example, we use the MCC as a factory to synthesize fluorescent gold nanoclusters (AuNCs). Individual non-fluorescent reagents are encapsulated in internal compartments. When a stimulus is applied, the reagents leave the compartments and come into contact with each other, thus producing AuNCs. The overall MCC thereby displays an emergent property (fluorescence) that is not exhibited by any of its individual components. In a second example, we encapsulate a chemical fuel and catalytic particles in separate compartments. When the compartments are triggered to open up, the catalyst comes into contact with the fuel, which results in the production of oxygen gas. The gas causes the entire MCC to inflate, and this inflation is again a property that emerges from the interactions between the components of the MCC.

Soft photonic materials formed from colloidal crystals are highly-desirable platforms for sensing and signaling in biomedical, chemical, and mechanical application scenarios ^1–3. A particularly accessible attribute of such materials is structural coloration; by using stimuli-responsive and reconfigurable colloidal crystals, dynamic coloration can be achieved, akin to the inspiring ability of chameleons to change their color appearance⁴. To date many concepts for the lab-scale creation of such photonic materials are known⁵, however a lack of efficient and scalable production methods with sufficient control of properties persists. In addition, in hybrid materials with multiple stimuli-responsive components, interactions among components tend to be overlooked. Here, we propose a simple and scalable method to prepare stimuli-responsive photonic hydrogel balls of several tens of microns in diameter, in which pH- responsive colloidal nanogels are embedded in a scaffolding hydrogel. We show a dynamic color-change spanning the entire visible spectral range through a variation of pH or temperature, which triggers the nanogels or the scaffolding hydrogel, respectively. We discuss the mutual swelling interactions between the colloidal nanogels and the scaffolding hydrogel. The response characteristics, such as timescale and spectral range of the photonic balls can be tuned by altering the composition, and responsive properties of the colloidal nanogel and the scaffolding hydrogel. These photonic hydrogel balls could be applied as optically interrogated sentinels in label-free multiplexed chemical, thermal, and mechanical sensing scenarios with sub-mm resolution. In addition, by employing modular assembly strategies, they can be used to form dynamic color-changing materials at scale.
(1) Zhao, Y.; Shang, L.; Cheng, Y.; Gu, Z. Spherical Colloidal Photonic Crystals. Acc. Chem. Res. 2014, 47 (12), 3632–3642. https://doi.org/10.1021/ar500317s.
(2) Burgess, I. B.; Lončar, M.; Aizenberg, J. Structural Colour in Colourimetric Sensors and Indicators. J. Mater. Chem. C 2013, 1 (38), 6075–6086. https://doi.org/10.1039/C3TC30919C.
(3) Chan, E. P.; Walish, J. J.; Urbas, A. M.; Thomas, E. L. Mechanochromic Photonic Gels. Advanced Materials 2013, 25 (29), 3934–3947. https://doi.org/10.1002/adma.201300692.
(4) Teyssier, J.; Saenko, S. V.; van der Marel, D.; Milinkovitch, M. C. Photonic Crystals Cause Active Colour Change in Chameleons. Nature Communications 2015, 6 (1), 6368. https://doi.org/10.1038/ncomms7368.
(5) Vogel, N.; Retsch, M.; Fustin, C.-A.; del Campo, A.; Jonas, U. Advances in Colloidal Assembly: The Design of Structure and Hierarchy in Two and Three Dimensions. Chem. Rev. 2015, 115 (13), 6265–6311. https://doi.org/10.1021/cr400081d.

Cephalopods are known for their remarkable ability to camouflage by rapidly changing the color and reflectance of their skin, a property that is enabled by the presence of subcellular structures composed of unique structural proteins called reflectins. Given the critical role played by reflectins in regulating the optical behavior of these organisms, and their technological potential for the development of biophotonic and bioelectronic devices, these proteins have recently emerged as a desirable target for the design of novel functional biomaterials. However, the development of such materials has been impeded by a lack of complete understanding of the structure and assembly of this class of proteins. Here we will highlight the proteins’ multi-faceted material properties within the context of bioelectronic and biophotonic platforms. Specifically, we will discuss how the structure and stimuli-responsive assembly of these proteins enables their electrical and optical functionality. Our findings not only underscore the potential of reflectins as functional materials but also hold relevance for the development of cephalopod-inspired bioelectronic technologies.

Marine mussels (Mytilus spp.) fabricate tough and self-healing collagenous biofibers known as byssal threads via self-assembly. The hierarchical organization of the protein building blocks comprising the fibers was previously demonstrated to be crucial for their outstanding mechanical properties. Evidence suggests that self-assembly of this hierarchical structure is aided by the storage of the collagenous precursor proteins as a colloidal liquid crystal (LC) phase within micron-scale secretory vesicles. Currently, however, very little is understood about the molecular level forces controlling LC phase formation. Here, we harnessed advanced electron microscopy methods to reconstruct the 3-dimensional LC nanostructure of the collagen precursors within the secretory vesicles with unprecedented detail, including visualization of specific LC defects. Specifically, we identified the presence of a lyotropic smectic LC phase that we posit arises from the block co-polymer-like primary structure of the specialized byssus collagen precursor, consisting of clear demarcations in hydropathy and charge distribution. We further propose that terminal pH-responsive protein domains enriched in histidine provide the impetus for the fluid to fiber transition during thread formation. These findings may inspire new strategies for fabricating nanostructured soft materials with complex material properties through supramolecular self-assembly, which is relevant to ongoing efforts in sustainable polymers and tissue engineering.

Numerous studies have focused on a low surface energy coating and a micro/nanoscale surface texture to design functional surfaces that delay frost formation and reduce ice adhesion. However, the scientific challenges for long-term icephobic surfaces have not been fully addressed because of degradation such as mechanical wearing. Inspired by the suppressed frost formation on concave regions of natural leaves, here we report findings on the frosting process on surfaces with various serrated structures. Dropwise condensation, the first stage of frosting, is enhanced on the peaks and suppressed in the valleys when the wavy surface is exposed to humid air, causing frosting to initiate from the peak. The condensed droplets in the valley are then evaporated, resulting in a non-frost band. The effects of surface topography on the frost pattern are systematically studied by varying the serrated geometry defined as the vertex angle, and numerically modeling the spatial distribution of diffusion flux of water vapor on the wavy surface. Under different ambient humidity levels, the magnitudes of diffusion flux at the non-frost boundaries of the surfaces are nearly identical, implying that the critical value of diffusion flux is the key to understanding the non-frost pattern.

Water pollution and freshwater shortages present two of most emerging societal challenging issues. Although many advances have been explored in obtaining clean water, such as reverse osmosis technologies, membrane treatments, ion exchange, and some multi-effect distillation systems, these technologies are still costly. Water desalination and purification from seawater and wastewater have been developed for addressing the globally growing need of clean water, among which solar-driven evaporation has drawn tremendous attention because it uses abundant solar energy and has a small environmental footprint. Conventional sunlight absorbers include carbon-based materials with strong light absorption abilities, heat localizing plasmonic nanoparticles, and hydrophilic sponges with carbonized surfaces. However, their relatively low energy conversion efficiencies, high cost, limited capacity for continuous steam generation, and salt accumulation induced efficiency decay have hindered the development. As a new solar technology, interface steam generation has great prospects for the application of desalination and fractionation. In this work, we report a sustainable, efficient and accessible solar evaporator with bilayer structure from lignocellulosic biomass. Loofah is a pervasive vegetable in our daily life. The mature loofah is comprised of natural fibers with high hydrophilicity, hierarchical macropores, and microchannels, which are essential features and structures for steam generators. We prepared a bilayer loofah-derived solar evaporator, which had a top carbonized layer that functioned as efficient solar absorbers with broad light absorption and high light trapping and a bottom loofah fiber layer for sufficient water pumping to the localized heating surface from different directions. During desalination, the salt concentration gradient of the macropores and microchannels allowed for efficient salt drainage in loofah and prevented the accumulation of salt on the surface of the evaporator, thus enabling the antifouling properties that provided the loofah solar evaporator a long-term stability. This economical light absorber and water-pumping natural fibers exhibited a steam generation rate of 1.42 kg m^-2 h^-1 and an efficiency of 89.9% under 1 Sun. This low-cost, abundant, and stable material from lignocellulose biomass thus have great potential for future large-scale solar steam applications.

Marine mussels secrete adhesive proteins that enable these organism to anchor themselves to various substrate (i.e., ship hull, rock) in a rough, intertidal zone. These mussel foot proteins contain a unique amino acid, L-3, 4 dihydroxyphenylalanine (DOPA), that is responsible for strong interfacial binding. Specifically, the catechol side chain of DOPA is capable of participating in reversible interactions and covalent crosslinking. Many investigators utilize the catechol adhesive moiety in designing biomimetic adhesives and coatings. In contrast to these applications, our lab has been developing antiviral and antimicrobial biomaterials utilizing the redox chemistry of catechol. Catechol generates reactive oxygen species (ROS), such as superoxide and hydrogen peroxide, when it becomes oxidized. The generated ROS was antimicrobial against both gram-negative (Escherichia coli) and gram-positive (Staphylococcus epidermidis) bacteria and reduced the infectivity of a non-enveloped porcine parvovirus and an enveloped bovine viral diarrhea virus. Most importantly, the generation of ROS can be easily activated by simple hydration of catechol-containing microgel or coating. Most recently, we chemically modified catechol with various halogens. These halogenated catechol demonstrated broad spectrum antimicrobial property against multiple strains of multidrug resistance bacteria. The combination of moisture-resistant adhesive property and inherent antimicrobial property greatly enhanced the potential for using catechol for designing multifunctional bioadhesives, wound dressings and coatings with antipathogenic properties.

There has been tremendous interest in optimizing artificial surfaces that can continuously morph their surface texture for various purposes, such as camouflage, signaling, and hunting. In recent years, smart materials like stimuli-responsive polymers and hydrogels were leveraged to achieve surface texture morphing. However, their real-world applications are limited given their slow actuation and weak mechanical properties. Thus, the aim of this research is to broaden the current knowledge of surface texture morphing by designing instability-induced morphable structures using patterned, auxetic geometries. Our previous study introduced 3D-printed and thin-film-like Active Skins based on a star-reentrant geometry, and it was shown that unique patterns of out-of-plane deformations could be induced when uniaxial strains were applied. Moreover, geometrical imperfections or notches were introduced to program the surface morphing behavior of Active Skin in a desired manner. In this study, the geometrical dependence of surface morphing response (i.e., the nonlinear response of 3D-printed Active Skins) was characterized using both experiments and finite element model (FEM) simulations. First, experimentally calibrated FEM simulations were employed to design the width and angles of the rib of unit cell geometries. Second, the locations of geometrical imperfections were selected by identifying regions where stress concentrations were greatest in the unit cell. Last, unit cells with these designed imperfections were replicated by 3D-printing. Both the experimental and FEM results confirmed that the Active Skins could deploy pre-programmed 3D features on-demand, reversibly, and effectively through a controlled buckling-induced deformation mechanism.

Nearly all methods of introducing bioactive compounds to the surface of a substrate rely on application from above or fail over time due to depletion. In this work, we use a bio-inspired approach to deliver target molecules to an interface from below, making use of both theoretical modeling and experimental validation to rationally design customizable patterns and gradients. Mimicking the vascular systems of living organisms, networks of empty 3D-printed channels are filled with liquid containing the compound of interest, which flows through the vascular network and diffuses through the polymer, eventually reaching the substrate surface. In proof-of-principle experiments using Escherichia coli and Bacillus subtilis as model organisms, we demonstrate both theoretically and experimentally that the concentration of antibiotic and duration over which it is delivered to the surface can be controlled by varying the location of the vascular channels and concentration of the antibiotic solution inside. The result is a well-defined and predictable patterned response from the bacteria growing on the surface, a first step toward developing new types of adaptive antifouling surfaces and cell culture tools.

Many natural surfaces are capable of shedding water droplets rapidly, which has been attributed to the presence of low solid fraction (Φ_s ~ 0.01) (1) according to the classical wetting theories (2-4). However, recent high-resolution microscopic observations revealed the presence of unusual high solid fraction nanoscale textures on water-repellent insect surfaces. For example, superhydrophobic mosquito eyes, springtails, and cicada wings possess solid fractions (Φ_s) as high as 0.25 – 0.64 (5-7). In addition, the texture size on these insect surfaces is typically on the order of 100 – 300 nm. To understand why both high solid fraction and nanoscale textures are important for these superhydrophobic insect surfaces, we systematically designed and fabricated a series of textured surfaces with texture size varying from 100 nm to 30 µm at solid fractions of 0.25 and 0.44, and investigated their static and dynamic wetting behaviors. Here we show that the contact time of bouncing droplets on high solid fraction surfaces can be reduced by reducing the texture size to nanometer scale. Specifically, we discovered that high solid fraction surfaces (Φ_s ~ 0.44) with texture size ~100 nm could reduce the contact time by ~2.6 ms compared to that with texture size >300 nm. This texture-size dependent contact time reduction on solid surfaces has not been observed previously, and cannot be explained by existing surface wetting theories. We showed theoretically that the reduction in droplet contact time can be attributed to the dominance of three-phase contact line tension (8) on compact nanoscale textures. Through pressure stability analysis and experiments, we have further shown that high solid fraction (Φ_s > 0.25) is an important requirement for insects to withstand high-speed impacting raindrops. Our results suggest that the compact and nanoscale textures on water repellent insect surfaces may work synergistically to repel and shed impacting raindrops rapidly, which could be an important survival strategy for flying insects. Technologically, the ability of compact nanoscale textured materials to repel high-speed impact of liquid droplets with reduced contact time may find use in a range of applications including fouling-resistant personal protective equipment (PPE), insect-sized flying robots, and miniaturized drones (9).
Keywords: contact time | drop impact | insects | nanoscale textures | pressure stability | superhydrophobic surfaces
References:
1. W. Barthlott, C. Neinhuis, Purity of the sacred lotus, or escape from contamination in biological surfaces. Planta 202, 1-8 (1997).
2. A. B. D. Cassie, S. Baxter, Large contact angles of plant and animal surfaces. Nature 155, 21-22 (1945).
3. A. B. D. Cassie, S. Baxter, Wettability of porous surfaces. Trans. Faraday Soc. 40, 0546-0550 (1944).
4. R. N. Wenzel, Resistance of solid surfaces to wetting by water. Ind. Eng. Chem. 28, 988-994 (1936).
5. X. Gao, X. Yan, X. Yao, L. Xu, K. Zhang, J. Zhang, B. Yang, L. Jiang, The dry-style antifogging properties of mosquito compound eyes and artificial analogues prepared by soft lithography. Adv. Mater. 19, 2213-2217 (2007).
6. H. Gundersen, H. P. Leinaas, C. Thaulow, Surface structure and wetting characteristics of collembola cuticles. PLoS ONE 9, e86783 (2014).
7. J. Oh, C. E. Dana, S. Hong, J. K. Román, K. D. Jo, J. W. Hong, J. Nguyen, D. M. Cropek, M. Alleyne, N. Miljkovic, Exploring the role of habitat on the wettability of cicada wings. ACS Appl. Mater. Interfaces 9, 27173-27184 (2017).
8. J. W. Gibbs, The scientific papers of J. Willard Gibbs. (Dover Publications, New York, 1961).
9. L. Wang, R. Wang, J. Wang, T.-S. Wong, Compact nanoscale textures reduce contact time of bouncing droplets. Sci. Adv., (2020), to appear.

Despite the enormous research activity in the field of Pickering emulsions and the study of diverse emulsion systems such as O/W¹, O/O², W/O³, O/W/O, W/O/W⁴. There are only very few studies which presents the implementation of Pickering emulsions toward the development of superhydrophobic coatings and surfaces^5-9. It is possible to obtain a hierarchical porous structure by application of Pickering emulsions on a given surface and evaporation of the solvents, this procedure is termed emulsion templating. Although that enormous amount of studies have previously reported the successful development of superhydrophobic coatings and surfaces, only very few of them exhibit significant durability and transparency that would be suitable for real life applications. The current study presents the development of highly durable and transparent superhydrophobic coating based on oil-in-oil (O/O) Pickering emulsions. The combination of superhydrophobicity with significant abrasion resistance and transparency is obtained due to the formation of unique structures of shrinked colloidosomes on the surface of the coating. The coating is formed by emulsion templating of the O/O Pickering emulsion. The studied Pickering emulsions were applied on different types of polymeric substrates such as polypropylene and polycarbonate by using standard coating application methods including spin coating and roll coating.
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Biofouling has a negative impact on human health and economic development. In particular, biofilms in the marine environment grow easily, adhere strongly on most surfaces, and continuously generate adhesive proteins from the living organisms in the film. They cause increased fuel penalty, attenuation of sensor signals, and more [1]. To overcome these challenges, several natural surfaces, including shark skin [2], crab eyes [3], and dragonfly wings [4], have shown reduced biofilm settlement, nucleation, and adhesion because of their micro- and nano- surface textures.
Inspired by natural surfaces, herein, we present the rational design and fabrication of ZnO/Al₂O₃ core-shell nanowire (NW) architectures to significantly reduce marine biofouling (algae: cyanobacteria and diatoms) and further suppress the biofilm formation by tuning the NW geometry (length, spacing, branching) and surface chemistry [5]. Specifically, for hydrophilic NWs, we demonstrated algal fouling on NWs was only 40% of the fouling coverage on planar control surfaces when they were fully covered. These NWs outperform the surfaces with micrometer length-scale textures in marine fouling reduction under a multi-species fouling environment. Two mechanisms of the fouling reduction were summarized with geometric and mechanical effect of the NWs: (1) reduced effective settlement area, and (2) mechanical cell penetration. For superhydrophobic NWs, we demonstrated anti-biofouling performance for up to 22 days, which is one order of magnitude longer duration than what have been reported in the literature [6] under biofouling environment. A mass diffusion and thermodynamic model was developed to explain and predict the anti-fouling duration on NWs in the Cassie state. Furthermore, the nanowire surfaces are transparent across the visible spectrum, making them applicable to windows and oceanographic sensors. Through the rational control of surface nano-architectures, the coupled relationships between wettability, transparency, and anti-biofouling performance are identified. We envision that the insights gained from the work can be used to systematically design surfaces that reduce marine biofouling in various industrial settings.
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[3] G. Greco, T. S. Lanero, S. Torrassa, R. Young, M. Vassalli, A. Cavaliere, et al., "Microtopography of the eye surface of the crab Carcinus maenas: an atomic force microscope study suggesting a possible antifouling potential," Journal of the Royal Society Interface, vol. 10, p. 20130122, 2013.
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To harness the spectacular functionality found in nature, scientists and engineers have developed a multitude of biomimetic and bio-inspired techniques, each with its own strengths and constraints. One classic example is structural color exhibited by organisms such as birds, insects, and cephalopods that produce compelling and vibrant visual displays, which provides a fascinating case study for exploring the role of material design on macroscale properties. Recent research has identified self-assembly of colloidal structures as a cheap, simple way to mimic aspects of this coloration, often using materials like polystyrene or silica as scattering elements.

Self-assembly of spherical and non-spherical particles is an appealing approach as it can be scalable, low cost, conducted under ambient and aqueous conditions, and versatile. There are many factors involved in the drying behavior of colloids which relate to self assembly and color visibility. Structure formation can be tuned by modulating particle composition, surface functionality, particle size and concentration, coating, solvent, substrate wettability and roughness, drying and deposition conditions, particle shape, and the temperature, humidity, and pH of the environment. By manipulating these conditions, the final colloidal assembly structure can be indirectly controlled, yielding a host of fascinating visual effects relevant to bio-inspired design. In this work, we examine the role of melanin for light absorption and polystyrene for light scattering in order to mimic the combination of pigment and structure found in nature, and ultimately demonstrate means to control patterns.

Here we explore the role of the substrate on evaporative dynamics and the interplay between pigment and structure in pattern formation. We influence the rate of the kinetics by tuning surface properties such as hydrophilicity, thereby controlling the color vibrancy. We observe the droplet behavior on different printed surfaces through optical microscopy and macroscopic imaging and demonstrate a visible difference in resulting patterns based on substrate wettability. We record the drying process to observe differences in the dynamics and relate kinetic processes to these final structures.

We utilize polystyrene microparticles with diameters from 173 – 500nm (Sigma Aldrich and Ted Pella), and eumelanin from cuttlefish ink (Sigma Aldrich and MP Biomedicals). By mixing polystyrene and melanin, we generate disordered structures in contrast to ordered structures formed by polystyrene alone, but take advantage of the absorptive properties of melanin to yield more saturated colors than typical amorphous colloidal systems. Polystyrene particle suspensions are mixed with melanin solutions at various ratios and evaporatively assembled on a variety of substrates with the ultimate goal of connecting initial droplet shape, contact angle and speed of evaporation, indirectly tuned using the substrate, to the resulting structure.

We thus present a comparison of drying behavior across several different surfaces, macro-patterning between pigment-based and structural responses to demonstrate color patterns, spectroscopic characterization of the performance of these assemblies on different surfaces, and novel insights about the dynamics of the drying process and the placement of absorbing melanin and scattering polystyrene on the dried surfaces. Properties such as reflectance, absorption, packing and organization, and global architectures are studied using a variety of methods, including timelapse imaging, scanning and transmission electron microscopy, light microscopy, and angular spectroscopy. This work provides a path towards expanding the palette of achievable colors and patterns through bio-inspired design techniques. Such colloidal assemblies are of interest for optical devices, cosmetics, displays and inks, functional coatings, biocompatible products, sensors, and art elements.

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 photonic materials used by these organisms are not just of interest to biologists, but have also captured the imagination of physicists, chemists, materials scientists, and engineers, who are trying to emulate their dynamic optical behavior in synthetic bio-inspired material systems. Mechanically-responsive soft photonic materials, for instance, represent a versatile material platform for colorimetric force sensing in a variety of different research and technology fields, including healthcare, robotics, and human-computer interaction. Existing fabrication approaches are varied, including self-assembly of colloids or liquid crystals, magnetically induced self-assembly, block copolymer self-assembly, sequential spin coating, and laser writing and interference lithography. However, the application of these materials has been limited by drawbacks relating to their optical quality, mechanical properties, limited scalability, or cost and complexity of manufacture. We have recently developed a new optical fabrication approach that is capable of tackling these challenges, harnessing the century-old technique of Lippmann photography combined with recent advances in holographic recording materials. This process can be performed using just a desktop projector, aluminum foil, and many off-the-shelf holographic recording materials, at low cost and over large areas. Our manufacturing approach also permits spatially patterning different photonic structures and mechanical properties, with micron-scale resolution. In principle, this technique can be extended to realize an almost unlimited range of pattern morphologies that we know from biological photonic materials. We anticipate that our mechano-responsive photonic sheets will facilitate a range of new applications, and we will demonstrate initial prototypes in the fields of human-computer interaction and robotics.

Mussel byssal threads are proteinaceous biofibers self-assembled by mussels in order to attach to surfaces at the rocky seashore. Byssal threads are protected by a thin cuticle that combines high hardness and extensibility, making it a useful role model for advanced flexible coatings. Cuticle mechanics have been shown to arise from DOPA-metal coordination cross-links, as well as from its composite micro- and nanostructure, which consists of biphasic granules within an amorphous matrix phase. Although the byssus cuticle has become an important source of bio-inspiration for producing tough, self-healing metallopolymers, the biochemical nature of the different cuticle structures and the assembly process by which the cuticle is formed are far from clear.

Here, we performed a compositional and ultrastructural investigation of the protein secretory vesicles used to fabricate cuticle and followed their self-assembly during cuticle formation utilizing advanced electron microscopy methods including FIB-SEM and STEM-EDX¹. Findings suggest that the different proteins destined to form granules vs. matrix are pre-organized in a co-existing condensed fluid phase within secretory vesicles via phase separation of immiscible DOPA- and cysteine-rich precursors. During thread formation, the condensed fluid protein phases from multiple vesicles coalesce and solidify during secretion with the immiscible phases forming the matrix and granules, respectively. FIB-SEM 3D reconstruction of granule ultrastructure revealed a bicontinuous internal structure resembling a phase-separated block-copolymer, while elemental analysis with STEM-EDX exhibited an unusual partitioning of vanadium and iron between the DOPA-rich granules and cysteine-rich matrix, respectively, which may play a role in determining cuticle mechanics. These findings have direct relevance for production of nanostructured soft materials with complex and dynamic material properties.

1) Jehle, F., Macias-Sanchez, E., Sviben, S., Fratzl, P., Bertinetti, L. and Harrington, M. J. (2020) Biofabrication of functional meso-structured metallo-protein composites using co-existing condensed liquid phases. Nature Communications. 11, 862.

Significant tissue damage, scarring, and an intense inflammatory response remain the greatest concerns for conventional wound closure options, including sutures and staples. In particular, wound closure in internal organs poses major clinical challenges due to air/fluid leakage, local ischemia, and subsequent impairment of healing. Herein, to overcome these limitations, inspired by endoparasites that swell their proboscis to anchor to host's intestines, we developed a hydrogel-forming double-layered adhesive microneedle (MN) patch consisting of a swellable mussel adhesive protein (MAP)-based shell and a non-swellable silk fibroin (SF)-based core. By possessing tissue insertion capability (7-times greater than the force for porcine skin penetration), MAP-derived surface adhesion, and selective swelling-mediated physical entanglement, our hydrogel-forming adhesive MN patch achieved ex vivo superior wound sealing capacity against luminal leaks (139.7 ± 14.1 mmHg), which was comparable to suture (151.0 ± 23.3 mmHg), as well as in vivo excellent performance for wet and/or dynamic external and internal tissues. Collectively, our bioinspired adhesive MN patch can be successfully used in diverse practical applications ranging from vascular and gastrointestinal wound healing to transdermal delivery for proregenerative or anti-inflammatory agents to target tissues.
Acknowledgements
Financial support was provided by National Research Foundation of Korea (NRF) grant (NRF-2020R1C1C1012881) funded by the Ministry of Science and ICT (MSIT).

The most finely tuned, rapidly responsive, and precisely directed optical systems currently known can be found on the surfaces of living organisms. Studies of brittlestars’ tunable microlenses, sea sponges’ optical fibers, butterflies’ and beetles’ intense colors, and squids’ nearly perfect camouflage have revealed 3D architectures so intricately patterned down to the nanoscale that the topography itself controls the wavelengths and direction of reflected light. We are developing bioinspired, bottom-up self-assembly techniques that allow us to create comparably elaborate yet tunable hierarchical photonic structures, and integrate these into the design of a new class of dynamic, responsive optical materials.

Chitin is the second most abundant polysaccharide after cellulose, which can be extracted from exoskeletons of crustaceans and also from cell walls of fungi and insects. Similar to cellulose nanocrystals, chitin nanocrystals can be isolated through acid hydrolysis and form cholesteric phase. We investigate chitin nanocrystals confined to pnipam microgels using microfluidics device. The twisted structure of chitin nanocrystals are preserved within the polymer spheres, as characterized by optical microscopy. The droplet radius, R of the microgels can be adjusted by changing the volumetric flow rate of oil phase in a microfluidics device. Interestingly, the fabricated microgels shows bipolar structure with the shape of prolate spheroids. They exhibit swelling-deswelling behavior upon temperature change along the axis of helix.

Research on synthetic mimics of microstructures found on natural organisms, such as the structured skin of the shark or the surface of the lotus leaf, have resulted in surfaces that dynamically change rigidity, adhesion, or wettability. Structured surfaces also have potential biomedical applications in tissue engineering and as drug delivery systems, sensors, and actuators. For the aforementioned biological applications, hydrogels are the materials of choice due to their biocompatibility, biodegradability, and tunable mechanical properties. Generating patterns of intricate microstructures onto the hydrogel surfaces, however, is challenging because of the low mechanical strength, adhesion, or chemical incompatibility of hydrogels with various molds. Here, we report the use of a soft lithography technique to successfully pattern arrays of micropillars onto a poly(2 –hydroxyethyl methacrylate) based hydrogel. The swelling of the hydrogel in solvents such as phosphate buffered saline, deionized water, 60% ethanol, and absolute ethanol, facilitates the reproducible replication of the pattern. Furthermore, the micropillar pattern promotes the attachment of HeLa cells onto this hydrogel which is not inherently adhesive when unpatterned.

Nature provides a huge range of biological materials with various smart functions over millions of years of evolution and serves as a big source of bioinspiration for biomimetic materials that can bring impetus to the development of multifunctional materials and structures. From small biological ion channels to large oil pipelines, the structures with "Pore" and "Channel" are everywhere. Ion channels existing in living organisms play a significant role in maintaining balanced physiological conditions and serve as “smart” gates to ensure selective ionic transport. Pipelines, which are commonly used in chemical industry, food industry, agriculture, and energy-petroleum transportation, can be treated as macroscale channels. Multiscale pore and channel systems have been intensively explored and contributed to new developments in materials science, membrane science and technology, or micro/nanotechnology for analytical, biomedical, and energy applications. Stimulated by the achievements and the even larger potential of multiscale pore and channel systems, increasing research activities are devoted to important aspects such as energy saving, anti-fouling, anti-corrosion, and anti-blocking functionalities, switch ability and controllability integration of various functionalities, and good stability in such confined space. The most recent examples of mechanisms and strategies the learning from Nature are described, including bioinspired and smart multiscale pore/channel systems, especially building bioinspired liquid-based gating systems for bringing a new generation of design ideas of membrane separation technology; and bioinspired stimuli responsive micro/nanochannel systems for biomedical applications.
[1] Hou, X.*, Natl. Sci. Rev. 2020, 7: 9.
[2] Hou, X.*, et al., Angew. Chem. Int. Ed. 2019, 58: 3967.
[3] Hou, X.*, et al., Adv. Mater. 2019, 31: 1805130.
[4] Hou, X.*, et al., Sci. Adv. 2018, 4: eaao6724.
[5] Hou, X.*, Adv. Mater. 2016, 28: 7049.

The polychaete worms of the Nereididae family are distinguished by lightweight, conical teeth that exhibit a hardness level analogous to human dentin. While comparable in material properties to the mineral comprising dentin, the polychaete worm’s teeth are proteinaceous material built from histidine rich proteins cross-linked with Zn⁺² ions through coordination chemistry. The exemplified material properties achieved through coordination cross-linking of such biomaterials has inspired us to extend this method of cross-linking to preceramic polymers. Preceramic polymers require rigorous cross-linking as a means to reduce volume shrinkage and mass loss during pyrolysis, and often require extensive thermal curing steps to prepare a green body viable for ceramitization. Coordination cross-linking offers a faster, dynamic platform to preparing preceramic green bodies. Herein, we report the functionalization of commercially available polysiloxane and polycarbosilane backbones with pyridyl-moieties and the subsequent coordination cross-linking of these polymers with Zn⁺² and Ti⁺⁴ ions. The rapidly cross-linked materials were characterized with ATR-FTIR, oscillatory rheology, and thermal gravimetric analysis. The cross-linked green bodies were then pyrolyzed at 1400°C to ceramic materials, and characterized with XPS, XRD, and TEM. Ceramics generated from coordination cross-linked preceramic polymers represent the metal ion cross-linker, with Ti⁺⁴ cross-linked polymers generating TiC/SiC, and Zn⁺² cross-linked materials generating SiC, as Zn⁺² evaporates between 1000–1200°C. Coordination cross-linking is a single dial that can adjust material characteristics before and after pyrolysis. Particularly, the viscoelastic properties, thermal stability, and ceramic yields at 800°C can be systematically changed with the loading equivalents of metal cross-linker and the ceramic composition can be changed by metal ion choice. To the best of our knowledge, this is the first example of silicon-based preceramic polymers cross-linked through pyridine-based metal ion coordination.

With learning and getting inspiration from Nature, many trivial scientific questions and industrial problems can be resolved via proper designing the materials and creating unique structures, which lead to emerging materials in the field of renewable energy, sensors, and nanomedicine. Mimicking nanotechnology existed in Nature, we are able to create unique assembled structures to improve certain properties of materials and device, and design tool box to generate functional emerging nanomaterials. The main goals of this research are to synthesize novel bio-inspired and biomimetic functional nanomaterials, characterize and investigate their properties, and apply them to understand fundamental science via creating their hierarchical nanostructured materials. Basic understanding from those above investigations are then applied to address problems in solar energy conversion, and coatings. This research will focus on the following topics: (a) synthesis of bio-inspired functional nanomaterials; (b) fabrication of unique nanoarchitectures to better understand fundamental science; and (c) Applying these unique nanomaterials and nanostructures to resolve the scientific and technical problems in energy harvesting and conversion, and functional coatings.

Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is a well known conducting polymer preferred owing to high conductivity and processability. PEDOT:PSS on application of a potential bias attracts oppositely charged ions causing volume expansion. This reversible expansion is exploited to prepare bilayer actuator with bacterial cellulose as the substrate. A stable fish tail like deflection of over 5 mm was observed at 1 V. Effect of amount and properties of PEDOT:PSS on deflection is studied along with energy conversion efficiency. This electro-chemical actuator can have potential applications in biomimetic soft robotics.

Organisms construct 'devices' based on assemblies of organic nano-crystals with optical functions. The structure, polymorph, size, morphology and superstructural arrangement of the crystals determine the optical properties of the 'device'. All the crystals have unusually high refractive indexes in the directions along which the light penetrates the crystal. The controlled assembly of nano-crystals forms multilayer reflectors that create structural colors, or mirrors and light scattering layers that function to increase vision sensitivity in the eyes of the organisms. Scallops have tens of eyes, each containing a concave multi-layered mirror perfectly tiled with a mosaic of square guanine crystals, made up of composite twins, reflecting light to form images onto the overlying retinas [1]. Crustacean decapods such as shrimps, crayfish and lobsters possess compound eyes that contain two sets of mirrors, composed of isoxanthopterin crystals. The two mirrors have very different ultrastructures and functions that we can rationalize in terms of the optical performance of the eye [2,3]. The unusual zander fish eyes contain two layers of organic crystals: thin guanine crystals, form a reflective layer in the back of the eye, whereas block-shaped crystals of 7, 8-dihydroxanthopterin in the inner tapetum layer back-scatter light onto the retina, increasing the light sensitivity of the eye [4]. Finally, insects commonly known as jumping bristletails, form large amounts of xanthine crystals in their median and lateral ocelli [5]. The structure-function relations in this last example are still under investigation. In all these examples, the constituent molecules are mostly purines and pteridines, which raises the question of what molecular and structural characteristics of these crystals, favor their use for optical functions in organisms. Furthermore, the organization of the crystalline functional components is controlled from the crystal structure at the nanoscale to the complex 3D structure at the millimeter level, extending the interest in the relation between structure and optical properties to higher hierarchical levels.

[1] B.A. Palmer, G.J. Taylor, V. Brumfeld, D. Gur, M. Shemesh, N. Elad, A. Osherov, D. Oron, S. Weiner, L. Addadi: The Image Forming Mirror in the Eye of the Scallop. Science 358, 1172–1175 (2017).

[2] B.A. Palmer, A. Hirsch, V. Brumfeld, E.D. Aflalo, I. Pinkas, A. Sagi, S. Rozenne, D. Oron, L. Leiserowitz, L. Kronik, S. Weiner and L. Addadi: Isoxanthopterin: An Optically Functional Biogenic Crystal in the Eyes of Decapod Crustaceans. PNAS, 115, 10, 2299–2304 (2018).

[3] B.A. Palmer, V. J. Yallapragada, N. Schiffmann, E. Merary Wormser, N. Elad, E.D. Aflalo, A. Sagi, S. Weiner, L. Addadi, D. Oron: Highly Reflective Biogenic Materials from Core-Shell, Birefringent Nanospheres. Nature Nanotechnology 15, 138–144 (2020).

[4] G. Zhang, A. Hirsch, G. Shmul, L. Avram, N. Elad, V. Brumfeld, I. Pinkas, I. Feldman, R. Ben Asher, B. A. Palmer, L. Kronik, L. Leiserowitz, S. Weiner and L. Addadi: Guanine and 7, 8-dihydroxanthopterin reflecting crystals in the zander fish eye: crystal locations, compositions and structures, J Am Chem Soc 141, 19736−19745 (2019).

[5] A. Böhm and G. Pass: The ocelli of Archaeognatha (Hexapoda): functional morphology, pigment migration and chemical nature of the reflective tapetum, The Journal of Experimental Biology 19, 3039-3048 (2016).

We describe a platform of temperature-responsive hydrogel nanocomposites adsorbed at air/water interfaces that exhibit a variety of bioinspired non-equilibrium behaviors due to temperature gradients generated by illumination with visible light. In one example, we exploit spatial variations in thermally-induced deswelling of the gel particles to drive buckling of thin sheets into 3D shapes with non-zero Gaussian curvature. Similar to the mechanism exploited by numerous insects to climb menisci or drive clustering, pinning of the three-phase contact line at the sheet edges gives rise to capillary ‘multipole’ interactions between different objects, leading to assembly, repulsion, and even sustained rotational motion, depending on the geometry. In a second example, we exploit Marangoni forces resulting from temperature gradients to drive motion and interaction of planar particles, once again inspired by well-known strategies employed by aquatic insects. A simple method for Marangoni optical trapping is realized by shining appropriate patterns of light on the interface, enabling the definition of easily customized geometries in which to study coupled motion of multiple oscillators and spinners.

From the cellular level up to the body system level, living organisms are able to sense and adapt to local environment for various functions, from detecting and transporting molecules in the complex bio-fluids to harvesting energy from the environment and generate motions to keep alive. These graceful capabilities arise from the coordination of the chemo-mechanical actions, such as the molecular configuration changes and micro/macroscopic mechanical motions. Stimuli-responsive hydrogels are a class of synthetic materials that can change their volume and physical properties in response to environmental cues including temperature, light, and specific molecules. Inspired by these unique abilities, we have developed a series of dynamic material systems based on hydrogels. This presentation will introduce several novel functionalities that this broad-based platform has demonstrated, ranging from beetle-inspired ultrafast colorimetric sensing of chemical and biological species (Adv. Mater. 2018; Adv. Opt. Mater. 2019), autonomous sorting of target molecules in complex biofluids or wastewater (Nat. Chem. 2015), and plant-mimetic adaptive light tracking and harvesting (Nat. Nanotech. 2019), as well as self-sensing actuators for soft robotics (Sci. Robotics 2019). Overall, the environment-adaptive, dynamic material systems would have broad impacts in areas ranging from wearable sensors to smart devices that regulate energy usage and fully autonomous soft robots.

The heart is a uniquely challenging organ to recreate due to its dynamic three-dimensional (3D) motion and its detailed internal structures. Motivated by the lack of a synthetic or biological method to recapitulate both the complex motion and anatomical features of the heart, we recently developed a biorobotic hybrid heart that combines passive organic structures (intracardiac tissue) whose motion is driven by an active synthetic cardiac muscle. In this talk, we will describe a biomimetic design approach to programming the active synthetic cardiac muscles by replicating the intricate arrangements of cardiac fibers, which synchronously contract along to achieve efficient pumping motion of the heart. Instead of replicating the complex fiber structures directly in 3D, we took inspiration from the helical ventricular myocardial band theory – which proposes that the ventricle of the heart can be unraveled into a singular muscular band that is spirally arranged in the 3D space – to simplify the design and fabrication process of the synthetic cardiac muscles. We constructed a two-dimensional (2D) biomimetic matrix that has multiple linearly contracting pneumatic artificial muscles, which were oriented to match that of the muscle fibers in the unraveled heart tissue, in a soft elastomeric sheet. Then, the soft robotic matrix was rewrapped in a 3D helical fashion to recreate the hierarchical, functional architecture, and the global 3D motion of the ventricular cardiac muscle. Once assembled with the organic component, the biorobotic hybrid heart replicated the volumetric displacement of the heart at a physiological level upon cyclic actuation.

From the thermodynamic point of view, most materials are either in their equilibrium states, such as inorganic and organic crystals, or in kinetically trapped non-equilibrium states, such as porous materials. Life, on the other hand, is in dissipative non-equilibrium (or dynamic) state, with hierarchically ordered complex structures and highly coordinated functions. Developing dynamic materials systems where structural orders are sustained by continuous energy input and dissipation will not only introduce a new paradigm in materials science but also impact robotics. In the context of robotics, a micro-robot collective is a dynamic and programmable materials system, where fundamental physical and chemical principles guide the designs of local interactions and global behaviors. Here we show the collective patterns and behaviors of up to 250 micro-rafts spinning at the air-water interface and demonstrate the link between order and information in the collective motion. These micro-rafts display a rich variety of collective behaviors that resemble thermodynamic equilibrium phases such as gases, hexatics, and crystals. Moreover, they show emergent properties and functions when coupled with reconfigurable magnetic potentials. We devise information theoretical measures to quantify the information content of the spatiotemporal patterns and demonstrate their close relations with the order. Our findings are relevant for analyzing collective systems in nature and for designing collective robotic systems.

Crystallisation is an important process in a wide selection of problems – from the manufacture of pharmaceutical ingredients and inorganic materials to the prevention of scale formation and the production of minerals in living organisms. An understanding of the mechanisms which promote crystallisation can allow control over the formation of specific polymorphs, preventing the formation of crystals where it is undesirable, and tailoring crystalline materials for applications. In an uncontrolled environment, crystallisation typically occurs on foreign surfaces. Understanding the surface characteristics which promote and direct nucleation is key to the design and control of surface-aided crystallisation.

Compelling examples from literature show that flexible surfaces can strongly affect crystallisation rates. Self-assembled monolayers (SAMs) of alkenethiols, supported on gold or silver, can promote the nucleation of CaCO₃ with a high degree of orientational specificity^1,2,3. We use molecular dynamics simulations to understand the mechanisms through which defect-induced disorder in the flexible SAM of 16-mercaptohexadecanoic acid (16-MHDA) on an Au (111) surface can affect the ability of Ca²⁺ and CO₃^2- to form clusters.

To achieve this, we use molecular simulations to study possible defects in the monolayers through the removal of one or several surface atoms from the underlying Au (111) surface. This procedure forms step edges and vacancy islands which promote interactions between head groups of neighbouring chains through the offset created. As a reference case, we use an ordered SAM with a characteristic spacing of 0.498 nm between chains and a 30^o angle of the carbon backbone with the underlying gold surface⁴. An all-atom AMBER⁵ forcefield is used to reproduce the interactions between the alkenethiol chains, while a forcefield developed by Raiteri et al.⁶ was used for an accurate representation of CaCO₃ and its interactions with water. The Schröder method was used to obtain the interactions between the SAM and the Ca²⁺ and CO₃^2- ions.

Our findings suggest that the presence of defects not only disrupts the local structure of the solvent, but in some cases can induce longer-ranged disorder effects, reducing the longevity of the solvent adsorbed state. The introduction of ions into the system reveals how the disrupted surface layer of the solvent affects ion mobility on and near the surfaces, shedding light on the role of defects in flexible surfaces on the formation of crystalline clusters. This is an important step towards the defining and understanding of effective nucleating agents.

References
¹ Nielsen et al. Farraday Discussion, 2012, 159, 105-121
² Aisenberg et al. Journal of the Chemical Society, Dalton Transactions, 2000, 21, 3963-3968
³ Tremel et al. Handbook of Biomineralisation Chapter 12, 2007, Wiley, 209-232
⁴ Ulman et al. Chem. Rev. 1996, 96, 1533-1554
⁵ Wang et al. Journal of Computational Chemistry, 2004, 25, 1157-1174
⁶ Raiteri et al. J. Am. Chem. Soc., 2010, 132, 17623-17634

The discovery that viruses such as the Human Immunodeficiency Virus (HIV) contain proteins that allow the virus to overcome cellular barriers and achieve efficient cell penetration without need for a receptor represents a milestone in medicinal research. Since then, the Trans-Activator of Transcription (Tat) protein has been identified as first cell-penetrating peptide (CPP) and was linked to various cargos including large multimeric protein complexes to allow for their transport across cell membranes. The high translocation efficiency is thereby highly dependent on the sequence, secondary structure, and charge of the protein.
Given the increasing demand for intracellular delivery of nanoparticle-based therapeutics, we studied how the cell uptake of silica nanoparticles can be modulated after decoration with differently active CPPs. Employed CPPs were derived from antimicrobial peptide CAP18 and were systematically modified regarding the position of specific amino acids in their sequence. Interestingly, we found out that significant differences in uptake efficiency and intracellular accumulation of nanoparticle-CPP conjugates were observed depending on amphipathicity, alpha-helical structure formation and charge of the peptide, as well as the carrier size. These results demonstrate how we can learn from viruses to overcome current medicinal challenges, revealing the huge potential of sequential fine-tuning of CPPs and providing insights into their interaction with inorganic nanocarrier surfaces.

Metal-coordination complexes are emerging as a broad class of supramolecular crosslinks for use in advanced structural materials with tunable mechanical properties. Unlike conventional covalent bonds, these bonds have the capacity to reform after rupture, thereby enabling dynamic, tunable, and reversible (self-healing) mechanical properties. An increasing number of biological organisms, such as marine mussels (Mytilus) and marine worm jaws (Nereis virens), have been found to take advantage of these unique properties of metal-coordinate complexes in the secretion of loadbearing materials for complex extraorganismal functions. Inspired by the role of these bonds in biological materials, several studies have incorporated metal-coordination bonds as crosslinks in model hydrogel systems to tune dynamic mechanical properties over a broad spectrum of timescales. However, a deeper understanding of how microscopic behavior of metal-coordination bonds affect bulk mechanical properties is still missing, rendering predictive implementation in designing mechanical properties of materials a continued challenge.

This study presents a multiscale computational model of various metal-coordination complexes to elucidate how these complexes affect bulk mechanical properties of protein and synthetic metal-coordinated materials. First, we study how coordinating ligands specific to biological and synthetic contexts affect mechanical properties of the bulk material. Comparisons are drawn between imidazole, naturally found in marine mussels and worm jaws, and histidine, used in synthetic hydrogel studies, to demonstrate clear differences between biological and synthetic materials. Density functional theory (DFT) and steered molecular dynamics (SMD) studies on individual coordination complexes reveal how the dissociation path of histidine-Ni2+ or imidazole-Ni2+ underpin bond lifetime and bulk material relaxation time. Second, we study how clusters of metal-coordination complexes affect bulk mechanical properties. To understand this effect, model systems with various coordination complexes are designed and tested. MD studies reveal that these different model systems significantly affect bulk relaxation time and strength. Results from studies on these model systems are qualitatively compared to metal-coordinate crosslinks in the Nereis virens marine worm jaw protein structure. This comparison may lend insight into how the structure of Nereis worm jaw optimizes the positioning of metal-coordination interactions for precise mechanical control. Altogether, this work proposes key design criteria for how metal-coordination chemistry can be advanced for biological applications with dynamic mechanical materials properties.

The imbalance between the production of reactive oxygen species (ROS) by various mechanisms, including both internal metabolic processes and external environmental stimuli, and the endogenous antioxidant defences in mammalian cells often leads to oxidative stress and contributes to various pathological conditions, such as aging, neurodegenerations in Parkinson and Alzheimer diseases, and cancer. Under oxidative stress, the ROS initiates a series of oxidation reactions of cell membranes through the formation of hydroperoxides at the sites involving double-bonded carbon atoms along unsaturated fatty acid chains of phospholipids. Being hydrophilic in nature, the hydroperoxide group tends to migrate towards the water-membrane interface and changes to the internal structure of the lipid membrane. Despite the improved knowledge in the biological and chemical events during lipid peroxidation, how lipid peroxidation modulate the mechanics of lipid membranes remains largely elusive. In this study, we have investigated the peroxidation of polyunsaturated (more than one double-bond per fatty acid chain) phospholipids, a process involved in a recently identified form of programmed cell death, namely ferroptosis. By performing systematic coarse-grained molecular dynamics simulations, we have identified that lipid peroxidation affects the physical and mechanical properties of lipid membranes in an oxidation site-dependent manner. Our results show that the lipid peroxidation softens the membrane when the oxidation site is deep inside the hydrophobic core, while it tends to strengthen the membrane when the location of the oxidation is close to the water-membrane interface. Our study provides an insightful understanding on the modulation of membrane mechanics by lipid peroxidation.

Many animals in nature possess musculoskeletal systems with astonishing actuation speed, strength, and adaptivity. To mimic their agile and forceful locomotion, liquid crystal elastomers (LCEs) are a promising candidate among all synthetic actuator materials, as they exhibit reversible and anisotropic deformation by multiple external stimuli. So far, most studies on LCEs have focused on accomplishing complex deformation in 2D thin films over centimeter scale areas with relatively small specific energy densities, which is different from the 1D fiber-based contraction mechanism of muscles. Herein, using an extrusion process, meter-long LCE composite filaments that are responsive to both infrared light and electrical fields are fabricated. In the composite filaments, a small quantity of cellulose nanocrystals (CNCs) is incorporated to facilitate the alignment of liquid crystal molecules along the long axis of the filament. Up to 2wt% carbon nanotubes (CNTs) is introduced into the LCE matrix without aggregation, which in turn greatly improves the mechanical property of filaments and their actuation speed, where the Young's modulus along the long axis reaches 40MPa, the electrothermal response time is within 10s. The maximum work capacity is 38J/kg with 2wt% CNT loading. Finally, shape transformation and locomotion in several soft robotics systems achieved by the dual responsive LCE/CNT composite filament actuators are demonstrated.

Actuators and artificial muscles require high-efficiency stimuli-responsive materials that transduce an energy form, such as electric voltage, thermal gradient, pneumatic pressure, or chemical potential, to their structural deformations. However, energy conversion efficiency of most man-made stimuli-responsive materials fail to compete with natural muscles, such as human and insect muscles whose efficiencies reach 40 and 16%, respectively. Here, we report that peptidoglycan (PG) isolated from Bacillus (B.) subtilis spores exhibits powerfully humidity-responsiveness, and it efficiently transduces water’s chemical potential energy into mechanical motions with an energy conversion efficiency of ~35%. We isolated PG from other protein-based components in spores by using several denaturing agents, and subsequently identified its structure by using a SEM and a liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS). Due to the lack of database of B. subtilis spore PG’s chemical structure, we developed our own algorithm to deconvolute the LC-ESI-MS detected mass to charge ratio (m/z) and identified 6 hydrolysates with an error less than 4 ppm. Our results suggest that our isolated PG are composed of long glycan chains that are loosely cross-linked by short peptide stems, forming a 3-dimensional amphiphilic hierarchical structure. When isolated PG is exposed to humidity changes or water gradients, we found that PG can forcefully swell and shrink. For example, when local relative humidity is increased from 5% to 90%, PG expands up to 50.1% of its original height with a swelling pressure of 302.17 MPa. Using a thermodynamic cycle, we characterized PG’s energy density and power density which reach 59.9 MJ m^-3 and 5.9 MW m^-3, respectively, exceeding that of all natural muscles. By using PG, we also created a large-scale bilayer structure that reversibly bends in response to RH changes, demonstrating the possibility of using PG to develop high-efficiency actuators.

In the conventional computing paradigm based on the von Neumann architecture, a tremendous amount of data is transferred between memory and processor and the program operates on the data in a step-by-step fashion, which imposes a bottleneck in the speed and scalability of the architecture. A new paradigm beyond the von Neumann architecture is needed to address the problem fundamentally. The most promising approaches include implementation of swarm intelligence algorithm, like ant colony, to solve optimization problems. In order to implement natural computing algorithm into some physical systems, phase change materials (PCMs) are advantageous as a key platform due to its plasticity and threshold behavior (nonlinearity), which provide memory and processing functionalities, respectively. Based on the idea, we proposed an idea to implement an algorithm for Ising spin glass problem to the system of coupled plasmon particles interacting with PCM.
In this study, we attempt to implement ant pheromone algorithm. Ant colony optimization is a problem to find the shortest path between their nest and food using pheromone trails. Ants emit pheromone on the ground which works as a signal to attract other ants. If an ant follows the pheromone trail, it itself also emits more pheromone, thus emphasizing the trail. The more ants follow the trail, the pheromone deposition also increases (positive spiral). Pheromone strength decays over time due to the evaporation resulting in much less pheromone on less popular paths (negative spiral). These positive and negative spirals enable ants to find the shortest path autonomously.
In the experimental setup, polystyrene beads (PBs) with a diameter of 500 nm suspended in water were used to mimic the behavior of agent ants. The suspension was confined in a two-dimensional slit formed with two glass plates. A GeSbTe film, as a PCM, was deposited on the bottom glass plate. The PBs move around in Brownian motion on the GeSbTe film, which was initially in the amorphous phase. Under uniform light irradiation (sub-nanosecond-pulsed laser) over a wide area, the GeSbTe just beneath the PBs is crystallized due to the near-field lens effect of PB. The crystalline trail, which is expected to work as the pheromone trail, absorbs more light and becomes more heated than the amorphous background and thus a convection flow is formed such as to attract other PBs towards the crystalline trail. In addition to the convection flow, the electrostatic interaction between the PB and GeSbTe in the crystalline phase, the PBs trace the crystalline trail. By providing larger fluence pulses, the crystalline trail is amorphized, which is equivalent to the evaporation of pheromone. On this experimental platform, we demonstrated mimicking smart behavior of ants, which includes formation of trail by following a PB ahead and finding shortcut path through thermal communication of PBs.

Overcoming the reversible nature of low-Reynolds number flow, a variety of biomimetic micro-robotic propulsion schemes and devices capable of rapid transport have been developed. However, these approaches have been typically optimized for a specific function or environment and do not have the flexibility that many real organisms exhibit to thrive in complex microenvironments. Here, inspired by adaptable microbes and using a combination of experiment and simulation, we demonstrate that one-dimensional colloidal chains can fold into geometrically complex morphologies including helices, plectonemes, lassos, and coils and translate via multiple mechanisms that can be varied with applied magnetic field. With chains of multi-block asymmetry, the propulsion mode can be switched from surface-enabled to bulk, mimicking the motion of organisms such as flagella-rotating bacteria, tail-whipping sperm, arching and stretching inchworms, and sidewinding snakes. We also demonstrate that reconfigurability enables navigation through three dimensional and narrow channels mimicking capillary blood vessels. Our results show that flexible microdevices based on simple chains can transform both shape and motility under varying magnetic fields, a capability we expect will be particularly beneficial in complex in vivo microenvironments.

Conventional soft robotic structures are actuated by inflating the elastomer with a pneumatic pump. However, this method involves heavy, bulky pumps that should be tethered to the system with multiple tubes. More recently, soft actuation by liquid vaporization is receiving much attention, since it only requires a small heater and liquid embedded in the elastomer. The volume of the liquid expands during vaporization, which inflates and deforms the structure. Despite their benefits, they still face several limitations that have prevented their practical use. For instance, vaporization requires heating the embedded fluid in the structure to its boiling point, while actuation ceases when the system is tilted, and the heater is no longer in contact with the liquid. In addition, cooling the system to return the structure to its original shape takes a long time, thus limiting actuation frequency. In this study, these limitations were addressed by designing a soft robotic structure that actuates based on the principles of atomization and vaporization. First, a soaked wick was embedded in the soft elastomer structure in lieu of directly encasing liquid in cavities. A miniature piezoelectric ring transducer with a metal mesh in its center was positioned on the surface of the wick, thus making contact with the embedded fluid at all times and even when the system is tilted. Second, the piezoelectric ring was excited using a high-frequency electrical signal to vibrate the metal mesh while dispersing the embedded liquid into small droplets. These droplets were ejected into a small, embedded heater to enable rapid evaporation of the ejected droplets, which required significantly less temperature, power, and time than directly boiling the embedded fluid. A uniaxial motion bellows structure was fabricated with the soaked wick, piezoelectric ring with a metal mesh, and miniature heater. Their force and displacement performance were tested, characterized, and compared with conventional liquid vaporization. Overall, the developed method was shown to be faster, consumed less power, and enabled rapid cyclic motions as compared to actuation by boiling. The results also showed promising performance attributes comparable to pneumatic pumps but with the added benefits of being easier to miniaturize for portable or untethered soft robotic systems.

Water-responsive (WR) materials that swell and shrink in response to changes in relative humidity or water gradient provide new engineering opportunities for adaptive structures, soft robotics, and sustainable energy. Spider dragline silk is a WR materal that have demonstrated a significant acutation energy density of 0.5 MJ m^-3, which is higher than most stimuli-responsive materials used for actuators and artificial muscles. However, spider silk’s low availability and the poor understanding of its structure-WR property relationship impede pratical applications or de novo design of its mimetic structures. Here, using Bombyx (B.) mori silk that shares a similar supramolecular structure to that of spider silk proteins, we demonstrate tunable water-responsinveness of B. mori silk and found that a higher β-sheet crystallinity strongly correlates to a higher WR energy density. To mimic spider dragline silk’s secondary structures and investigate its structure-WR relationship, we used a series of solvent treatments that allow us to control the crystallinity of regenerated B. mori silk. Suprisingly, when B. mori silk is processed to have a similar β-sheet content (48.6 %) as that of spider dragline silk, the B. mori silk possess a similar WR energy density (0.48 MJ m^-3) to spider silk. When B. mori silk’s crystallinity was further increased to 57.6 %, its WR energy density reaches 1.6 MJ m^-3, surpassing that of all known natural muscles. Response time of WR B. mori silk could be reduced by rendering surface hydrophilicity and pore structures. As a proof-of-concept, we have demonstrated a regenrated B. mori silk muscle that can reversibly lift a load about 1200 times heavier than the silk’s own weight.

Nature’s intelligent design of composite materials leads to enhanced mechanical properties compared to the individual constituents, which can for example lead to a combination of high stiffness and toughness [1]. Nature design principles have inspired scientists to fabricate reinforced synthetic materials by mimicking the architecture of biological systems. Nacre is one of the most studied systems [1-3]. It is a composite material formed of alternating layers of inorganic aragonite platelets intercalated by a biopolymer [4]. Nacre displays remarkably high mechanical properties going far beyond the rule of mixture of its constituents.
We tried to mimic this layered composite structure using silica as inorganic material. In order to obtain a layered porous and anisotropic silica network, we modified the conventional sol-gel process, which leads to porous silica monoliths, by adding superparamagnetic iron oxide nanoparticles (SPIONS) and applying an external rotating magnetic field during the sol-gel transition [5-6]. The magnetic nanoparticles will self-assemble into layered structures in the presence of a high frequency rotating field, aligned in the plane of rotation of the field. Silica having an affinity for the iron oxide nanoparticles will nucleate on them adopting the same structure as the SPIONS, which act as smart templates to dictate the final structure of the monolith, which is permanently fixed after gelation. The final inorganic-organic nacre inspired composite is created by filling the porous structure with a polymer. Compressions tests of the platelet-structured composite show the desired increase of the mechanical properties of the silica monolith.

[1] M. Meyers, P.Y. Chen, A. Lin, Y. Seki, Progress in Materials Science, 2008, 53, 1.
[2] F. Barthelat, CM. Li, C. Comi and H.D. Espinosa, Journal of Materials Research, 2006, 21, 1977.
[3] H. Zhao and L. Guo, Advanced Materials, 2017, 29, 1702903.
[4] T. Niebel, F. Bouville, D. Kokkinis and A.R. Studart, Journal of the Mechanics and Physics of Solids, 2016, 96, 133.
[5] M. Furlan and M. Latuada, Langmuir: the ACS journal of surfaces and colloids, 2012, 28, 12655.
[6] M. Furlan, B. Brand and M. Lattuada, Soft Matter, 2010, 6, 5636.

Human-made materials are generally considered to be the resultant of heat-beat-treat strategies due to their energy-intensive, high temperature/pressure and harsh chemical treatments, whereas the biomaterials made by living cells are fabricated at ambient conditions from abundantly available benign components. Thus, drawing inspirations from nature and harnessing the unparalleled manufacturing capabilities restored in living cells could lead to the development of an ultimate materials technology. Just like a seed that can grow into a living wood, we envision that living cells can be engineered to fabricate living materials that have life-like properties. In this regard, we present a simple and versatile strategy to fabricate living materials from engineered microbial cells at ambient conditions. Remarkably, our living materials comprises of living cells and a fraction of the material can self-regenerate itself. This work opens up unprecedented avenues to integrate synthetic biology, materials engineering, microbiology, nanotechnology and biomimicry - to develop futuristic materials and systems for a sustainable world by employing microbial factories.

Nature produces outstanding materials for structural applications such as bones and woods that can adapt to their surrounding environment. For instance, bone regulates mineral quantity proportional to the amount of stress. It becomes stronger in locations subjected to higher mechanical loads. This leads to the formation of mechanically efficient structures for optimal biomechanical and energy-efficient performance. However, it has been a challenge for synthetic materials to change and adapt their structures and properties to address the changes in loading conditions. To address the challenge, we are inspired by the findings that bones are formed by the mineralization of ions from blood onto scaffolds. We report a material system that triggers mineral deposition from ionic solutions on organic scaffolds upon mechanical loadings so that it can self-adapt to mechanical loadings. For example, the mineralization rate within the material system could be modulated by controlling the loading condition, and a 30-180% increase in the modulus of the material was observed upon cyclic loadings whose range and rate of the property change could be modulated by varying the loading condition. We envision that our findings can open new strategies for making synthetic materials with self-adaptable mechanical properties.

Reference: S. Orrego, Z. Chen, U. Krekora, D. Hou, S.-Y Jeon, M. Pittman, C. Montoya, Y. Chen, S. H. Kang, “Bioinspired materials with self-adaptable mechanical properties,” Advanced Materials, 1906970 (2020).

Diffusiophoresis refers to the motion of colloid materials in concentration gradients. I describe some of our studies of these problems, using experiments and mathematical modeling, such as the influence of ion valence and the effect of multiple electrolytes. Also, we demonstrate that these effect can influence of the movement of bacteria. For example, I summarize our observations of the migration of wild-type V. cholerae and a mutant lacking flagella (ΔflaA), as well as S. aureus and P. aeruginosa, near a dissolving CO2 source, which shows that diffusiophoresis of bacteria is independent of shape and Gram stain. With long-time experiments, we show that CO2-driven diffusiophoresis can reduce surface contamination, which suggests that the mechanism can be applied to cleaning systems and anti-biofouling surfaces. This work involves contributions from Suin Shim, who investigated the diffusiophoretic response of bacteria, as well as Ankur Gupta, Jessica Wilson and others in my research group.

The shape-morphing of two-dimensional elastic materials into three-dimensional structures is a vital and ubiquitous transformation in biological systems, as evidenced, for example, by the morphogenesis in cells and tissues, the formation of well-defined curvatures in growing flowers and leaves, and reconfiguration of seedpods in the release of seeds. The functionality of such biological reconfigurations has inspired the development of synthetic shape-changing materials that are useful for soft robotics and soft actuators. Here, we use theory and simulation to devise a distinctive approach for driving shape changes of 2D elastic sheets in fluid-filled microchambers. The sheets are coated with catalyst to generate controllable fluid flows, which transform the sheets into complex 3D shapes. A given shape can be achieved by patterning the arrangement of the catalytic domains on the sheet and introducing the appropriate reactant to initiate a specific catalytic reaction. Moreover, a single sheet that encompasses multiple catalytic domains can be transformed into a variety of 3D shapes through the addition of one or more reactants. Materials systems that morph on-demand into a variety of distinct structures can simplify manufacturing processes and broaden the utility of soft materials.

Morphogenesis is a phenomenon by which a wide variety of functional organs are formed in biological systems. In plants, morphogenesis is primarily driven by differential growth of tissues. Much effort has been devoted to identifying the role of genetic and biomolecular pathways in regulating cell division and cell expansion and in influencing shape formation in plant organs. However, general principles dictating how differential growth controls the formation of complex 3D shapes in plant leaves and flower petals remain largely unknown. Through quantitative measurements on live plant organs and detailed finite-element simulations, we show how the morphology of a growing leaf is determined by both the maximum value and the spatial distribution of growth strain. With this understanding, we develop a broad scientific framework for a morphological phase diagram that is capable of rationalizing four configurations commonly found in plant organs: twisting, helical twisting, saddle bending, and edge waving. We demonstrate the robustness of these findings and analyses by recourse to synthetic reproduction of all four configurations using controlled polymerization of a hydrogel. Our study points to potential approaches to innovative geometrical design and actuation in such applications as building architecture, soft robotics and flexible electronics.

Melanin, a ubiquitous material present in all forms of the living kingdom, and its synthetic mimics have been extensively studied owing to its intriguing properties like broadband absorption, ultraviolet (UV)-protection, and other multi-functional properties. In the recent decade, synthetic melanin (especially polydopamine) has been extensively employed to study structural color, optical filters and other optical applications. However, there is a lack of understanding on how the optical properties of these materials would be affected after intensive exposure to UV radiation (320-450 nm). In this work, we characterize the complex refractive index of synthetic melanin thin films using spectroscopic ellipsometer through the UV-NIR range, before- and after-UV treatment. Atomic force microscopy (AFM) is used as an independent technique, recording thickness changes to improve the fitting process of the ellipsometric parameters (delta and psi) for derivation of the complex refractive index. This information has a crucial meaning in elucidating the optical properties of melanin and provides new prospective to melanin’s UV protection behavior.

The eggs of birds and many reptiles are protected by hard eggshells composed mainly of calcium carbonate (~94 wt%). While the evolutionary success of birds and reptiles clearly suggests an effective biological design of eggshell, how eggshells achieve structural safety and robustness from such a thin shell with weak constituents is not fully understood. Even more puzzling is the observation that the inner side of eggshells is abundant with crack-like defects resulted from mammillary cones, which appear to weaken the eggshells. In this study, we developed a micromechanics model that takes microstructural defects, post-fracture deformation, and the underlying soft membrane of eggshell into account. With this model, we discover that membrane and crack-like defects play a critical role in amplifying the energy absorption and structural safety of eggshells. Impressively, the membrane can remain intact at displacements an order of magnitude greater than instances in which fracture is initiated in the hard shell. This improves the energy absorption by over 200%. On the other hand, the crack-like defects between mammillary cones accommodate the membrane deformation over a large area, enhancing the integrity of the membrane during post-fracture deformation. These findings are verified by three-point bending tests on both emu and hen eggshells, suggesting a general design strategy for eggshells. Such smart engineering of defects and a soft membrane in eggshell may further be adapted to the design of pressurized vessels and space capsules, where hard outer shells and structural safety are required simultaneously.

Bone is mineralized tissue that constitutes the frame of the musculoskeletal system to support and protect body structures. In addition to other functions, bone plays a remarkable role in sound conduction. From a mechanic standpoint, bone is an anisotropic viscoelastic material, capable of transmitting and dissipating energy, preventing structural failures and their propagation.
We propose a computational study that aims at fully exploring the viscoelasticity of collagenous fibrils with different mineralization contents. We investigate the mechanical response of the tissue upon cyclic and impulsive loads to observe the viscoelastic phenomena from either shear or extensional strains via atomics scale modeling. We perform a sensitivity analysis that takes into account a number of benchmarks: intrafibrillar mineralization percentage, hydration state, and amplitude of the external load.
We prepare the building block of collagen (COL) fibrils, the so-called D-period of about 67 nm, composed of the overlap and gap region. The gap volume is the part where hydroxyapatite (HA), the mineral component of bone, is mostly accumulated. Based on the amount of HA, we define three structures for our study: COL/HA 100/0 (w/w%), for resembling pure collagenous tissues; COL/HA 80/20 and 60/40, to describe mineralized tissues.
We pre-process our structures based on the boundary conditions: full periodicity is used for the cyclic-loading study (CLS) while, concerning the investigation with impulsive loads (ILS), we apply the periodicity only to the axes that are transversal to the wave direction. We apply to the CLS a sinusoidal shear strain (γ) with two amplitudes (viz., 0.017 rad and 0.17 rad) ranging in 1-10 GHz frequency. As for the ILS, we cut the bonds along the loading axis in order to apply the impulsive load at one edge (viz., a uniform displacement delivered in 2 ps with input velocities ranging between 100 m/s and 1000 m/s) and a fixed constraint to the opposite one. All the topologies are equilibrated via LAMMPS aiming at relaxing the structures and reaching the convergence of the potential energy and RMSD (Root-mean-square deviation).
Our results from the CLS show a growth of the elastic modulus (G’) with the increase of the mineral percentage, which is more pronounced at low angular strains (up to 3000 MPa). The viscous part (G’’) increases with %HA at high values of γ (up to 40 MPa) while it is almost constant at low γs, below 10 MPa. When considering the intrafibrillar water, the material softens the elastic component with a wet/dry ratio that is almost 0.5, but increase considerably its viscosity, especially at high frequencies (G’’ up to 600 MPa). This behavior is also confirmed by the response of the material in ILS, in which water drastically reduces the relaxation times by one order of magnitude with respect to the dehydrated topologies, independently of the input velocity.
Our results may be used to improve the knowledge of the physiology of pure collagenous tissues or intrafibrillar mineralized tissues upon different conditions (e.g., traumas, diseases like osteoporosis or osteogenesis imperfecta). Moreover, although the main focus of this study is about the effect of the mineralization and hydration on the mechanical behavior of bone, our results are not limited to tissue engineering applications. From a materials science standpoint, our research may represent a contribution to the development of a larger class of bioinspired/biomimetic bone-like materials for impact loading, fatigue, prosthetics, and acoustic applications.
This work has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement COLLHEAR No 794614.

Nature abounds with examples of living beings that can change their morphologies in complex ways to rapidly adapt to changing environmental conditions. Soft actuators able to generate programmable and reconfigurable shapes will enable the development of dynamic and adaptive systems. Simultaneously having both reconfigurability and high holding forces is a central challenge.
We report here a model and its experimental validation for a programmable soft material sheet that allows both dynamic control of shape and zero-power shape locking. The multimorph soft actuator combines the deformation mechanism of dielectric elastomers actuators (DEAs) with the multistability of heat-activated shape memory polymers (SMPs). Stretchable heaters are integrated to spatially tune the stiffness of SMP fibers. Spatial and temporal stiffness modulation allows us to actively define temporary soft axes. By controlling the location and the orientation of these axes, we use a single DEA covering the entire sheet to reach many distinct deformations. The shape can be fixed by cooling down the heated fibers when the target deformation is reached. This approach has potential to bridge the gap between soft and conventional robotics by offering both soft actuation state and load-bearing latched state.
The actuator sheets have an active area of 28 mm x 28 mm with a total thickness of less than 750 µm. Two SMP layers in a grid pattern are bonded to the stack of the DEA and the heaters. Two sets of three heater arrays are aligned in different directions, allowing spatially varying temperature distribution. The six heaters reduce the Young’s modulus of SMP segments by 250 times. By dynamically addressing a combination or a time sequence of these heaters, complex and different shape deformations are achieved upon DEA actuation. We previously demonstrated that this technique can be implemented in DEA grippers to augment their grasping ability to pick and place objects with different shapes that are not possible with a single shape transformation.[1]
The actuator sheets consist of several layers (up to 11 layers include including one or two DEA layers, SMP grids, heaters, and electrical and thermal insulator layers). This requires a carefully optimization of the design parameters to reach both large actuation deformation and high load-bearing capacity: thick SMP layers enable high blocking forces thanks to high stiffness in the glassy state, however they limit the deformation due to the non-zero stiffness in the rubbery state. We report here an analytical model that provides insights into the role of SMP thickness and as well as other design parameters on the device performance, e.g. the location of the DEA and the order of passive layers. The model couples the Maxwell pressure from a dielectric elastomer, beam deflection, and thermo-mechanical modeling of different materials. It accurately predicts the quasi-static behavior of the devices at different states of the actuator and the predictions agree well with the experimental results. The actuator sheet designed based on the model output can achieve a bending deflection of over 300° and can hold a force greater than 25 mN. It can be easily adapted to different scenarios where specific displacement and blocking force are needed.
This approach to shape-programmable sheets does not require joints or additional latching mechanisms, it can be easily integrated into a range of biomimetic soft robotics or wearable robotic applications.
[1] B. Aksoy and H. Shea, Advanced Functional Materials, 2020.

Nature has engineered biological materials with remarkable mechanical properties, including stiffness, toughness, and self-healing properties. Transition metal coordination chemistry is an important component of proteinaceous materials that can impart such properties. Unlike conventional covalent bonds, metal coordination bonds are kinetically labile and tunable, enabling access to a wide range of dynamic mechanical properties. As such, coordination complexes have generated interest as a biomimetic strategy for engineering the mechanics of bioinspired artificial materials. For instance, Zn(II) metal-coordinated cross-linking is responsible for the high stiffness of the Nereis marine worm jaw (10-20 GPa), which is comparable to that of biomineralized materials. Interestingly, Zn(II) metal ion coordination can also play a structural and mechanical role in the assembly and aggregation of amyloid proteins. Natural amyloid peptides have the intrinsic capacity to self-assemble and form extraordinary fibrillar nanostructures rich in β-sheets with elastic moduli as high as 10-30 GPa. This aggregation has received much attention due to its pathological role in neurodegenerative disease, such as Alzheimer’s Disease (AD). Given the remarkably high concentrations of Zn(II) (up to millimolar range) in the plaques of AD brains, experimental studies have sought to understand the effect of Zn(II) on amyloid-β peptide aggregation; however, this still remains poorly understood.

This study aims to contribute to a mechanistic, molecular-level understanding of the role Zn(II) plays in the mechanics and assembly of structural proteins, such as Nereis virens jaw protein (Nvjp-1) and amyloid-β (Aβ). Computational tools present a useful strategy to achieve this molecular-level understanding. Molecular dynamics simulation techniques, including replica exchange molecular dynamics (REMD) and steered molecular dynamics (SMD), are employed to study the concentration-dependent effect of Zn(II) metal ion coordination on the conformational free energy landscape and mechanical stability of these structural proteins. Through the comparison of structure-property relationships in Nvjp-1 and Aβ, this work has the potential to inform the design and engineering of transition metal coordination complexes in bioinspired nanomaterials.

The quest for improving mechanical properties of synthetic materials has been, unexpectedly, bolstered by the structure and organization of natural materials such as animal shells, bone, silk, etc. Among this class of biomaterials, the mollusk shell, also called as nacre has proved to be a fascinating material with superior toughness. Though the bulk (95%) of nacre is made up of the hard but brittle crystalline aragonite phase, the hierarchical “brick-and-mortar” nature of the microstructure of nacre held together by organic fillers is thought to be responsible for these superior properties.

Atomistic simulations on nacre-inspired materials have predominantly focused on expressing the inorganic and organic components via high-fidelity force fields that are computationally expensive and have limited scope for detailed structure-property elucidation. Here, we employ large-scale atomistic coarse-grained simulations of nacre-inspired microstructures, made up of crystalline grains that are held together by polymer chains. We show that coarse graining allows us to study the effect of several properties such as microstructure (grain morphology and size), polymer-crystal interactions and the effect of grafting. We explore tensile, compressive and viscoelastic behavior of these composites along with elucidation of nanoscale mechanisms. While being able to capture mechanisms for mechanical behavior reported in the literature qualitatively (such as the saw-tooth behavior in stress-strain curve under tensile loading), we show that our coarse grained models offer a promising alternative for efficient structure-property studies for design of novel biomimetic architectures.

3D mesostructures represent essential, ubiquitous design features in biology, from the spherical constructs of living organoids to the aerodynamic shapes of swirling maple seeds. This talk presents our work in two corresponding areas of 3D materials engineering. The first focuses on mechanically compliant, 3D multifunctional neural interfaces to cortical spheroids and assembloids. Detailed studies of the spreading of coordinated bursting events and the cascades associated neuroregeneration represent two of the many opportunities in neuroscience research uniquely enabled by these platforms. The second area is in exploratory 3D materials architectures that mimic the aerodynamic features of gliding, spinning and twirling seeds that facilitate their dispersal. The talk will emphasis both basic and applied aspects of these two distinct classes of materials systems.

A small number of animals have the ability to actively change their visual appearance to perform important biological tasks. Cephalopods rank high on this list due to their ability to rapidly change color and texture - in some cases - for defense and signaling and have been a source of inspiration for the design of next generation adaptive systems. Recently, the electrochemical properties of the primary pigment found in cephalopod skin, xanthommatin, have been harnessed and applied in color-switching electrochromic displays with low power requirements. We describe the translation of this technology into a compact form factor that can sense and measure color from the environment then activate spatially patterned coloration with rapid (ca. seconds) response times. Our device uses reflectance-based sensors to measure color then triggers the formation of hue matched patterns by arrayed display components that can match and/or “hide” on surfaces of varying geometry, color, and luminous intensity. In future iterations of our approach, these principles may be applied to expand the palette of measured and displayed colors or to construct soft, deformable systems that can alter their optical signatures in response to environmental cues.

The most brilliant colours in nature are obtained by structuring transparent materials on the scale of the wavelength of visible light. By controlling/designing the dimensions of such nanostructures, it is possible to achieve extremely intense colourations over the entire visible spectrum without using pigments or colourants. Colour obtained through a structure, namely structural colour, is widespread in the animal and plant kingdom [1]. Such natural photonic nanostructures are generally synthesised in ambient conditions using a limited range of biopolymers.
In this seminar, I will review our recent advances to fabricate bio-mimetic photonic structures with cellulose and chitin and I will give examples of how to fabricate novel photonic materials based on chiral nematic architectures using low-cost polymers in ambient conditions [2-7].
[1] Kinoshita, S. et al. (2008). Physics of structural colours. Rep. Prog. Phys. 71(7), 076401.
[2] Narkevicius A, et al. (2019). Controlling the Self-Assembly Behavior of Aqueous Chitin Nanocrystal Suspensions, Biomacromolecules 20, 2830
[3] Chan C. L. et. al. (2019) Visual Appearance of Chiral Nematic Cellulose-Based Photonic Films: Angular and Polarization Independent Color Response with a Twist, Adv Mater 31, 1905151
[4] Frka-Petesic et al. (2019) Angular optical response of cellulose nanocrystal films explained by the distortion of the arrested suspension upon drying. Physical Review Materials 3, 045601
[5] Parker R. et al. (2018) The Self-Assembly of Cellulose Nanocrystals: Hierarchical Design of Visual Appearance. Adv Mat 30, 1704477
[6] Parker R. et al. (2016). Hierarchical Self-Assembly of Cellulose Nanocrystals in a Confined Geometry. ACS Nano, 10 (9), 8443–8449
[7] Liang H-L. et al. (2018). Roll-to-roll fabrication of touch-responsive cellulose photonic laminates, Nat Com 9, 4632

The soft and hard materials that make up biological systems are a great source of inspiration in materials science for design of functional systems, particularly those that are critical in supporting the most intelligent processes in the plantea and animalia kingdoms. Great ideas from these systems include, the notion of self-assembly and reversible formation of structures, creating adaptive behaviors for specific environments, materials with capacity for self-repair, the engineering of autonomous motion, and the integration of multiple functions in a single structure, among many others. In this lecture bio-inspired synthetic systems are described based on supramolecular polymers as well as “hybrid bonding polymers (HBPs), which we define as materials that rationally integrate covalent and supramolecular polymers. HBPs are biomimetic structures critical in systems such as biological membranes, muscles, tendons, and the cytoskeleton. One of the systems to be described is based on supramolecular polymers that are highly dynamic and therefore strongly effective at signaling cells for regeneration. The lecture will also describe photosynthetic materials, inspired by leaves, in which HBPs are used to couple light harvesting assemblies and catalysts to make fuels. Finally robotic materials that emulate living creatures will be discussed in which HBPs or organic-metal hybrid hydrogels are configured to respond to light and magnetic fields in order to generate locomotion of macroscopic objects on surfaces.

Recent advances of biomaterials research have shown that biopolymers can be served as versatile materials in a variety of applications including structural, and electronics. Melanins are the broad class of biopolymers that can be found from many types of living organisms, including bacteria, fungi, plants, and animals. When melanin is extracted from different natural sources, or even synthesized in vitro, variability in the resulting macromolecular structures leads to different properties. There have been many studies that focus on the melanin isolated from the cuttlefish Sepia officinalis ink (SepiaMel) or synthetic melanin (SynMel). However, the properties of melanins sourced from dark-color fibers of mammalian fur are less studied, comparatively. Herein, we isolate melanins from dark-color horse fibers (EquusMel) using the acid hydrolysis method to investigate its structural and functional properties. Electron microscopy and X-ray scattering studies showed that EquusMel has a homogeneous elliptical shape in a sub-micron scale while SepiaMel exhibits a spherical nanostructure. EquusMel consists of chemical functionalities of pendant catechols and secondary amines that are similar to SepiaMel and SynMel. We hypothesized that well-ordered microstructure with chemical functionality of EquusMel can facilitate the generation of reactive oxygen species (ROS) within the hydrated condition. The antibacterial activity of melanins was tested against Escherichia coli. Our results reveal that EquusMel has considerable antibacterial activity due to its generation of ROS. After a four-hour incubation with E. coli, the bactericidal activity rate of EquusMel was 6.87%, 69.06%, 98.12%, and 100% at melanin concentrations of 2.5 mg/ml, 5 mg/ml, 20 mg/ml, and 150 mg/ml, respectively. Measurable levels of H₂O₂ were detected in all samples, indicating the potential of EquusMel to generate ROS, which can damage bacterial cells. Facile extraction of melanins and their unique antibacterial property would make this biomaterial an ideal candidate for use as an antibacterial agent to mitigate bacteria colonization and biofilm formation. Potential applications in food packaging, filtration membranes, and medical device surfaces should be further explored.

Halide perovskites (HPs) have recently experienced unprecedented development as outstanding materials for optoelectronic applications. Because HPs are water soluble, they have been synthesized using organic solvents and ligands (mainly toxic solvents and materials), and thus, the aqueous synthesis routes and biological applications have been hardly considered. Nonetheless, preliminary studies demonstrate stabilization of HP nanocrystals in aqueous buffers by balancing solubility equilibrium. Here, we report the implementation of a sustainable and environmentally friendly aqueous synthesis, using biomaterials (proteins, natural biomolecules, etc.) as nucleation templates to produce novel HPs morphologies. Via this biomineralization approach, electrostatic forces together with hydrogen bindings contribute to interactions between inorganic crystals and bio-templates over multiple length scales, and the bio-templates act as biological scaffolds to assemble hierarchical structures. In thisstrategy, first, we form metal carbonates (MCO3, M = Ca, Ba) using different bio-templates with desirable nano- and microstructures. Second, we apply ion exchange reactions to introduce appropriate cations and halide groups to from the HPs while the original morphology is preserved. Consequently, we can engineer the structure of the HPs at the nano- and microscale to acquire a variety of complex structures that would be hardly attainable via other methods. In addition, working in aqueous media has the potential to improve the biocompatibility of HPs synthesis process, paving the way towards greener synthesis approach.

A comprehensive understanding of nature’s strategies to manipulate light spectrally and spatially, gained through the ongoing efforts in the field of biological optics and photonics has repeatedly provided opportunities for the design of bio-inspired dynamic optical materials with utility in specific applications. Here, we demonstrate how insights into the optical mechanisms and structural designs underlying the wing coloration of the Papilio blumei butterfly have informed the conception of a novel light management strategy that enables dark field imaging of low-contrast biological specimen. We simplify and downsize dark-field microscopy equipment by generating the high-angle illumination cone required for dark-field microscopy directly with a luminescent photonic substrate that relies on a structural design informed by the photonic structures found on P. blumei’s wing scales. The surfaces’ light-emitting micro- and nanoscale components provide a controlled angular emission profile. We demonstrate the ability of these hierarchically structured luminescent surfaces to generate high-contrast dark-field images of micrometer-sized living organisms using standard optical microscopy equipment. This new type of substrate forms the basis for miniaturized lab-on-chip dark-field imaging devices that are compatible with simple and compact light microscopes.

Biominerals possess superior mechanical properties relatively to their synthetic counterparts. This, among else, is due to internal stresses induced by incorporation of organic molecules. Similarly, inorganic hosts, such as CaCO₃^, ZnO and Cu₂O can synthetically incorporate single amino acids. This incorporation induces lattice strains and morphology changes, along with changes in the mechanical and optical properties of the host.
In this work, we wanted to expand our knowledge regarding this phenomenon to a more complicated non-oxide system: the hybrid organic-inorganic perovskite methylammonium lead bromide (MAPbBr₃). Hybrid lead halide perovskites have demonstrated exceptionally high performance as the active materials in opto-electronic applications (i.e. photovoltaics, photodetectors and light emitting diodes). Their major set-back is their poor stability under ambient conditions, especially due to decomposition under humidity, which hinders their commercialization.
We grew MAPbBr₃ in the presence of all 20 common amino acids, in two growth routes: fast growth (low temperature), and slow growth (high temperature). We noticed that Lysine (Lys), possessing two NH₃⁺ groups (similar to the MA⁺ cations), is incorporated in a significant higher extant than all the others amino acids. We used high-resolution powder X-ray diffraction, together with in-situ cooling, to measure the lattice parameter of MAPbBr₃ grown with different amounts of Lys. Both lattice parameter and thermal expansion coefficient demonstrated a significant decrease with the increase of the amount of incorporated Lys. This decrease, along with the observed changes in the cubic-to-tetragonal phase transition temperature of the perovskite, suggest that Lys acts as a "molecular bridge", holding the crystal together. While all the Lys-containing samples showed an increase in the optical band gap, a drastic difference between slow and fast grown samples was observed. This difference can be attributed to the difference in incorporation mechanisms between the two growth routes. Moreover, electrochemical measurements of the perovskite dissolution kinetics revealed noticeable changes in the dissolution rate constants of MAPbBr₃ with and without incorporated Lys molecules. Specifically, when grown in high temperature (i.e. slow growth), MAPbBr₃ dissolution rate decreased in ~40% due to Lys incorporation.

Natural organisms hold mastery over designing intricate structures in various length scales that exhibits remarkable mechanical properties, one such ingenious biomineral structure is nacre’s brick and mortar like structure. In light of the demand for mechanically robust synthetic material, researchers have amply studied nacre. Here, we present an extensive exploit on nacre’s structural features employing a machine learning model to predict composite design with high strength and toughness often mutually exclusive in artificial materials, over a large design space of 3.6*10¹⁰ including 320 topologies. The predicted models show multi-stage gracious failure with two major peaks in the tensile stress-strain curve, which are distinct from conventional brittle, ductile, or tough type deformation curves. The design guideline extracted from the predicted models is adapted to fabricate nacre inspired composites using a multi-material 3D printer. In addition to the composite with a rectangular tablet, an interlocking tablet design inspired by geometrically interlocking suture of the diatom is also synthesized. We report previously unseen and tunable work hardening phenomena and subsequent failure mechanisms in nacre inspired composites leading to the magnification of mechanical properties. Toughening mechanisms like crack reorientation during multi-stages failure under normal and shear stress, plastic deformation of soft phase, sliding and the interlocking of tablets and elastic deformation of the hard phase are elucidated by comparing experimental and simulation results. Interlocked tablet composites outperform the rectangular tablet composite in all regards, simulation results reveal that the geometry of interlocked tablets promotes higher normal stress concentrations on the tablets before the stress flow to the soft interfaces leading to higher load-bearing capacity, delay of crack initiation, and gracious propagation which amplifies the overall mechanical properties reasonably. These novel observations provide significant new insights into developing synthetic composites with superior mechanical properties.

Despite the wide variety of aquatic species on our planet, the microscopic architecture of gills in fish remains largely self-consistent, suggesting an evolutionary optimization [1]. These organs, used predominantly as gas exchange interfaces against an external, parallel-flowing aqueous solution, are used as inspiration for the design of a hierarchical electrochemical reactor. Leveraging insights from a new method for comparing porous electrodes used in redox flow batteries [2], this work explores the physical and electrochemical properties pertinent to enhancing the performance of these bio-inspired structures. Inspired by the high fidelity of the single-pass oxygen uptake inherent to ram ventilation in continuously moving fish, we explore the opportunities and limitations for high, single-pass electrochemical conversion. A computational model will be presented, applying these design principles to a liquid-fed CO₂ utilization system. The ohmic, kinetic, viscous, and mass transport loss limitations across a range of gill-like architectures and operating conditions will be discussed. This work provides a framework for applying bioinspired gas-exchange architectures to enhance the performance of electrochemical systems including flow batteries and CO₂ reactors for efficient energy conversion.

[1] Park, Keunhwan; Kim, Wonjung; Kim, Ho-Young. “Optimal lamellar arrangement in fish gills.” PNAS 111 (22) 8067-8070 (2017).
[2] Wong, Andrew A.; Aziz, Michael J. “Method for Comparing Porous Carbon Electrode Performance in Redox Flow Batteries.” (under review).

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Diatoms are a large class of single cell microalgae combining photosynthetic activity with production of mesoporous biomineralized silica shells, called frustules [1]. Frustules exhibit features such as high surface area, transparency, mechanical resistance and periodic porosity, that make them appealing biomaterials for applications in photonics, sensing, optoelectronics and biomedicine [2]. Furthermore, in vivo and in vitro protocols enable frustules silica modification with functional molecules or nanoparticles. We have recently demonstrated that in vivo incorporation of organic [3] and organometallic emitters, such as iridium complexes [4], into Coscinodiscus spp. frustules represents a promising biotechnological route to biohybrid luminescent silica-based materials, whose properties result from the combination of the frustule nanostructures with the photoluminescence of incorporated molecules. We have also recently demonstrated that Phaeodactylum tricornutum diatom cells self-populate and propagate on transparent conductive ITO electrodes, either in the presence or in the absence of biochemical activators of adhesion. Our results demonstrate the suitability of diatoms as self-adherent microalgae capable of photocurrent production under eco-friendly conditions, paving the way to the development of a new generation of living photosynthetic organisms-based devices for optoelectronic applications.

[1] ] R. Ragni, S. R. Cicco, D. Vona, G. M. Farinola, in Green Materials for Electronics (Eds: M. Irimia-Valdu, E.D. Glowacky, N.S. Sariciftci, S. Bauer), Wiley-VCH, Germany 2017, 287.
[2] R. Ragni, S. R. Cicco, D. Vona and G. M. Farinola, Adv. Mater., 1704289, 1-23 (2017).
[3] 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).
[4] 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).

In the fabrication processes of photonic crystals, structural disorder arises in the synthesised structures from the limitations in the resolution of the synthesis processes. Such undesired disorder affects the optical properties of the fabricated photonic crystals. It must often be taken into account. Elucidating the influence of structural disorder helps reducing its optical effects and allows using it in technological applications.
Photonic structures found in the integuments of insects are interesting examples to investigate since they are known to be very tolerant of and resilient to structural or material defects and imperfections. The benefit and cost of these defects have not been so far comprehensively assessed.
In this contribution, we investigated the extent of structural disorder in Bragg mirrors occurring on the wings of beetles [1]. Some beetles exhibit indeed shiny iridescent colours ranging from violet to red thanks to such photonic structures. Due to structural disorder, variations in the optical response can be observed by optical microscopy. Using electron micrographs, we analysed the disorder in these photonic structures. We related this disorder to the optical properties, thanks to microspectrophotometric measurements of reflected light. We performed optical simulations for typical Bragg mirrors occurring in beetle wings. It allowed to assess the optical benefit and cost of structural disorder. This analysis showed that the optical response of natural Bragg mirrors in beetle wings is very resilient to disorder.

[1] J. A. Noyes, P. Vukusic, I. R. Hooper, Experimental method for reliably establishing the refractive index of buprestid beetle exocuticle, Optics Express 15, 2007.

Organic macromolecules are a key ingredient in the formation of biogenic crystals. One example of biominerals formed in the presence of organic macromolecules is calcite scales, or coccoliths, created intracellularly by marine microalgae. Organic components associated with coccoliths can be divided into two groups, soluble coccolith-associated acidic polysaccharides (CAPs), and an insoluble organic plate-like structure called a base plate. Previous in vitro work has shown that these components cooperate to bind and localize calcium ions as a dense phase around the base plate, where calcite eventually crystallizes. However, the function and composition of this dense interphase in calcite nucleation in coccoliths is unknown.
To further our understanding of the role of this dense Ca-rich interphase in calcite nucleation, we sought out a synthetic compound able to mimic the function of the biogenic macromolecules in vitro. Using scanning electron microscopy and dynamic light scattering, we have identified a polymer, poly(acrylic co-maleic acid), able to reproduce the particulate morphology of the CAP-calcium precipitates on the base plate. We also discovered that the precipitation of calcium with this polymer on the base plate commences at concentrations below the saturation point of calcium and polymer in solution. Thus, the base plate functions as a nucleator, engendering a chemical environment distinct from the bulk solution.
Current experiments focus on nucleating calcite within the dense polymer-calcium phase on the base plate. Preliminary observations show precipitation of elongated calcium carbonate crystals growing from the base plate rim. We aim to identify the mechanism by which the organic components determine how living cells control calcite crystallization.

Hydroxypropyl cellulose (HPC) is a cellulose derivative that combines the biocompatibility and edibility of cellulose and the processability of a water-soluble polymer. Therefore, it has found large industrial applications from coatings in pharmaceutical products to binder or thickening agent in food applications. Recently, HPC has also become a very attractive material for photonic applications due to its capability of forming a lyotropic chiral nematic liquid crystal phase in aqueous solution, which is responsible for a metallic and iridescent colour response. As a direct result of the chiral nematic phase, HPC, in fact, is capable of reflecting right–handed circular polarized light with specific colours and such colouration is usually strongly dependent of the direction of observation.

Here, we present a crosslinking method which allows us to drastically alter the visual appearance and photonic properties of HPC, in terms of both angular and polarisation response. Specifically, we demonstrate that it is possible to achieve an angular independent colour reflection as well as a strong reflection of light with both handedness.

Our method not only allows us to preserve the photonic response of HPC in the absence of solvent, but highlights an approach to, using the same system, completely redesign the visual appearance of the material from iridescent and metallic to matte. With such control of appearance, we therefore demonstrate the potential of HPC as a biocompatible, biosourced photonic material that can replace traditional pigment and dyes.

Eggshell is crucial for the reproduction and development of birds. The optical properties of the shells have an impact on biological functions such as heat and UV protection, recognition by the parents and camouflage. Whereas ultraviolet reflection by bird eggshells has been superficially described in the scientific literature [1,2], the physical origin of this phenomenon has remained poorly understood so far. In this contribution, macropores have been morphologically characterised by electron microscopy and mercury intrusion porosimetry in the eggshells of several breeds of domestic hens (Gallus gallus domesticus), one breed of duck and one breed of quail. They are located in the so-called “calcified shell” part of the eggshells (namely, at depths ranging from ca. 20 µm and ca. 240 µm from the shell outer surface). Two reflectance peaks (ca. 20-50%) were observed in the near UV range by spectrophotometric measurements from these eggshells. Progressively thinning down the cuticle of eggshells with ethylenediaminetetraacetic acid (EDTA) solutions allowed us to show that the so-called calcified shell is an efficient UV scattering structure whereas the cuticle partly absorbs UV radiation. Thanks to modelling relying on Mie scattering theory and an effective approach accounting for multiple scattering, we found the observed macropores were most likely giving rise to these peaks through Mie backscattering [3]. This optical response was discussed in terms of the visual sensation of chickens and human beings. Eggs displaying an achromatic visual appearance for humans appear chromatic for chickens. Fluorescence emission from the eggshells was measured and attributed to molecules of biliverdin IXα and protoporphyrin IX embedded within the shell. This emission is rather low in terms of quantum efficiencies and probably does not play any role in the visual appearance of the eggshells. In addition, electron microscopy imaging revealed the presence of pores within the so-called “calcified shell” part (i.e., between ca. 20 µm and ca. 240 µm deep from the outer surface). The average radii of these pores range from 120 to 160 nm, depending on the egg varieties. Mercury intrusion porosimetry allowed to highlight a distribution of pore radii around 175 nm. Spectral measurements of excitation and emission by fluorescence revealed the presence of fluorophores embedded in the shells. In addition, numerical and analytical predictions using scattering theory indicate that these pores are responsible for the optical response observed in the UV range. Due to the similarities between the pore size distributions observed among the eggshells of the investigated poultry eggshells, we expect Mie backscattering to be at the origin of the UV response from the eggshells of many other bird species.

[1] D. C. Fecheyr-Lippens, B. Igic, L. D’Alba, D. Hanley, A. Verdes, M. Holford, G. I. N. Waterhouse, T. Grim, M. E. Hauber and M. D. Shawkey, The cuticle modulates ultraviolet reflectance of avian eggshells, Biology Open, 2015, 4, 753-759.
[2] B. Igic, D. Fecheyr-Lippens, M. Xiao, A. Chan, D. Hanley, P. R. L. Brennan, T. Grim, G. I. N. Waterhouse, M. E. Hauber and M. D. Shawkey, A nanostructural basis for gloss of avian eggshells, J. R. Soc. Interface, 2015, 12, 20141210
[3] M. Ladouce, T. Barakat, B.-L. Su, O. Deparis and S. R. Mouchet, Scattering of ultraviolet light by avian eggshells, Faraday Discussions, 2020, accepted.

Biological structures perform a variety of complex functions with a limited material set. One particularly exciting area of bio-inspired research is structural color, though present synthetic analogs are still limited, either by fabrication challenges or an incomplete understanding of structure-property relationships. Structural color not only provides a fascinating case study for exploring the role of material design on macroscale properties, but can provide insights on animal evolution, photonic devices, human and animal communication, signalling, and art. While this is a lively and active area of research, we are still finding the balance between what is physically possible and easy to fabricate and understanding the full extent of the color gamut that we can access. As replicating natural structurally-colored designs can be challenging and costly, we instead explore methods for generating structures inspired by nature to create desired effects, while proposing surface designs that are physically producible with rapid prototyping. Interaction of light with Morpho butterfly structures is used as a starting point to determine key parameters and these principles are applied towards our simulations and designs. Methodologies for combined design, simulation, and material fabrication to generate colors through new structural surfaces are implemented. A computational inverse design methodology has been developed for the formulation of nanostructures exhibiting structural coloration, and opportunities for scalability are identified. A simple model based on scalar diffraction theory is used for the relationship between structural elements and optical response, where altering the surface changes the visible functionality. Through the use of larger scale optimization based on tiled repeat units and motifs, large scale arrays, displays, sensors, and art can be achieved. Simulated surfaces are then fabricated using two-photon polymerization, and optically characterized. We compare our simulations to fabricated structures using optical microscopy, scanning electron microscopy, and angular spectrometry to quantify reflected color and angular response. Through these methods, we contribute to an understanding of a) the limitations of this approach, b) the extent of the parameter or design space, c) the feasibility of this inverse design approach, and c) the limitations imposed by fabrication restrictions. By exploring different levers for production of structural color, the boundaries of our ability to mimic and expand upon natural color production are illuminated. This work provides an additional perspective on bio-inspired materials design with applications ranging from light harvesting and steering, to chemical sensing, high performance displays, responsive products and architecture. The limitations and trade-offs of our approach as it relates to scale-up and industrial use are discussed.

Electronic material properties are conventionally considered the domain of man-made materials and devices, but electronically conductive materials are also synthesized by some organisms as part of their native metabolic pathways. These biological conductors lack many of the structural characteristics typical of inorganic and organic conductors or semiconductors, and therefore represent an exciting new opportunity to study electron transport at the nexus of physics, chemistry, and biology. Well-studied microbes in oxygen-free environments, such as aquatic sediment, respire anaerobically by accessing alternative extracellular oxidants. This class of microbes displays a variety of mechanisms to shuttle spent electrons from inside the cell to remote electron acceptors. Some anaerobic bacteria, such as Geobacter sulfurreducens, synthesize protein supramolecular assemblies that exhibit inherent electronic conductivity and are key to their respiratory metabolism. Based on fundamental differences between the protein building blocks of these assemblies and the canonical building blocks of inorganic and organic conductors and semiconductors, it is clear that Nature has developed unique design principles for long-range electronic conductivity in amino acid materials. The biomolecular identity and supramolecular order underpinning biological conductive materials are poorly understood, as are the mechanisms by which these structures support electron transport. This talk will cover our ongoing work in the characterization of structure-function relationships in conductive protein and peptide materials. These efforts establish distinctive biomolecular design principles for long-range electron transport in self-assembling de novo peptide nanofibers, engineered biological materials, and native bacterial appendages. Such materials serve as an experimental platform to understand long-range charge transport in biological materials in general, and as promising technological platforms for bioelectronic interfaces.

Blood clots are an active biomaterial in which anucleate cells, called platelets, can extend micrometer-long filopodia to impose contractile forces on the fibrin scaffold that lead to drastic macroscopic changes in clot volume and elastic modulus. Blood clots are involved in physiologic and pathologic processes, such as wound healing, fibrosis, and musculoskeletal contractures. We use experiments and mesoscale modeling to examine the biophysics of clot contraction by directly linking the microscale platelet movements to macroscale biomaterial properties and behavior. We find that the clot contraction is optimized through the intrinsic heterogeneity of platelets. When platelets within the clot are exposed to thrombin, they do not contract simultaneously as one can be expected, but rather contract over time at a sequential manner. We show that this temporal heterogeneity of platelets leads to emergent behaviors that significantly enhance the biomaterial volumetric contraction. We rationalize this surprising effect by the ability of heterogeneous platelets interact with fibers that are initially located out of their influence range. We show that only by accounting for platelet the cellular heterogeneity we are able to replicate the experimentally measured clot forces. This points to the importance of examining biomaterials as a 4D (space + time) system in which natural cellular heterogeneity can be harnessed to enhance the mechanical efficiency. Furthermore, our results suggest a new direction of developing synthetic and hybrid stimuli-responsive composites in which engineered heterogeneity can serve to enrich the mechanical responses and shape transformations.

The blue coloration in nature is mainly of non-pigmentary origin [1] and is known as Rayleigh or Tundall blue. This non-pigmentary or structural blue coloration is, for example, the blue color of the sky and mountains in the distance, the blue color of human or animal eyes, the blue color of feathers of some birds like cotinga maynama, a turquoise bird of Peru and Ecuador, for instance. The origin of this non-iridescence blue color is attributed to the constructive interference of scattered light from quasi-amorphous structures of self-assembly of mono-dispersed particles, typically closely packed air cavities in b-keratin for eyes or plum. Reproducing the phenomenon in thin film materials requires nanoparticles randomly dispersed in a transparent layer deposited on a highly absorbent dark film. The refractive index between the particles and the matrix must be different, thus pores containing air or contrary particles of high refractive index could be used. In our research work, the original idea to produce this coloration has originated from an encounter with a contemporary artist who intuitively realized for the first time this blue color from crushed white chalk, colorless oil and viscous black mineral peas collected in a natural resurgence. The using tools are only brushes, a mortar and a marble table to manually grind the materials. A collaboration with our scientific research laboratories made it possible to identify the optical phenomenon involved and to find a robust protocol to create this blue color in a reproducible and intense way, keeping the materials and the artist's tools and by optimizing the gestures [2]. The intensity of the produced blue color highlights the potentialities of using this coloring with simple materials and technologies for ecological and environmentally friendly coloring applications. Beyond this important issue, the intensity of this blue color has led to a discussion among the history of art, and the possibility that the ancient masters used this non-pigmentary blue coloring in their famous paintings at a time when the blue color was a major economic issue, before the advent of chemistry and the discovery of synthetic pigments and coloring [2]. Some ancient manuscripts mention it but, on the works it is not yet proven, knowing that this blue color is very fragile as it is very much linked to the architecture of the material and therefore very sensitive to ageing.

1 Andrew R Parker, Review, Phil.Trans. R. Soc. (2009) 364, 1759-1782
2 A. Goyer & al, Arts et Science Journal, 2019, 19, 3

Natural structures made of silk fibroins, such as cocoons and spider webs, have inspired researchers to utilize their mechanical properties and biocompatibility for various engineering applications. Recently, silk fibroins extracted from Bombyx mori silkworm cocoons have emerged as promising technical materials for food contact applications due to their non-toxic and edible nature, in addition to their tunable mechanical and chemical properties. Here, by leveraging water-based processing of Bombyx mori silk fibroin, we build a porous silk microneedle platform for the detection of bacteria in food. The microneedles can transport internal food fluid by capillary action to a colorimetric sensor on the backside of the array. We demonstrate detection of food contamination within 16h after injection of E. coli in fish fillets, by color-change of a polydiacetylene-based sensor printed onto the backside of the microneedle array. This response by E. coli contamination can be distinct from common food spoilage measured via an increase in sample pH. We also show that the microneedle sensor can pierce commercial food packaging, indicating the feasibility of successful adaptation of the technology downstream in current food supply chains. The platform developed in this study can contribute to food quality monitoring, which is critical to global food safety and to minimizing food loss and waste.

It is well-acknowledged that nature uses ordered nanostructures to generate vivid iridescent color such as opals. To mimic such structures, colloidal particles are widely used, due to their uniform and tunable sizes, to form colloidal crystals of densest closed-packed structure in bulk. Recent discoveries in butterfly scales reveal the role of isolated finite-size crystallites as building blocks for their hierarchical structure. In this contribution, we present discrete colloidal clusters fabricated from self-assembly of colloidal particles encapsulated in emulsion droplets. Unusual equilibrium crystal structures with icosahedral, decahedral or fcc symmetry arise from the spherical droplet confinement. Combining simulations and electron tomography, we show that these colloidal clusters are in energy minima when the number of particles satisfies certain rules, leading to a “magic number” effect previously known only at subatomic and atomic length scale. We analyse their unique structural color resulting from the complex cluster structures, which can be used to monitor cluster rotation and colloid crystallization in spherical confinement in real-time. At last, we give examples of hierarchical structural design using colloidal clusters.

Neurons generate electrical signals in response to chemical stimuli by altering the selective permeability of their membranes in the presence of an electrolyte gradient. After some integration, these signals move quickly along the length of the neuron before triggering a downstream chemical signal. Nervous systems, which are complex assemblies of these chemo-electro-chemical signaling units, are capable of guiding the autonomous function of animals.

Inspired by the architecture and biophysics of neurons, we present a hydrogel/organogel/hydrogel trilayer scheme capable of generating electrical potentials from chemical and optical signals. Energy is stored in an electrolyte gradient between the two aqueous compartments. Triggering the selective permeabilization of the initially insulating organogel membrane using stimuli-responsive chemistry causes a change in the electrical potential between the two aqueous domains on the order of 100 mV. We compare the spatial decrement of the signal along these membranes to the passive spread of an electrical potential in neurons. We further describe an electrochemical end effector intended to produce a chemical response spatially decoupled from the initial permeabilizing signal. We aim to interface this scheme with electrical detectors or network them to enable computation, feedback loops, or autonomous behavior.

Biominerals produced by living organisms have superior properties compared to their synthetic counterparts. Even though biominerals are formed at ambient conditions and from a limited variety of available building blocks, they possess remarkable structures and often combine desired qualities such as low weight and improved mechanical properties.
The coralline red algae secrete high-Mg calcite as a part of their skeleton, with Mg levels exceeding the thermodynamically stable one. They are highly prevalent around the world's oceans and contribute to reef ecology. The structure of these algae has not been widely studied previously and information on their nanostructure is largely missing.
In our attempt to gain a better understanding of nature's extraordinary designs, we study an articulated coralline red alga that resides in the shallow waters of the Mediterranean Sea. Because of its erect structure growing upright, this alga has to endure the great stresses applied to it by the sea waves. We explored its structure from the nano to the macroscale utilizing various state-of-the-art techniques such as synchrotron radiation nanotomography and high-resolution aberration-corrected TEM. We discovered that its structure is highly porous, with porosity levels reaching as high as 64 vol%. We showed that its structure is intricate and is hierarchical with several orders from the nano to the macroscale, formed by plate-like crystals with nanometric diameters. Surprisingly, we revealed its macrostructure is helical rather than cylindrical and proved that this configuration confers the alga great compliance, allowing it to be ~20% more compliant under compressive stress, as compared to a cylindrical structure with the same porosity.
The result is a sophisticated lightweight and compliant structure allowing the alga to sustain external stresses from its natural environment. This study can lead toward a better understanding of the structure-function relation of biomineralized structures, and the synthesis of lightweight structures with improved mechanical properties.

The most finely tuned, rapidly responsive, and precisely directed optical systems currently known can be found on the surfaces of living organisms. Studies of brittlestars’ tunable microlenses, sea sponges’ optical fibers, butterflies’ and beetles’ intense colors, and squids’ nearly perfect camouflage have revealed 3D architectures so intricately patterned down to the nanoscale that the topography itself controls the wavelengths and direction of reflected light. We are developing bioinspired, bottom-up self-assembly techniques that allow us to create comparably elaborate yet tunable hierarchical photonic structures, and integrate these into the design of a new class of dynamic, responsive optical materials.

Organisms construct 'devices' based on assemblies of organic nano-crystals with optical functions. The structure, polymorph, size, morphology and superstructural arrangement of the crystals determine the optical properties of the 'device'. All the crystals have unusually high refractive indexes in the directions along which the light penetrates the crystal. The controlled assembly of nano-crystals forms multilayer reflectors that create structural colors, or mirrors and light scattering layers that function to increase vision sensitivity in the eyes of the organisms. Scallops have tens of eyes, each containing a concave multi-layered mirror perfectly tiled with a mosaic of square guanine crystals, made up of composite twins, reflecting light to form images onto the overlying retinas [1]. Crustacean decapods such as shrimps, crayfish and lobsters possess compound eyes that contain two sets of mirrors, composed of isoxanthopterin crystals. The two mirrors have very different ultrastructures and functions that we can rationalize in terms of the optical performance of the eye [2,3]. The unusual zander fish eyes contain two layers of organic crystals: thin guanine crystals, form a reflective layer in the back of the eye, whereas block-shaped crystals of 7, 8-dihydroxanthopterin in the inner tapetum layer back-scatter light onto the retina, increasing the light sensitivity of the eye [4]. Finally, insects commonly known as jumping bristletails, form large amounts of xanthine crystals in their median and lateral ocelli [5]. The structure-function relations in this last example are still under investigation. In all these examples, the constituent molecules are mostly purines and pteridines, which raises the question of what molecular and structural characteristics of these crystals, favor their use for optical functions in organisms. Furthermore, the organization of the crystalline functional components is controlled from the crystal structure at the nanoscale to the complex 3D structure at the millimeter level, extending the interest in the relation between structure and optical properties to higher hierarchical levels.

[1] B.A. Palmer, G.J. Taylor, V. Brumfeld, D. Gur, M. Shemesh, N. Elad, A. Osherov, D. Oron, S. Weiner, L. Addadi: The Image Forming Mirror in the Eye of the Scallop. Science 358, 1172–1175 (2017).

[2] B.A. Palmer, A. Hirsch, V. Brumfeld, E.D. Aflalo, I. Pinkas, A. Sagi, S. Rozenne, D. Oron, L. Leiserowitz, L. Kronik, S. Weiner and L. Addadi: Isoxanthopterin: An Optically Functional Biogenic Crystal in the Eyes of Decapod Crustaceans. PNAS, 115, 10, 2299–2304 (2018).

[3] B.A. Palmer, V. J. Yallapragada, N. Schiffmann, E. Merary Wormser, N. Elad, E.D. Aflalo, A. Sagi, S. Weiner, L. Addadi, D. Oron: Highly Reflective Biogenic Materials from Core-Shell, Birefringent Nanospheres. Nature Nanotechnology 15, 138–144 (2020).

[4] G. Zhang, A. Hirsch, G. Shmul, L. Avram, N. Elad, V. Brumfeld, I. Pinkas, I. Feldman, R. Ben Asher, B. A. Palmer, L. Kronik, L. Leiserowitz, S. Weiner and L. Addadi: Guanine and 7, 8-dihydroxanthopterin reflecting crystals in the zander fish eye: crystal locations, compositions and structures, J Am Chem Soc 141, 19736−19745 (2019).

[5] A. Böhm and G. Pass: The ocelli of Archaeognatha (Hexapoda): functional morphology, pigment migration and chemical nature of the reflective tapetum, The Journal of Experimental Biology 19, 3039-3048 (2016).

Bone is both a tissue, comprising cells, vasculature and extracellular matrix, and a material comprising mainly mineral, collagen and water. It is thus a challenge to characterize bone’s 3D structural organization in order to gain insights into how bone forms and functions. Focused ion beam-scanning electron microscopy (FIB SEM) can provide information at nanometer resolution to enable, for instance the identification of the collagen D-banding. At this resolution the spatial arrangement of fibrils can be assessed in volumes of thousands of microns cubed which can include tissue components. For example, examination of mineralized osteonal pig bone shows unidirectional collagen arrays oriented alternatively in different directions or changing direction progressively. These unidirectional arrays are separated by layers of collagen organized in a bidirectional patchwork motif. Earlier studies of demineralized lamellar bone showed that the layers with the patchwork motif stain heavily with osmium and Alcian Blue and have a disordered appearance.
Another example is the cryo- FIB SEM examination after cryo-fixation and under cryo-conditions, of the mineralized murine growth plate. It reveals the presence of a complex zone that includes blood vessels with mineral containing vesicles, blood vessel extremities surrounded by bone mineralizing matrix, and cartilage hypertrophic cells surrounded by ordered and disordered cartilage mineralizing matrix.
By exploiting the options for examining mineralized bone, demineralized bone matrix and the soft tissue components as well as the bone, FIB SEM can provide invaluable insights into bone organization. By combining FIB SEM in a correlative manner with 3D confocal light microscopy and microCT, it will be possible to address many fundamental questions in bone biology and mechanics.
Reznikov, N., Shahar, R. and Weiner, S. 2014. Bone hierarchical structure in three dimensions. Acta Biomaterialia 10, 3815-3826.
Haimov, H., Shimoni, E., Brumfeld, V., Shemesh, M., Varsano, N., Addadi, L. and Weiner, S. 2020. Mineralization pathways in the active murine epiphyseal growth plate. Bone 130, https://doi.org/10.1016/j.bone.2019.115086.
Raguin, E., Rechav, K., Brumfeld, V., Shahar, R. and Weiner, S. 2020. Unique three-dimensional structure of a fish mandible bone subjected to unusually high mechanical loads. J. Structural Biol. (in press).

Biological extracellular tissues are based on proteins, polysaccharides and, in certain cases, minerals. Their complex multiscale structure confers them a wide range of properties in accordance with the tissues’ functions. While active functionality are usually attributed to cells, there are also examples of materials synthesized by living organisms, such as plant seeds, which fulfil an active function without living cells and work as mechanosensors and actuators. Water is an important component of all such extracellular tissues. While it is well known that the level of hydration determines the mechanical properties of many biological materials, it is less appreciated that water also plays an active role in generating forces within the materials. In particular water absorption and desorption provides actuation in a variety of plant seeds, including wild wheat, stone plant and banksia seed capsules. The shape change upon water uptake that provides the actuation is controlled by specific cellulose fibre architectures. In this way, well-controlled movements, such as bending, twisting or curling are programmed in these materials by structure of the underlying cellulose microarchitecture. The required deformation energy is provided by the absorption of water from the environment. Finally, the absorption of water to specific molecules and the resulting osmotic pressure is also providing internal stresses which control, for example, the mechanical behaviour of collagen in tendon, bone and dentin. The lecture will review general concepts for the roles of water in biological materials, both in the context of biology and of bioinspired engineering.

3D mesostructures represent essential, ubiquitous design features in biology, from the spherical constructs of living organoids to the aerodynamic shapes of swirling maple seeds. This talk presents our work in two corresponding areas of 3D materials engineering. The first focuses on mechanically compliant, 3D multifunctional neural interfaces to cortical spheroids and assembloids. Detailed studies of the spreading of coordinated bursting events and the cascades associated neuroregeneration represent two of the many opportunities in neuroscience research uniquely enabled by these platforms. The second area is in exploratory 3D materials architectures that mimic the aerodynamic features of gliding, spinning and twirling seeds that facilitate their dispersal. The talk will emphasis both basic and applied aspects of these two distinct classes of materials systems.

The soft and hard materials that make up biological systems are a great source of inspiration in materials science for design of functional systems, particularly those that are critical in supporting the most intelligent processes in the plantea and animalia kingdoms. Great ideas from these systems include, the notion of self-assembly and reversible formation of structures, creating adaptive behaviors for specific environments, materials with capacity for self-repair, the engineering of autonomous motion, and the integration of multiple functions in a single structure, among many others. In this lecture bio-inspired synthetic systems are described based on supramolecular polymers as well as “hybrid bonding polymers (HBPs), which we define as materials that rationally integrate covalent and supramolecular polymers. HBPs are biomimetic structures critical in systems such as biological membranes, muscles, tendons, and the cytoskeleton. One of the systems to be described is based on supramolecular polymers that are highly dynamic and therefore strongly effective at signaling cells for regeneration. The lecture will also describe photosynthetic materials, inspired by leaves, in which HBPs are used to couple light harvesting assemblies and catalysts to make fuels. Finally robotic materials that emulate living creatures will be discussed in which HBPs or organic-metal hybrid hydrogels are configured to respond to light and magnetic fields in order to generate locomotion of macroscopic objects on surfaces.

A small number of animals have the ability to actively change their visual appearance to perform important biological tasks. Cephalopods rank high on this list due to their ability to rapidly change color and texture - in some cases - for defense and signaling and have been a source of inspiration for the design of next generation adaptive systems. Recently, the electrochemical properties of the primary pigment found in cephalopod skin, xanthommatin, have been harnessed and applied in color-switching electrochromic displays with low power requirements. We describe the translation of this technology into a compact form factor that can sense and measure color from the environment then activate spatially patterned coloration with rapid (ca. seconds) response times. Our device uses reflectance-based sensors to measure color then triggers the formation of hue matched patterns by arrayed display components that can match and/or “hide” on surfaces of varying geometry, color, and luminous intensity. In future iterations of our approach, these principles may be applied to expand the palette of measured and displayed colors or to construct soft, deformable systems that can alter their optical signatures in response to environmental cues.

Bio-enabled nanocomposites represent a novel class of functional bioderived materials, which uses principles of bioinspiration and biomimetic to design hierarchically organized hybrid materials with co-assembled biological and synthetic components to bring best of synthetic and biological worlds: versatile functions with responses to mechanical, optical, chemical, and light stimuli and mechanical strength, flexibility, biocompatibility, and environmental robustness [1, 2]. In first set of examples, we discuss uniformly aligned chiral bio-photonic films from a liquid crystal phase formed by a cellulose nanocrystal solution placed in a thin capillary [3]. This spatial and fluidic flow confinement facilitates homogeneous growth of chiral pseudo-layers parallel to the interface in contrast to the highly heterogeneous assembly of random tactoids. The resulting iridescence films show a narrower optical reflectance band and uniform birefringence over larger macroscopic regions than heterogeneous conventional drop-cast films. In another example, enhanced chiral properties of organized helical patterned films with high asymmetry of circular polarization have been template-assembled via preferential orientation of high-aspect cellulose nanocrystals onto optical microgrids [4]. Bright chiral emission has been co-assembled in organized biopolymer photonic films from core-shell nanorods of cellulose nanocrystals and co-assembled carbon quantum dots mediated by polymer linkers [5]. Finally, co-assembly of cellulose nanocrystals with amorphous polysaccharides resulted in the formation of robust and flexible films with the preservation of the original structural photonic and fine control of the pitch length due to intimate intercalation of macromolecular backbones into the interstitial nanoscale pores of neighboring nematic monolayers [6].

[1] R. Xiong, J. Luan, S. Kang, S. Singamaneni, V. V. Tsukruk, Natural Biopolymers for Organized Photonic Structures, Chem. Soc. Review, 2020, 49, 983.
[2] R. Xiong, A. M. Grant, R. Ma, S. Zhang, V. V. Tsukruk, Naturally-derived biopolymer nanocomposite: interfacial design, properties and emerging applications, Mat. Sci. & Eng. Reports, 2018, 125, 1.
[3] V. Cherpak, V.F. Korolovych, T. Turiv, D. Nepal, J. Kelly, T.J. Bunning, O.D. Lavrentovich, V.V. Tsukruk, Robust Chiral Organization of Cellulose Nanocrystals in Capillary Confinement, Nano Lett., 2018, 118, 6770.
[4] R. Xiong, S. Yu, S. Kang, K. M. Adstedt, D. Nepal, T. J. Bunning, V. V. Tsukruk, Integration of Optical Surface Structures with Chiral Nanocelluloses for Enhanced Chiroptical Properties, Adv. Mater., 2019, 1905600.
[5] R. Xiong, S. Yu, M. J. Smith, J. Zhou, M. Krecker, L. Zhang, D. Nepal, T. J. Bunning, V. V. Tsukruk, Assembling Carbon Quantum Dots on Cellulose Nanocrystals for Chiral Luminescent Biophotonic Materials, ACS Nano, 2019,13, 9074.
[6] K. Adstedt, E. A. Popenov, K. J. Pierce, R. Xiong, R. Geryak, V. Cherpak, D. Nepal, T. J. Bunning, V. V. Tsukruk, Broad iridescence of natural polymer nanocomposites: chiral nanocrystals intercalated with amorphous polysaccharides, 2020, in press.

Supramolecular interactions may hold the key to the development of network systems with tunable mechanics and modulated architecture, such as observed in the muscle protein titin. It is the dynamic nature of these physical associations that we have exploited in the design of tough supramolecular materials that super-impose covalent and non-covalent interactions to tailor tensile response. We have developed supramolecular elastomers and interpenetrating network (IPN) systems that probe the interplay of non-covalent and covalent interactions in structural organization and mechanical response. By tailoring physical associations via control of self-assembly and composition, we have demonstrated enhanced supramolecular dynamics driven by architecture and toughness enhancements due to phase behavior. Recently, non-covalent interaction strength, network regularity, and chemoresponsiveness have been utilized as handles to derive gradient materials and to induce actuation behavior. New insights into supramolecular nanoscomposites are also highlighted.

The shape-morphing of two-dimensional elastic materials into three-dimensional structures is a vital and ubiquitous transformation in biological systems, as evidenced, for example, by the morphogenesis in cells and tissues, the formation of well-defined curvatures in growing flowers and leaves, and reconfiguration of seedpods in the release of seeds. The functionality of such biological reconfigurations has inspired the development of synthetic shape-changing materials that are useful for soft robotics and soft actuators. Here, we use theory and simulation to devise a distinctive approach for driving shape changes of 2D elastic sheets in fluid-filled microchambers. The sheets are coated with catalyst to generate controllable fluid flows, which transform the sheets into complex 3D shapes. A given shape can be achieved by patterning the arrangement of the catalytic domains on the sheet and introducing the appropriate reactant to initiate a specific catalytic reaction. Moreover, a single sheet that encompasses multiple catalytic domains can be transformed into a variety of 3D shapes through the addition of one or more reactants. Materials systems that morph on-demand into a variety of distinct structures can simplify manufacturing processes and broaden the utility of soft materials.

Diffusiophoresis refers to the motion of colloid materials in concentration gradients. I describe some of our studies of these problems, using experiments and mathematical modeling, such as the influence of ion valence and the effect of multiple electrolytes. Also, we demonstrate that these effect can influence of the movement of bacteria. For example, I summarize our observations of the migration of wild-type V. cholerae and a mutant lacking flagella (ΔflaA), as well as S. aureus and P. aeruginosa, near a dissolving CO2 source, which shows that diffusiophoresis of bacteria is independent of shape and Gram stain. With long-time experiments, we show that CO2-driven diffusiophoresis can reduce surface contamination, which suggests that the mechanism can be applied to cleaning systems and anti-biofouling surfaces. This work involves contributions from Suin Shim, who investigated the diffusiophoretic response of bacteria, as well as Ankur Gupta, Jessica Wilson and others in my research group.

We describe a platform of temperature-responsive hydrogel nanocomposites adsorbed at air/water interfaces that exhibit a variety of bioinspired non-equilibrium behaviors due to temperature gradients generated by illumination with visible light. In one example, we exploit spatial variations in thermally-induced deswelling of the gel particles to drive buckling of thin sheets into 3D shapes with non-zero Gaussian curvature. Similar to the mechanism exploited by numerous insects to climb menisci or drive clustering, pinning of the three-phase contact line at the sheet edges gives rise to capillary ‘multipole’ interactions between different objects, leading to assembly, repulsion, and even sustained rotational motion, depending on the geometry. In a second example, we exploit Marangoni forces resulting from temperature gradients to drive motion and interaction of planar particles, once again inspired by well-known strategies employed by aquatic insects. A simple method for Marangoni optical trapping is realized by shining appropriate patterns of light on the interface, enabling the definition of easily customized geometries in which to study coupled motion of multiple oscillators and spinners.

The encapsulation of biomacromolecules is an important area of research, particularly in the context of medicine where increasing numbers of therapeutics are protein based. One particular encapsulation strategy takes advantage of the associative liquid-liquid phase separation phenomena known as complex coacervation. The self-assembly of complex coacervates is spontaneous, driven by electrostatic attractions and the entropic gains associated with the release of small ions upon complexation. Furthermore, coacervation enables the sequestration of therapeutic proteins and other cargo at high concentrations, and without the need for organic solvents.

A number of recent studies have highlighted strong parallels between the dense, polymer-rich droplets resulting from coacervation and membraneless organelles that have been observed in cells. Of particular interest is the ability of these liquid-liquid phase separated granules to recruit specific proteins, RNAs, and other biomolecules, either for storage in times of stress, or as a hub of catalytic activity. Inspired by these biological structures, we look to understand the design rules whereby complex coacervation can be used to encapsulate and potentially stabilize cargo proteins. Our work focuses on complex coacervation involving two oppositely-charged polypeptides and a cargo protein. The use of two-polymer coacervates allows for the encapsulation of even weakly charged proteins at a variety of different conditions, even near their isoelectric point. We look to map out range of conditions where both phase separation is observed, and the degree to which proteins are incorporated into the coacervate phase as a function of the composition of the two polymers and the encapsulated protein. Preliminary results suggest the potential for using the protein itself as a majority component of the coacervate to achieve incorporation at levels that could be used for therapeutic injection. We intend to use proof-of-concept studies with model proteins as a foundation upon which further research into therapeutic proteins can be built.

In this presentation two case of studies involving the use of the protein wrapped β-chitin matrix from the squid pen Loligo vulgaris are presented.
In the first one we addressed how the mechanical properties of the squid pen are related to intra- and inter- interactions among chitin and proteins. Chemical treatments were applied to modify the interactions involving proteins, through unfolding and/or degradation processes. The data analysis showed that chemical treatments did not modify the multi-scale hierarchical structure of the β-chitin matrix. This allowed to derive from the mechanical test analysis the following conclusions: (i) the maximum stress (σ_max) relies on the presence of the disulfide bonds; (ii) the Young's modulus (E) relies on the overall correct folding of the proteins; (iii) the whole removal of proteins induces a decrease of E (> 90%) and σ_max (> 80%), and an increase in the maximum elongation. These observations indicate that in the chitin matrix the proteins act as a strengthener, which efficacy is controlled by the presence of disulfide bridges. This reinforcement links the chitin fibrils avoiding them to slide one on the other and maximizing their resistance and stiffness.¹
In the second case of study the multi-scale hierarchical structure of the β-chitin matrix used as substrate to prepare new materials bio-inspired. Finding inspiration from the byssus, and with the aim to mimic its peculiar mechanical properties, we chemically functionalize the chitin matrix with catechols, the main functional group of the byssus. The obtained functionalized matrix preserves its multi-scale structural organization and is able to chelate reversibly Fe(III). Thus, it behaves as the byssus, acting as a metal cross-linkable matrix that upon metalation increases the Young‘s modulus, E (> 10 times). This new material can be further cross-linked by oxidation of the catechols. This process generates an increase of the E (> 10 times) and first failure stress (> 5 times). The combination of oxidation and metalation of the functionalized matrix only slightly increases the mechanical properties. The produced stimulus responsive materials show that levels of complexity can be added to a multi-scale organized natural hierarchical matrix providing new properties.²
In conclusion we showed that the mechanical properties of the squid pen are controlled by the di-sulfide bonds and that its multi-scale organized β-chitin matrix can be chemically functionalized providing additional properties.

1. D. Montroni, F. Sparla, S. Fermani, G. Falini. (2020) Acta Biomaterialia, https://doi.org/10.1016/j.actbio.2020.04.039
2. D. Montroni, M. Palanca, K. Morellato, S. Fermani, L. Cristofolini, G. Falini. (2020) Carbohydrate Polymers, submitted

The most brilliant colours in nature are obtained by structuring transparent materials on the scale of the wavelength of visible light. By controlling/designing the dimensions of such nanostructures, it is possible to achieve extremely intense colourations over the entire visible spectrum without using pigments or colourants. Colour obtained through a structure, namely structural colour, is widespread in the animal and plant kingdom [1]. Such natural photonic nanostructures are generally synthesised in ambient conditions using a limited range of biopolymers.
In this seminar, I will review our recent advances to fabricate bio-mimetic photonic structures with cellulose and chitin and I will give examples of how to fabricate novel photonic materials based on chiral nematic architectures using low-cost polymers in ambient conditions [2-7].
[1] Kinoshita, S. et al. (2008). Physics of structural colours. Rep. Prog. Phys. 71(7), 076401.
[2] Narkevicius A, et al. (2019). Controlling the Self-Assembly Behavior of Aqueous Chitin Nanocrystal Suspensions, Biomacromolecules 20, 2830
[3] Chan C. L. et. al. (2019) Visual Appearance of Chiral Nematic Cellulose-Based Photonic Films: Angular and Polarization Independent Color Response with a Twist, Adv Mater 31, 1905151
[4] Frka-Petesic et al. (2019) Angular optical response of cellulose nanocrystal films explained by the distortion of the arrested suspension upon drying. Physical Review Materials 3, 045601
[5] Parker R. et al. (2018) The Self-Assembly of Cellulose Nanocrystals: Hierarchical Design of Visual Appearance. Adv Mat 30, 1704477
[6] Parker R. et al. (2016). Hierarchical Self-Assembly of Cellulose Nanocrystals in a Confined Geometry. ACS Nano, 10 (9), 8443–8449
[7] Liang H-L. et al. (2018). Roll-to-roll fabrication of touch-responsive cellulose photonic laminates, Nat Com 9, 4632

Hierarchical porous materials are attractive structures for a variety of applications due to their enhanced mechanical efficiency and their high surface area with minimum permeability loss. Nature showcases remarkable examples of hierarchical porous materials that benefit from such unusual set of properties, including bamboo, bone, marine sponges and wood. However, synthetic porous materials have yet to reach the elaborate architectural design found in their biological counterparts. To fill this gap, processing routes that enable deliberate control over the material’s porous structure at multiple length scales are highly demanded. In this talk, I will show how 3D printing technologies can be exploited to fabricate hierarchical porous materials with unprecedented mechanical efficiency and architectural control. The key feature of our approach is to design inks with an internal structure that serves as a template for the formation of tailored pores within the printed object. Using oil droplets, air bubbles or phase-separating mixtures as templating structures, this methodology enables independent tuning of porosity and pore sizes at multiple length scales. To demonstrate the potential of the process, we 3D printed complex-shaped parts with bioinspired multiscale porosity and enhanced mechanical efficiency that cannot be achieved through conventional fabrication technologies.