Symposium SB09—Biological and Bioinspired Functional Materials—From Nature to Applications

In this work, we fabricated omniphobic structural surface with the property of anisotropic droplet sliding using a composite of nano sized ceramic particles and polymers. Inspired by rice leaves, the micro-scale overhang groove structures exhibit omniphobic property and determines the sliding direction of the droplets. The polymer except for the mineral particles on the prepared surface was selectively etched through UV ozone etching treatment, and as a result, nano-bump morphologies were partially exposed. A reliable criterion was presented for the formation of nano-bumps that control the sliding velocity of droplets. It was confirmed that the sliding velocity of various types of liquid droplets with different surface tensions was also controlled according to the exposure level of nanoparticles.

The dye-sensitized solar cells based on synthetic Ruthenium dyes and organic metal-free dyes are widely recognized, however, their toxicity, scarce availability of raw material, high cost, and complex synthesis procedures have been a limitation [1]. This led to the exploration of nature-based dyes. Metabolites from plants such as chlorophyll, carotenoid, flavonoid, and betalains have been tested in dye-sensitized solar cells (DSSC) [2] but their narrow absorption spectrum, absence of functional groups to bind strongly with semiconductor [3], and non-availability of the electron-withdrawing group to achieve efficient intramolecular charge transfer (ICT) [4] resulted in low-efficiency of solar cells, also these metabolites have drawbacks such as low photo and thermal stability [5]. On the other hand, microbial metabolites have additional advantages over plant-based metabolites such as broad sunlight absorption [3], good photostability [6], non-toxic properties [7], and the ability to be produced in bulk through bioreactor approach [8]. There are more than 22000 microbially generated bioactive metabolites reported to date [9] which can be potentially explored for their application in solar cells. However, only a few reports are available on the use of microbial pigments in dye-sensitized solar cells [3] with the highest power conversion efficiency (PCE) of 2.3 % for monascus yellow [10] which is very encouraging. Though this research is in its infancy it shows the promise of these sensitizers for solar cell applications. In our research, purified bacterial cultures were isolated from roots of eggplant, chili, sweet potato, and okra plant, and the extracellular pigments extracted and were characterized for their structural, optical, and electrochemical properties. The initial data showed broad absorption in the range of 350 – 600 nm, presence of functional groups required for binding with the semiconductor, and HOMO-LUMO levels required for favorable charge transport in solar cells. The data clearly indicated the promise of microbial pigment as suitable photosensitizer for solar cell application.
References:
1. Adedokun, O., K. Titilope, and A.O. Awodugba, Review on Natural Dye-Sensitized Solar Cells (DSSCs). International Journal of Engineering Technologies, IJET, 2016. 2(2).
2. Pandey, A.K., et al., Natural Sensitizers and Their Applications in Dye-Sensitized Solar Cell, in Environmental Biotechnology: For Sustainable Future. 2019, Springer Singapore. p. 375-401.
3. Maddah, H.A., V. Berry, and S.K. Behura, Biomolecular photosensitizers for dye-sensitized solar cells: Recent developments and critical insights. Renewable and Sustainable Energy Reviews, 2020. 121: p. 109678.
4. Cherepy, N.J., et al., Ultrafast electron injection: implications for a photoelectrochemical cell utilizing an anthocyanin dye-sensitized TiO2 nanocrystalline electrode. 1997. 101(45): p. 9342-9351.
5. Millington, K.R., K.W. Fincher, and A.L. King, Mordant dyes as sensitisers in dye-sensitised solar cells. Solar Energy Materials and Solar Cells, 2007. 91(17): p. 1618-1630.
6. Ordenes-Aenishanslins, N., et al., Pigments from UV-resistant Antarctic bacteria as photosensitizers in Dye Sensitized Solar Cells. J Photochem Photobiol B, 2016. 162: p. 707-714.
7. Kumar, A., et al., Microbial pigments: Production and their applications in various industries. 2015. 5(1).
8. Jayaseelan, S., D. Ramaswamy, and S. Dharmaraj, Pyocyanin: production, applications, challenges and new insights. World J Microbiol Biotechnol, 2014. 30(4): p. 1159-68.
9. Berdy, J.J.T.J.o.a., Bioactive microbial metabolites. 2005. 58(1): p. 1-26.
10. Ito, S., et al., Fabrication of dye-sensitized solar cells using natural dye for food pigment: Monascus yellow. Energy & Environmental Science, 2010. 3(7): p. 905-909.

From natural ingredients to present-day chrome tanning, the art of leather making can be found across cultures dating back to prehistoric times, with each process imparting unique properties and chemical markers on the leather they produce. Leather tanning processes manipulate and strengthen the collagen matrix of skin, resulting in a long-lasting material with desirable mechanical characteristics, including durability and malleability. Emulsion tanning is a traditional method using natural emulsifying agents (oils/lipids), generally from the organs (brain or liver) of skinned animals, to preserve skin and has been used by cultures globally because of its efficiency. Despite all that is known of historic leathers, there is currently no scientific method to identify emulsion tanned leathers. Determining the effects of tanning agents on animal skin at the molecular level is critical to understand how structural changes induced by the tanning process affect the chemical properties and lifespan of the leather product.

In the 17^th century, the Dutch colonization of Taiwan affected the local culture in the form of religion and architecture and introduced European artifacts and practices. Within the collection at the Metropolitan Museum of Art is a pictorial map wall hanging depicting the Taiwanese town of Tainan painted on leather, a technique that may have been exported from Europe by the Dutch. This painting, entitled Forts Zeelandia and Provinitia and the City of Tainan is one of three versions depicting the Dutch forts, some of which exist today. This version likely dates from the 19^th century, due to the lack of foreign ships and figures signifying the post Dutch colonial-era (>1662) and presence of the city wall built in 1791. The repetition of figures and pictorial elements suggests the use of stamps or stencils and that the wall hanging may have been created in a local workshop for European tastes. The image of the map is executed in ink and colors on a leather support made of several smaller skins stitched together and suspected of being deerskin. The leather itself is free of any tannins or chromic acid, yet remains pale, soft, supple, and malleable, begging the question: is this an example of emulsion tanned leather?

In order to determine the tanning method used on the painted leather in the pictorial map, a series of unique reference materials were created to establish the proteomic fingerprints and lipidomic profiles of different emulsion tanning agents using mass spectrometry (MS). Additionally, material structural studies were performed to compare the chemistry of leathers tanned with different emulsion tanning agents. Further examination using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDAX), Fourier-transform infrared spectroscopy Imaging (FTIR-I), and X-ray photoelectron spectroscopy (XPS) to shed light on the composition, structural assembly and surface elemental/chemical distribution. Together, the molecular fingerprinting and functional chemical mapping studies will provide new insights into emulsion tanning, a global phenomenon which remains vastly understudied, and can guide and establish criteria for identifying emulsion tanning methods.

Cephalopods, including squid, octopus, and cuttlefish, can rapidly camouflage in different underwater environments by employing multiple optical effects including light scattering, absorption, reflection, and refraction. They can do so with exquisite control and within a fraction of a second—two features that indicate distributed, intra-dermal sensory and signaling components. However, the fundamental biochemical, electrical, and mechanical controls that regulate color and color change, from discrete elements to interconnected modules, are still not fully understood despite decades of research in this space. This talk highlights key advancements in the biochemical and structural analysis of cephalopod skin and discusses compositional connections between cephalopod ocular lenses and skin with features that may also facilitate signal transduction during camouflage.

Guanine crystals are responsible for an extraordinary variety of optical phenomena in animals. The crystals are formed from stacked, planar layers of H-bonded molecules. The optical utility of guanine derives from its extreme refractive index (n=1.83) within the H-bonded plane. Little is known about how these crystals form and how the organisms precisely control crystal morphology. Key questions include whether crystallization proceeds via an amorphous precursor phase or whether physical confinement by de-limiting membranes dictates morphology. To illuminate pathways governing the crystallization, we studied model guanine-producing organisms during development, including spiders, lizards, and scallops. The onset of crystallization was determined by the emergence of birefringence in the crystal-forming cells. the tissues were then examined by cryogenic scanning electron microscopy (cryo-SEM) and transmission electron microscopy (TEM). In all three models, crystallization occurs within a spherical, double-membrane delimited vesicle. In white widow spiders, which produce prismatic guanine crystals, the crystals are progressively laid down along the H-bonded direction on parallel fibers which stretch across the length of the vesicle. As crystallization proceeds these 2D sheets of crystals merge along the π-stacking direction to form a single crystal. In lizard tails, vesicles containing very small crystals are observed and grow in all directions to form the final crystal. Evidence of a layered structure is sometimes observed in the side faces of mature guanine crystals in all three models. Though we cannot yet fully describe the crystallization pathway of biogenic guanine, initial observations are consistent with a classical 2D growth model where H-bonded layers of guanine molecules are deposited epitaxially on lipid membranes. Biological crystallization pathways can inspire new ways to synthetically control morphologies of organic crystals which then can be utilized in many optical systems.

The study of protein-based materials has enabled the development of several optical, electronic, and medical technologies. Within this context, cephalopod structural proteins called reflectins have recently gained attention due to their demonstrated potential for the development of biophotonic and bioelectronic devices. Moreover, reflectins make up the subcellular structures found in optically active cephalopod skin cells that play a critical role in cephalopods’ remarkable camouflage abilities. Given reflectins’ significance from both technological applications and fundamental biology perspectives, these proteins have recently emerged as a desirable target for the design of functional biomaterials. However, the development of such materials has been hindered by a lack of complete understanding of their structures and properties. Here we highlight the structure, self-assembly, and multi-faceted applications of reflectin-based materials within the context of biophotonic and bioelectronic platforms. Specifically, we discuss how the structure and assembly of these biomaterials enable their optical and electrical functionalities. Our findings not only underscore the potential of these unique cephalopod proteins as functional biomaterials but also hold relevance for the development of cephalopod-inspired optical and electronic technologies.

Articulated coralline red alga is abundant in the shallow waters of oceans worldwide. Its structure exhibits hierarchical organization from the macro to the nano-scale. We revealed that the high-Mg calcite cell wall nanocrystals of Jania sp. are arranged in layers with alternating Mg contents. This non-homogenous elemental distribution assists the alga in preventing fracture caused by crack propagation. The mechanism of the layered structure formation was proposed as a periodic spinodal decomposition (SD) of the Mg-ACC matrix.
The crystallization in the coralline red algae occurs on an organic template via an amorphous precursor. SD of amorphous precursor to Mg-rich ACC nanoparticles and subcritical Mg-ACC matrix is activated near the cell wall/organic interface and advances to the internal regions. Following crystallization of the subcritical Mg-ACC to Mg-calcite is accompanied by an exclusion of excess Mg ions to the adjacent ACC layer. After a certain time, Mg concentration in this layer exceeds the critical value, and a secondary SD occurs, thus a layer of Mg-ACC with increased density of Mg-rich nanoparticles forms. Parameters of the layered structure were calculated based on the diffusional model developed. Using reasonable values for diffusion coefficient of Mg in gel/liquid ACC, D≈10^-15m²/s, and crystallization rate V≈10^-9m/s, the typical layer thickness ~0.3 μm was obtained, which corresponds rather well to experimental data.

Biomaterials and bio-inspired materials like biopigments (xanthommatin (Xa), melanin, etc.) are of increasing interest for photonics applications and for basic science to understand how some species create an impressive array of photonic effects, ranging from bright color due to structural coloration or photonic crystals in tropical birds to stunning visible camouflage in underwater animals like the cephalopods, which still partially defies understanding (how can they blend into the background so well?).

Small-molecule biopigments dissolve in polymer hosts and are robust against ultraviolet light and toxicologically benign, and could form optical thin films (e.g., anti-reflective coatings). The chromatophores in squid skin, which contain the biopigment Xa in nanostructured bioparticles (granules) (100-500 nm dia.), influence light scattering and color; they achieve both pancake-like, expanded and spherical, punctate states. The granules are well-sized for nanophotonic scattering of visible light, especially blue-green wavelengths, instead of absorbing it, even in sub-monolayer arrays [1]. Recently, researchers have succeeded in mimicking chromatophore color and the light scattering granules within them, using artificial materials in the laboratory and chemically synthesizing Xa; the latter was produced in large (hundreds of mg) quantities via a straightforward, scalable process, and spraycoated onto surfaces [2]. The chromatophore could be approximated as containing multiple layer of sub-monolayers. Under the chromatophores lie iridocytes; multilayered Bragg reflectors that reflect color iridescently. By understanding how the color of the chromatophore plus iridocyte changes, artificial and novel material platforms will enable more efficient control of light at the nanoscale.

We have discovered that the Xa pigment in cephalopod chromatophores has a high refractive index (RI) (n > 1.55) at fixed wavelengths [3]. Recently, we have carried out comprehensive broadband (300 nm – 3200 nm) ellipsometric spectroscopy to determine the UV-to-infrared optical indices (n and k) of Xa pigment, using natural Xa from the squid’s chromatophores and forming smooth, high-quality films using a novel method. These broadband measurements of Xa’s fundamental optical properties allow the design of new lightweight optical components, such as lenses, that can adaptively change in response to external stimuli.

In this presentation, we will use our new experimental data for a 4-flux model (forward and backwards-propagating specular and diffuse light), to better understand squid skin optics, improving on an earlier analytical model (Kubelka-Munk). An optical model [4] made important discoveries on the optics of combined squid skin organs, but lacked separate experimental data on Xa. We improve this model analytically, coupling the chromatophore and iridocyte and not ignoring the background reflectivity and scattering. Armed with experimental n and k, our model will better assess the optical response (e.g. scattering, reflectivity) of the combined chromatophore-iridocyte to best understand the squid skin optical system. This will enable biopigments and bio-inspired pigments to serve as optically and sensing functional materials (perhaps even with electrical functionality [2]). Such a high-RI material will demonstrate strong and interesting new scattering and coloration functionalities and, when synthesized in large scale in an environmentally-friendly way, may enable new lightweight optical systems that can adapt and change shape, that may aid in underwater detection or imaging. We discuss possible new functional and optical nanophotonic systems, using the interesting biopigments and bio-inspired pigments, and possible applications in optical sensing.

[1] A. Kumar et. al. AOM 6 2018.
[2] A. Kumar et. al., ACS AMI 2018, 10.
[3] S. Dinneen et. al. JPCL 8 2017.
[4] Sutherland, R. L. et al., C. JOSA A 25.

Organic crystals are widely used as the reflective materials in animal coloration and vision [1]. Guanine crystals, for example, have been studied for over 100 years and their role in structural coloration is well-established. Here we focus mainly on the less-studied pteridine molecules which are used, in crystalline form, as colorants and as reflectors in vision. Isoxanthopterin crystals form reflectors in the eyes of decapod crustaceans which are used in image-formation, enhancing photon-capture and camouflage [2]. The isoxanthopterin crystals are arranged in nanoparticles, constructed from a shell of plate-like isoxanthopterin crystals arranged in concentric lamellae around an aqueous core. The reflectors are formed from dense assemblies of nanoparticles. Isoxanthopterin crystals are characterized by layers of planer H-bonded molecules, and the reflectivity of the material derives from the extreme refractive index (n=1.96) parallel to these layers. The reflectivity and scattering of the particles are enhanced by the alignment of the crystals and an optimized core-shell ratio [3]. We also present recent insights on the formation of biogenic crystals from cryo-SEM studies of developing organisms. This includes the formation of guanine-based photonic structures in lizards and spiders and the formation of isoxanthopterin crystals in larval crustaceans. The exquisite control organisms exert over formation of these materials provides a wealth of inspiration for the design of new optical materials.
[1] B. A. Palmer, D. Gur, S. Weiner, L. Addadi, D. Oron, Adv. Mater., 30, 1800006 (2018).
[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, 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, Nature Nanotechnology 15, 138–144 (2020).

Biomineralization – the synthesis of inorganic materials using proteins – has recently gained interest as a low cost, green route for the production of metal chalcogenide semiconductor nanocrystals. Typically, biomineralized nanocrystals are synthesized using proteins or biomolecules identified from organisms which possess a native biomineralization response. Natural biomineralization pathways utilize proteins which either catalyze or template mineralization, but rarely possess a single biomolecule capable of both functions. Here, we demonstrate an alternative biomineralization approach which uses the artificially designed de novo protein, Construct K (ConK), to both catalyze and template metal chalcogenide nanocrystals. ConK was found to catalyze a PLP-dependent reaction which produces H₂S from L-cysteine. In the presence of metal precursors, such as Cd, enzymatically produced H₂S then reacts to form metal sulfide quantum dots in solution. In addition to having enzymatic activity, ConK is also structurally stable and highly tolerant to mutations in amino acid sequence, allowing for facile addition of new functionalities and properties. Using site directed mutagenesis, we selectively modified ConK to contain strong metal binding amino acids, such as histidine and cysteine, which act as stabilizing capping ligands to template nanocrystal populations of various controllable sizes. We characterized the optical properties of the resultant nanocrystal populations using absorbance and fluorescence spectroscopy, and verified the crystal structure using XRD and TEM measurements. Semiconductor nanocrystals synthesized using ConK demonstrate well-controlled growth and high stability when compared to naturally derived biomineralization pathways, making them ideal for commercial implementation and use.

Lipid vesicles are aqueous volumes surrounded by a bilayer of lipid molecules, which are amphiphilic molecules with their head groups facing water and tail groups facing oil. These vesicles are simple models for cell membranes and can be used for drug delivery. Similarly, block copolymers are amphiphilic molecules that form vesicles by themselves or with lipids. Like lipid vesicles, polymer vesicles can also be used for drug delivery and cell membrane mimicry. One interesting type of lipid/polymer vesicle is the asymmetric vesicle, in which its bilayer is composed of two dissimilar lipid monolayers or a lipid monolayer and a polymer monolayer. Importantly, all eukaryotic cell membranes exhibit this type of asymmetry and asymmetry is also proposed to enhance mechanical properties of the membrane. Here, we use microfluidics to fabricate mono disperse and highly controllable asymmetric vesicles, which unlike the conventional methods that often end up wit
h highly poly disperse samples. To achieve this, asymmetric vesicles are produced using water/oil1/oil2/water emulsions in a glass capillary device, with different lipids/polymers immersed in two different volatile oil phases. In future, we envision asymmetric lipid/polymer vesicles could open a new door in the drug delivery field.

In recent years, there has been a significant thrust towards the creation of sustainable green polymers and polymer composites ^1,2. Reductions in manufacturing resources, synthetic polymer waste, and greenhouse emissions are all driving forces for advancements in this area. Cellulose, the world’s most abundant polymer, is not only derived from renewable resources, but also combines remarkable specific mechanical properties (comparable to steel wire, Kevlar and carbon fibers ^3,4) with biodegradability, biocompatibility, and a molecular structure that allows for easy functionalization ^4–6. Compared to cellulose extracted from wood, nanocellulose secreted from bacterial cultures (also referred to as bacterial cellulose, ‘BC’) is matrix-free, has high aspect ratio and crystallinity, and can be obtained with minimal processing ^3,4. Emerging applications of BC include nanopapers and microfibers showing remarkable Young’s modulus (~66 GPa³), strength (~1GPa³) and toughness (16.9 MJ/m^{3 7}) for binder-free, pure nanocellulose materials. The incredible mechanical properties and ability to self-bind without additives stem from the combination of high aspect ratio nanofibrils, vast hydrogen bonding network, high degree of crystallinity, and for the mentioned cases arise from fiber alignment effects that enhance further the hydrogen bonding interactions between the cellulose nanofibrils^7,8. However, BC-based materials are naturally brittle and hydrophilic due to the molecular structure of cellulose. In natural wood, phenolic molecules forming large lignin networks, serve, together with other biopolymers, as a binder to the cellulose matrix, tuning mechanical properties, conferring hydrophobicity, and protecting against pathogens⁴. In fact, recent research into sustainable biocomposites has shown significant increases of mechanical properties, thermal stability and hydrophobicity on wood-extracted cellulose-lignin composite papers with hot press treatment, compared to conventional cellulose paper⁹.
In this work, we present an exploration into the development of BC-lignin nanocomposites through a design of experiments approach which allows the systematic investigation of the governing structure-processing-property relationships in these nanocomposites. Specifically, we explore a matrix of hot press processing conditions including time (10-30 minutes), temperature (120-160 °C), and pressure (5-15 MPa) and correlate the performance of those nanocomposites in response to the processing conditions. Our characterization includes scanning electron microscopy, thermogravimetric analysis, X-ray diffraction and nanoindentation tests. Additionally, the effects of lignin binding the cellulose matrix are further examined through contact angle analysis and Fourier-transform infrared spectroscopy.

References
1. Mohanty, A. K., Vivekanandhan, S., Pin, J.-M. & Misra, M. Science 362, 536–542 (2018).
2. Liu, C. et al. Adv. Mater. n/a, 2001654.
3. Wang, S. et al. Adv. Mater. 29, 1702498 (2017).
4. Moon, R. J., Martini, A., Nairn, J., Simonsen, J. & Youngblood, J. Chem. Soc. Rev. 40, 3941 (2011).
5. Rahman, M. M. & Netravali, A. N. ACS Macro Lett. 5, 1070–1074 (2016).
6. Qiu, K. & Netravali, A. N. Polym. Rev. 54, 598–626 (2014).
7. Zhu, H. et al. Proc. Natl. Acad. Sci. 112, 8971–8976 (2015).
8. Ling, S. et al. Prog. Polym. Sci. 85, 1–56 (2018).
9. Jiang, B. et al. Adv. Funct. Mater. 30, 1906307 (2020).

The non-biodegradability of petrochemical-based plastics has led to its pollution in almost all parts of the globe causing severe damages to our ecosystems, while the recent discovery of microplastics in human gut and lungs, shows alarming signs of the potential health problems. One promising long-term solution to this global problem of plastic pollution is to design and develop novel biodegradable bioplastics that can replace the conventional plastics. In this regard, we have engineered E. coli biofilms to produce the world’s first water-processable protein nanofiber-based bioplastic termed as AquaPlastic, which biodegrades to ~90% in just 45 days.^[1] AquaPlastic is resistant to organic solvents, strong acid, and base, which can be further utilized to form the protective coatings on various 1D and 2D substrates. Remarkably, AquaPlastic can also be molded, healed, and welded by using water. This work on AquaPlastic paves the way for packaging and coating applications, and to build a sustainable world.
[1] Nature Chemical Biology, 2021, 17, 732.

Most of the structural materials found in nature are characterized by a complex multi-scale hierarchy, which ultimately contributes to their multiple functions and mechanical properties1. Recent studies have shown that crystal orientation is yet another element of hierarchical structure that affects the mechanical properties of mineralized biological materials 2^,3. In this talk I will describe how correlative chemical, mechanical, and crystallographic characterization tools can be used to explore structure-property relationships in crystallographically anisotropic biological minerals. I will show how the combination of polarized piezo-Raman and micro-indentation can be used to quantify the residual strain energy in nacreous material. Nacre's work of fracture is approximately 3,000 times that of monolithic aragonite, and its high toughness has been attributed to various chemo-mechanical mechanisms generally related to its hierarchical structure. We show that the cooperative movement of the co-oriented aragonite stacks contributes to the strain hardening of the nacre, defining a new length scale of nacre toughening⁴. In a similar fashion we studied the contributions of the chemical and crystallographic texture in the enameloid and dentin layers to mechanical properties of the drumfish teeth material. We show that the chemical doping of fluoride and zinc on the outer surface, the high crystallinity, and the crystallographic misalignment all contribute to the superior stiffness, hardness, and fracture resistance of the enameloid. The incorporation of these features into the design strategies paves the road for crystal orientation-driven mechanical enhancement of bio-inspired composite materials.
References
Dunlop, JWC, Weinkamer, R, and Fratzl, P. 2011. “Artful Interfaces within Biological Materials.” Materials Today 14 (3): 70–78.
Beniash, E, Stifler, CA, Sun, C-Y, Jung, GS, Qin, Z, Buehler, MJ, and Gilbert, PUPA. 2019. “The Hidden Structure of Human Enamel.” Nature Communications 10 (1): 4383.
Griesshaber, E, Schmahl, WW, Ubhi, HS, Huber, J, Nindiyasari, F, Maier, B, and Ziegler, A. 2013. “Homoepitaxial Meso- and Microscale Crystal Co-Orientation and Organic Matrix Network Structure in Mytilus Edulis Nacre and Calcite.” Acta Biomaterialia 9 (12): 9492–9502.
Loh, H, Divoux, T, Gludovatz, B, Gilbert, PUPA, Ritchie, RO, Ulm, F, and Masic, A. 2020. “Nacre Toughening Due to Cooperative Plastic Deformation of Stacks of Co-Oriented Aragonite Platelets.” Communications Materials 1 (77): 1–10.

Our current understanding about the seemingly broad range of self-assembly mechanisms involved in natural silk production has been developed predominantly from studies of dragline spider silk. Protein monomeric units (spidroins) polymerize via terminal interactions and allow the material to undergo an orchestrated liquid-to-solid transformation, ultimately resulting in the silk thread. However, despite its widespread availability, there have been limited mechanistic investigations on the analogous protein fibroin, which is the main component in silkworm silk. This is attributed to both its complexity and perceived inferior mechanical properties. Paradoxically, silkworm silks are the most commercially exploited of the natural silks. The inherent biocompatibility has driven applications in biomedicine, where a liquid precursor form of fibroin can be processed into a myriad of materials, from vesicles, nano and microparticles, films, hydrogels, and sponges. To obtain liquid fibroin from the solid fibre, it must first endure a process termed regeneration, where the protein is considered to be returned to a state similar to its pre-spun condition. This work explores fundamental aspects of silkworm silk fabrication that encompasses, simultaneously, a fundamental biophysical understanding of the regeneration process at the molecular scale and its effects. We use the acquired knowledge to exploit the delicate and metastable equilibrium between protein self-assembly and aggregation in a more controlled manner to fabricate complex materials with a special focus on the regeneration of hard tissue.

Biological organisms are covered with a cuticle as outermost extracellular material and interface between organs and the environment. A precise understanding of the structure-function relation of these interfaces is still an open issue. In particular for the case of wetting, it is far from clear how nanoscale chemistry and structure determine macroscopic wetting. In our opinion, Nature is still ahead of “first principles calculations”: if surfaces with well-defined and robust wetting properties are to be designed, it is still more effective to “look” at what Nature offers, than to rely on theoretical modeling. The Lotus and Rose Petal effect are two striking examples of how Nature fine-tunes nanoscale physics to obtain an appropriate (biological) function on the macro-scale.
We use Atomic Force Microscopy (AFM) to simultaneously measure nanoscale topography and chemistry of (natural!) Rose Petals. We found two extraordinary features linked to their peculiar wetting properties, namely: (i) surface roughness is concentrated on the nanoscale and fractal-like, and (ii) the surface has an extreme nanoscale chemical variability. While high roughness is generally accepted to be the origin of peculiar wetting (super-hydrophobicity) the role of nanoscale chemical variability is usually not really a topic of discussion; most probably because -up to now- it could not be “seen”.
An extreme roughness on the scale from 5 nm to 25 µm was measured. Although the total roughness is very different (25 µm vs. 3 µm), the Power Spectral Density of surface roughness of the upper and lower side are very similar, both surfaces being fractal with df ≈ 2.45. For water, the contact angle on both surfaces is similar, which proves that rather than total roughness, other parameters -and in particular fractal dimension- are relevant for their wetting behavior. In addition, we find an extreme chemical heterogeneity of the surfaces, with very hydrophilic and very hydrophobic patches being close together. In our opinion, both, extreme roughness and chemical variability are the basis for the Rose Petal Effect.
From our data, we conclude that a liquid drop will strongly adhere to nanoscale hydrophilic patches, and detach from all the other hydrophobic parts of the surface, since the combined effect of roughness and chemical (nanoscale) wetting properties will induce a high effective local contact angle (=nanoscale wetting parameter). This explains the surprising and in principle antagonistic properties associated with the Rose Petal Effect, i.e., high contact angle and high drop adhesion. We are convinced that, although this work has focused on rose petals, the fundamental mechanism by which Nature is able to generate high contact angle and drop adhesion will apply to other surfaces with similar characteristics. In addition, the application of this fundamental mechanism will trigger the development of new functional surfaces by “learning from Nature”.

Despite extensive research, the manufacture in the bulk of high–performance flake–based magnetic composites with a highly aligned, nacre–like structure remains challenging. Many challenges can be overcome by freeze casting in an externally applied, uniform magnetic field, which causes both the flakes and the composite walls of the cellular solid to align parallel to the B–field lines. When appropriately sized, the flakes experience a second alignment parallel to the freezing direction because of a shear flow that occurs due to both the volumetric expansion of the ice phase and mold contraction during the directional solidification. The resulting orthotropic structure of the freeze–cast magnetic composite is reflected in orthotropic mechanical and magnetic properties of the material. The magnetic composites manufactured by magnetic–field assisted freeze casting outperform by a factor of 2–4 in terms of stiffness, strength, and toughness materials that are processed in the absence of a magnetic field and do not exhibit a monodomain architecture. Additionally, the anisotropic freeze–cast magnetic composites achieve lower losses in two directions of flux excitation so that they can be used without an additional high permeability flux return path in applications like power transformation. Because of the highly aligned microstructure, it is possible to compact the initially lamellar composite with 90% porosity to at least 80% strain. The results presented in this study illustrate the tremendous potential for magnetic freeze casting of nacre–like magnetic composites for use in power conversion.

The high quantum efficiency of photosynthetic reaction centers (RCs) makes them attractive for bioelectronics and biophotovoltaic applications. In the bacterial species Roseobacter denitrificans, Roseobacter lotoralis and Erythrobacter litoralis the photovoltaic machinery which is located within few nm diameter transmembrane protein can be removed from the cells and interfaced with electrodes. Cytochrome c (cyt c) has been utilized as an electron-transfer (ET) element between electrodes and RCs. Diatoms are a major group of microalgae ubiquitous in the oceans. They have developed a unique light-harvesting apparatus, the Fucoxantin Chl a/c binding protein (FCP) which shows a sequence similarity to light harvesting complex (LHC II) of higher plants but with pigment composition significantly different. In FCP, Chl b is replaced by Chl c₂ and Fucoxanthin (Fx) is the major carotenoid instead of lutein in LH II.
In the present work the photodynamics and spectroscopic characterization, including Resonance Raman, FTIR, Fluorescence, light induced adaptations, and Electrochemistry, of membranes from Roseobacter denitrificans, Roseobacter litoralis and Erythrobacter litoralis and from the diatoms Thalassiosira pseudonan, Chaetoceros ceratosporus and Chaetoceros sp will be presented.
References
1. Vincent M. Friebe et al. ACS Appl. Mater. Interfaces 2017, 9, 28, 23379–23388
2. Photonics and Optoelectronics with Bacteria: Making Materials from Photosynthetic Microorganisms Francesco Milano, Angela Punzi, Roberta Ragni, Massimo Trotta, and Gianluca M. Farinola Adv. Funct. Mater. 2019, 29, 1805521
3. Photoreduction of Carotenoids in the Aerobic anoxygenic photoheterotrophs probed by Real time Raman spectroscopy Marios Papageorgiou,Charalambos Tselios , Constantinos Varotsis submitted

Ceramides are the main component of the stratum corneum, the outermost layer of the skin, providing an epidermal barrier against dehydration or external microorganisms. However, much wider application of ceramides has been limited since molecular crystallization readily occurs in aqueous formulations. To solve this problem, this study introduces a practically useful approach to encapsulate ceramide molecules, in which hydrophobically modified bacterial cellulose nanofibers (BCNFs) were employed as a thin film-forming fiber surfactant. We confirmed that the ceramide microparticle core with a multi-lamellar structure could be enveloped with a BCNF wall of which thickness is about hundreds of nanometers. The multi-lamellar structure was characterized by analyzing the inter-layer distance through small-angle x-ray scattering. The inter-layer distance could be manipulated by using fatty alcohols with different alkyl chain length; 4.3 nm, 4.9 nm, and 5.9 nm for 1-tetradecanol, 1-octadecanol, and 1-docosanol, respectively. Wide-angle x-ray scattering showed that the ceramide exhibited hexagonal lateral packing with 1-tetradecanol and orthorhombic lateral packing with 1-octadecanol and 1-docosanol. These results suggest that the chain length of fatty alcohols critically involved in the process of ceramide molecules forming the multi-lamellar structure. Furthermore, we demonstrated that the longer chain length of fatty alcohols prevented more effectively the microcrystalline phase from penetrating the capsule wall and protruding out due to the formation of thicker hydrophobic lamellar phase. The results obtained in this study highlight that BCNF-based encapsulation technology provides a practical methodology to control the crystallization behavior of ceramide molecules, thus enabling the development of various types of skin-friendly formulations that can strengthen the skin barrier function.

Exosomes, a class of extracellular vesicles secreted by almost eukaryotic cells, are known as an important mediator for signaling in cell-cell communication and cellular processes including immune response and antigen presentation. Since exosomes contain therapeutic proteins, a variety of cell therapeutic strategies are developing while avoiding side effects such as low survival rate and immune rejection response associated with direct use of cells as a therapeutic agent. Most of the exosome studies conducted so far are based on animal-originated cells. Recently, there are challenging attempts to extract exosomes from other types of raw materials such as plant cells and microalgae. The approach to obtain exosomes from microalgae is of special interest, because they have abundant biomolecules such as proteins, vitamins, minerals, and amino acids. Herein, we first propose a microalgae-derived exosomal nanovesicle (ExoNV) system for cellular drug delivery. Our ExoNVs were extracted from euglena gracilis, representative microalgae, containing b-glucans, vitamins, and minerals, via cell-extrusion. Extruding euglena gracilis through a series of polycarbonate membrane from 5μm to 0.2μm pores allowed us to produce ExoNVs with a particle size of ~190 nm and the number of 6.55x10⁹ particles/ml. The ExoNVs produced by using this approach encapsulated 14% of β-glucans, which was confirmed by aniline blue fluorescence analysis. In our continued studies, we also confirmed through in vitro cellular ROS detection and cell proliferation assays that β-glucans-containing ExoNVs not only exert improved cellular antioxidation activity but also aid dramatically in cell proliferation. These results highlight that our ExoNV system has great potential as an exosome-mimetic therapeutic agent that can activate cells or deliver drugs to cells.

Improvement of tribological properties with the enhancement of lubrication by applying surface texturing has been paid much attention recently in wide ranges of applications. The laser texturing, a surface texturing using a laser has been received lots of attention to improve the tribological performance of various surfaces and this laser surface texturing could be considered in a large extent as one of various biomimetic approaches to improve surface performance. In this work, the surface engineering using bio-inspired patterns had been introduced and the results from the laser texturing on the PVD coated steel substrate were illuminated so that the feasibility of combining surface texturing and hard coating to further improve the tribological properties could be examined. The tribological properties of the surface were evaluated using a ball on disk type tribometer with a 9.25 mm diameter Al₂O₃ ball as a counterpart material. The tests were performed at room temperature in air environment with oil lubrication under an applied normal load of 5.0 N. Our results indicated that laser texturing affected the tribological performance of the surfaces extensively and the size as well as pattern type of laser texturing were critical factors affecting the tribological performance of the coatings. For CrZrSiN coatings applied on the laser textured steel specimens, much improvement of the friction coefficient at room temperature, nearly 10 times depending upon the type of the bio-inspired pattern could be obtained under lubrication condition.

Coloration in nature has evolved for a long time to become biologically diversified for camouflage, predation, signal communication, and mate choice. Birds are representative examples of nature's coloration. More than 10,000 bird species have amazing diversity of colors in their feathers. Nature's coloration methods are mainly divided into two parts: pigments and structural colors. Structural colors are produced by selective light reflection of certain wavelengths from nanostructures, not by light absorption in contrast to pigment-based colors. Birds also show the colors not only with pigments but also with optical nanostructures. The optical nanostructures are highly organized with keratin, melanin, and air in varying refractive indices, thus producing the most brilliant colors in nature through structural coloration. In birds, structural colors are mainly observed in feather barbules and feather barbs.

Avian structural colors are produced by constructive interference of coherent backscattering of light. Although this single-scattering model helps to analyze reflectance peaks, color pattern variations are not well understood due to the limitations of single-scattering model to analyze real structural colors of blue birds. So, we use the theoretical model based on transport length, which provides improved understanding on the multiply scattered light in birds. The transport length in a strongly diffusing medium is the length over which the direction of the photon’s propagation is randomized. We select Eurasian jay and Oriental dollarbird as the target species and analyzed the transport length based on the thickness of spongy layer. Eurasian jay and Oriental dollarbird show color pattern variations from white to sky blue, blue, and dark, and the thickness of disordered medium could be defined as thickness of spongy layer in this transport system. We calculate transport length by energy-density coherent-potential approximation (ECPA). From the results, we also observe that light propagation regime is in intermediate state between ballistic and diffusive transport. Therefore, we need to consider color pattern or spectrum variation by the relationship between transport length and thickness of spongy layer. For blue bards with thin spongy layer, red light that could not be scattered through the layer will be absorbed by basal melanin layer. In the case of white barbs, the spongy layer is sufficiently thick so the multiply scattered light spans from blue to red light, resulting in white. Our results also suggest that the peak broadening by multiple scattering could only occur when spongy layer is sufficiently thick. Based on this knowledge, we develop thickness-dependent bio-inspired structural colors via self-assembly. This enhanced understanding on the nature's coloration has a potential for various biomimetic application to reflective colors such as pigment-free coating materials to digital signage, and deformable display.

Strategies such as covalent cross-linking, chemical modification and blending of polymers or nanotechnology can be used to enhance the physicochemical and mechanical properties of soft polysaccharides-based materials. In an alternative approach, we used metal coordination bonding of vanadium ions to polysaccharides tocreate strong, and water-stable bio-based films. Two naturally occurring polymers, pectin and chitosan were combined with glycerol to impart stretchability. Vanadium ions were incorporated into the films and the formation of ionic interactions as well as hydrogen bonding and coordinate bonding was confirmed via FT-IR. Scanning electron microscopy showed laminated sheets with intermolecular distance of ~0.16 µm for V(V) containing films as compared to a much larger~ 0.75 µm for films without vanadium. Moreover, we showed that V(V) coordinated films possessed higher storage modulus, water and thermal stability than films without vanadium. More interestingly, we observed striking changes in color from yellow to blue inside the V(V)-containing films upon irradiation with blue light. This corresponds to reduction of V(V) to V(IV) according to previous studies. A small change in modulus was observed with light stimulus, with no significant changes in the structure of the film. Based on these results, we can conclude that it is possible to create robust, water-stable and photoresponsive polysaccharides-based materials through the strong supramolecular metal-coordination interactions between metals and polysaccharides.

Guanine crystals are a common natural material used in biological photonic crystals and photonically active structures. Layered guanine crystals produce the characteristic structural colors of iridophores in cephalopods and tree frogs, as well as producing complex optical structures such as the concave mirrors in the eyes of scallops. They can also produce dynamic structural color, as some species of frogs can change the shape and alignment of layered guanine in their iridophores to produce skin colors ranging from yellow-green to dark gray. The production of β phase guanine platelets with various morphologies was achieved by recrystallizing guanine in formamide in the presence of poly(1-vinylpyrrolidone-co-vinyl-acetate) and small organic molecules such as uric acid. The diamagnetic anisotropy of guanine crystals created the opportunity to both align guanine crystals and to affect their morphology to create interesting photonic structures, such as C-shaped crystal stacks, by applying a magnetic field. Magnetically aligned guanine platelets and platelet stacks were then embedded inside a hydrogel or elastomer matrix to create bioinspired photonic crystals with dynamic photonic properties, taking inspiration from the iridophores of tree frogs. By examining the effect of magnetic fields on guanine crystal structure and assembly, we can better understand how magnetic fields affect the crystallization dynamics of diamagnetic molecules and better utilize guanine crystals in applications where alignment is a critical factor, including in the assembly of bioinspired photonic structures.

A variety of physical phenomena create color, such as selective absorption by dyes or pigments, optical dispersion, and structural color from light interference. Nature has exquisitely harnessed structural color, with examples including opals, butterfly wings, and iridescent bird feathers, which traditionally exploit nanoscale periodic geometries to create optical interference. Here, we explore an optical mechanism for creating iridescent structural color that is accessible in larger, microscale geometries. In this mechanism, light traveling by different trajectories of total internal reflection along a concave interface interferes to generate patterns of color. The effect is generated at interfaces with dimensions that are orders of magnitude larger than the wavelength of visible light and is readily observed in materials as simple as sessile water droplets. We further exploit this phenomenon in more complex systems, including multiphase droplets, solid micro-particles, and 3D patterned polymer surfaces to create patterns of iridescent color that are consistent with theoretical predictions. Given the ease by which controllable structural coloration is generated at microscale interfaces, we expect that the design principles and predictive theory outlined here will be of interest for fundamental exploration in optics and application in functional colloidal inks and paints, displays, and sensors.

Melanin, a ubiquitous dark pigment present in various living organisms, is well-known for its two unique optical properties - high refractive index (RI) and broadband absorption, that contribute to structural coloration, photoprotection, and thermoregulation in many biological systems. These dark melanin particles self-assemble strategically in many organisms including avian species to produce a wide gamut of structural colors ranging from vibrant iridescent to earthy colors. Nevertheless, little is discussed about how absorbing species like melanin participate in color production. In this work, we perform optical modeling using the finite-difference time-domain (FDTD) method on melanin particle supraballs and binary melanin and silica particle supraballs to elucidate the role of melanin in structural color generation. By filling this void in the literature, we can open exciting avenues to tune structural colors, and these insights are of interest for many applications including cosmetics, paints, inks, and food colorings.

Self-assembly is one of the cornerstones of the development of nanometer-scale functional materials in living systems. Inspired by nature, researchers have developed methods that use specific short-range interactions between building blocks made possible by DNA to self-assemble prescribed structures. For example, grafting single-stranded DNA to the surfaces of micrometer-scale particles can direct the particles to self-assemble into a diverse set of crystal structures. However, a relatively poor understanding of the dynamic pathways that lead to crystallization has made it difficult to assemble the types of large, defect-free crystals that are required for practical applications in plasmonics or photonics. In this talk I will present a detailed study of the nucleation and growth of DNA-coated particles. I will show an experiment that uses several droplets containing DNA-coated particles that under specific conditions nucleate and grow a single crystal per droplet due to the crystal’s growth depleting monomers from the solution, quickly lowering the supersaturation below where further crystals are likely to form. I will also describe the development of a model, grounded in classical nucleation theory, that predicts the absolute nucleation and growth rates that we observe in experiments. Finally, we apply this knowledge to develop protocols that create colloidal crystals that are large, mono-disperse, faceted, and exhibit pronounced structural coloration using a combination of microfluidics and commercial temperature-control hardware. These advancements in understanding and controlling the dynamic pathways to crystallization with DNA-coated micrometer-scale particles is a firm foundation for future experiments involving the creation of large crystals of the wide variety of structures that thus far have only been self-assembled in small amounts which is a significant step towards approaching the impressive resourcefulness of the natural world.

Over the last few decades, the camouflage capabilities of cephalopods were extensively studied and shown to be enabled by their unique skin morphology. These capabilities are achieved via the complex optical phenomena that occur within the multiple layers of cephalopod skin. The layers may contain one or more types of cells: pigment-based organs called chromatophores that act like color filters; reflective cells called iridophores that act like Bragg stacks; and scattering cells called leucophores that act like broadband diffusers. Iridophores and leucophores possess reflective and scattering properties due to the presence of unusual proteins known as reflectins, which assemble into high refractive index subcellular ultrastructures. We show that such high refractive index structures can be produced in human cells as well. We discuss optical properties of the human cells with and without high refractive index structures, associated challenges, and future potential. The reproduction of the optical elements within the human cells holds a potential for the development of bio-derived optical living materials.

Micron-scale surface modulations such as wrinkles or folds underly a number of modern engineering applications, such as photonic structures in photovoltaics and flexible metasurfaces. Controlled and precise fabrication of these modulations is a challenge for human manufacturing techniques. In stark contrast, biological systems robustly utilize morphological changes in their developmental program to create multi-germ bodies, hairs and scales on spatial scales which would be costly to replicate with human manufacturing. In this talk I will present recent measurements of in-vivo butterfly scale development exhibiting wrinkling. The observations are rationalized with a parsimonious continuum mechanics model.

Accretion of mineralized thin wall-like structures via localized growth along their edges is observed in a range of physical and biological systems ranging from molluscan and brachiopod shells to carbonate-silica composite precipitates. Controlled self-assembly drawing inspiration from these systems holds great potential for fabrication of functional materials with complex geometries. To understand the shape of these mineralized structures, we develop a mathematical framework that treats the thin walls as a smooth surface left behind an evolving space curve which corresponds to the growth front. Our theory that takes an explicit geometric form indicates that in addition to prescribing the interfacial growth speed, the growth of a non-planar 2D pattern in a 3D domain requires a closure equation related to the nature of surface curling, unlike the growth of a bulk crystal in 3D that solely requires a condition for the surface growth rate. The result is a set of equations for the geometrical dynamics of a curve that leaves behind a compatible surface. Solutions of these equations capture a range of shapes such as those of clam shells, rippled chemical garden tubes, and other curled precipitate patterns. Overall, our theory provides a versatile framework for the practical realization of intricate functional morphologies that harness accretive mineralization.

The surface free energy of soft coatings determines the adhesion, friction, and wettability response of solid surfaces in several applications of engineering and biomedical interest. However, the multiscale nature of these phenomena limits a bottom-up prediction of the resulting surface properties.

In this work we use computational experiments to characterize the surface and solid-fluid interface of low-surface-free-energy coatings and materials [1,2]. In particular, the free energy perturbation approach is first used to evaluate the work of adhesion between polymer surfaces and fluids; then, the Young-Dupré equation is adopted to compute the ideal contact angle [3]. Such molecular dynamics and coarse-grained simulations allow to explore the interfacial properties of soft materials, enabling a more comprehensive understanding of their effect on the adhesion, friction, and wettability of solid surfaces. Differently from standardized experimental approaches, numerical experiments allow to understand and decouple the different mechanisms regulating the wetting properties of soft coatings with atomistic precision. The aim is to propose a first step towards a multiscale standard framework for the computational characterization of surfaces, required for the optimal design of materials with tailored surface properties.

The results obtained in this work are validated against experiments and then used as input parameters for materials modelling at higher scales, such as finite elements simulations, to investigate the contribution of surface topology on wettability, in terms of nano- and micro-roughness or patterning. In perspective, multiscale models linking the chemical and topological characteristics of soft surfaces with their effective response will allow predictive in silico testing of new materials with tunable functionalities.

This work received funding by the European Union’s Horizon research and innovation programme under gran agreement No 760827 (OYSTER: OpenCharacterisation and Modelling Environment in Nanoarchitectured Hard/Soft Interfaces,www.oyster-project.eu)

[1] Cardellini et al. "Multi-scale approach for modeling stability, aggregation, and network formation of nanoparticles suspended in aqueous solutions". Nanoscale, 2019.
[2] De Angelis et al. "Exploring the Free Energy Landscape To Predict the Surfactant Adsorption Isotherm at the Nanoparticle–Water Interface". ACS central science, 2019
[3] Cardellini et al. "Integrated Molecular Dynamics and Experimental Approach to Characterize Low-Free-Energy Perfluoro-Decyl-Acrylate (PFDA) Coated Silicon". Material & Design, 2021

Nature provides inspiration for next-generation materials that can dynamically adapt to the changing environments by modulating their properties such as color, adhesion, and stiffness. Inspired by natural examples, there have been many impressive progresses in synthesizing tunable materials that can either actively or passively switch their properties. However, they usually allow a finite number of (usually two) pre-determined configurations, there are few material systems that can “sense” and adapt their properties in response to a dynamically changing environment.

Inspired by bone mineralization mechanisms, we have investigated a multifunctional material system that “senses” mechanical loading and proportionally triggers mineral formation from media with mineral ions so that the material can adaptably change its mechanical property and mitigate damages. The mineralization rate is autonomously modulated in response to changing loading conditions, for example, resulting in a 30-180% increase in the modulus of the material upon 1 to 5 N cyclic loadings (frequency: 2 Hz). Moreover, the material adds more minerals to the region of high stress and vice versa for that of low stress so that the material can mitigate the damage and enhance its fatigue life. We envision that our findings can open new strategies for synthesizing multifunctional materials with dynamically adaptable mechanical properties and damage mitigation.

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).

Acknowledgments: This work was supported by the Air Force Office of Scientific Research Young Investigator Program Award (Award number: FA9550-18-1-0073, Program manager: Dr. Byung-Lip (Les) Lee), Johns Hopkins University Whiting School of Engineering start-up fund, and Temple University Maurice Kornberg School of Dentistry start-up fund (PI: Orrego). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the United States Air Force.

Natural materials often exhibit complex material properties due to hierarchically organized structural motifs at the molecular, nano, micro, and macroscopic size regimes. They have inspired a whole generation of advanced multifunctional synthetic materials that utilize structural hierarchy to reach new property spaces. Self-assembly approaches have been heavily utilized to fabricate these hierarchical materials as its ability to build materials via weak, dynamic interactions between nanometer-sized build blocks provides great control over material structure from the molecular to the micro-scale.

In particular, self-assembled nanoparticle superlattices — three-dimensional ordered arrays of nanoparticles — have been the subject of significant interest due to their emergent properties that arise from the ordering of their nanoparticle building blocks. As a result, these nanoparticles superlattices are promising materials for a variety of applications, from optoelectronics to energy storage. While significant efforts have been made on understanding and controlling the formation of these nanoparticle superlattices, investigations on their mechanical properties are scarce. As the mechanical properties of a material impacts its processing and its suitability for a given application, it is critical that we understand the mechanical behavior of these self-assembled nanoparticle superlattices and develop chemistries to control them.

Here, we discuss how the self-assembly chemistry and superlattice structure impacts the mechanical behavior of these nanoparticle superlattices. Nanocomposite tectons (NCTs), a recently developed nanoparticle superlattice system that uses polymer brush particles functionalized with supramolecular binding groups to drive assembly, are ideal for exploring these parameters as the strength of the supramolecular interactions and the superlattice structure can be easily tuned. In-situ uniaxial compression of substrate-grown hydrogen-bonded nanoparticle superlattices show that these materials undergo significant plastic deformation with an associated loss of nanoparticle ordering. Our systematic nanomechanical experiments, performed to various compression states (up to 50% strain), shed light on the mechanisms of deformation as well as the evolution of properties such as Young’s modulus and yield strength. By modulating the strength of the nanoparticle interactions, via the use of different supramolecular binding groups or covalent bonds, we show that the mechanical properties and deformation behavior of these nanoparticle superlattices can be controlled. The impact of superlattice crystal structure on the mechanical properties are also discussed. These observations provide a more general understanding of how self-assembly chemistry and superlattice structure can be used to control the mechanical properties of these nanoparticle superlattices.

Achieving nanopatterning of a surface is a key point in fields covering microelectronics, photovoltaic, biomedial and biosensors. The purpose of nanopatterning a surface is to increase the surface specificity to improve, for example, nanotechnological devices sensitivity. As cutting-edge technics (e.g. top down methods) are reaching physical limitations and become more and more expensive, light has been put on bottom up methods. This approach relies on the organization of small building blocks to create supramolecular 2D lattices. Nowadays, constructing 2D lattices for nanopatterning is mainly based on self-assembly process with an emphasis on biological self-assembled building blocks. However, these 2D lattices depict thin height which limits their grafting capability and thereby their wider use in nanotechnological field.
In this work, we present a self-assembled protein oligomerization domain able to create large 3D honeycomb lattice based on the natural ability of the protein to self-assemble through head-tail interaction. With electron microscopy analysis, we showed that the orientation of the honeycomb structure on carbon or SiO₂ surface can be modulated. Atomic force microscopy measurements revealed a height of 30 nm corresponding to 40-stacked protein for one pore of the honeycomb. Furthermore, we showed that the amino acid sequence of the protein can be modulate without altering the honeycomb structure. Noteworthy, depending on the amino acid present inside the honeycomb pores, we also showed a specific metal chelation inside the pore.
Altogether, these characteristics make this protein-based 3D lattice a grafting platform never described until now paving the way to design adaptive self-assembled structure for nanotechnological purpose.

An important area of materials research is the development of adaptive structures capable of sensing, reconfiguring, and self-healing with minimal intervention. Such structures will enable the realization of a new class of materials capable of on-demand assembly, reorganization, and disassembly. Inspiration for the development of such structures is found in the survival strategies demonstrated by many insects. For example, fire ants quickly organize themselves into a buoyant raft in the presence of floods, and honey bees aggregate to form bivouacs during turbulent weather conditions. Notably, the structures formed demonstrate viscoelastic behavior with one remarkable feature which distinguishes these aggregations from their synthetic polymer counterparts: the aggregate’s ability to morph from a fluid-like swarm to a global solid-like material. This dynamic behavior is achieved through each insect’s ability to attach and detach to its neighbors. In order to mimic this behavior, liquid crystal elastomer (LCE) rectangular films (strips) (250 µm x 6 mm x 50 µm in cross-section) are programmed to reversibly actuate from a straight to a coiled configuration. By heating these LCE strips and allowing them to aggregate and mechanically interlock with each other, structures capable of reversibly transitioning from a liquid-like state to a solid-like state are achieved. Rheological data of these structures demonstrate an increase in yield stress from 23 Pa at 50 °C to 329 Pa at 150 °C. Along with this increase in yield stress, a reversible negative thermal expansion of 30% is observed. Notably, mechanical properties of the aggregate structure are controlled by tuning individual strip properties. By increasing the length of the individual strips from 3 mm to 12 mm, yield stress increases from 200 Pa to 725 Pa, and by increasing the cutting angle from 0° to 45°, a decrease in yield stress from 459 Pa to 38 Pa is observed. This synthetic aggregate’s ability to reversibly transition from low yield stress to high yield stress on-demand enables various functionalities such as clogging, targeting, and self-healing.

The realization of artificial complex surface pattern, inspired by nature or driven by specific technological needs, requires the use of lithographic techniques which have brought to prominent progress in several fields. However, the standard lithographic techniques are often costly and time-consuming, and do not allow further modification of the pattern once fabricated. The fabrication of superficial micro-textures, in simple and cost-effective way, is high desirable in this framework. A versatile technique for surface micropatterning is based on surface reconfiguration of photosensitive materials, such as light-responsive polymers containing azobenzene molecules.
Azopolymers are material systems able to be directly structured in a reversible way over large scale in simple fabrication schemes without any further development step. Spatially structured UV/visible light fields generate topographic modulations on the free surface of films of such materials by activating cyclic structural transitions between trans and cis isomerization states of the azomolecules. The final surface geometry depends on the irradiated intensity pattern and the light polarization state over the sample, which control the degree of the surface deformation and its directionality, respectively.
Here we demonstrate several large-scale surface textures, with different degrees of complexity and anisotropy, realized by means of simple illumination schemes based on interference lithography and light-induced reconfiguration of pre-structured azopolymer microtextures. In particular, periodic and aperiodic complex surface textures are obtained by means of multiple exposures steps or multiple beam interference. Furthermore, surfaces with programmable directionality and degree of anisotropy have been achieved by reconfiguring symmetric prepatterned azopolymer films, exploiting the peculiar anisotropic response of the material motion to the polarization distribution of the optical field.
The techniques described here allow the all-optical tailoring of surface functionalities directly affected by relief geometry, including anisotropic wetting effects (such as controlled directionality or unidirectional spreading) and substrate-influenced cell growth that opens to the design of new biomaterials generation with improved functionalities and bioactive properties.

The control of shape and intraparticle heterogneity of nano and microstructures in some cases is extremely complex and often even impossible. However, it is important for practical applications, since complex shapes may have influence on rheology, wetting, coating stability, and mechanical properties of bulk composites. Recently, we described a simple and low-cost approach to synthesize nanoparticles applying a delicate composition of monomer, water, and surface properties. We call this synthesis approach Droplet assisted growth and shaping (DAGS). It has been applied in many variants to synthesize various nano- and microstructures based on polysiloxanes which are applied in industrial products, e.g. filters, insulation materials, etc. Beside the different shapes, e.g. filaments, rods, spirals, stars, and others, subsequently, we have been able to extend the range of structures to other materials, e.g. Germaniumoxide, Aluminum oxide and Al-Si-based structures. These structures are useful as coatings for luminescence and/or wetting control of surfaces. In this presentation we will show that further nano- and micromaterials can easily be created: Ceramic structures with defined shapes as well as nano and microstructres with incorprated ultrasmall reactive sites and other heterogeneities which show new properties and can be used for building highly anisotropic and complex coatings. The sequential use of different chemical entities during the synthesis of the nano and microstructures allows for completly new and highly sophisticated shapes. Using those structures as coatings, a precise tuning of surface properties, i.e. wetting, loading with reactive particles and nanocatalysts, adsorption properties and others more, becomes possible.

Beyond these structural properties and performance tuning, this DAGS chemical synthesis strategy is of interest also because of its simple execution: The process can be executed at room temperature, normal pressure, and with simple equipment and low-cost chemicals. The process execution in gas phase of liquid phase both is possible. We also demonstrate potantial for industrial applications.

References:

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Electric fields provide a flexible means to manipulate soft matter, however, they interact with polarizable materials in electrolytic solutions through numerous distinct phenomena making the outcome of field-directed assembly difficult to predict. In this work, a suspension of nanoparticles is found to assemble into a macroscopic cellular phase with particle-rich walls and particle-free voids under the collective influence of AC and DC voltages. This unique, porous structure is observed here at a volume fraction and particle size an order of magnitude smaller than previous examples. Systematic variation of the applied field revealed that the onset of the cellular phase is determined by the volume fraction of the particles, the AC voltage, and the DC voltage. Additionally, a series of control experiments revealed that the complex interactions required to produce a cellular phase in this system include (1) electrochemistry to generate a DC current, (2) electrophoresis to aggregate particles into a 2D arrangement on one electrode, and (3) an instability driven by the long-ranged repulsive and short-ranged attractive electrohydrodynamic interaction that is nucleated at regions on the electrode with high local field enhancement. This mechanistic understanding, along with comparison to prior work, reveals two characteristics needed to observe a cellular phase: a system that is considered two-dimensional and short-range attractive, long-range repulsive interparticle interactions. Furthermore, photolithography was used to localize assembly thus proving the potential to tune the location of the pores in the cellular structure. This understanding paves the way towards electrically-driven assembly of hierarchical porous structures that may impact fields including energy storage and filtration.

Plants exhibit a phototropic growth response and direct the addition of new biomass to optimize collection of solar insolation. Analogous inorganic phototropic growth has been demonstrated via the light-mediated electrodeposition of chalcogen semiconductor materials and can generate highly ordered mesostructures with anisotropic nanoscale features conformally over macroscopic length scales. This process mirrors the phenotypic plasticity exhibited by plants, wherein despite a fixed genotype a wide range of different morphologiess can be displayed depending on the environmental conditions: the precise structure produced is determined by the characteristics of the growth illumination and wide array of structures can be despite a consistent material composition and phase. No structured light field (no photomask) and no physical or chemical templates are utilized. The structure pitch is dependent on the spectral distribution of the input light with shorter wavelengths effecting higher feature densities, similar to how blue light effects branching in many shade-intolerant plants. The out-of-plane growth direction is related to the propagation direction of the input light, mirroring the way in which palm trees develop an observable tilt toward the average position of the solar azimuth. In-plane anisotropy is a function of the input polarization. Modeling of the growth using a combination of full-wave electromagnetic simulations of light absorption and scattering coupled with Monte Carlo simulations of mass addition successfully reproduced the experimentally observed morphologies and indicated that morphology development was directed by evolution of the growth interface to maximize anisotropic light collection. The growth process was observed to be a highly emergent phenomenon involving optical communication between neighboring features including cooperative scattering and synergistic absorption and thus is similar to the manner in which neighboring plants exchange information and avoid competition for light resources.

Biological systems commonly use complex multiscale and multiphasic structures to provide functions that surpass those of artificial systems. Although knowing the chemical makeup of these systems is essential, understanding the passive and active mechanics inside biological systems is critical when examining the various natural systems that reach advanced features like high strength and stimuli-responsive adaptability. Finding out how and why biological systems achieve these desirable mechanical functions frequently exposes concepts that can be used to inform future synthetic designs based on biological systems. In eukaryotic cells, the cytoskeleton is a three-dimensional dynamic structure that helps cells retain their form, internal organization, and mechanical rigidity. The polymer biomolecules in eukaryotic cells that function as structural elements of the cytoskeleton are the actin microfilaments, microtubules, and intermediate filaments. The diseases like cancer transform the cell's cytoskeletal structure. Altered cytoskeletal structures modify cancer cell's ability to contract or stretch by affecting their deformation mechanics. The abnormal cellular motility is a signature characteristic of metastatic cancer cells, promoting tumor cells' spread to both local and distant locations in the body. The dynamic reorganization of the actin cytoskeleton is a fundamental requirement of this process. We have also shown that the cancer cells' altered mechanical properties during disease progression are connected with the actin reorganization. In actin assembly dynamics, actin filaments are severed constitutively by an essential regulatory protein, ADF/Cofilin. Therefore, Several studies were performed to examine the mechanical properties of F-actins. However, the fundamental mechanism that controls F-actin's response to deformation is not understood. In the present study, steered molecular dynamics (SMD) simulation approach has been utilized to understand actin filament mechanics. The work was performed in four computational sets of experiments, namely bending, compression, tension, and torsion simulations. Our findings demonstrate that F-actin's deformation response is regulated by the pattern of dissociation of conformational locks at intra-strand and inter-strand G-actin interfaces. F-actin elongation enabled salt bridge formation at the inter-strand interfaces improving the G-actin-G-actin bond strength. Furthermore, we noticed an inter-strand serrated locking pattern connecting G-actin subunits, restricting their relative movement, thus enabling F-actin's ability to resist deformation. Additionally, we found ADF/Cofilin to cause structural transmutations in f-actin, thus altering their physical properties. The F-actin mechanics described here are vital for constructing a mechanobiological eukaryotic cell model that mimics cell mechanics with disease progression.

Mesoporous, anisotropic architectures that integrate two-dimensional nanomaterials with protein-based polymers are highly promising as biologically-inspired functional materials. In particular, ice-templated freeze-casting offers a facile and economical process to create aligned, nacre-like architectures. Here, we investigated freeze-casting of biologically-inspired composites that incorporate graphene oxide (GO). Silk fibroin, a naturally-occurring polypeptide, forms crystalline β-sheets as a result of hydrogen bonding between repetitive subunits. However, in mesoporous structures, natural polymers like silk fibroin often exhibit limited chemical stability and mechanical strength. We hypothesized that silk fibroin could be reinforced by leveraging the inherent structural stiffness and surface functionalization of GO, a nanomaterial that would readily form hydrogen bonds between silk subunits. By studying the physical, chemical and mechanical properties, we were able to gain insight into the nature of self-assembly of this composite meso-structure.

Our work optimized the freeze-casting process by tuning the pH and freezing direction which resulted in aligned and porous microstructures. Next, we varied the ratio of GO to silk content by weight. We found alterations to the micro-porous structure, mechanical stiffness and uptake of both water and oil with the addition of GO. Moreover, with increasing amounts of GO, there is an increase of stability in water, ionic solutions and oil over relatively long periods of time. Using analytical techniques including FTIR-ATR, Raman, contact angle, compression and other mechanical tests, we were able to deduce structural information and interactions of GO with silk sub-units. Overall, these self-assembled mesoporous materials exhibit outstanding physicochemical properties for extreme mechanics, environmental remediation, and energy storage.

Polymeric particle-based hemostats have been demonstrated to be an attractive technology to halt bleeding through extensive testing in animal models, ranging from arterial injury to blast trauma. While the results of these in vivo experiments have been well documented and utilized to develop subsequent generations of hemostats, the details of particle-target interactions in vitro and their predictive capabilities for in vivo performance has yet to be fully explored. In this work, the size of GRGDS-conjugated PEG-b-PLGA nanoparticles was tuned and its effect on platelet binding, particle adherence to wound-mimetic surfaces, aggregation capability, biodistribution, and circulation lifetime were systematically assessed using various in vitro and in vivo experiments. Smaller and intermediate-sized nanoparticles were all found to specifically bind a larger number of activated platelets when compared to larger (>250 nm) particles, while incubation of these larger particles on collagen and activated platelet-coated surfaces led to a higher total mass of polymer bound. Intermediate particle diameters led to the greatest number of platelets aggregated on a surface relative to agonist-only positive controls. Finally, larger particles experienced faster clearance and higher pulmonary accumulation per organ mass in an uninjured murine model, whereas smaller particles exhibited longer circulation and retention times and increased accumulation in the liver. To assess hemostatic efficacy, these three distinct sizes were challenged with a lethal inferior vena cava (IVC) puncture model. The intermediate nanoparticle size was observed to result in the most significant increase in survival over the course of two hours (P = 0.0060), as well as the greatest accumulation at the injury site relative to uninjured vessel controls. These results indicate that tuning particle size provides a key handle for engineering the performance of particle-based hemostat systems, and may influence its efficacy in treating various types of lethal internal hemorrhage.

The creation of inter-crystalline organic inclusions is one of Nature’s strategies to enhance the mechanical properties of biominerals. As was shown synthetically for calcite, the most abundant marine biomineral, incorporated pinned organic species act as barriers for dislocations movement. Thus, they increase the hardness of the single-crystalline calcite host.
Inspired by this phenomenon, we showed in the past that a variety of semiconductors, both fully inorganic and hybrid organic-inorganic, are able to incorporate single amino acids. This incorporation induces a measurable increase in the optical band gap of the semiconducting host, which results from charge localization created by the incorporated amino acids.
Here, we decided to study the influence of amino acids incorporation on yet another set of properties, namely the magnetic properties of manganese (II) carbonate (MnCO₃). Similarly to the isostructural calcite, we discovered that certain amino acids can be incorporated into the crystalline structure of the host. Using high-resolution powder X-ray diffraction (HR-PXRD, using synchrotron source), we measured an anisotropic lattice expansion, of both a- and c-parameters, resulting from amino acids incorporation. These induced lattice distortions can be relaxed upon heating and organics decomposition. When we measured the magnetic properties of amino acid-incorporated MnCO₃, we observed the predicted paramagnetic behavior, namely, a positive and linear relation between the magnetization, M, and the applied magnetic field, H. Nevertheless, the magnetic susceptibility (which was taken as the slope of the M-H curve), was observed to decrease with the increase of incorporated amino acids concentration. This decrease follows the simple rule of mixtures, indicating the creation of a MnCO₃-amino acid composite.
MnCO₃ is known to possess a Néel temperature of about 32 K. At this temperature, it undergoes a magnetic phase transition, from a paramagnetic to a canted antiferromagnetic phase. When we repeated our M-H measurement at 2 K, we discovered the opposite trend: the increase in magnetic susceptibility upon the increasing amount of incorporated amino acid. Moreover, the Néel temperature itself decreases. During amino acids incorporation, the inter-atomic distances inside MnCO₃ increases. This results in a weakening of the magnetic interaction, which makes the MnCO₃ crystal more sensitive to external changes, such as the applied magnetic field and the changes in temperature.

Bioinspired ion transport membranes have been widely investigated for energy storage applications. The high theoretical specific energy density (2600Wh/kg) and high specific capacity (1675mA/g) along with the natural abundance and low toxicity of sulfur have been attracting significant attention for the development of an alternative battery system to replace traditional lithium-ion batteries which suffer from safety and capacity/energy density limitations in various applications. However, challenges such as polysulfide dissolution and shuttling prevent the mass commercialization of metal sulfur batteries. Inspired by biological ion transport mechanisms, we show a practical yet comprehensive approach for the development of high-performance metal sulfur batteries. Aramid nanofiber (ANF) based composite ion transport membranes not only prevent dendrite formation but also confine polysulfides on the cathode side. ANF composite battery separators provide diverse and opposing properties including high mechanical properties, high ionic conductivity, and high thermal/chemical stability. The highly selective ion sieving properties of these biomimetic separators provide safe and high-performance batteries. Fabrication of such biocompatible, affordable, flexible, and high energy density battery is quite crucial in powering next-generation electronics including but not limited to portable, wearable, and implantable biomedical devices.

Compartment systems encapsulating RNAs have gained significant interests as artificial cells and drug delivery systems. Cells form liquid membraneless organelles to localize and control RNAs’ activities. Specifically, multiphasic biomolecular condensates are appealing as material systems to have an impact on functional control of RNA and other biomolecular processes. However, the understanding of the relationship between RNA chemistry and multiphasic biomolecular condensates is still lacking that limits the development of such RNA compartments for various applications. Therefore, inspired by these multiphasic biomolecular condensates, we investigated complex coacervates composed of simple biomolecules, such as oligopeptides, and their impact on RNA partitioning and hybridization. Complex coacervates are organic-rich phases or droplets, formed by spontaneous liquid-liquid phase separation of mixed oppositely charged molecules. Complex coacervates share similarities to liquid biomolecular condensates in cells and have great encapsulation efficiency of RNAs. Here, we present that coacervates can have different levels of RNA partitioning and hybridization depending upon the length and identity of oligopeptides. We recently found that multiphase complex coacervate droplets can have different RNA partitioning and hybridization levels in each phase due to local differences in RNA-peptide interactions without specific RNA binding motifs. This study aids fundamental understanding of how biocondensates influence RNA localization and function, and points to design strategies for artificial cells construction using coacervate droplets.

Responsive materials capable to autonomously and reversibly adapt to their chemical environment hold great promise in the design of artificial chemo-intelligent life-like soft material platforms. In this context, we are using active complex emulsions, kinetically stabilized multiphase dispersions of fluids, as an intrinsically out-of-equilibrium material platform that can act as structural controlling elements for the generation of a variety of functional intricate, responsive and adaptive, precision objects. The dynamic multiphase emulsion droplets are formed from two or more immiscible fluids that are immiscible at room temperature but exhibit a lower (LCST) or upper critical solution temperature (UCST). Emulsification of the mixture below LCST or above UCST enables a simple one-step generation of complex multicomponent emulsions with highly uniform internal droplet morphologies. The internal droplet geometry of these dynamic liquid colloids is exclusively controlled by the force-balance of interfacial tensions acting at the individual interfaces, which allows altering the droplet geometries also after emulsification.
The complex emulsions can be hardened or gelled, e.g. by using photo-crosslinkable acrylate monomers as the constituent droplet phases. Upon polymerization, the shape of the droplet molds is essentially retained and a compartmentalization of designer surfactants, biologicals, polymer, and nanoparticle solutes enables their use as functional “cytoskeletons” for the generation of Janus particles with tunable shape, functionality and wettability profiles, functional thin-films as well as defined 3D objects and meso- and macroscale assemblies. In addition, as a result of the refractive index contrast of the individual phases, the particles can manipulate the pathway of light passing through these micro-scale colloids. Examples on how an associated understanding of the unique chemical-morphological-optical coupling inside these chemically functionalized active soft matter colloids give rise to a variety of new and improved application concepts, including in biomimicry, (photo-)catalysis, optical imaging platforms, as structural templates for the generation of precision objects, and as chemo-intelligent transducers in chemo- and biosensing applications will be presented.

Physically-crosslinked hydrogels exhibit highly useful properties that are impossible with traditional hydrogels but crucial for a wide variety of emerging applications in industry or biomedicine. Yet, these materials typically employ enthalpy-dominated crosslinking interactions that become more dynamic at elevated temperatures, leading to network softening. Indeed, standard mathematical frameworks typically assume network softening and faster dynamics at elevated temperatures. Yet, deriving a mathematical framework connecting the crosslinking thermodynamics to the temperature-dependent viscoelasticity of physical networks suggests the possibility for entropy-driven crosslinking interactions to provide alternative temperature dependencies. Herein, we will discuss the investigation of a physical hydrogel platform exploiting dynamic multivalent interactions between biopolymers and nanoparticles that are strongly entropically driven. We will discuss the implications of these crosslinking thermodynamics on the observed mechanical properties, demonstrating that tuning the thermodynamics and kinetics of these crosslinking interactions enable broad modulation of the mechanical properties of these materials, including their shear-dependent viscosities, temperature responsiveness, self-healing, and cargo encapsulation and controlled release. In particular, these materials exhibit viscous flow under shear stress (shear-thinning) and rapid recovery of mechanical properties when the applied stress is relaxed (self-healing), affording facile processing though direct injection or spraying approaches, making then well served for applications ranging from wildfire prevention to biomedicine. Overall, this talk will illustrate our recent efforts exploiting dynamic and multivalent interactions between polymers and nanoparticles to generate hydrogel materials exhibiting properties not previously observed in physical hydrogels and affording unique opportunities in industry and biomedicine.

Insulin was first isolated a century ago, yet commercial formulations of insulin and its analogues for hormone replacement therapy falls short of mimicking the endogenous glycemic control that occurs in non-diabetic individuals. Insulin formulations that better mimic secretion from the beta-cells, by enabling more rapid insulin absorption kinetics and/or co-delivering complementary hormones (i.e. amylin), are needed to reduce patient burden and improve glucose management. However, formulation innovation is complicated by the poor stability of insulin monomers and amylin. We have developed a polymeric excipient platform using amphiphilic acrylamide copolymers that can be used to increase the stability of insulin in formulation. Here I will present on the use of these designer excipients, to develop an ultrafast monomeric insulin lispro and an ultra-stable insulin for improved global access.

A formulation of insulin monomers would more closely mimic endogenous postprandial insulin secretion, but monomeric insulin is unstable in solution using present formulation strategies and rapidly aggregates into amyloid fibrils. Amphiphilic acrylamide copolymer (AC/DC) excipients preferentially adsorb to the air-water interface and disrupt interfacial insulin-insulin aggregation events. Combining a AC/DC excipient with monomeric insulin lispro enables stable formulation under stressed-aging conditions for up to 25 hours compared to only 5 hours for commercial fast-acting insulin lispro formulations (Humalog). In a diabetic pig model, our ultrafast monomeric lispro formulation demonstrated unprecedented ultrafast absorption kinetics, exhibiting peak action at 9 minutes, whereas commercial Humalog exhibited peak action at 25 minutes. The more rapid onset and shorter duration of action observed in our monomeric lispro formulation has the potential to better control mealtime glucose excursions.

Moreover, the prevalence of diabetes is rising in middle and low-income countries. Current commercial insulin formulations require costly refrigerated transport and storage to prevent loss of insulin integrity. Our AC/DC excipients can be used as a simple additive to current standard commercial insulin formulations and demonstrated we can extend stability, while maintaining formulation integrity, bioactivity, pharmacokinetics and pharmacodynamics, for over 2 months in stressed aging conditions that cause current formulations to fail in under 2 days. These enhanced insulin formulations are promising candidates for improving glucose control and reducing burden for patients with diabetes.

Self-propelling micro- and nano-motors (MNMs) have been extensively investigated as an emerging oral drug delivery carrier for gastrointestinal (GI) tract diseases. However, the propulsion of current MNMs reported so far is mostly based on the redox reaction of metals (such as Zn and Mg) with severe propulsion gas generation, remaining non-degradable residue in the GI tract. Here, we develop a bioinspired enzyme-powered biopolymer micromotor mimicking the mucin penetrating behavior of Helicobacter pylori in the stomach. It converts urea to ammonia and the subsequent increase of pH induces local gel-sol transition of the mucin layer facilitating the penetration into the stomach tissue layer. The successful fabrication of micromotors is confirmed by high-resolution transmission electron microscopy, electron energy loss spectroscopy, dynamic light scattering analysis, zeta-potential analysis. In acidic condition, the immobilized urease could efficiently converted urea to ammonia, comparable with that of neutral condition because of the increase of surrounding pH during propulsion. After administration into the stomach, the micromotors show enhanced penetration and prolonged retention in the stomach for 24 h. Furthermore, histological analysis shows that the micromotors are cleared within 3 days without causing any toxicity in the GI tract. The enhanced penetration and retention of the micromotors as an active oral delivery carrier in the stomach would be successfully harnessed for the treatment of various GI tract diseases.

Resilin-like polypeptides (RLPs), bioinspired protein-engineered polymers derived from the elastomeric insect protein resilin undergo phase separation upon cooling below their Upper Critical Solution Temperature (UCST), which can be precisely controlled by altering their amino acid composition. The native extracellular matrix (ECM) is characterized by structural and compositional heterogeneity across varying length scales. Current state-of-the-art soft matter patterning techniques for generating sophisticated ECM mimics are limited due to their reliance on expensive equipment and multiple time- and energy-intensive steps. Therefore, photocrosslinking distinct morphologies of multicomponent RLP solutions undergoing phase separation offers a relatively simple alternative for the fabrication of microstructured hydrogels. RLPs enriched in select aromatic and aliphatic residues were recombinantly produced in bacterial expression hosts and purified via immobilized metal affinity chromatography. Gel electrophoresis and mass spectrometry were used to confirm their composition and purity. The thermal response of distinct RLPs and their multicomponent solutions was investigated via turbidimetry. The RLPs reported in this study fall into two main categories based on their physicochemical properties. Molecules in the first category, defined as phase separating RLPs (psRLPs) demonstrate robust UCST-type behavior, and function as cell-friendly porogens/templating agents. Lysine residues along the polypeptide backbone of the molecules in the second category were modified to produce photocrosslinkable RLP-acrylamide (pcRLP-Ac), which upon UV irradiation in the presence of photoinitiator and psRLPs result in the formation of microporous hydrogels. Confocal microscopy data indicate that harnessing the interplay of inter-and intramolecular interactions between distinct psRLP and pcRLP-Ac molecules allows further control over pore size. The average pore size observed in hydrogels enriched in aliphatic residues was approximately 10 μm, an order of magnitude lower than the average pore size observed in hydrogels enriched in aromatic residues (ca. 100 μm). We report a simple biofabrication method to produce microstructured hydrogels for use as cell-instructive materials to support regenerative medicine applications.

In nature, plants use water-responsive (WR) materials that deform in response to humidity changes to drive their essential movements. Recent studies have shown that such kind of WR actuation could be extremely powerful and hold great potential to be used as actuating components for robotics, shape-morphing, and energy harvesting. Here, we present that peptidoglycan (PG) extracted from gram-positive bacteria Saccharomyces cerevisiae and Staphylococcus aureus show significant water-responsiveness such that their WR actuation energy density and efficiency reach 39.6 MJ m^-3 and 38.4%, respectively, surpassing those of frequently used actuator materials. PG is the primary component of gram-positive bacterial cell walls, and it shows distinct architectures and molecular structures across different bacteria species. For example, peptidoglycan extracted from Saccharomyces cerevisiae (~2000 nm) is thicker than that from Staphylococcus aureus (~500 nm). Moreover, PG of Staphylococcus aureus have polysaccharides of alternating N-acetyl-glucosamine and N-acetyl-muramic acid crosslinked by peptide stems, whereas PG of Saccharomyces cerevisiae consists of two types of polysaccharides: β-1,3 and β-1,6 linked glucose and β-1,4 linked NAG. Meanwhile, Saccharomyces cerevisiae PG is not crosslinked by peptide stems but by the alkali-sensitive bond to mannoproteins or disulfide link to the PIR protein. By using a liquid AFM, we also showed that these PG consist of nanoscale pores with different porosities, pore sizes, and geometries. Using a customized AFM, we characterized WR strain and energy density of Staphylococcus aureus PG and Saccharomyces cerevisiae PG, and found that Staphylococcus aureus PG, with a lower WR strain (11.2 %), exhibits a much higher WR energy density (39.6 MJ m^-3) than that of Saccharomyces cerevisiae PG (6.0 MJ m^-3). By introducing pressure disturbance on PG’s surface using the AFM, we also measured these two PGs’ relaxation dynamics, and found that Staphylococcus aureus PG’s higher WR energy density strongly correlates to its super viscous nanoconfined water. Our findings suggest that highly viscous confined water resulted from nanoporous Staphylococcus aureus PG’ plays an important role in the energy conversion from water’s chemical potential to PG’s mechanical deformations, which could be serving as general criteria for high-efficiency WR structures.

Millions of years before people began to generate functional nanostructures, biological systems were using nanometer-scale architectures to produce unique functionalities. Some nocturnal moths use hexagonal arrays of subwavelength nipples as antireflection coatings to reduce reflection from their compound eyes. Similar periodic arrays of nanopillars have also been observed on the wings of cicada to render superhydrophobic surfaces for self-cleaning functionality. Inspired by these natural nanostructures, we have developed various bottom-up nanofabrication technologies for producing wafer-scale, self-cleaning, broadband antireflection coatings on a large variety of technologically important optical substrates, such as crystalline silicon, GaAs, polymer, and glass. These techniques combine the simplicity and cost benefits of bottom-up self-assembly with the scalability and compatibility of standard top-down microfabrication. The resulting subwavelength-structured antireflection coatings can greatly suppress light reflection, promising for a spectrum of applications ranging from highly efficient photovoltaics and light emitting diodes to smart optical devices. By integrating this biomimetic design with smart shape memory polymers, we have demonstrated tunable antireflection coatings with multi-stimuli-responsive optical properties.

Architected biomaterials, as well as sound and music, are constructed from small building blocks that are assembled across time- and length-scales. Here we present a novel deep learning-enabled integrated algorithmic workflow to merge the two concepts for radical discovery of de novo protein materials, exploiting musical creativity as the foundation, and extrapolating through a recursive method to increase protein complexity by successively injecting protein chemistry into the process. Indeed, music is able to overcome differences among people and nations, creating bridges between cultures, and to find associations between seemingly unrelated concepts, and can form a novel way to generate bio-inspired designs that derive functions from the imaginations of the creative mind. Earlier work (Buehler et al., ACS Nano, 2019) has offered a pathway to concert proteins into sound, and sound into proteins. Here we build on this paradigm and translate a piece of classical music into matter. Based on a sytematic analysis of different pieces including J.S. Bach’s Goldberg variations and Leonard Bernstein's Chichester Psalms, we offer a series of case studies to convert the musical data imagined by the composer into protein design, and folded into a 3D structure using deep learning. The quest we seek to address is to identify semblances, or deep-time memories, or information content in such musical creation, that offers new insights into pattern relationships between distinct manifestations of information. The resulting protein forms the basis for iterative musical composition, and an evolutionary paradigm that defines a variational pathway for melodic development, complementing conventional creative or mathematical methods. This paper broadens the concept of what is understood as bio-inspiration to include a broad array of signals and designs created by humans, animals, or complex physical mechanisms.

Piezoelectric biomaterials are intrinsically suitable for coupling mechanical and electrical energy in biological systems to achieve in vivo real-time sensing, actuation, and electricity generation. However, the inability to synthesize and align the piezoelectric phase on a large scale remains a roadblock toward practical applications. We present a wafer-scale approach to creating piezoelectric biomaterial thin films based on γ glycine crystals. The thin film had a sandwich structure, where a crystalline glycine layer self-assembles and automatically aligns between two polyvinyl alcohol (PVA) thin films. The heterostructured glycine-PVA films exhibited piezoelectric coefficients of 5.3 pC/N or 157.5×10−3 Vm/N, and nearly an order of magnitude enhancement of the mechanical flexibility compared to pure glycine crystals. With its natural compatibility and degradability in physiological environments, glycine-PVA film may enable the development of transient implantable electromechanical devices

The optical properties of the primary pigment that facilitates rapid and precise appearance changes in cephalopods, xanthommatin, have been evaluated for a variety of applications including electrochromic displays and photoprotective films. However, the fundamental mechanisms underlying the optical performance of xanthommatin upon irradiation with solar light remain incompletely characterized. We investigated irradiation-induced color changes of xanthommatin that could be controlled by manipulating the pH of the surrounding environment. Photoreduction of the pigment in acidic conditions was enhanced by incorporating additional ultraviolet (UV)-responsive materials (e.g., disulfides) to generate redox agents upon irradiation. We leveraged these dose-dependent optical changes to create colorimetric UV light sensors, which can be incorporated into a user-friendly microfluidic architecture that can be worn or surface-mounted. These devices provide radiation-driven responses that may be useful for personal solar monitoring, tracking exposure of perishable goods, or verifying UV dose thresholds for germicidal sterilization.

This work presents the results of a combined experimental and analytical study of the mechanical properties of bioprocessed mycelium nanocomposites that are reinforced with self-organized cellulosic fibers. The bioprocessed mycelium nanocomposite blocks were composed of cellulose/hemicellulose hemp-duct with varying laterite percentage compositions. The mycelium functions as a supportive matrix holding the reinforcing hemp-duct particles within its filamentous structural network. In-situ studies of the mechanical properties of the composites were conducted to determine the hardness, compression/flexural properties, and fracture toughness/resistance-curve behaviors. For supportive evidence and to gain further insight into the failure mechanism, the microstructure and strain mapping of the resulting composites at relevant stages of compression was characterized using SEM and DIC, respectively. The observed deformation and fracture mechanisms are then used to provide insights for the prediction of the composite strength and resistance-curve behavior. The implications of the results are discussed for the bioprocessing of mycelium-nanocomposite for sustainable building materials.

Nature produces soft materials possessing exceptional mechanical properties. These properties are to a large extent related to the well-defined structures and locally varying compositions of these natural materials. Key to the excellent control nature possesses over the structure and local composition of its materials is their fabrication: Many of these materials are formed from compartmentalized reagents that are transported to the desired locations where they are released locally. Inspired by nature, we use emulsion drops as compartments to build macroscopic granular hydrogels. In this talk, I will demonstrate how we convert individually dispersed emulsion drops into selectively permeable viscoelastic capsules that enable controlled localized release of reagents. These capsules are most frequently employed as individually dispersed delivery vehicles. In the second part of this talk, I will demonstrate how we go a step beyond the current use of capsules by converting them into inks that can be 3D printed into strong and tough double network granular hydrogels.

Biominerals are a class of inorganic-organic composite materials that exhibit function-optimized properties. These properties arise from a hierarchical organization of primary building blocks. While some biomineral producing organisms can alter these properties in response to environmental stresses, this generally involves a time-intensive process of resorption and reprecipitation. In this presentation, we show that the load-bearing shells of the brachiopod Discinisca tenuis can dynamically modulate their mechanical properties in response to environmental changes. They gradually transition from hard and stiff to fully malleable as a function of water content in the environment/ their structure. Using a combination of Cryo ptychographic X-ray computed tomography, electron microscopy, spectroscopy, in-situ wide-angle X-ray scattering and mechanical testing, we describe the hierarchical structure and composition of these shells to reveal the structural motifs and deformation mechanism that endow the shells with this adaptability.

Continental is widely known as the tire company. However, the company has a wide product range for multiple applications in the automotive industry as well as beyond.
Contitech Business Unit Surface Solutions specializes in innovative and functional films and multilayer textile laminates which are applied in the automotive industry, transportation, and many other business fields e.g. cruise ships, stadiums, and hotels.
In this presentation we describe smart and functional materials that exhibit self-healing properties and breathability for seating applications in the field of artificial leather materials. These materials must fulfill a wide range of specific tests, ranging from flame retardant behavior, stain-, flexibility- and abrasion- resistance as well as decent haptic touch and environmental impact resistance. The breathable material is made by several layers and pores that are generated in situ, allowing the penetration of air and humidity. Furthermore, the hybrid approach of soft PVC and polyurethane allows the free passage of water vapor through the material depending on the relative humidity level. This technology may allow a reduction of energy use (for example by reducing the need for air conditioning), especially in seating applications. Use of upcycling raw materials such as used coffee grounds reduce the CO₂ footprint of the material.
The second topic of self-healing materials is an in situ generated polyurethane system based on a solid phase reaction of a diamine. A chemically controlled reaction allows production of a defined polymer chain length range, which leads to a self-healing coated fabric. Material cuts heal within minutes by the adhesion of small fast migration molecules which tend to concentrate on the surface of the cut material, leading to an initial adhesion similar to the healing process of human skin. Longer chain polymers migrate and stabilize the cut to its full strength. Mechanical tests show no reduction of performance of the healed materials.

Self-cleaning is the most prominent feature of superhydrophobic surfaces [1]. Macroscopic contamination such as dust is indeed easily cleaned away by water drops rolling across the superhydrophobic surface. A lot of research went into exploring different strategies to achieve long-lasting and highly liquid-repellent surfaces [2]. Despite the enormous interest in superhydrophobicity, it is still unclear when microscopic and in particular nanoscopic contamination (soot, aerosols, etc.) influences superhydrophobicity and how self-cleaning works in detail.

To gain an in-depth insight into self-cleaning, we monitored self-cleaning at the micron scale using laser scanning confocal microscopy [3]. Aiming to correlate self-cleaning, surface topography and particle size and hydrophilicity, we contaminated different surfaces with particles varying four orders of magnitude and having different polarities. When the drop is moved over the contaminated surface, individual particles were picked up at the advancing edge. Upon further movement of the drop, these particles accumulated at the lower air-water interface of the drop. To design superhydrophobic surfaces that are resistant to hydrophobic as well as hydrophilic particle contamination, the pore size of the superhydrophobic surface needs to be smaller than the contamination particle size. Even smaller nanoscopic contaminants do not necessarily degrade superhydrophobicity.

While the ability to withstand various kinds of contamination is essential, the ease of self-cleaning is equally crucial. To remove particles from a superhydrophobic surface, the capillary force acting on the particle at the rear side of the drop needs to overcome the adhesion force between the particle and the surface. We quantified the forces involved in the self-cleaning process and compared the experimental results with quantitative calculations.

To compare the results based on model contamination to real-world outdoor exposure, we fixed several coated fabrics on a car. These fabrics repelled water and organic liquids and were chosen because of their robustness. They were obtained by coating polyester fabrics silicone filaments. These superhydrophobic surfaces having a nanoscale pore size surfaces are capable of resisting long-term real-world exposure and industrial contamintion tests.

[1] Barthlott, W. & Neinhuis, C.: Purity of the sacred lotus, or escape from contamination in biological surfaces. Planta 202, 1–8 (1997).
[2] Bhushan, B. & Jung, Y.C.: Natural and biomimetic artificial surfaces for superhydrophobicity, self-cleaning, low adhesion, and drag reduction. Prog. Mater. Sci. 56, 1–108 (2011).
[3] Geyer F., D’Acunzi M., Sharifi-Aghili A., Saal A., Gao N., Kaltbeitzel A., Sloot T.F., Berger R., Butt H.J. &Vollmer D.: When and how self-cleaning of superhydrophobic surfaces works, Science Adv., 2020, 6: eaaw9727

Many aquatic animals use reflective optics in their eyes. The nature of the reflective materials underling these systems is often unknown. A fascinating example is the reflecting superposition compound eye of decapod crustaceans. This eye contains a distal mirror which focusses light across onto the retina and a photon-enhancing tapetum reflector. Previous reports¹ suggested that both the tapetum and distal mirror were formed from high refractive index crystals of isoxanthopterin. We present a comparative study of reflecting optics in the eyes of several decapods to reveal that: (i) the distal mirror is formed from xanthopterin crystals, not isoxanthopterin and (ii) many species contain a third reflector – the ‘reflective cap’ which underlies the cornea and which appears to function as a camouflage device. Cryo-SEM, TEM in-situ X-ray diffraction studies showed that the distal mirror in the eyes of decapods is formed from polycrystalline rods of xanthopterin crystals. These rods are aligned in a 3-tiered multilayer reflector surrounding the distal portion of the ommatidia. The mirror boosts the reflection of off-axis light at the walls of the ommatidia, enhancing the amount of light of focused on the retina. In several species a third reflector – the reflecting cap resides immediately above the distal mirror. The reflective cap is formed from a dense array of crystalline isoxanthopterin nano-spheres identical to those found in the tapetum². Optical ray-tracing and comparative anatomy of decapods from diverse habitats shows that the reflecting cap is a camouflage device, which deflects light away from the underling conspicuous screening pigments.

Structural colour is a widespread phenomenon in nature, especially well-known in its production of brilliant high intensity hues in insects and feather. More recent developments have demonstrated the sometimes more subtle effects of structural colour in plants, for example fruits [1], leaves [2] and flowers [3].
Epicuticular waxes are well known for their striking hydrophobic qualities [4], and many other potential functions across plant organs. We discuss a previously unreported phenomenon of coloration from natural epicuticular wax crystal surface coatings. Widespread in nature, these offer a new self-assembled avenue to alternative coloration for artificial application without dye molecules. We report on the chemical and mechanical composition of these materials, and their in vitro recrystallisation for use as colorants.
[1] R. Middleton, M. Sinnott-Armstrong, Y. Ogawa, G. Jacucci, E. Moyroud, P. Rudall, P.J. Prychid, M. Conejero, B.J. Glover, M.J. Donoghue, S. Vignolini, Current Biology, 2020 Viburnum tinus Fruits Use Lipids to Produce Metallic Blue Structural Color
[2] M. Jacobs, M. Lopez-Garcia, O. Phrathep, T. Lawson, R. Oulton, & H. Whitney, H. Nature Plants, 2016. Photonic crystal structure of Begonia chloroplasts enhances photosynthetic efficiency
[3] E. Moyroud, T. Wenzel, R. Middleton, P.J. Rudall, H. Banks, A. Reed, G.Mellers, P. Killoran, M.M. Westwood, U. Steiner, S. Vignolini, & B.J. Glover, B. J. Nature, 2017. 550(7677), 469–474. Disorder in convergent floral nanostructures enhances signalling to bees
[4] K. Koch & W. Barthlott, W. Natural Product Communications, 2006 Plant Epicuticular Waxes: Chemistry, Form, Self-Assembly and Function.

The orientation of fibers in the arthropod cuticle, made of chitin and proteins, strongly affects its physical properties, which in turn determines morphogenesis and functionality. Fiber orientation therefore needs to be spatially and temporally controlled by the animal. The arthropod cuticle is often described as liquid crystal (LC) analogues as it exhibits structural similarity to LC but are solid in its functional state. Using focused ion beam/scanning electron microscopy (FIB/SEM) volume imaging and scanning X-ray scattering, we show that the epidermal cells depositing the cuticle, determine an initial fiber orientation, from which the final architecture emerges by the self-organized co-assembly of chitin and proteins. Fiber orientation in the locust cuticle is therefore determined by both active and passive processes.

Melanins are natural biopolymers that have remarkable properties including UV-protection, coloration and antioxidant activity. Their biosynthesis is regulated both spatially and temporally and involves supramolecular templating and compartmentalization of enzymes and reactants within specialized organelles called melanosomes. In contrast, the laboratory-based bulk synthesis of melanin by tyrosine or dopamine oxidation is a poorly controlled process, resulting in materials with undefined properties. Inspired by the pigment's biosynthesis, we developed a methodology to spatiotemporally regulate melanin formation in liquid droplets. The spatial control is achieved by sequestration of the reaction in dextran-rich droplets of a polyethylene glycol/dextran aqueous two-phase system, where the use of a photocleavable protected tyrosine provides a temporal control over its enzymatic oxidation-polymerization. This methodology opens tremendous opportunities for applications in skincare and biomedicine.

Ultrastructural analysis of morphological features of highly hydrated biomaterials is still a difficult task. In structural biology, specifically protein structure determination, cryo-preparation and cryo-imaging have led to a “resolution revolution” [1]. While vitrification – the embedding in amorphous ice – is routinely achievable for concentrated protein solutions, the situation is different for carbohydrates or bio-inspired hydrogels. Their water content can be so high that conventionally used freezing methods – e.g. “flash freezing” followed by lyophilization – may not provide accurate ultrastructural features such as the exact size of pores [2]. For alginate hydrogels the effects on matrix morphology of different freezing techniques - including high-pressure freezing, the gold standard for cellular material – were analyzed in detail using cryo-SEM [3]. Pore sizes varied by two orders of magnitude from micropores in the range of tens of nanometers to macropores in the micrometer range, depending on the freezing method used. Although high pressure freezing was found in this study to be the most suitable freezing method it cannot be applied to large or more complex systems, because sample size is limited to roughly 2x2x0.2 mm. Analyzing e.g. the interaction of a pectin-based pleural sealant with the outer surface of the mammalian lung [4] is not possible with this approach.

Another important aspect when imaging low atomic number Z materials in an electron microscope is the lack of contrast – conventionally this is solved by “staining” materials with high Z metal (Ru, Os, U) compounds. For carbohydrates and many hydrogel materials without reactive groups this procedure is not straightforward.

Due to these numerous limitations and the need for rather sophisticated machinery for cryo-preparation and cryo-imaging we were looking for alternative, more easily accessible methods.
One approach, which has been used in the early days of cryo-preparation, is the replacement of freely diffusible water in a sample by a number of reagents, which either directly dehydrate the sample in a gentle way or help prevent formation of ice-crystals during a sub-optimal freezing regime. We tested partial dehydration with ethanol or tannic acid, and infiltration with trehalose to reduce the amount of free water, which would otherwise be available for crystallization. In combination with osmium tetroxide alone or together with ruthenium red we were able to introduce sufficient contrast to image bulk samples or thin sections from resin-embedded hydrated carbohydrates in an SEM at highest resolution.
For biomaterial films fabricated with pectins from different plant sources we could demonstrate different morphologies – from a more globular aspect for potato pectin to a highly branched network of interconnected carbohydrate chains for lemon and orange pectin. Controlling the degree of dehydration during the initial preparation step allowed us to visualize carbohydrate networks with different pore sizes.
We are currently investigating how to apply our preparation protocols to a number of different hydrogel classes with different pores sizes and validating the effects of the different reagents used on water content and morphology.

[1] Kühlbrandt W. (2014) The Resolution Revolution. Science 343, 1443; DOI: 10.1126/science.1251652
[2] Kaberova Z. et al. (2020) Microscopic Structure of Swollen Hydrogels by Scanning Electron and Light Microscopies: Artifacts and Reality. Polymers 2020, 12, 578; https://doi.org/10.3390/polym12030578
[3] Aston R. et al. (2016) Evaluation of the impact of freezing preparation techniques on the characterisation of alginate hydrogels by cryo-SEM.European Polymer Journal, 82,1https://doi.org/10.1016/j.eurpolymj.2016.06.025
[4] Servais A.B. et al. (2018) Functional Mechanics of a Pectin-Based Pleural Sealant after Lung Injury. Tissue Eng Part A 24, 199; DOI: 10.1089/ten.tea.2017.0299

Nature-inspired nanopatterning offers exciting multifunctionality spanning antireflectance and the ability to repel water/fog, oils, and bacteria; strongly dependent upon nanofeature size and morphology [1,2]. Broadly, this multifunctionality is inherent to and bridged by the nanocone structure, yet such patterning in glass (SiO₂) – a material of great practical importance – remains a bottleneck due to its high chemical stability alongside structuring at the nanoscale itself, which becomes increasingly challenging to manage as the pattern resolution advances (pitch <100 nm).
Here, we demonstrate a novel Regenerative Secondary Mask Lithography process which enables customized glass nanopillars through dynamic nanoscale tunability of the side-wall profile and aspect ratio (>7). Our method is facile and versatile, comprising just two steps. Firstly, we generate sub-wavelength scalable soft etch-masks (55-350 nm) through an example of block copolymer micelles or nanoimprinted photoresist. Secondly, we overcome their inherent durability problem – typically addressed by metal/metal oxide incorporation which adds time and complexity – through our innovative cyclic etching. During this etching, the original mask becomes embedded within a protective secondary organic mask, which is tuned and regenerated, permitting dynamic nanofeature profiling with etching selectivity >1:32.
We envision that such structuring in glass will facilitate fundamental studies and be useful for myriad of practical applications – from displays to architectural windows. Providing the highly-tunable nature of our method (size/shape/pitch), we tailor glass features and present excellent broadband omnidirectional antireflectivity, self-cleaning, and unique antibacterial activity towards Staphylococcus aureus.

[1] D. P. Linklater, V. A. Baulin, S. Juodkazis, R. J. Crawford, P. Stoodley and E. P. Ivanova, Nat. Rev. Microbiol., 2021, 19, 8–22.
[2] P. Lecointre, S. Laney, M. Michalska, T. Li, A. Tanguy, I. Papakonstantinou and D. Quéré, Nat. Commun., 2021, 12, 3458.

A little beetle (Stenocara Gracilipes) living in the desert collects water from early morning mist. Nature has equipped its back with a biphilic wettability pattern: small hydrophilic patches embedded into a hydrophobic matrix made of wax. Since the discovery of this wettability pattern, extensive research was conducted to analyze and create biphilic surfaces for various purposes such as boiling heat transfer, and freezing or defreezing, and water collection from air. Hydrophilic surfaces favor nucleation, whereas hydrophobic surfaces favor water transport. The role of surface design is not well elaborated. In most cases, the patches are randomly or circularly shaped. We investigate the effect of patch asymmetry, size, distribution, and surface direction on droplet growth and droplet transport. To achieve efficient water collection, asymmetric patches can induce directional transport in capillary regime, and thus, fast water removal from the surface. Nucleation favors droplet growth in hydrophilic patches, however, for roll-off droplets need to overcome strong adhesion forces due to hysteresis hindering water removal. The influence of area fraction, distribution, and size of asymmetric patches on growth dynamics such as coalescence and droplet motion has been studied. We developed superbiphilic surfaces with isosceles triangular patches with a varying length to width ratio (l/w) from 2.0 to 10 and sizes between l = 200 microns and 4 mm. Droplets grow favorably in patches with accumulation on the base of the triangle. Experiments have been conducted in a controlled environment (T, RH) under a tilting angle (0° - 90°). A top-down camera records details about droplet distribution and area coverage. A quantitative image analysis reveals droplet dynamics, in which we identify various phases of droplet growth until roll-off. Adhesion forces have been determined depending on the direction of the triangles.

Many nano- and microstructured surfaces found in nature can serve as an inspiration for improving technical applications. Although most biomimetic archetypes can be replicated with advanced techniques on a lab-scale, it remains a challenge to develop processes for large-scale fabrication techniques appropriate for commercial applications. Here, I review recent approaches with high potential for up-scaling.
The super-hydrophobic surfaces of water ferns like Salvinia and Pistia can be mimicked with nanofur, a dense fur of nanoscale hair hot pulled from polymer surfaces. This fractal surface is super-hydrophobic and oleophilic at the same time. With these properties it is the perfect material to separate oil and water and to clean up oil spills [1, 2].
White beetles of the genus Cyphochilus are well-known for their scales producing a nearly perfect whiteness in a very efficient way with an astonishing low amount of material. Inspired by this biological architecture, we developed two techniques allowing for the fabrication of ultra-thin, yet highly scattering, white polymer films [3,4]. Both approaches can be utilized for various applications ranging from extremely white but ultra-thin coatings to scattering particles as potential replacements for titanium dioxide.
Many snakes feature nano-scale fibril structures on their scales which are only some 10 nm high and feature a periodicity of some µm. Although they cannot be observed in the visible range and the surfaces appear smooth, these nano-steps cause significant anisotropic frictional properties which are helpful for the locomotion of snakes. These nano-step structures can be copied to artificial polymeric surfaces which can be utilized for the self-cleaning of photo-voltaic modules.
[1] C. Zeiger, I. C. Rodrigues da Silva, M. Mail, M. N. Kavalenka, W. Barthlott, H. Hölscher, Microstructures of superhydrophobic plant leaves - inspiration for efficient oil spill cleanup materials, Bioinspir. Biomim. 11, 056003 (2016)
[2] M. N. Kavalenka, F. Vüllers, J. Kumberg, C. Zeiger, V. Trouillet, S. Stein, T. T. Ava, C. Li, Matthias Worgull, Adaptable bioinspired special wetting surface for multifunctional oil/water separation, Sci. Rep. 7, 39970 (2017)
[3] J. Syurik, R. H. Siddique, A. Dollmann, G. Gomard, M. Schneider, M. Worgull, G. Wiegand, H. Hölscher. Bio-inspired, large scale, highly scattering films for nanoparticle-alternative white surfaces, Sci. Rep. 7, 46637 (2017).
[4] J. Syurik, G. Jacucci, O. D. Onelli, H. Hölscher, S. Vignolini. Bio-inspired Highly Scattering Networks via Polymer Phase Separation, Adv. Funct. Mater. 28, 1706901 (2018).
[5] W. Wu, M. Guttmann, M. Schneider, R. Thelen, M. Worgull, G. Gomard, H. Hölscher, Snake-Inspired, Nano-Stepped Surface with Tunable Frictional Anisotropy Made from a Shape-Memory Polymer for Unidirectional Transport of Microparticles, Adv. Funct. Mater. 2009611 (2021)

The demand for materials with strong thermal and mechanical properties that can withstand harsh environments, such as pulsed power facilities, magnetic fusion reactors and space environments, is rapidly increasing. The ideal materials need to survive a range of individual and combined threats such as mechanical, shock, and x-ray insults. However, such materials are presently not available.
An innovative biomimetic method has been developed to synthesize layered nanocomposite coatings using silica and sugar-derived carbon to mimic the formation of natural seashell structure. The layered nanocomposites are fabricated through alternate coatings of condensed silicate and sugar. Sugar-derived carbon is a cost-effective material due to sugar being abundantly available, making it a relatively inexpensive chemical, as well as environmentally friendly. Pyrolysis of sugar will form polycyclic aromatic carbon sheets, i.e., carbon black.
Each layer is thermally pretreated at ~ 200 °C for 3-5 minutes in order to solidify the composite before coating the next layer. The final nanocomposite coatings are then thermally treated at temperatures higher than 800 °C which converts the sugar into carbon black and condenses silicate to form a silica network through cross-linking of carbon with silica. Infrared spectra show chemical crosslinking of Si-O with carbon ring and Si- with carbon ring. Chemical crosslinking between silica and carbon contributes to the enhanced mechanical properties, and thermal pretreatment plays the important role in solidification of the composite coatings while initiating crosslinking. Without this step, the hardness and modulus of the nanocomposite is not enhanced. Molecular dynamics models, incorporating the crosslinking between silica and carbon layers, are conducted to simulate the interfacial bonding energy and shear strength.
The resulting final nanocomposite coatings can survive temperatures of more than 1150 °C and potentially up to 1700 °C. These coatings have strong mechanical properties, with hardness of more than 23 GPa, elastic modulus of 240 GPa, and yield stress of more than 20 GPa, which are 62 – 94% greater than those of pure silica. The layered coatings have more than 80% transmission for >10keV x-rays and have many applications besides use in pulsed power facilities, such as shielding in the form of mechanical barriers, body armors, and space debris shields.
SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525

Coupled motions are frequently observed in living systems, such as oscillatory gait patterns of terrestrial animals, flocking behaviors of birds, and oscillatory motion of bacterial flagella. These motions are dynamically reconfigurable, with the possibility to select from multiple oscillatory patterns from a single system. Here, we describe an oscillatory material system, which relies on optically-defined boundary conditions to guide photothermal Marangoni propulsion and coordinate multiple particles. Hydrogel nanocomposite particles containing plasmonic gold nanoparticles are illuminated by patterned light at an air-water interface, leading to coupled oscillatory motions with on-demand reconfiguration through variations in light patterns. This experimental platform may prove useful in understanding oscillatory dynamics in natural and synthetic systems.

Reference : Hyunki Kim, Subramanian Sundaram, Ji-Hwan Kang, Nabila Tanjeem, Todd Emrick, and Ryan C. Hayward. Coupled oscillation and spinning of photothermal particles in Marangoni optical traps, PNAS, 2021, 118 (18)

Implantable bioelectronics have a wide range of applications in basic biomedical research and clinical medicine. The encapsulation of these systems represents a key challenge as they demand perfect isolation of electronics from surrounding biofluids to prevent current leakage and the degradation of underlying devices. To date, all the barrier materials for flexible bioelectronics, including polymer layers, inorganic coatings, and transferred barriers, are solid materials. These solid materials suffer from limited barrier lifetime due to pinholes, cracks, and nanopores or from complicated fabrication processes and limited stretchability for interfacing with complex biological tissues. This paper reports a solution to this materials challenge by introducing an bioinspired oil-infused rough silicone elastomer as a transparent, flexible, stretchable, slippery, and damage-tolerant biofluid barrier material. Accelerated lifetime tests suggest robust water barrier characteristics that approach 226 days at 37 degrees, even under severe mechanical damage using a knife. A combination of temperature- and thickness-dependent experimental measurements and reaction-diffusion modeling reveal the key water-proof property. In addition to serving as a barrier to water, oil-infused rough elastomer demonstrates an attractive ion prevention property. All these exceptional properties suggest the potential applications in flexible bioelectronics implants for emerging applications ranging from chronic neural recording to bioelectronic medicine.

Cellular solids, or foams, are an important class of structural materials for packaging, transportation, sports, and infrastructure due to their mechanical efficiency. While many current foams are primarily based on metallic and polymeric materials, ceramic foams are usually used for non-mechanical applications, such as filtration, catalysis, thermal insulation, etc. The major limitation of using ceramic cellular solids as structural components are their brittleness and flaw sensitivity. Overcoming the fragile nature of ceramic foams, making them lighter while reaching higher stiffness, strength and energy absorption capability is challenging but critical toward many applications. In this talk, I will present our ongoing work in elucidating the structural design principles in natural ceramic cellular solids from a variety of model systems, particularly echinoderm stereom, cuttlefish bone, and sponges. These structures are characterized by their highly mineralized porous morphology, yet exhibiting remarkable damage tolerance, which is in stark contrast to synthetic ceramic foams. We utilize a combinatorial approach by integrating quantitative 3D structural analysis, 4D in-situ mechanical analysis, theoretical and mechanical modeling in order to establish the structure-property relationship for this unique group of biological materials. In this talk, we demonstrate important microstructural design strategies to overcome the intrinsic brittleness of porous ceramics learned from these model systems, which could inspire novel lightweight ceramic cellular solids. In addition, the formation mechanisms of these complex biomineralized structures will also be briefly discussed.

Larval crustaceans use transparency to camouflage themselves in rivers and the open ocean. Many of these animals have evolved an ingenious optical device to conceal the conspicuous screening pigments in their eyes – an ‘eyeshine’ reflector that deflects light away from the opaque pigments [1]. Using cryo-SEM and TEM we show that the eyeshine reflection of larval shrimp is produced by light-scattering from dense arrays of high refractive index, core-shell nanoparticles of crystalline isoxanthopterin. The same nanoparticles were recently found in the tapetum of adult shrimp where they are used in image-formation and enhancing photon-capture [2]. The reflectivity and scattering of the particles are enhanced by their birefringence, which results from the anisotropic arrangement of refractive indexes within the particle shell [3]. These particles are located in specialized cells overlaying the screening pigment and extending down the sides of the rhabdoms. The location of the particles indicates that the reflector has a dual function: camouflaging retinal pigment and preserving visual acuity by preventing crosstalk between neighboring rhabdoms. Reflectivity measurements and optical modeling demonstrate that the color of the scattering is determined by the size of the particles and their degree of short-range ordering. The eyeshine color is spectrally-matched to the watercolor in the native habitat of the shrimp and also changes upon light-dark adaptation. This enables the crustaceans to remain inconspicuous against the background. For example, the prawn M. rosenbergii which inhabits yellow/green rivers in the Indo-Pacific exhibits yellow/green eyeshine, produced by 400 nm particles. While Marine shrimp from the gulf of Eilat have blue eyeshine, produced by 220 – 330 nm particles.
[1] K.D. Feller, T.W. Cronin, Journal of Experimental Biology, 217, 18, 3263-3273 (2014).
[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, 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, Nature Nanotechnology 15, 138–144 (2020).

Systems of high aspect ratio of 2D nanolayers of fluorohectorite clay mineral, suspended in saline solutions of various clay and salt concentrations, exhibit a rich nematic phase behavior. This system is studied here using Ultra Small-Angle X-ray Scattering (USAXS): the anisotropy of the obtained images is quantified, and, together with reflective spectrophotometric measurements, this provides a precise determination of the nematic organization and inter-particle distance. In addition, the USAXS analysis provides information about nematic phase order such as misalignment or turbostratic organization. We find that the inter-nanolayer distances can be related to electrostatic interactions combined with osmotic pressure effects.

Metal-coordination bonds are dative chemical bonds that arise when a ligand donates a lone pair of electrons to a metal ion. These bonds are dynamic, reversible, and easily tunable, allowing them to span a large range of different strengths and timescales. Several biological organisms have been found to utilize metal-coordination bonds to synthesize a wealth of bioinspired materials. One such organism, the Nereis virens, is a species of marine worm with a remarkably strong and stiff jaw that owes its strength not to bones or minerals, but to metal-coordination bonds. Understanding how metal-coordination bonds affect the structure and properties of the Nereis virens worm jaw Nvjp-1 protein would enable the understanding and design of new metal-coordinated materials with complex and optimized mechanical properties.

Nvjp-1 contains over 25 mol % of histidine, which is believed to play a key role in the metal-coordinated crosslinking that gives the worm jaw its strength. To understand the understand the nanoscale mechanism behind the crosslinking and its pathway to macroscopic mechanical behavior, we analyze the effect of Zn²⁺ on the form and structure of the Nvjp-1 protein. To gain insight into the behavior of the Nvjp-1 protein in the presence of metal ions, replica-exchange molecular dynamics (REMD) simulations are run with explicit solvent conditions to investigate the formation of the protein structures in various environments. REMD enables an efficient computational search of likely protein structures by overcoming kinetic trapping in local energy minima during the protein folding simulation of Nvjp-1. Metal ions are initiated in different positions of the Nvjp-1 protein, previously solved by REMD in Chou et. al (ACS Nano, 2017) to understand how the protein folds in the presence of metal ions and how differing conditions of metal ions impact the strength of the metal-coordination bonds that the Nvjp-1 protein forms. We find that the initial location of metal ions has an effect on the resulting protein structure.

Largely, this work helps elucidate further details on the roles of metal-coordination binding in protein structures to lend better insight into how the bonds affect macroscopic mechanical properties. Further, information about Nvjp-1 binding with metal ions will enable its broader use in mechanomutable engineering materials. With this information, optimized bioinspired materials could be created for a variety of practical applications.

Modern polymers have a wide range of surface characteristics, from polar plastics such as polycarbonate, to highly non-polar plastics such as polystyrene and polypropylene. The poor reactivity of many polymers makes adhesion an ongoing challenge. This challenge is particularly pronounced in hydrophobic polymers, which require extensive pre-treatment, priming, solvent plasticization, or high temperatures to adhere. While adhesion of more-polar polymers is typically easier to achieve, these polymers are susceptible to water infiltration, which can lessen the strength of the adhesive contact in humid environments. New strategies to enable good adhesive bonding would allow for facile repair in the field, and the creation of new types of composites.

The large diversity of peptides in both sequence and functional groups makes them potentially useful to search for strong interactions with polymer substrates. Furthermore, the insights provided by peptide binding may eventually allow the design of more-effective synthetic adhesives. Screening the chemical compositional space afforded by peptides and the natural amino acids would be nearly impossible if undertaken in a serial fashion. Recently, the Army Research Laboratory developed a peptide surface display and high-throughput library screening system to find candidate peptides capable of adhering to polylactic acid [1], and to gold nanoparticles [2]. The on-cell peptide screening has the advantages of easy recoverability, the ability to propagate and sequence the genetic code of the adhesive peptides, and possible further improvements of the peptides by directed evolution. In this presentation, we will provide updates on peptide library construction, screening methods, and initial results of screens against substrates with a range of polarities.

References
[1] S.D. Stellwagen, D.A. Sarkes, B.L. Adams, M.A. Hunt, R.L. Renberg, M.M. Hurley, D.N. Stratis-Cullum, The next generation of biopanning: next gen sequencing improves analysis of bacterial display libraries, BMC Biotechnol. 19(1) (2019) 12.
[2] J.P. Jahnke, H. Dong, D.A. Sarkes, J.J. Sumner, D.N. Stratis-Cullum, M.M. Hurley, Peptide-mediated binding of gold nanoparticles to E. coli for enhanced microbial fuel cell power generation, MRS Commun. 9(3) (2019) 904-909.

Liposomes, vesicles formed by self-assembly of lipid bilayers, have a similar structure to biological membranes, making them a model system for biotechnological and biomedical purposes. Liposomes are composed of one or more lamellae, consisting of a phospholipid bilayer and enclosing a small volume of aqueous liquid. Liposomes diameter can vary (from tens of nanometers up to tens of micrometers) depending on amphiphilic lipid structure, synthetic procedure and solution properties. Biodegradability, biocompatibility, and ability to encapsulate different substances, to isolate and permit controlled release of drugs make these lipid vesicles attractive drug carriers. Indeed, development of lipid-based formulations to enhance recombinant vaccine antigens immunogenicity is of high interest to modern vaccine research [1].
With a growing interest in high precision drug therapies, it is critical to assess microemulsions in a liquid environment similar to living systems. However, fragile structures and susceptibility to electron beam damage, imaging liposome delivery vehicles is challenging with transmission electron microscope (TEM). Low contrast between lipid-based species and aqueous environment causing liposomes imaging particularly challenging without contrast reagents or staining. Emergence of graphene liquid cell-transmission electron microscopy (GLC-TEM) with ability to attain the lowest possible solvent thickness, mitigation of the electron radiation-induced damage by conductive graphene layers, significantly contributed to attain high-resolution TEM images of dynamic processes in real time [2,3].
In this work, and for the first time, in-situ GLC-TEM is employed to observe liposomes dynamics (nucleation and evolution) in real time. Liposomes are synthesized by using phosphatidylcholine and cholesterol in PBS buffer solution. We were able to visualize some of fundamental and important steps in the formation of liposomes. Based on our observations, liposome formation mechanism can be described by initial amphiphilic lipids assembly into micelles followed by turning into small vesicles (liposomes). Coalescence of small liposomes results in the formation of larger liposomes.

References
[1] Abolfazl Akbarzadeh et al., Liposome: classification, preparation, and applications, Nanoscale Research Letters 2013, 8:102.
[2] Sarah M. Hoppe, Darryl Y. Sasaki, Aubrianna N. Kinghorn, and Khalid Hattar, In-Situ Transmission Electron Microscopy of Liposomes in an Aqueous Environment, Langmuir 2013, 29, 9958−9961.
[3] Vahid Jabbari, David J. Banner, Abhijit H. Phakatkar and Reza Shahbazian-Yassar, (2020). Nucleation and Growth Visualization of Self-Assembled Polymeric Micelles/Vesicles Using in Situ Liquid Cell-TEM. Microscopy and Microanalysis, 26(S2), 2576-2578. doi:10.1017/S1431927620022084.

Structural colors originate from the constructive interference by reflection and scattering of light from structures with length scales in the visible region of wavelengths. Structural colors can be iridescent or non-iridescent depending on the degree of disorder in the structures. Bright and non-iridescent structural coloration could not yet be achieved for the most abundant two-dimensional (2D) sustainable material, clay minerals. Recently we have demonstrated that bright non-iridescence structural coloration easily and rapidly can be achieved from nematics of suspended clay mineral nanolayers. We demonstrated how brightness can be enormously improved in this system, and moreover that non-iridescence is readily obtained. The clay nanolayer distances, and thus the structural colors are precisely controlled by clay concentration and water salinity.

Living cellular systems are active materials typically consisting of an extremely crowded environment, in which millions of different enzyme-catalysed reactions happen any second. The complexity and out-of-equilibrium nature of these systems makes it very hard to comprehend the underlying mechanisms governing their behaviour.
In this work, we present a model system consisting of protein droplets that are driven out of equilibrium by enzymatically catalysed reactions, at activity and crowding levels comparable to the cellular cytoplasm, yet retaining compositional simplicity. The droplets possess remarkable stability, and show a plethora of interesting biomimetic activity driven behaviours. We hope our findings can provide an effective framework to design active systems, study biological and biochemical phenomena in a controllable yet biologically relevant environment, and ultimately design active materials that possess superior properties.

Fluorescent proteins (FPs) provide a novel opportunity to design highly efficient and eco-friendly display devices and technology. Current organic and inorganic display materials (i.e., fluorescent dyes and quantum dots) are toxic and environmentally harmful. In contrast, nature evolves proteins to produce highly efficient and photostability chromophore, FPs together with intrinsic eco-friendly and biocompatibility features. The integration of FPs into light-emitting devices, however, presents several scientific and technical challenges including stability of chromophores and mechanical rigidity in harsh manufacturing conditions. In this study, we designed a novel bio-inspired functional optical material by combining fluorescent proteins as color down-converters conjugated with elastin-like polypeptide (ELP) to enhance mechanical processability. ELPs are naturally evolved biopolymers in nature to endow the flexibility and rigidity of our body in blood vessels and muscles. Using recombinant DNA technique, we fused FPs and ELP genes and synthesized novel functional proteins, and fabricated a composite material of FP/ELP as a thin film to integrate into a blue-emitting LED chip. The resulting thin FP/ ELP film exhibited excellent optical properties as well as mechanical properties such as elasticity, stiffness, and tensile strength. We anticipate that biocompatible and eco-friendly elastic biopolymer coating of FP/ELP onto LED would pave a new way to create robust, biocompatible, and environment friendly display technology and its applications in human-machine interfacing materials in the future.

Introduction: The textile industry’s linear model of production and reliance upon nonrenewable resources to manufacture synthetic fibers, dyes, and finishing agents make it one of the most polluting industries globally, and the leading source of carbon emissions, global waste water, and microplastic pollution. Similarly, medical textiles fabricated in the tissue engineering field also utilize harsh solvents during development, not only limiting their biocompatibility and scalability, but also creating environmental concern in large, industrial volumes. Consequently, new fabrication strategies are required to design functional biomaterials that support a sustainable and circular material economy. Inspired by the complexity of nature and its robust regenerative potential, we harness microbial biosynthesis of nanocellulose using Gluconacetobacter xylinus (G. xylinus) bacteria for the synthesis and production of regenerative, high performance biotextiles. A variety of carbon sources can be metabolized by G. xylinus to tailor microbial cellulose (MC) for different textile applications, in which changes in bioavailability and molecular weight affect biochemical pathways, production rates and ultimately, structural properties. Here, we evaluate the effect of several carbon sources (mannitol, dextrose, and sucrose) and concentration (2% and 8% w/v), on the production of microbial cellulose. It is hypothesized that both sugar type and dose will regulate cellulose yield, crystallinity, and tensile properties.

Methods: Fabrication: Microbial cellulose pellicles were biofabricated by culturing G. xylinus (ATCC 31174, Manassas, VA) in Hestrin–Schramm (HS) medium with varying carbon sources. Culture medium pH was adjusted to 4.5 using citric acid (Fisher Scientific, Chicago, IL). Prior to investigating the effects of carbon source and concentration, G. xylinus was pre-cultured in HS medium (2% w/v sucrose) at 30^oC for 72 hours under static conditions. Medium prepared with various carbon sources were inoculated with 5% v/v preculture. All cultures were held under static conditions at 30 oC for 14 days. Media and Cellulose Production Analyses: pH was assessed at each timepoint with a pH meter (n=3/group). MC samples were weighed before and after freeze drying to obtain wet and dry weights, respectively (n=3/group). Morphology was assessed with electron microscopy (Zeiss Sigma VP, Oberkochen, Germany; 3 kV; n=5/group). The fiber diameter of each sample was measured by analyzing randomly selected fiber segments in SEM images using NIH ImageJ software (Bethesda, MD; n=50/group). For mechanical testing, samples (1 x 5 cm) were mounted in a uniaxial tensile testing machine (Instron, Norwood, MA, USA; n=5/group), equipped with a 100N load cell. Samples were maintained to have a gauge length of 30 mm and were tested to failure. MC Young’s modulus, toughness, and ultimate tensile strength were determined from stress-strain curves.

Results/Discussion: Electron microscopy revealed that MC produced from either mannitol, dextrose, or sucrose as carbon sources exhibited a nanofibrous morphology and are comparable in fiber diameter. However, use of dextrose (2% and 8% w/v) resulted in a significant decrease in medium pH, indicative of gluconic acid formation, and is associated with a lower cellulose yield. In contrast, mannitol, a sugar alcohol, added at 2% w/v resulted in significantly higher cellulose production by day 7. Although differences in yield between carbon sources was minimized at higher sugar concentrations, the overall increase in production led to an increase in Young’s modulus and ultimate tensile strength. The ability to tailor mechanical properties of MC by altering carbon sources, offers a versatile platform for tailoring material properties during synthesis. Clearly, biofabrication of MC can be readily engineered to meet target material properties, with broad applicability for the production of both medical or non-medical biotextiles.

Biologically extracted cellulose nanocrystals (CNCs) have drawn significant attention for the development of multifunctional materials for many research communities, ranging from bioresource engineering to materials science and engineering. CNCs are rod-like materials that exhibit unique physicochemical properties such as high surface area, high mechanical strength, high aspect ratio, and unique self-assembly with a rheological and liquid crystalline nature. CNCs not only offer hydroxyl (OH) group-rich surfaces that are amenable and suitable for surface functionalization, but their ability to phase change is also triggered by the formation of self-assembled networks, which are held together by hydrogen (H) bonds. While the intramolecular H-bond interactions in CNCs are responsible for their observed relative stiffness and rigidity, the intermolecular H-bond interactions are the major contributors to the organization of CNC networks, holding the interactions among pristine CNCs as the predominant factor responsible for their assembly through packed units into films or gel-like forms, and leading to a preferential tendency to form ordered structures. However, accessible OH groups of colloidal CNCs at the (10)β/(100)α and (110)β/(010)α facets and their intermolecular H-bonds account for the good water molecule adsorption at their surface, making them structurally instable in moist environment.
In this work, exposed OH groups of CNCs were crosslinked with adjacent ones to develop a hydrogel (crosslinked (x) CNC). The intermolecular H-bond was controlled by the type and concentration of cross-linkers, as well as CNC concentrations. Rheological analyses showed tunable viscoelasticity of formed hydrogels, using loss tangent for the determination of the degree of crosslinking. Fourier transform infrared spectroscopy demonstrated that H-bond intensity (HBI) was inversely proportional to increasing crosslinking degree when using an acid-reactive (i.e., pH<7) crosslinker, but proportional for a base-reactive (i.e., pH>7) crosslinker. Wettability showed that water contact angle (CA) increased with degree of crosslinking by an acidic crosslinker, indicating tunable water stability of CNC network structures from hydrophilic to hydrophobic surfaces. While the diffraction intensity of the crosslinked CNC network varied, the diffraction patterns, as shown by X-ray diffraction, remained identical to that of pristine CNCs, suggesting the interface modification process did not alter the intrinsic molecular crystal structure, and confirming crosslinking was solely achieved from the exposed OH groups. Atomic force microscopy showed images with varied CNC organization and surface roughness inversely proportional to increasing CA when an acidic crosslinker was used, as opposed to a basic one, suggesting cross-linking is related to degree of intermolecular regularity of cellulose chains, which were consistent with observations made with HBI. The technology of crosslinking CNCs does not only generate a potential pathway to fabricate water-stable network of colloidal CNCs, but also provide an alternate approach to integrate CNCs in biological and synthetic nanomaterials, as well as polymer matrices for the development of cutting-edge multifunctional materials. The non-toxic, renewable, and biocompatible nature of x-CNCs could see potential use as building blocks to produce advanced 3D printed scaffolds, beads, and nanofibers for their related functions.

This project is supported by the Center for Advanced Surface Engineering (CASE), under the National Science Foundation (NSF) Grant No. IIA-1457888 and the Arkansas EPSCoR Program, ASSET III.

Liquid-liquid phase separation of protein is a burgeoning area that is thought to be related to functional and aberrant biology, and can inspire the conceptualisation and processing of smart and multifunctional materials. Conventionally, fluorescence recovery after photobleaching, the fusion of liquid droplets, and rheology were used to characterise the liquid nature of the phases in liquid-liquid phase-separated systems. Other simple methods can also realise the above-mentioned characterisation, and are expected to be developed.
Recently, we demonstrated that protein microgels, from droplet microfluidics, could function as the precursors of the formation of all-aqueous liquid-liquid phase-separated systems that were two-phase or multiphase. We developed oil-free anisometric protein microgels, such as elongated microgels, hole-shell microgels, and buckled core-shell microgels. More interestingly, we demonstrated that these three forms of anisometric microgels could undergo gel-sol transition and convert into isometric droplets or isometric core-shell droplets. In summary, the microgels can be the consequences and the outcomes of liquid-liquid phase separation. The protein microgels and all-aqueous liquid-liquid phase-separated systems are promising candidates for extracellular matrix analogues, tissue engineering scaffolds, as well as implantable or injectable biosensors.

References:
Xu Y, et al. Small 16 (32), 2000432, 2020.
Xu Y, et al. Advanced Materials, 2021. In production.
Xu Y, et al. arXiv preprint arXiv:2009.13413, 2020. Submitted.

Animals use guanine crystals to manipulate light, producing a variety of plate-like habits in which the reflective (100) face is preferentially expressed. These habits differ from the stable prismatic growth-form produced synthetically. How does biology so precisely control crystal morphology? One hypothesis is that the biogenic guanine contains additives that inhibit crystal growth along certain directions. In the 1960s hypoxanthine was found in guanine-containing tissues in fish but it could not be determined whether this molecule was included within the crystal lattice or was simply a solute in the crystal-forming cells. Our study aims to determine the chemical composition of biogenic guanine in order to support or refute the ‘additive hypothesis’.
Here we report nine unique guanine crystal morphologies from different animals, characterized by SEM and TEM. These include prisms, regular hexagonal and square plates, irregular hexagonal plates and a variety of irregular polygonal plate habits. We developed an enzymatic/centrifugation method for extracting and purifying the crystals from their surrounding- a key weakness in previous studies. Solid-state Raman spectroscopy and MALDI-TOF analysis on the purified crystals showed that hypoxanthine was present in plate-like crystals but was absent from prismatic crystals. UV-vis analysis of dissolved crystal solutions showed that fish guanine contains approximately 16 mol% hypoxanthine. UV-vis and NMR studies are ongoing to quantify the chemical compositions of the remaining crystal morphologies. Preliminary analysis of synchrotron PXRD data reveals only minute differences in the lattice parameters of guanine crystals with differing compositions, but substantial differences in crystal strain.
We show for the first time that ‘guanine’ crystals are, much like inorganic biominerals, composites. The impact that additives have on crystal structure and morphology remains an intriguing open question we are actively pursuing.

Each year icing significantly impacts energy production, transportation, and human activities. For example, the entire state of Texas came to a standstill in February 2021 due to the unexpected freeze. Typically, active strategies (e.g., electrical heating elements, infrared hangars) and passive strategies (e.g., surface coatings) are used for fighting against icing. However, most of the active approaches are complex and costly. Consequently, passive anti-icing strategies relying on durable surface coatings are highly desired. The current state-of-the-art anti-icing technologies, such as liquid-infused surfaces and superhydrophobic surfaces, dramatically reduce ice adhesion strength. Nevertheless, severe durability challenges of lubricant depletion and coating damage during the ice removal process hinder their practical applications. Taking inspirations from how the mobile cilia in the bronchus of human lungs remove microbes and debris, we developed a quasi-liquid surface (QLS) coating that can effectively reduce the ice adhesion strength. QLS is made by chemically grafting flexible polymer of polydimethylsiloxane on a substrate where one end of the molecular chain is tethered to the solid substrate and the other end is mobile. These highly mobile chains of the flexible polymer with nanometer thickness serve as persistent interfacial lubrication and transfer the steady ice/solid interface to a non-sticky ice/quasi-liquid interface. This dramatically reduces the interfacial shear strength between ice and the substrate as well as provide long-term de-icing even after harsh chemical rinsing when state-of-the-art anti-icing surfaces fail. We envision that the robust QLS with sustainable ultralow shear strength to ice will provide design guidelines to the next generation anti-icing technologies that can be potentially applied on wind turbine blades, aircrafts, power lines, and vehicles.
Keywords: Anti-icing, ultralow ice adhesion, cilia-inspired, quasi-liquid surface, sustainable

A circular materials economy can disrupt linear production models while mitigating environmental threats. The linear economy that has been the dominant production model since the Industrial Revolution presents serious ecological and human health concerns and threatens potentially catastrophic climate instability. In particular, the textile industry is reliant on industrial agriculture for cellulosic fibers, and nonrenewable resources and petrochemicals to produce synthetic fibers, dyes, tanning and finishing agents, as well as chemically and energy intensive processing, making it one of the most polluting industries globally. We harness extracellular biosynthesis of microbial nanocellulose (MC), coupled to a protocol inspired by a serendipitous intersection between ancient textile techniques and biobased processing as a route to high-performance bioleather with a circular life cycle. Specifically, we used lecithin phosphocholine as a plasticizer to modify MC’s crystallinity and cross-linking, to create a material with excellent mechanical properties and outstanding flame retardance, without introducing toxicity or compromising end of life biodegradability. A broad color palette and controlled color modulation was achieved with cultural heritage dyes and waste-to-resource strategies. Life cycle impact assessment shows up to an order of magnitude reduction in environmental impacts relative to conventional textiles, making MC relevant for widespread application in fashion, interiors, construction and insulating materials. The sustainable development of regenerative, high performance biotextiles shown here highlights how biofabrication and green chemistry can strategically address the most damaging impacts of a linear economy, as encapsulated by the fashion industry.

Water harvesting through condensation of water vapor in air has the potential to alleviate water scarcity in arid regions around the globe. When water vapor is condensed on a cooled surface, tiny water droplets are formed on the condensing surface and act as thermal barriers for further vapor condensation. Thus, water droplets must be removed rapidly for efficient water harvesting. State-of-the-art passive technologies for droplet removal rely on in-site growth and direct contact of densely distributed droplets, such as coalescence-induced jumping droplets. However, it is challenging to remove submicrometer droplets that lead to a large area of water coverage and poor water harvesting. There exists a scientific gap of droplet size evolution from nucleated droplet to shedding droplet. Here, we present a meniscus-mediated spontaneous droplet climbing and coalescence, namely a coarsening effect, to rapidly remove water droplets with diameters below 20 μm from the hydrophilic slippery liquid-infused porous surface (SLIPS). The self-propelled microdroplets move along the oil meniscus to approach and coalesce with larger water droplets. This passive droplet movement rapidly reduces the number of droplets below 20 μm and simultaneously increases the number of droplets with diameters above 150 μm. We quantitatively study the driving and drag forces for droplet movement and provide important design rationales to enhance the coarsening effect-enabled rapid droplet size evolution. The self-propelled climbing droplet on hydrophilic SLIPS shows rapid removal of droplets below 20 μm and growth of droplets above 150 μm, showing a promising mechanism compared to hydrophobic SLIPS, PEGylated hydrophilic surface, and superhydrophobic surface in water harvesting.

Fishes, cephalopods, and clams can dynamically change their appearances with a wide range of hues and patterns, closely matching their respective environments for camouflage, signaling, or energy regulation. Structural colors offer many advantages over dye or pigment colors, such as brighter color, longer lifetime, and environmental friendliness. However, their tunable range is often limited by the sample’s physical size and geometric constraints, making it difficult to achieve broadband, pixelated color switching. Here, we fabricate thin membranes from the main-chain chiral nematic liquid crystalline elastomers (MCLCEs) with large elasticity anisotropy and Poisson’s ratio (> 0.5). We demonstrate pneumatic inflation of the thin membranes with geometrically patterned air channels to achieve broadband color shift from near-infrared to ultraviolet wavelengths with less than 20 % equi-biaxial transverse strain. Each channel could be individually programmed as a color “pixel” to match with surroundings for on-demand camouflage.

Mycelium-based bio-composites materials have been invented and widely applied to different areas including the construction industry, manufacturing industry, agriculture, and biomedical. As the vegetative part of a fungus, mycelium has the unique capability to utilize agricultural crop waste (e.g., sugarcane bagasse, rice husks, cotton stalks, straw, and stover) as substrates for the growth of its network, which integrates the wastes from pieces to continuous composites without energy input nor generating extra waste. Their low-cost and environmentally friendly features attract interest in its research and commercialization. For example, mycelium-based foam and sandwich composites are commonly used for construction structures. We are working toward combining computational simulation and experimental methods to synthesize and optimize the mechanics of lightweight mycelium composites. Our result shows that by growing mycelium in a humid environment and using the heat-press process, we can turn the mixture of hardwood and straws into a lightweight synthetic plate with a strength higher than 10 MPa, the same order as that of medium density fiberboard. It is shown that the material function of these composites can be further tuned by controlling the species of fungus, the growing conditions, and the post-growth processing methods. Our multiscale computational simulations help to explore the interface between mycelium and wood fibers and reveal that the entanglement and binding from mycelium fibers can enhance the composite mechanics and thus yield maximum strength and toughness through structural optimization.

Nature’s vast array of multifunctional proteins and peptides provides inspiration for synthetic stimuli-responsive nanomaterials. Both amino acid sequence and solution environment are key to dynamic protein folding/assembly into these multifunctional materials. Building on this foundation, novel pH-sensitive peptide-based assemblies were designed and synthesized. In this work, the assembly mechanism of a de novo class of Phe-Ile zipper coiled-coil peptides were studied through point mutations of the amino acid sequence and varying assembly solution conditions. The resulting structures represent polymorphic assemblies ranging from β-sheet amyloid-like fibers to highly ordered, hierarchical fibers of α-helical peptides in coiled-coil building blocks as analyzed by their cryo-electron microscopy structure. Buffer concentration and pH affect multi-scale aspects of supramolecular assembly, including peptide monomer secondary structure and interactions between hexamer building blocks. Here, the library of self-assembling peptide sequences has been expanded to include new sequences and structures that can be used to create amino acid-based biomaterials that mimic the complexity and stimuli-responsiveness of their natural counterparts.

Three-dimensional (3D) structures that can mimic the characteristics of biological systems such as camouflage, adaptivity to environment, and material heterogeneity are desired for a lot of applications. In this talk, I will discuss our recent effort in designing and fabricating bioinspired multifunctional structures by using liquid crystal elastomers (LCEs) as a platform. Color-changing and adaptive capabilities will be incorporated into LCEs that are capable of large, reversible shape changes. In addition, stiffness heterogeneity in the material will be created by utilizing the different domains of the material. Structures that resemble the shape and the functionality of a butterfly and a chameleon will be presented. The studies would provide important insights for the development of intelligent bioinspired systems.

We investigated the self-assembly of a series of stimulus-responsive block copolypeptides (BCPs) composed of a hydrophobic, resilin-like domain and a hydrophilic, elastin-like domain in the bulk and on surfaces using small-angle X-ray scattering (SAXS) and atomic force microscopy (AFM). We observed classical, microphase-separated nanostructures, such as hexagonally-packed cylinders and alternating lamella, in concentrated solutions of the block copolypeptides. The emergence of these nanostructures was strongly dependent on copolymer composition and temperature. Discrete order-order transitions were observed for higher molecular weight species, and order-disorder transitions were observed with increasing temperature for all species due to the lower-critical solution behavior of the elastin-like block. BCP thin-films also exhibited microphase-separated nanostructures that resembled those in solution and could be further refined by annealing in a high humidity environment, resulting in long-range, periodic nanostructures. Structures that form via microphase-separation of distinct polypeptide blocks can display linear peptide motifs that serve as sites for protein / peptide recognition, or enable the selective and ordered presentation of functional proteins with high spatial density.

The introduction of bio-inspired patterned surfaces exhibiting wettability gradient has presented a new approach towards enhancing environmental water harvesting from fog and dew. A wide range of multifunctional patterned surfaces has been designed by drawing inspiration from different natural surfaces to outperform conventional surfaces in terms of atmospheric water harvesting capacity. However, intricate and expensive fabrication is a major bottleneck that discourages the large-scale implementation of these surfaces. Therefore, efforts are ongoing to address these challenges to make the use of bio-inspired patterned surfaces more viable for practical applications. In this direction, herein, we introduce a novel facile and cost-effective fabrication approach capable of delivering multipurpose patterned surfaces with millimeter to micrometer-level precision.
Our method involves the controlled deposition of superhydrophobic carbon nanoparticles onto the masked hydrophilic or moderately hydrophobic surface for printing a predefined array of adjacent superhydrophobic and hydrophilic patterns. Unlike conventional methods such as laser engraving and photolithography, the developed method does not require any sophisticated instrumentation or costly masks. Steel mesh and PDMS sheets having carved patterns of desired shapes are successfully used as masks. To demonstrate the flexibility and wide-scale applicability of the method, we have successfully created biomimetic patterns on a wide range of substrates, including polymers and metals. These include surfaces with patterns mimicking the surface textures of Namib Desert beetle, rice leaf, and pitcher plant which have inspired many of the recent studies on water harvesting. Subsequently, we test these patterned surfaces for fog harvesting in a controlled environment to investigate the underlying mechanism of water collection and the influence of the size and shape of the patterns. Through judicious tailoring of the shapes of patterns and careful optimization of their dimensions, we are able to achieve significantly higher fog harvesting performance compared to several state-of-the-art interfaces.
Apart from fog harvesting, we also demonstrate that the developed method can be utilized for creating channels exhibiting sharp wettability contrast for surface microfluidics applications. We show that these channels can be used for water drop manipulation, storage, and guided fluid transport. Overall, the current study not only reports a versatile method for the fabrication of bio-inspired patterned surfaces but also demonstrates the use of these surfaces for multiple applications.

Recent progress in mobile optoelectronics and machine vision has increased the demand for advanced image acquisition and sensing technologies. Conventional optical imaging and sensing devices require bulky and sophisticated optical systems to obtain high-quality information. Over the last decades, photonic metamaterials have attracted considerable interest in various imaging and sensing applications due to their compactness and on-chip processing capabilities. However, millions of years of evolution in the biological world has developed a plethora of unique micro- and nanoscopic photonic structures to perform versatile vision and sensory functions.

In this talk, I will discuss how the development of metaphotonic devices harnessing bioinspired attributes can provide novel yet highly practical solutions for novel imaging and sensing applications. First, I will present our studies on biophotonic nanostructures found in butterfly wings that show unique optical properties with tailored structural disorder, and their successful replication in laboratories using a self-assembly based scalable nanofabrication technique. We utilize this approach to pattern Si₃N₄-based metasurfaces onto a Fabry-Perot-resonator-based intraocular pressure (IOP) sensor for glaucoma management. The metasurface integration onto the IOP sensor led to a 2.5-fold improvement in readout angle allowing easy handheld monitoring and in a one-month in vivo study conducted in rabbits, showed a 3-fold reduction in IOP error and 12-fold reduction in tissue encapsulation and inflammation, compared to an IOP sensor without nanostructures.

We will further show its application in optical wearables and contact lenses where, we developed a nanostructured scleral lens with enhanced optical, bactericidal, and sensing capabilities. The bioinspired nanostructures, made on biocompatible parylene thin-films are mounted on the anterior and posterior side of a traditional scleral lens. Compared to a traditional scleral lens, the nanostructured scleral lens minimizes glare at large viewing angles of 80^o by 4.3-fold, and block UVA light while offering greater transmission in the visible regime. Furthermore, they display potent bactericidal activity against Escherichia coli, killing 89% of tested bacteria within 4 hr in vitro. The same nanostructures conformally coated with gold are used to perform simple, rapid, and label-free multiplex detection of lysozyme and lactoferrin (protein biomarkers of chronic dry eye disease) in artificial and whole human tears using drop coating deposition Raman spectroscopy within their physiological and pathological concentration range of 0-6 mg/mL, each.

I will conclude the talk showing our recent progress on developing an ultracompact optical spectrometer for smartphones using bioinspired tricks with high angular tolerance, resolution and throughput, suitable for realization of high-performance point-of-care biosensing. Using the smartphone spectrometer, we demonstrated sub-5 nm spectral resolution, 30^o FOV, and high throughput sensing and detection.

In this paper, a novel multi-functions cylindrical structure with donut-shaped tips was produced inspired from teacup-shaped mushrooms (Nidula niveotomentosa) which has a seed carrier function with concave structure and a chamber function with a roof. With unique structural characteristics, a cylindrical column having donut-shaped tips inside and outside the top of it was fabricated using a simple yet robust lithography method. Due to the structural properties of its donut-shaped tips, the surface on which this unique structure was formed has remarkable omniphobic properties without additional chemical surface treatment. By applying the micro-dewetting phenomenon on micro/nano structure surfaces with omniphobic properties, the NOA polymer roof was covered. The stable polymer roof formation was proved in that it has omniphobic properties without additional chemical surface treatment and its micro-chamber function was demonstrated by inserting an average of 1.5µm nanoparticles into the structure and covering with polymer roof. Consequently, this work introduces a matchless fabrication method for fabricating cylindrical structure with donut-shaped tips and proves its multi-functions of omniphobic properties and particles storage function.

In recent years, solar interfacial evaporation has been one of the most promising techniques to alleviate freshwater scarcity. However, the salt deposition on the evaporation surface limits the long-term operation of evaporators. Herein, inspired by the salt dilution and secretion mechanisms in halophytes, a solar evaporator with a bundle-cross-layer structured absorber and salt secretion bundles is reported. The unique bundle-cross-layer structure realizes the salt dilution by enhancing the water storage and transport, which enables the absorber a high and stable evaporation efficiency of 90.2% over 60 h in brine. More importantly, the salt secretion bundles can completely separate salt crystallization from the absorber by a humidity-controlled salt creeping mechanism. The solar desalination prototype equipped with this evaporator exhibited a stable water collection rate over 600 h of continuous operation, realizing zero liquid discharge in desalination. The study provides new insights into the solar evaporator design and advances other applications such as sea-salt extract, wastewater treatment, and resource recovery.

Natural ceramic composites present complex microstructures that lead to tortuous crack path and confer them high toughness. Current microreinforced composites do not yet reach the level of complexity found in natural microstructures. To achieve this, we developed an automated set up for controlling 2D microplatelet orientation using magnetic fields. The setup has 4 degrees of freedom and allows fine control of platelet angles in 3D as well as position. With our setup, we can thus build microstructured porous ceramic materials (alumina) with local orientation of microplatelets, at a concentration of about 40 vol%. Other work in our group has shown that the same setup can be used to process microstructured ceramics up to 95 vol%.
Among the infinite possible microstructures, a nacre-like helicoidal arrangement was selected due to its ability to tilt and twist the crack path. Indeed, we used an analytical model based on the laminate theory to compare energy dissipation due to mixed modes of failure. Nacre-like helicoidal arrangement was predicted to exhibit the highest energy dissipation. Then, we fabricated the hybrid microstructured porous specimen fabricated and infiltrated them with a silicone matrix. Using compression tests, our hybrid dissipated 1.6 times more energy as compared to nacre-like samples of same composition. The fabrication strategy proposed here could thus be a simple route to increase the toughness of microplatelet reinforced composites.

Shape memory polymers (SMPs) have been utilized for versatile applications due to their stimuli responsive behavior which recovers its original shape after deformation. Compared to shape memory metals, shape memory polymers have exhibited light weight, larger elastic region, and biocompatibility. However, the fabrication method of shape memory polymers mainly dependent on traditional strategies like molding, casting, and extrusion. Those traditional methods are limited to generate customer specific structure rapidly since additional constraint to hold the shape during hardening process of polymer solution. Regarding that, researches adopted 3D printing techniques such as direct ink writing, polyjet, and fused filament fabrication (FFF) to produce objects consisting of shape memory polymers. On the other hand, challenges in acquiring higher resolution and characteristics of usable material are still remained. Alternatively, researches have considered the utilization photopolymerizable raw materials to digital light processing (DLP) technique. Through DLP technique, layer-by-layer stacking of raw materials are possible with excellent precision and resolution. In this study, we aimed to fabricate shape memory polymers which could be facilitated to biomedical applications with biomimetic structure. Mixture of photopolymerizable soft branching material and hard branching material was cured in the aid of photoinitiator. The systematic analyses of the produced objects were carried out in terms of light power, exposure time, layer thickness, and composition. Printability was firstly assessed to determine possible candidates for printing. And degree of precision, compressive properties, tensile properties, and recovering ability were further examined using produced photopolymerized objects. Additionally, bioinspired design of certain seed was applied to SMP and its biomimetic functions was observed. In vitro cell tests using pre-osteoblast cells were carried out to assess feasibility of SMPs to biomedical applications.

Self-organization of magnetic composites that mimic the collective swarming of natural living creatures has been explored as potential means of accomplishing more complicated tasks. Micron/submicron-scale composite particles can organize into chain-like morphology which allows for directionality of the magnetic response. However, organized shapes and positions could not be reproduced due to unfixed positions of the composite particles. To develop the programmable and reproducible magnetic organization of microscale objects, we introduce periodically arranged micropillar arrays consisting of elastomeric polymer/magnetic particle composites. The magnetic polarities of embedded particles are arranged from S to N pole when an external magnetic field is applied using two permanent magnets. Accordingly, the micropillars act as individual micromagnets where quadrupolar magnetic interactions occur between two vicinal micropillars. As magnetic flux density increases, two vicinal pillar-tops assemble as a pair. At higher magnetic flux density, the two pairwise-assembled micropillars further assemble into a quad-body, and long-range connectivity is ultimately accomplished. We will delve into the mechanisms and governing parameters of this stepwise magnetic-organization via a thorough look into these micropillars consisting of isotropic/anisotropic cross-sections with the directionality of an external magnetic field relative to the geometry of the micropillars.

In soft robotics, agile and adaptable collective motion has been challenged due to sophisticated path programming of individual soft robots. Herein, we present multimodal collective swimming of musculoskeletal system-mimetic soft robots which can control vorticity of fluids. For agile locomotion with lightweight body, the architecture of soft robot consists of nanoporous carbon nanotube yarn (CNTY) filled with magnetic polymer composites, mimicking spongy bone and surrounding skeletal muscle. Under a pulsed rotating electromagnetic field, single magnetic soft robots swim with rectilinear translational motility or rotational motility according to the rotational frequency of the magnetic field. Multiple soft robots articulate with other soft robots owing to magnetic attraction, enabling the assembled swimming. The multiple soft robots are adaptably organized and competition between magnetic attractive force and fluid drag results in trimodal assembly: assembled rectilinear translational swimming, assembled rotational swimming, and interactive vibrational swimming. We will discuss collective swimming of the modular soft robots which can clean hundreds of microbeads and transport multiple semi-submerged millimeter-scale beads.

Numerous studies have been conducted on the functional structures of living organisms due to their unique properties derived from their intrinsic topological structures and chemistry, which apply to various applications, including nano-micro robotics, self-cleaning surfaces, and water harvesting.For example, all plants have optimized cellular structures and tissue systems for protective function and water absorption. Additionally, among plants with functional surfaces or structures, some, such as Mimosa pudica, exhibit extreme wettability, allowing for a strong self-cleaning against water drops to protect their tiny leaves, which is attributed to the well-distributed microscale clusters composed of nanoscale wax flake.
In this study, we proposed a hybrid nanocomposite of TiO₂ nanoparticle encapsulated Aluminum (Al) flake clusters by mimicking the hierarchically grown flake clusters on the leaf of Mimosa pudica. These flake clusters could be produced not only on Al and TiO₂ but also on the various surface including 3D structures such as 3D printed polymer surface. When Al substrate is immersed in a heated TiO₂ nanofluid with a three-dimensional substrate, it reacts with the hydroxyl ion decomposed water in the nanofluid to form a flake-like Al nanostructure, with TiO₂nanoparticles serving as the nucleus of the Al flakes. Due to the dual scale roughness of hierarchical Al flake clusters and the TiO₂ effect, the TiO₂-Al based flakes exhibit long-term stability (more than 90 days) in superhydrophilicity and underwater oleophobicity, whereas the Al base substrate alone exhibited mild hydrophilicity but did not last as long. Since the method to fabricate the durable superhydrophilicity and anti-oil fouling surface is simple and easy to scale up, it would have a broad range of applications in numerous industrial fields. We were able to apply hierarchical structures with long-lasting superwetting to water-transport structures and oil-collecting systems by developing multi-scale functional structures inspired by plant tissue systems such as leaf vein and xylem.

Bicontinuous membranes in cell organelles epitomise nature’s ability to create complex functional nanostructures. Like their synthetic counterparts, these membranes are characterised by continuous membrane sheets draped onto topologically complex saddle-shaped surfaces with a periodic network-like structure. In cell organelles, their structure sizes around 50–500 nm and fluid nature make Transmission Electron Microscopy (TEM) the analysis method of choice to decipher nanostructural features. Here we present a tool to identify bicontinuous structures from TEM sections by comparison to mathematical “nodal surface” models, including the hexagonal lonsdaleite geometry. Our approach, following pioneering work by Deng and Mieczkowski (1998), creates synthetic TEM images of known bicontinuous geometries for interactive structure identification. We apply the method to the inner membrane network in plant cell chloroplast precursors and achieve a robust identification of the bicontinuous diamond surface as the dominant geometry in several plant species. This represents an important step in understanding their as yet elusive structure-function relationship.

High-performance polymeric fibers with merit of lightweight, strong and tough are of great interest for various applications from functional textiles to structural composites. Carbon nanotubes (CNTs) fibers have an inherently hierarchical structure with high internal surface area approaching 100 m² g^-1 and provide good thermal and electrical conductivity. However, difficulties remain in the exploitation of these nanomaterials’ exceptional properties on a macroscopic length scale. CNTs in a CNT fiber are interconnected by “weak link”, Van der Waals forces, the properties of bare CNT fiber are far below single CNTs. In practice, the imbalance between strength and toughness not only exist in CNT fibers but also widely occurs in engineering materials. The high-strength materials, such as high-performance Kevlar and carbon fibers, are often brittle, whereas the elastic materials, such as rubbers and elastomers, possess low strength. However, certain exceptions can be observed in nature. The alternating organic-inorganic nanostructures of bone, nacre and other biological structures, are the secret to achieve an elegant balance between strength and toughness. The organic-inorganic interfaces, on the other hand, play a crucial role in improving fracture toughness and fracture resistance through energy dissipation due to breaking of mineral bridges, inelastic shear of nano-biominerals and presence of interlocking nanobuilding blocks during sliding.

Ductile and damage-tolerant CNT fibers were produced at large scale by utilizing conductive ionic silk fibroin (ISF) glue to regulate the CNTs’ interface. Benefiting from the low energy barrier of solvent molecules within CNTs, the ISF glue can intercalate between CNTs interfaces and, thereby, form an alternating soft and hard interface. Consequently, the inorganic-organic cooperative interactions enhanced the performance of CNT-ISF fiber, rendering an elongation at break of 14%, toughness of 22 MJ m^-3 and electrical conductivity of 4.4 × 10⁴ S m^-1. Similar to other biological nanocomposites, the CNT-ISF fibers exhibit remarkable damage tolerance behavior due to confined CNT sliding and shearing during tensile fracture, supported by TR-SAXS characterization and MD simulations.

Besides mechanical and electric features, the composite fibers can also achieve fog collecting functions. Similar as the cactus, which uses structures and composites to collect fog and retain the water in the body. The fog first deposits on the barb and spine to form water droplets, and the larger droplets are transported along the gradient microchannel. Mucilage is present in the cells of the cactus stem, which is composed of complex polysaccharides including pectin and calcium ions. The existence of calcium ions allows pectin to form hydrogel molecular networks, capable of retaining a large amount of water to meet life activity under arid environmental conditions. The CNT-ISF yarn can capture water molecules from the surrounding foggy environment, and the spine-like microgroove structure was created on the surface of CNT yarn, which provided the driving forces for the directional movement of water droplets. The chemical and structural synergetic effects allow the fog-collecting yarn to absorb the fog, gather water, and directionally transmit the droplets to the ends of yarn.

These structure, mechanical and electric features of CNT-ISF fibers enable them to be used in functional textiles, and flexible and wearable devices.

Reference
Dong, S.; Gan, Z.; Chen, X.; Pei, Y.; Li, B.*; Ren, J.*; Wang, Y.*.; He, H. Y.; Ling, S.*, Materials Chemistry Frontiers 2021, 5,5706-5717
Zhang, W.; Ren, J.; Pei, Y.; Ye, C.; Fan, Y.; Qi, Z.; Ling, S.*, ACS Biomater. Sci. Eng.2020.https://dx.doi.org/10.1021/acsbiomaterials.0c00892
Ye, C.; Ren, J.; Wang, Y. L.; Zhang, W. W.; Qian, C.; Han, J.; Zhang, C. X.; Jin, K.; Buehler, M. J.; Kaplan, D. L.; Ling, S.*, Matter 2019, 1 (5), 1411-1425.

Nature has astonishing nanostructures in which periodicity is highly crystalline or amorphous exhibiting brilliant or matte structural colors, respectively. Humans have used colloids to mimic the structural colors in nature, where the periodicity is manipulated to design photonic crystals or glasses. Many researchers have used various strategies for creating structural-color patterns. However, both structures mostly require colloid-wasting, complicated, and multistep processes, which is time-consuming especially for colloidal crystals. Inkjet printing is one of the most promising methods to solve those limitations, but it does not make monolithic structures so that it shows poor mechanical and optical properties. Furthermore, 3D architectures with structural colors have been rarely explored.
Here, we report a direct writing of two- and three-dimensional structural-color patterns using highly viscoelastic colloidal dispersions, first making their patterning highly customizable. We disperse silica nanoparticles in acrylate polymers, where the particles are repulsive as the overlap of solvation layers exerts disjoining pressure. For 2D patterns, the particle fraction in the dispersion is set right before the solid transition fraction over which the dispersion becomes solid. The high fraction brings about good printability including fluid resistance to a sudden flow and a high resolution along with a high printing speed. The particles are crystallized by a shear force when the polymer viscosity is moderate in a range of a few tens of cps. In contrast, a high polymer viscosity over 1000 cps frustrates the crystallization of particles as the high viscosity prevents particles from being sheared to find the energetically optimal state and just kinetically captured in the amorphous state.
By choosing the polymer viscosity, we can customize a photonic-crystal or -glass line pattern with the highest speed of 15 mm/s in a width-controllable manner. It is outstanding to print a 2D Eiffel tower with a dimension of 13×7 mm² in 10 min, of which color is either iridescent or matte according to the polymer viscosity. The rheological properties of the two kinds of inks are examined for the first time, and the analysis is directly linked to the crystallization aspect and to the final colloidal arrangement that is found to have relations with the shear history. Aside from a line, a face is direct-written by merging individual lines at a rate of 4 cm²/min and shows the highest reflectance over 80% by thermal annealing for 10 min. Additionally, this strategy facilitates a multicolor patterning as different inks are not mixed even after being dispensed adjacently. Finally, we can target any kinds of substrates—including glass, plastic, metal, paper, and fabric—and any kinds of mechanical properties of final patterns—they can be rigid, foldable, and stretchable.
Interestingly, the colloidal inks can be piled up when ethanol inhibits the solvation layer formation so that the colloids are linked in the dispersion. The dispersion loses flow resistance and becomes transparent around optimal ethanol content as ethanol disrupts the solvation layer that requires shear force to make particles slip and matches the two refractive indices. The particle content must be higher than a threshold where the colloids are close enough to be linked entirely after the solvation layer disruption, which is still much lower than the solid-transition fraction defined at an ethanol-free basis. However, a higher particle fraction is better in that printed structures retain their morphology better as the overall linkage between particles is sturdy. The matte colors are shown after ethanol evaporation, first realizing the 3D-printable colloidal glasses. To sum, direct-writing of these colloidal systems opens a new avenue for creating customizable structural-color patterns both in 2D and 3D spaces by fast and local deposition of the dispersion with programmable trajectories.

Fractals are ubiquitous in nature. Examples include snowflakes, lightning, clouds, river networks, mountains, trees, and coastlines. Fractal geometry formed by simple components has long been applied to many fields, from physics and chemistry to electronics and architecture. The Sierpinski carpet (SC) has a two-dimensional space-filling ability and therefore provides many structural applications. However, few studies have investigated its mechanical properties and fracture behaviors. Here, to understand how fractal iterations affect their mechanical properties and crack propagation, we utilize the lattice spring model (LSM) to construct SC composites with two base materials and to simulate uniaxial tensile tests. The results show that, for either the soft-base or stiff-base SC composites, the one with two hierarchies has the optimal mechanical performance in the terms of stiffness, strength, and toughness compared to the others with higher hierarchies. The reason behind this surprising result is that the largest stress intensities occur at the corners of the smallest inclusion squares, which consequently induces crack nucleation. We also find that the main crack tends to deflect locally in SC composites with a soft matrix, but in global main crack behavior, SC composites with a stiff matrix have a large equivalent crack deflection. Furthermore, considering the inherent anisotropy of SC composites, we rotate the SC composites by 45°. The tensile strength and toughness of the rotated SC composites are inferior and the crack propagating behaviors are distinct from the standard SC composites. Moreover, the rotated SC composites have notable different crack behaviors between the soft-base and the stiff-base ones. This finding infers advanced engineering for crack control and deflection by adjusting the orientation of SC composites. Overall, our study opens the door for future engineering applications in stretchable devices, seismic metamaterials, and structural materials with tunable properties and hierarchies.

‘Viscous fingering’ is an example of fluidic flow, 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, because of the transitional nature of these phenomena, there are difficulties to utilize such fluidically regulated interfaces for preparation of materials. 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. For establishing a universal model of dissipative structures in nature, investigation of biopolymer’s behaviors in air-water interface is an important practical challenge. Recently, the phenomena have been successfully developed to an ordered structure by controlling the evaporation of an aqueous mixture of polysacccharides.¹ Furthermore, by introducing crosslinking points into the deposited polymer, it has huge potentials to use for uniaxially swellable hydrogels.
In this study, we present a brief discussion of nonequilibrium phenomenon, ‘meniscus splitting’ through mathematical approaches. As an experimental model, when the mixture is dried from a top open cell with a millimeter-scale gap, the polymer forms deposits at specific positions to split the air-water meniscus by bridging the gap. Because water irreversibly evaporates to the air phase through a gap, the air-water interface is in a nonequilibrium state between polymer deposition and water evaporation. As a result, the air-liquid interface is divided into multiple interfaces to partition a space. Based on such facts, the interface from the cross-sectional view are focused for the mathematical modeling. The interfacial curves at the typical times for the meniscus splitting are ideally expressed using catenary curves. By validating the length of the multiple curves, the area of the evaporative interface would be evaluated. We envision that this mathematical approach will help general understandings for the phenomena and design of advanced materials independent from kind of substances.
[1] Okeyoshi, et al, Sci. Rep. 7, 5615 (2017); Adv. Mater. Inter. 5, 1701219 (2018); Adv. Mater. Inter. 6, 1900855 (2019); Polymer J. 52, 1185 (2020); Sci. Rep. 11, 767 (2021).

Fractal structures are ubiquitous in biology, such as blood vessels, plant leaves and roots, etc. They are designed for the efficient contact with a larger volume by a smaller length and fewer branches as well as the efficient transport. In the field of microfluidics, the open microfluidic channel, which is made of a patterned surface with different wettability properties, has been studied for trapping and unidirectional transport of aqueous droplets by capillary force. We developed open microfluidic channels with fractal branching that densely fill a substrate surface (H. Kai et al., RSC Adv. 2018, 8, 15985; H. KAI, MicroTAS 2020). It can collect water droplets from a wide area of the surface to the center by hierarchically repeated transport and fusion of the droplets. The developed space-filling open microfluidic channels are reminiscent of fractal biological systems, both of which can efficiently contact a larger volume (or area in the case of two dimensions).

The microfluidic channels were fabricated by coating the substrate surface followed by photolithographic patterning. A film of polyethylene terephthalate was coated with a mixture of titanium oxide nanoparticles and Capstone (R) ST-100 fluoroacrylate copolymer to make the surface superhydrophobic (the contact angle of water droplet > 150°). The coated film was irradiated with 365 nm UV light through a photomask, where the only irradiated area turned superhydrophilic (contact angle ~ 0°), to obtain the open microfluidic channels with wettability patterning.

The droplet collection efficiency of the microfluidic channel was investigated by spraying water droplets into the channel and observing the volume of the water droplets collected in the center of the channel. Various photomasks were designed with the different numbers of branching, and the efficiency of water droplet collection was compared. As the number of repeated branching ("generation number") was increased, the collection efficiency monotonically increased up to the generation number of eight, where the efficiency reached 74%±9%. This indicated the effectiveness of the space-filling structures by fractal branching. In addition to the above experiment, we also conducted the computational fluid dynamics simulation to systematically understand the dynamic behavior. Details of the simulation methods as well as the comparison between the numerical and experimental results will be presented.