Symposium SM12—Bioinspired Macromolecular Assembly and Hybrid Materials—From Fundamental Science to Applications

Effective and cell-type-specific delivery of CRISPR/Cas9 gene-editing elements remains a challenging open problem. Here we report the development of biomimetic cancer cell coated zeolitic imidazolate frameworks (ZIFs) for targeted and cell-specific delivery of this genome editing machinery. Coating ZIF-8 that is encapsulating CRISPR/Cas9 (CC-ZIF) with a cancer cell membrane resulted in the uniformly covered C3-ZIF(cell membrane type). Incubation of C3-ZIFMCF with MCF-7, HeLa, HDFn, and aTC cell lines showed the highest uptake by MCF-7 cells and negligible uptake by the healthy cells (i.e., HDFn and aTC). As to genome editing, a 3-fold repression in the EGFP expression was observed when MCF-7 were transfected with C3-ZIFMCF compared to 1-fold repression in the EGFP expression when MCF-7 were transfected with C3-ZIFHELA. In vivo testing confirmed the selectivity of C3-ZIFMCF to accumulate in MCF-7 tumor cells. This supports the ability of this biomimetic approach to matching the needs of cell-specific targeting, which is unquestionably the most critical step in the future translation of genome editing technologies.

Biomineralization processes are controlled by organic templates such as peptides and polysaccharides. Acidic peptides and proteins exert effects on morphologies of biominerals, which are organic/inorganic hybrids [1-3]. Inspired by these processes, we have obtained a variety of synthetic organic/inorganic hybrids. Here we show recent developments of nanorod and nanodisk hybrid materials based on calcium carbonate [4] and hydroxyapatites (HAP) [5-8]. These hybrid materials are obtained in the presence of an acidic synthetic polymer, poly(acrylic acid). These nano-hybrids form colloidal liquid-crystalline states due to their anisotoropc shapes. The dynamic and alignment behavior has been examined for these nano-hybrids by x-ray and neutron scattering [6,7]. Biofunctions of these materials have been studied for HAP nanomaterials [8].


References
[1] M. Suzuki, T. Kato, and H. Nagasawa et al., Science, 325, 1388-1390 (2009).
[2] A. Sugawara, H. Nagasawa, T. Kato et al., Angew. Chem. Int. Ed., 45(18), 2876-2879 (2006).
[3] T. Kato et al., MRS Bulletin, 35(2), 127-132 (2010).
[4] M. Nakayama and T. Kato et al. Chem. Sci., 6(11), 6230-6234 (2015); Nanoscale Adv., 2(6), 2326-2332 (2020).
[5] M. Nakayama and T. Kato et al. Nat. Commun., 9, 568 (2018).
[6] T. Hoshino, M. Nakayama and T. Kato et al., Soft Matter, 15(16), 3315-3322 (2019).
[7] S. Kajiyama, H. Seto, and T Kato et al., Nanoscale, 12, 11468-11479 (2020).
[8] M. Nakayama, T. Kato and Y. Zhao et al. ACS Appl. Mater. Interfaces, 11(19), 17759-17765 (2019).

Polymeric colloidal particles play important roles in applications including coatings, adhesives, paintings, drug delivery, and personal cares. Often they are prepared from emulsion polymerization with well-controlled chemical compositions of surfactants and monomers. Polydispersity tends to impede self-assembly processes and the control of particle morphologies. In contrast, nature provided us diverse examples of microparticles that have unique surface textures from mixtures of polypeptides. Further, shape transformation from one state to another is not uncommon in biology.

Here, I will present two examples of self-assembled colloidal particles polymerized from nematic liquid crystal oligomers (LCOs), where oligomerization and polydispersity of the chain lengths is a feature. In the first example, we synthesize microparticles using a microfluidic device, followed by solvent evaporation and photopolymerization, leading to with robust, tunable surface patterns. Phase separation of LCOs occurs at the interface of the oil-in-water droplet upon organic solvent evaporation, which is facilitated by the mechanical coupling of LCOs of different chain lengths at the droplet interface. In the second example, we show dramatic shape transition of nematic LCO drops to a rich variety of non-spherical morphologies with unique internal structures upon cooling from the isotropic state to the nematic state. Here, molecular heterogeneity promotes and stabilize the reversible transitions. These studies suggest that heterogeneity and anisotropy together with shape control will offer new exciting routes to create a wide variety of bioinspired materials.

Allen Turing suggested that a system of chemicals reacting with each other and diffusing across space, termed a reaction-diffusion system, could account for the chief phenomena producing exoskeletal patterns in morphogenesis. Turing Patterns remained dormant for some time due to Turing’s untimely death and the dominance of the Second Law of Thermodynamics in the scientific world. Some alternatives to the reaction-diffusion theory have also been proposed now. For instance the mechanochemical theory of morphogenesis. However, there are several puzzles to be solved in Turing Patterns. Chief among such puzzles is: which chemicals are the most fundamental of biological patterns? Neither Turing, nor the latter researchers have addressed this question. The present work is an effort to seek answer to this question through a simplistic approach.
The study's focus started with melanin, which is the chief pigment of exoskeleton color and pattern prints. Evidence shows that in the complex genetic expression of melanin, casein is involved through an enzyme called casein kinase. Therefore, it was realized that exploration of caesin's Turing patterns in a physiological fluid model deserves a study. In the simplified model of the physiolgical fluid chosen for this study, certain key ingredients were incorporated into cow's milk; they are: sucrose, collagen, and sodium chloride. The rationalel for the choice of these ingredients is given below.
Sucrose is involved in embryonic development as the energy source and it also serves as the signaling material for gene expression. Collagen is a fibrous protein and constitutes nearly 50% of body protein in mammals. Collagen also comes to the central stage from the osteogenesis (bone development) phase in embryonic development. Given that casein, collagen, and sucrose are macromolecules, they serve a major role as the basic building blocks of embryonic development. The importance of sodium chloride comes from the fact that it is the dominant physiological electrolyte.
Casein is a popular globular protein; as is well known, globular proteins have complex structures (conformation) and have a far greater variety of biological functions. They are thus very dynamic rather than static in their activities. Notably, casein is involved from the start in the embryonic development both in vertebrate and invertebrate animals as well as in plants.
In consideration of the relevance to morphogenesis, Turing patterns of the interaction between casein, sucrose, collagen, and sodium chloride in aqueous medium were investigated in the present study. The stains used are the dye/pigment components of common food coloring agents. The present investigation provides a strong support to casein being the most fundamental macromolecule, which initiates, controls, and guides pattern formation. Salt helps in the polarization of casein and loosens the micelles to different patterns depending on the degree of polarization determined by salt concentration. Sucrose cross links casein strands in unique ways to produce different patterns, guided by its concentration. As revealed by the Turing patterns, sucrose's effect is so magical and seemingly different unique conformational structures are created by casein-sucrose interaction. The Turing patterns also indicate that the effects of these substances are synergistic. Furthermore, some of the patterns revealed by casein and collagen are similar to that of the embryo in gastrulation and neurulation. The present investigation also leads to an understanding that stripes of alternative colors we see on the animal skins (such as zebras) do not seem to come from two different pigments; but they seem to be different tones of the same color. The tone is determined by the kinetics of the underlying physicochemical phenomena.

We have developed a peptide-based approach for designing and constructing structurally complex nanoparticle superstructures. In this approach, peptide conjugate molecules bind to inorganic nanoparticles and direct their assembly. This presentation will detail first generation ‘static’ superstructures, including 1-D assemblies such as gold nanoparticle helices and discrete 0-D assemblies such as hollow spherical superstructures. We will discuss the subtle differences between the peptide conjugates which direct the assembly of these morphologically distinct superstructures and suggest design criteria for conjugates that can be used to construct second generation ‘dynamic’ superstructures. As a proof of principle, we design a family of photoresponsive peptide conjugates to control the reversible assembly of gold nanoparticles. The conjugates have different responses to input of UV radiation. We demonstrate that the nanoparticle superstructures constructed from these conjugates can undergo morphological shifts from spheres to 1-D assemblies. These results point toward new methods for dynamically controlling nanoparticle assembly via photo stimulus and new families of structurally complex dynamic nanoparticle superstructures.

This talk will present our recent effort towards achieving nanoscale site-specific doping of Si wafer using DNA as both the template and the dopant carrier. Upon thermal treatment, the phosphorous atoms in the DNA diffuse into Si wafer, resulting in doping within the defined region right below the DNA template. A doping depth of 30 nm is achieved for 10s of thermal treatment. We have fabricated prototype field effect transistors using the DNA-doped Si substrate. By using DNA nanostructures to pattern self-assembled monolayers, we are able to achieve both n-type and p-type site-specific doping of Si. This work shows that DNA nanostructure template is a dual-use template that can both pattern Si and deliver dopants.

This talk will provide an overview of our recent developments in self-assembling and gradient materials for regenerative medicine. We are using remote fields to engineer complex 3D architectures that mimic anisotropic and multiscale tissue structures and produce spatially arranged bioinstructive biochemical cues. We have used acoustic stimulation to produce engineered muscle with bundles of aligned fibres [1], and magnetic fields and buoyancy to achieve biochemical gradients in osteochondral scaffolds [2]. These versatile technologies can be applied to wide range of tissue engineering and drug delivery. We also use light stimulation on our photocaging gRNA strategy for spatiotemporally resolved CRISPR-Cas gene editing [3]. Using this system, we have achieved in vivo spatiotemporally controlled gene editing in living zebra fish embryos upon brief exposure to UV light. Finally, we will discuss recent developments in our tunable nanoneedle arrays for multiplexed intracellular biosensing at sub-cellular resolution and modulation of biological processes [4].
[1] J. P. K. Armstrong, J. L. Puetzer, A. Serio, A. G. Guex, M. Kapnisi, A. Breant, Y. Zong, V. Assal, S. C. Skaalure, O. King, T. Murty, C. Meinert, A. C. Franklin, P. G. Bassindale, M. K. Nichols, C. M. Terracciano, D. W. Hutmacher, B. W. Drinkwater, T. J. Klein, A. W. Perriman, M. M. Stevens. “Engineering anisotropic muscle tissue using acoustic cell patterning.” Advanced Materials. 30(43): 1802649.
[2] C. Li, L. Ouyang, I. J. Pence, A. C. Moore, Y. Lin, C. W. Winter, J. P. K. Armstrong. “Buoyancy-driven gradients for biomaterial fabrication and tissue engineering.” Advanced Materials. 31(17): 1900291.
[3 ] E. V. Moroz-Omori, D. Satyapertiwi, M.-C. Ramel, H. Hogset, I. K. Sunyovszki, Z. Liu, J. P. Wojciechowski, Y.Zhang, C. L. Grigsby, L. Brito, L. Bugeon, M. J. Dallman, M. M. Stevens. “Photoswitchable gRNAs for spatiotemporally controlled CRISPR-Cas-based genomic regulation.” ACS Central Science. 2020. 6(5): 695-703.
[4] C. Chiappini, E. De Rosa, J. O. Martinez, X. W. Liu, J. Steele, M. M. Stevens, E. Tasciotti. “Biodegradable silicon nanoneedles delivering nucleic acids intracellularly induce localized in vivo neovascularization.” Nature Materials. 2015. 14: 532-539.

Peptidic biomaterials have been receiving great interest because of their easiness of scale-up production, absence of pathogen-transfer risk, biomimetic properties, nanostructured morphology and customization potential for the specific tissue engineering application. However, their proper usage requires the understanding of multiple phenomena taking place at different scale levels during self-assembling. In this presentation, focused on the nanotech advancements in the field of regenerative medicine, we will see some multi-disciplinary researches and advances toward the regeneration of nervous tissues and pancreatic islets transplantation. This will bring us from molecular dynamics to cross-linking and electro-spinning of self-assembling peptides, from high-density 3D cells cultures to in vivo testing.

In nature, many filamentous macromolecules self-assemble into complex, hierarchically ordered fiber structures. The formation of fibers proceeds as cells secrete the macromolecules into a confined extracellular space. The filamentous macromolecules stabilize into diverse non-equilibrium structures that exhibit exquisite optical, mechanical and biological functions. To explain the mechanism of fiber formation in nature, biophysicists have constructed a variety of theoretical and experimental models. These models could not propose real-time processes of fiber formation and assume no interaction between macromolecules in general. Because it is not trivial to design an interaction-controllable system; this basic limitation and assumption, however, is highly simplified and does not represent the reality of nature. We demonstrate our recent efforts to design a biomimetic self-templating fiber formation process under the interaction-controllable system. M13 bacteriophage possesses a long filamentous shape with a helically-arranged protein surface, analogous to naturally existing basic building blocks. As a result of amplification through bacterial infection, M13 bacteriophage is identical, homogenous, and can be easily genetically engineered to make M13 bacteriophage a promising biomaterial in designing a biomimetic system. In this study, we genetically engineer M13 bacteriophage to install a functional peptide motif (VGVPGVG (V: Valine, P: Proline, G: Glycine)) at the end of the major capsid protein p8 to tune interactions between biomolecules during assembly. The introduced functional peptide motif possesses hydrophobic residue which can trigger hydrophobic interaction between phages. In addition, we applied depletion attraction force to manipulate interaction more precisely. We demonstrate that by controlling thermodynamic factors (e.g. concentration of phage and depletant, ionic strength and temperature, etc) we could investigate real-time evolution process of fibrous structure formation and understand how the molecular level interaction acts to the process. Engineered phages go through loosely assembled tactoids, densely packed domains, stacking of domains to fibrils formation and further hierarchical structures. Our approach provides the understanding how the formation of each ordered structure could be the basis of the next hierarchical structure formation. To investigate the time dependent evolution process of fibrous hierarchical structures, we employed polarized optical microscopy (POM). Other microscopic and nanoscopic structure characterization were carried out by atomic force microscopy (AFM) and scanning electron microscopy (SEM).

Pyroelectricity is a physical phenomenon of polarization change under temperature fluctuation in the environment. Biological building blocks such as amino acids, deoxyribonucleic acid (DNA), ribonucleic acid (RNA), proteins, and biomaterials such as soft and hard and tissues with hierarchical structures are composed of polar molecules and also known to induce pyroelectric property. However, the molecular mechanism of the pyroelectric effect in biological materials is still elusive. Here we report M13 bacteriophage (phage) as a programmable biomacromolecule building block to study the structure and function relationship of the pyroelectric biomaterials. M13 phage is a benign and non-harmful virus to infect only bacterial host cells. It has a filamentous shape with 880 nm in length and 6.6 nm in diameter. The M13 phage is assembled with 2700 copies of major pVIII coat protein hierarchically with spontaneous polarization. Through genetic modification, we can precisely control the chemical and physical structures of the phage proteins and investigate how the polarization changes under heat application. We can further easily amplify to produce identical copies of the phage on a large scale and self-assemble the phage into highly ordered arrangements. Here we developed a novel pyroelectric material and device using M13 phage. We first created a unidirectionally polarized monolayer phage film and characterized its pyroelectric characteristics. To determine how the heat can manifest polarization of the phage, we used piezoresponse force microscopy and Kelvin probe force microscopy and observed the polarization changes by visualizing the changes in the amplitude, phase, and surface potential under temperature changes. We then modified the polarization of the phage protein by inserting a variable number of negatively charged amino acids to demonstrate the origin of the pyroelectricity of the phage and to suggest the controllability of the pyroelectricity in biomaterials. We finally fabricated phage-based pyroelectric devices that can be used for thermosensor and energy harvester to show the feasibility of future applications. Our approach shows how the hierarchical assembled polar molecules contribute to the pyroelectricity in a biological system in a molecular level and how we can utilize the pyroelectric biological materials for future self-powered system and biomedical applications.

Small molecule assemblies in biological systems, such as cell membranes, benefit from high-surface-areas, tunable surface decoration, and responsiveness for interaction with their environments. In these systems and the synthetic analogues inspired by them (e.g. those derived from peptides), molecular migration, molecular exchange, and other dynamic instabilities are pervasive. These dynamic processes can be beneficial in applying supramolecular assemblies in biological environments, but increasing nanostructure stability may provide a route to their use in non-biological contexts. Here, we introduce the design of the aramid amphiphile (AA) motif to form microns-long nanoribbons with a dense, percolated hydrogen bonding network. These nanoribbons exhibit suppressed molecular exchange dynamics, mechanical properties on par with silk, and morphological stability outside of water. We utilize this stability to, for the first time, produce dried macroscopic threads of small molecule amphiphiles and demonstrate tunability of their mechanical properties. Finally, we incorporate photoswitchable moieties into the amphiphile design and show their triggerable, reversible morphological transitions between nanoribbon and nanotube states. Both morphologies exhibit months-long stability, persistence in air, and convert fully upon triggering. The AA platform overcomes dynamic limitations of conventional supramolecular systems to provide a novel route to solid-state nanostructured molecular materials.

Our laboratory is focused on the design of synthetic functional systems that can emulate the most intelligent processes in supramolecular structures of plantea and animalia kingdoms. Two functional hallmarks of naturally occurring chemical systems are the photosynthetic machinery of green plants, which “safely” sustains life on the planet, and the amazing signaling pathways that rule the behavior of cells. Both use hydrogels as the “material” environment in which evolutionary events have optimized their respective functions. In this lecture we describe bio-inspired synthetic hydrogels inspired by green leaves that are based on light harvesting supramolecular polymers and enzymes. These systems synthesize molecules such as hydrogen peroxide, potentially useful as liquid fuels in sustainable energy systems. The lecture will also describe highly dynamic supramolecular polymer hydrogels that mimic extracellular matrices and effectively signal cells to promote regenerative signaling pathways. This particular work will highlight the use of hydrogels in promoting regeneration in the central nervous system, a goal that for many reasons has great societal impact to be explained in the lecture.

Peptoids, N-substituted glycine oligomers, are an important class of peptide mimics that are generated from primary amines rather than from amino acids. Their facile and efficient synthesis on solid phase support enables the incorporation of various functional groups at specified N-positions along their spine including metal-binding ligands and catalysts.¹ Peptoids can adopt polyproline type helices if the majority of their sequence consists of chiral bulky pendent groups.² Such side-chains are structure inducers but they have no functional value. In my talk I will present the inclusion of metal-binding ligands within peptoid sequences as a new platform for the development of functional bio-inspired materials and supramolecular peptoid architectures. Thus, I will describe: (i) Controlled aggregation of Ag(0) NPs at room temperature in water near neutral pH mediated by peptoids, where tuning the sequence or of the peptoid or changing the metal-binding ligand impact the morphology of the Ag(0) NPs assemblies.³ (ii) Cu(II) mediated self-assembly of short peptoids to form double-stranded peptoid helicates,⁴ and distinct copper-peptoid duplexes, where changing only one non-coordinating side-chain leads to different supramolecular structures including tightly packed helical rods or nano-channels, and to different the pore sizes of the nano-channels.⁵ The selective recognition abilities of the nano-channels towards biologically relevant small molecules and anions will be also demonstrated. (iii) The direct correlation between the structure of short metal-binding peptoids varied in their monomer sequence, and the photoluminescence of their Ru(II) complexes, where .helical peptoids do not affect the fluorescence of the embedded Ru(II) chromophore, while unstructured peptoids lead to its significant decay.⁶

References:
1. (a) T. Zabrodski, M. Baskin, P. Jeya Kaniraj, G. Maayan Synlett 2015, A1. (b) P. Jeya Kaniraj, G. Maayan, Chem. Commun. 2015, 11096. (c) M. Baskin, G. Maayan, Chem. Sci. 2016, 7, 2809.
2. (a) K. Kirshenbaum et al., Proc. Natl. Acad. Sci., USA 1998, 95, 4303. (b) B.C. Gorske, et al. J. Am. Chem. Soc., 2007, 129, 8928. (c) O. Royet, et al., J. Am. Chem. Soc. 2017, 139, 13533
3. (a) H. Tigger-Zaborov, G. Maayan, J. Coll. Inter. Sci. 2017, 508, 56-64. (b) H. Tigger-Zaborov, G. Maayan J. Coll. Inter. Sci. 2019, 533, 598-603.
4. T. Ghosh, N. Fridman, M. Kosa, G. Maayan, Angew. Chem. Int. Ed. 2018, 57, 7703.
5. P. Ghosh, N. Fridman, G. Maayan, Chem – A Eur. J, in press.
6. L. Zborovsky, H. Tigger-Zaborov, G. Maayan, Chem. Eur. J. 2019, 25, 9098 –9107.

Tissue engineering offers great promise as a therapy for damaged tissues, a replacement for whole organs, or a platform for drug screening; however, many biomaterial scaffolds fall short on yielding reproducible and functional constructs. Hydrogels in particular have garnered intense interest as tissue engineering scaffolds due to their tailorable permeability, mechanics, and degradability. Synthetic materials are attractive due to their known chemical compositions and reproducibility, but the challenge with their use lies in the lack of complexity as compared to biological systems, especially with regard to sequence-specific bioactivity and hierarchical structure. Hence, our work aims to expand the toolbox for building complexity and functionality into synthetic hydrogel biomaterials by using precise polymer architectures, specifically those of polypeptoids. Using non-natural polypeptoid crosslinkers, we achieved control over the mechanics of poly(ethylene glycol) (PEG) hydrogel platforms by varying monomer sequence and chain structure. Unlike traditional crosslinking methods, our polypeptoid crosslinkers enabled control over hydrogel mechanics without altering network connectivity. Due to their biomimetic backbone, the polypeptoid crosslinkers also conferred stability to cellularly-secreted proteases, as compared to biological substrates. Furthermore, we examined the ability of non-natural peptoid monomers to tune proteolytic degradation rate using hybrid peptide-peptoid structures. Overall, our results suggest that sequence control of synthetic polymers may be a general strategy for expanding the functionality of biomaterial scaffolds for tissue engineering, particularly with respect to mechanics and degradation in complex biological environments.

The high information content of proteins drives their hierarchical assembly and complex function, including the organization of inorganic nanomaterials. Peptoids offer an organic scaffold very similar to proteins, but with a wider solubility range and easily tunable side chains and functional groups to create a variety of self-assembling architectures with atomic precision. If we could harness this paradigm and understand the factors that govern how they direct nucleation and assembly of inorganic materials to design order within such materials, new dimensions of function and fundamental science would emerge. In this work, peptoid tubes and sheets were explored as platforms to assemble colloidal quantum dots (QDs) and clusters. We have successfully synthesized CdSe QDs with difunctionalized capping ligands containing both carboxylic acid and thiol groups and mixed them with maleimide containing peptoids, to create an assembly of the QDs on the peptoid surface via a covalent linkage. This conjugation was seen to be successful with peptoid tubes, sheets and CdSe QDs and clusters. Particle identity was confirmed on the peptoid surface using EDX and high-resolution TEM. The particles were seen to have a high preference for the peptoid surface but non-specific interactions with carboxylic acid groups on the peptoids limited control over QD density via the maleimide conjugation. Replacing the carboxylic acid groups with methoxy ethers allowed for control over QD density as a function of maleimide concentration. ¹H NMR analysis demonstrated that binding of QDs to peptoids involved a subset of surface ligands bound via the carboxylate functional group, allowing sulfur to bind via covalent linkage to the maleimide. Overall, we have shown the compatibility and control of CdSe-peptoid interactions via a covalent linkage with varying peptoid structures and CdSe particles to create complex hybrid structures. Future work looks to expand the library of compatible nanoparticles to tune the properties of the hybrid materials and pattern complimentary nanoparticles onto a single peptoid surface and to investigate the assembly of peptoid nanostructures after conjugation with nanoparticles

A fundamental challenge in materials science is to create synthetic, organic nanostructures with the same architectural sophistication as proteins. One of the most exciting ways to do this is to mimic nature, and synthesize sequence-defined, non-natural polymer chains that spontaneously fold and assemble into precise three-dimensional structures. Peptoid polymers offer a unique platform to advance this general approach. We developed an automated synthesis method, the solid-phase submonomer method, which can efficiently synthesize high-purity, sequence-defined peptoid polymers up to 50 monomers in length. The method uses readily available primary amine synthons, allowing hundreds of chemically diverse sidechains to be cheaply introduced. We use this method, along with computational modeling, to design, synthesize, assemble and engineer a variety of protein-mimetic nanostructures, and to probe fundamental questions in self-assembly and polymer physics. Here, we show by NMR, direct imaging using cryo-TEM, X-ray scattering, and MD sumulations, that all known crystalline peptoid assemblies share a fundamental secondary structure motif based on a backbone fold containing all cis-amide bonds. This unexpected universality of peptoid backbone folding offers a unique opportunity to rationally design and engineer these materials to create robust, atomically-defined nanomaterials capable of protein-like functions.

Despite their technological potential and decades of advances in synthetic and biological chemistry, the construction of hierarchical architectures that intimately integrate synthetic polymer, natural biomolecules and inorganic components remains difficult. Two promising building blocks to tackle this challenge are peptoids, a class of peptide mimics that can be designed for self-assembly into well-defined structures, and solid-binding peptides (SBPs), which offer a biological path to controlled inorganic assembly and mineralization. Here, we report on the synthesis of ~3.3 nm-thick, thiol-reactive peptoid nanosheets assembled from equimolar mixtures of unmodified and maleimide-derivatized version of the Nbpe₆Nce₆ oligomer, optimize the location of cysteine residues in silica-binding derivatives of superfolder green fluorescent protein (sfGFP) for maleimide conjugation, react the two components to form peptoid-protein hybrids that exhibit partial or uniform protein coverage on both of their surfaces, and use 10 nm silica nanoparticles to trigger the stacking of these 2D structures into a multi-layer material comprised of alternating peptoid, protein and inorganic layers. We also exploit the display of solid-binding proteins on peptoid nanosheets and nanotubes to template the organization and control the precipitation of various inorganic materials, establishing peptoid-protein hybrids as a promising platform for materials science.

Inspired by Nature, numerous biomolecules with complementary binding affinity to inorganic surfaces have been designed. These biomimetic molecules, including peptides, proteins, and peptoids, have convincing applications in molecular recognition, fabrication of bio-hybrid materials, (bio)mineralization, energy conversion, storage, and transportation of matter and information, etc.
Peptoid is a class of biomimetic polymer with compatible bio-functions to peptide but has better thermal and chemical stabilities. It offers unique advantages for creating hierarchical assemblies at solid-liquid interfaces, serving as templates with outstanding spatial order for further functionalization. In this talk, I will present the most recent achievements of assembling short peptoid oligomers on MoS₂. By adjusting the pH of the assembly solution and the size of peptoid hydrophobic side chains, we demonstrated that peptoid assembly on MoS2 could have diversity phases, including the homogeneous film with high crystallinity, disk-like single-layer domains, and lamella patterns. We further found that these phases can co-exist with each other, and the homogeneous film is the template for the growths of the other two phases. After comparing the results to the simulations, it is clear that the peptoid-peptoid interaction and peptoid-MoS₂ interaction, mediated by pH, both play crucial roles in this multi-phase assembly. These results improve the knowledge of designing hierarchical architectures with biomolecules at solid-liquid interfaces. It also provides opportunities to optimize the performance of semiconductor devices in the future.

Controllable assembly of materials with regiospatial precision remains a grand challenge where complex arrangements are required to achieve emergent properties. Such structures are required for a wide range of applications, including metamaterials, optical limiting, catalysis, biosensing, etc. Bio-inspired approaches represent unique avenues to achieve such organized structures based upon the precision achieved through biorecognition. Such assembly capabilities are well known in biological systems; however, translation of these approaches to non-natural materials remains difficult to achieve due to the lack of fundamental information concerning the interactions between biomolecules and material surfaces, especially for material compositions not typically observed in nature. In this talk, initial steps to access bio-based approaches for the assembly of two dimensional nanosheets of graphene and hexagonal boron nitride (h-BN) in three dimensions will be discussed. Our research has demonstrated that peptides can be used to drive graphene exfoliation from bulk graphite where modification of the peptides with fatty acid domains can be exploited to minimize defect incorporation in the final materials. Through a combination of experimental analyses and computational modeling, we have identified key parameters to control both the binding at the nanosheet surface for both graphene and h-BN, as well as the selectivity between the two different materials. Interestingly, the length of fatty acid modifications to the peptide sequence plays an important role in controlling the final bound structure, including achieving highly viscoelastic biointerfaces. Such capabilities are key for the design of new biomolecules with multiple materials binding domains, which could eventually be exploited to drive nanosheet heterostructure formation.

Protein nanoribbons are believed to direct the organization of soft, amorphous mineral into tough, crystalline composites, however, how these ribbons scaffold an amorphous layer remains elusive. Inspired by tooth enamel, wherein amyloid-like amelogenin protein guides apatite mineralization, we investigated the impact of protein and peptide nanoribbon structure on thermodynamics and kinetics of heterogenous calcium phosphate nucleation and growth. Using in situ atomic force microscopy, supported by X-ray diffraction and molecular dynamics simulations, the molecular self-assembly, structure and function of nanoribbons arrays on graphite were resolved. We find that the nanoribbons lowered the barrier for formation of an amorphous phase, likely due to the hydrophilic side groups that protrude into solution with periodicity. Modification of the periodic domain with phosphorylation enhanced nucleation rates, whereas addition of a hydrophilic, disordered domain at C terminus promoted growth rates. These relationships provide empirical evidence for mineralization scaffolded by amelogenin nanoribbons and fundamentals for synthesis of hierarchical hybrid composites controlled by functional domains in nanoribbons.

A thermoelectric generator is a promising approach to recovering this low-grade energy and provides a circular economy method for energy sustainability. So far, only 70% of humanity's total energy dissipates as waste heat, further exacerbating the energy crisis and global warming. This study will demonstrate the scalability of coating polyaniline (PANi) on carbon nanotubes (CNTs) for efficient thermoelectrical energy conversions. We start from the in-situ polymerization of aniline with mixed CNTs, and found that the coating of PANi on CNTs showed distinct phases as compared to mixed PANi/CNTs blends. A further examination of their properties showed higher thermal stability and mechanical robustness. More importantly, with different CNT concentrations, the thermoelectric performance was optimized in bioinspired gill structures. We demonstrated the uses of this structure in current/voltage measurement and showed efficiency in powering in-house designed sensors. Our manufacturing is applicable in conjugating polymers for thermoelectric devices.

Control over the self-assembled hierarchical structure of functional biomolecules at solid interfaces is essential for the fabrication of micron-scale bio-nanodevices. Promising candidates are solid-binding peptides selected for specific inorganic solids by directed evolution techniques. Many of these selected peptides exhibit spontaneously long-range ordering at two-dimensional atomically flat solid surfaces. Advanced bio-nanotechnologies, such as multi-enzymatic bioreactors, require multiple, independently tunable functionalization of two or more different peptides to tailor interfacial molecular structures and functions. However, the current understanding of miscibility and binary assembly of peptides at interfaces is lacking. Here we present our findings on binary peptide assemblies at cleaved graphite surfaces with extraordinarily well behaved immiscible long-range ordered structures. We show that nucleation rates of the binary assembled system exceed those of the constituent peptide systems and are tunable by blending ratio and total peptide concentration. Molecular dynamics simulations and nanoscale atomic force microscopy attribute peptide immiscibility to peptide specific substrate recognition and self-assembly directions. Collectively, these findings lead to model predictions of the binary assembly structures of immiscible peptides based on 2D nucleation parameters of the single peptide assemblies. Our findings facilitate the molecular scale engineering of structured bio-nano interfaces through a multi-species self-assembly process and advance the fabrication of high-density patterning of biomolecules for biomimetic technologies, e.g., in multienzyme bioreactors and multiplexed biosensors. The research was supported by NSF-DMREF program through the grant DMR-1629071, 1848911, and 1922020 as part of the Materials Genome Initiative.

Self-assembly of particles to form superlattices and other ordered structures is typically thought of in terms of colloidal forces and liquid crystal ordering. Considerations of shape and solvent entropy dominate the controls on organization while atomic-scale details are of lesser importance due to the fairly homogeneous nature of the building blocks. Proteins offer unique advantages over inorganic particles as nanoscale building blocks, including monodisperse structures and specific interactions that are both atomically precise in their location on the protein and tuneable in their strenghts. For this reason, ordered assemblies of protein building blocks exhibit a wide range of structural motifs including 1D nanofibers and tubes, 2D lattices and 3D capsids and frameworks. Protein-based systems have the further advantage that they are readily assembled in interrogated in mild aqueous conditions, making them amenable to molecular resolution imaging techniques that provide a unique window into the assembly process. Here we report on two systems of engineered proteins. The first consists of a highly patchy 4-fold symmetric protein building block (L-rhamnulose-1-phosphate aldolase; RhuA), whose self-assembly is driven at the shortest length scale by disulphide bonds designed into four corners of the protein. By introducing a charged, atomically patterned substrate and varying charge states via solution ionic strength, we achieve simultaneous control of four different classes of interactions (covalent bonding, electrostatic surface templating, dipole-dipole interactions and desolvation-induced complexation) to yield four distinct, precisely patterned 2D crystals. The second system consists of a de novo designed rod-shaped helical repeat protein, DHR MicaN whose length can be set arbitrarily to N units of one repeat. These MicaN proteins are designed to interact in an epitaxial manner with the K⁺-sublattice of muscovite mica. Variation of the design created an end-to-end hydrophobic interactions that were either dimeric at both ends or trimeric interface at one end and dimeric at the other. As with RhuA, we show that the interplay of the specific intermolecular interactions, regional electrostatic interactions and global colloidal forces lead to a variety of distinct ordered phases that are not expected for uniform or non-interacting colloids. In all cases, in situ AFM reveals the development of order and its relationship to protein design and surface and solution interactions. The results provide a mechanistic picture of assembly by protein building blocks that links pathways and outcomes to the influence of interactions over many length scales.

There is an increasing need for the development of multifunctional lightweight materials with high strength and toughness. Natural systems have evolved efficient strategies, exemplified in the biological tissues of numerous animal and plant species, to synthesize and construct composites from a limited selection of available starting materials that often exhibit exceptional mechanical properties that are similar, and frequently superior to, mechanical properties exhibited by many engineering materials. These biological systems have accomplished this feat by establishing controlled synthesis and hierarchical assembly of nano- to micro-scaled building blocks. This controlled synthesis and assembly require organic that is used to transport mineral precursors to organic scaffolds, which not only precisely guide the formation and phase development of minerals, but also significantly improve the mechanical performance of otherwise brittle materials.
Here, we investigate an organism that have taken advantage of hundreds of millions of years of evolutionary changes to derive structures, which are not only strong and tough, but also demonstrate abrasion resistance. All of this is controlled by the underlying organic-inorganic components. Specifically, we discuss the formation of heavily crystallized radular teeth the chitons, a group of elongated mollusks that graze on hard substrates for algae.

Our investigation of the formation of a fully mature radular tooth from Cryptochiton stelleri found in the eastern Pacific, occurs over a series of more than 40 teeth. The initial stage of tooth formation begins with the synthesis of a three-dimensional fibrous α-chitin organic matrix, prior to the onset of crystallization. Microscope analysis of early stage teeth shows ferrihydrite mineral particles growing on α-chitin fibers. Synchrotron x-ray, combined with TEM analyses show that ferrihydrite exists as randomly oriented aggregates, but undergoes a phase transformation to magnetite within a few rows of teeth. We discuss potential mechanisms of nucleation of ferrihydrite, its transformation to magnetite as well as its subsequent mesoscale ordering, crystal growth and the resulting mechanical properties. From the investigation of synthesis-structure-property relationships in these unique organisms, we are now developing and fabricating multifunctional engineering materials for energy and water purification based applications.

A versatile method for the design of colloidal crystals involves the use of DNA as a particle-directing ligand. With such systems, DNA-nanoparticle conjugates are considered programmable atom equivalents (PAEs), and design rules have been devised to engineer crystallization outcomes. This work shows that when reduced in size and DNA grafting density, PAEs behave as electron equivalents (EEs), roaming through and stabilizing the lattices defined by larger PAEs, as electrons do in metals in the classical picture. This discovery defines a new property of colloidal crystals—metallicity—that is characterized by the extent of EE delocalization and diffusion. As the number of strands increases or the temperature decreases, the EEs localize, which is structurally reminiscent of a metal-insulator transition. Colloidal crystal metallicity, therefore, provides new routes to metallic, intermetallic, and compound phases.

Deciphering the structure and function of nanocages in macromolecules is essential to understand how the confined and finely tuned nanostructure assists and catalyzes reactions. Furthermore, we have been able to develop new strategies to employ unique functionalities of these nanocages unavailable by conventional methods. However, the identification and characterization of nanocages in macromolecules are always challenging; particularly, a fast and straightforward detection of the nanocage size is still missing. FRET can sense nanometer-scale dimensions while keeping the target intact. We have applied the silver nanodot FRET pair to the measurement of nanocages in reverse micelles successfully. Our results also clearly demonstrate that the water nanocage size of the Triton X-100/1-hexanol/cyclohexane-based reverse micelles expanded as more water was added into the system, clarifying long-term confusion regarding the size of the nonionic surfactant-based reverse micelles. The diameter of the nanocage obtained from the FRET of the nanodots was consistent with the size of the nanocage revealed by the cryo-TEM, suggesting that the FRET of silver nanodots to detect nanocage size is an easy and accurate tool. Our approach can be further applied to the measurement of nanocages in proteins in the future.

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Hierarchical inorganic materials are highly desirable for the development new advanced technologies¹. Using programmable macromolecular building blocks such as protein², peptoid³ and polymers³ as templating agent is an effective approach to achieve the hierarchy of inorganic materials. Inducing the successful preparation of functional inorganic materials, these programmable building blocks allow us to control their optical and electronic properties. Due to theie outstanding properties, these materials can be applied in a wide range of applications, such as plasmonics¹ and quantum optics¹. However, there still lack of a conclusive guiding rule for the successful synthesis of hierarchical inorganic materials with desired properties via designing macromolecular building blocks. Here, we studied the assembly behavior in a simple system, where de-novo designed protein nanofibers⁴ act as the building block, and Au nanoparticles as the inorganic units, towards a general rule for the effect of ionic strength on macromolecule templated assembly of inorganic materials. The protein fibers were designed to be negatively charged and the Au nanorods were synthesized to be positively charged; the electrostatic force were assumed to be the driving force of the hybrid assembly. After electrostatic assembly of Au nanorods along the protein fibers were achieved, we conducted a series of experiments to study the influence of external parameters, such as the aspect ratio of Au nanorods and salt concentration (ionic strength) on the assembly of Au nanoparticles on protein fibers. Moreover, we have developed an automated image analysis tool to help understand the as-obtained experimental data including scanning electron microscope images. With the new image analysis tool, we were able to calculate and analyze the attachment angle of Au nanorods with respect to protein fibers. Our results demonstrate that the average attachment angle varies depending on the ionic strength of the solution. This work is a promising step to the successful synthesis of functional inorganic materials and provides a guiding rule of ionic strength on the orientation of inorganic building blocks in electrostatically-driven hierarchical assembly.
1) Qian, Z., Ginger, D.S. Reversibly Reconfigurable Colloidal Plasmonic Nanomaterials J. Am. Chem. Soc. 139, 15, 5266-5276 (2017)
2) Dou, J., Vorobieva, A.A., Sheffler, W. et al. De novo design of a fluorescence-activating β-barrel. Nature 561, 485–491 (2018)
3) Yan, F., Liu, L., Walsh, T.R. et al. Controlled synthesis of highly-branched plasmonic gold nanoparticles through peptoid engineering. Nat. Commun. 9, 2327 (2018)
4) Shen, Hao, Fallas, J.A., Lynch E., et al. De novo design of self-assembling helical protein filaments. Science 362 (6415)705-709 (2019)

Soft piezoelectric materials are an important group of functional material for state-of-the-art energy harvesting, energy conversion and sensing technologies. Since piezoelectric materials can couple mechanical energy and electric polarization, they can serve as appealing sensing materials, alternative to the described passive semiconductors and capacitive polymers, for self-powered force sensors. While polyvinylidene difluoride has been a well-known and broadly used soft piezoelectric polymer material over years, non-degradability raises a significant concern in terms of safety issues and often requires an invasive removal surgery, which can damage directly interfaced tissues/organs. Poly-L-lactic acid (PLLA), a biodegradable medical polymer, has been shown to exhibit piezoelectricity when appropriately processed, thereby offering an excellent platform to construct safer, biodegradable piezoelectric implants, which can avoid problematic removal surgeries. However, unlike ceramic-based piezoelectric materials, to reach desired high piezoelectric property and long-term stability in biological environment still stand as a big challenge in PLLA soft biodegradable nanomaterial development.
In our work, we report a one-step strategy for fabricating core/shell PLLA/Glycine (Gly) NFs with a very high crystalline content and orientation of the polymer chains. The self-assembled core/shell structure is believed essential for the formation of crystalline phase and alignment of polymer chains, where strong intermolecular interaction between the -NH₂ groups on Gly and –C=O groups on PLLA is responsible for aligning the PLLA chains and promoting crystalline nucleation. The orientation of polymer chains in the PLLA/Gly NFs along their axes is up to 0.88 observed at atomic scale through high resolution transmission electron microscopy, and the crystallinity ratio is found to be 0.73. The as-obtained PLLA/Gly NFs exhibit significantly enhanced piezoelectric performance and excellent stability and biocompatibility. We also verify that PLLA/Gly NFs functioned well in its predefined lifetime and eventually self-degraded. In addition, the successful formation of high crystallinity ratio with a well-oriented polymer chains offers a structural-assisted design strategy, as opposite to traditional stretching and thermal process, to fabricate high-performance soft biodegradable piezoelectric materials at molecular level.

Crystallization of biomolecule offers to form long-range ordered molecular structures in an energy efficient manner under aqueous conditions[1]. Peptide sequences can be designed to establish desired crystal structures. These structured biomaterials will give rise to new functional devices which can be used for various applications. However, the method to form aligned peptide crystalline structures on substrates with a controlled manner is still limited. In this research, we aimed at developing a solution process to align crystals on a substrate in a thin film form. Solution shearing is a promising method to fabricate aligned molecular thin films, which has been studied with synthetic organic molecules, especially for organic semiconductor [2]. In this process, the solution is sandwiched between a blade and substrate. Evaporation of solution occurs at the meniscus formed at the edge of a blade. As the solution evaporates, molecules form thin film with a certain molecular orientation on the substrate. To the best of our knowledge, there is no report applying this method for biomolecules to form their oriented films. Biomolecules have different features from organic semiconductors for the solution shearing process. (1) while synthetic semiconductor organics are dissolved in organic solvents, biomolecules are dissolved in water. Water has a relatively higher boiling temperature than usual organic solvents. (2) while semiconductor organics have planar conformation which is advantageous for the crystallization, peptides or amino-acids are relatively flexible and hard to form a crystal. Thus, optimization of the sweeping speed and temperature of the substrate in the solution shearing is important for the formation of uniform and large-area thin film.
In this study, we developed a fabrication technique of oriented biomolecular thin film based on the solution shearing method. To achieve this goal, we developed a hand-made system for the solution shearing with biomolecules in aqueous solutions, and optimized the sweeping speed and temperature in the process. We utilized amino acids and peptides to test the ability of our system, and we analyzed the structures of deposited thin films of amino acids and peptides by X-ray diffraction (XRD) and angle dependent polarized Raman spectroscopy [3]. As a result of the parameter optimization, we succeeded in fabricating 300 nm-thick oriented films with a size of more than 500 μm square. We have characterized thin films using polarized Raman spectroscopy and X-ray diffraction (XRD) measurements. Raman spectra revealed that the solution shearing allows us to form crystalline amino acids and dipeptides on Si wafers. These experiments exhibited that the crystal orientations were along the direction of shearing. Furthermore, XRD spectra also revealed a formation of polymorph. It was found that we can suppress the polymorph formation by optimizing the condition of the solution shearing.
Reference
[1] Yuan, Chengqian, et al. "Hierarchically oriented organization in supramolecular peptide crystals." Nature Reviews Chemistry 3.10 (2019): 567-588.
[2] Giri, G. et al. Tuning charge transport in solution-sheared organic semiconductors using lattice strain. Nature 480, 504–508 (2011).
[3] Motai, K. et al. Oriented crystal growth of phenylalanine and dipeptide by solution shearing. J. Mater. Chem. C (2020) doi:10.1039/D0TC01208D.

Achieving controlled assembly of functional inorganic nanoparticles is a requirement for developing new applications in areas such as optoelectronics, sensing, and photocatalysis. Traditional methods, however, are often diffraction-limited or confined to small scale assemblies. Bioorganic templating of inorganic nanomaterials capitalizes on nature’s evolutionary design to achieve highly ordered nanostructures, often otherwise inaccessible through conventional ligand-mediated or nanofabrication methods. To efficiently design biological scaffolds for the controlled ordering of nanoparticles, we must first identify and characterize the intersurface interactions governing the assembly process. Here, we study the protein-directed electrostatic assembly of spherical gold nanoparticles along high aspect ratio, de novo-designed protein nanofibers anchored to an ITO substrate. We achieve these structures via a layer-by-layer assembly process, in which alternating surface charges of each component drive the highly specific attachment of gold nanoparticles to the anchored protein nanofibers. We then characterize the composite structures by scanning electron microscopy. To probe the charge-dependent particle-substrate and particle-fiber intersurface interactions, we vary particle diameter and pH of the nanoparticle solution and measure particle density and specific binding efficiency to benchmark these interactions. We find an inverse correlation between nanoparticle diameter and particle density. We attribute this trend to more effective screening of the like-charge repulsion between the nanoparticle and substrate by the oppositely-charged protein nanofiber. We then explore how varying pH can tune the local interactions to adjust particle density and the specific binding efficiency. We observe the maximum attachment density at neutral pH at which the layers of the assembly have alternating charges. Furthermore, we note a significant decrease in particle density at low pH at which all surface moieties are protonated and prohibit electrostatic attachment. However, only a slight decrease at high pH is observed as the result of a monotonic decrease of specific binding efficiency with increasing pH due to the neutralization of the substrate surface charge. Finally, we predict optical properties of these composite structures by finite-difference time-domain simulations. These results demonstrate the importance of understanding intersurface interactions for electrostatic assemblies and will guide the design of future bio-templates for the ordering of inorganic nanoparticles.

De novo designed proteins enable the precise placement of functional groups in three-dimensional space, which can be leveraged to guide the precise nucleation and growth of inorganic phases to form complex hierarchical nanostructures. Proteins have diverse functional groups which enable them to access an array of applications. Utilizing a strict control of chemical moieties in building blocks and designing repetitive interfaces enables precisely arranged structures to bridge scales. This control is shown to direct nucleation of precursors in solution at room temperature. Investigating the effect that organic molecules can have on nucleation by confining nucleation sites to specific geometries can lead to the formation of hierarchical materials with controlled microstructure. Understanding the effects that spatial presentation of different amino acid moieties has on the nucleated crystal phase and structure will facilitate the intentional design of self-assembled inorganic materials. Herein we demonstrate the influence that sequence can have on the phase of nucleated titania as well as the spatial control over nucleation that we can leverage using homo oligomeric de novo protein assemblies. We show that point mutations of different positively charged amino acids can favor anatase or beta phase titania. The templates shown here include small protein oligomers that display a favorable surface for nucleation, and large assemblies of protein fiber with mineralization directing moieties presented in the confined interior.

In fabricating polymer and nanoparticle composite or hybrid materials, the soft macromolecules' selective arrangement and the rigid nanoparticles’s orders have been a bottleneck to overcome. We will use the bioinspired design of the composite structure to demonstrate the interface and interphase effects in stress transfer, energy transport, stabilization of dispersant, degree of confinement or bonding, and, other new property generations. This poster will introduce the polymer and nanolayered structures in fiber forms. Different polymers and different nanoparticles will be spun via in-house designed fiber spinning techniques. These fibers possess different layer thickness, nanoparticle concentration, and particle morphologies. As a result, these composite fibers display controllable mechanics and conductivity. We leveraged these properties for versatile sensors that are responsive to mechanical strain and gaseous analytes. Our manufacturing of the fibers has not been reported anywhere else and sheds light on a new sensor fabrication for environmental or human health monitoring.

Biological templates that can facilitate nanostructure assembly are widely used in next-generation remediation, electrochemical, photovoltaic, catalytic, sensing and electronic memory devices, but the fundamental features that control their dynamics have yet to be elucidated. By using large-scale molecular dynamics simulations, we reveal, in atomistic detail, the M13-biotemplating kinetics. We observe the assembly of gold nanoparticles on two experimentally-based M13 phage types using full M13-capsid structural models and with polarizable gold nanoparticles in explicit solvent. Moreover, mechanistic and structural insight into the selective binding affinity of the M13 phage to gold nanoparticles are obtained based on a previously unconsidered clamp-based binding-pocket-favored N-terminal-domain assembly and also on surface-peptide flexibility. Our results may open the route for the prospects of utilizing computational tools for genetically engineering a wide range of 3D electrodes for high density low-cost device technologies.

Membraneless organelles (MOs) formation via liquid-liquid phase separation (LLPS) is a versatile spatiotemporal organizing mechanism in biological cells. They control biochemical reactions efficiently while being molecule enhancing hubs. Due to these diversified functionalities of MOs, there has been an increasing interest to develop novel bio-active materials and drug delivery systems to imitate MOs in recent years. Intrinsically disordered proteins (IDPs) are found to be one of the significant constitutes in MOs and our lab has been inspired to synthesize a new class of polymer-peptide conjugate known as Intrinsically disordered protein mimicking Polymer-oligopeptide Hybrid (IPH) to mimic Fused in Sarcoma (FUS) protein. Liquid droplets reminiscent of MOs have been formed by IPHs under physiological conditions in-vitro.

We develop a computational method to describe the phase separation of IPHs. To describe IPH in a minimalist model, we consider an IPH of having a stickers-spacers architecture, leveraging on classical associative polymer theory. We employ molecular dynamics simulations to estimate the driving forces from the interactive oligopeptide segments (as stickers). The favorable enthalpy between oligopeptide segments provides the driving force for reversible binding between IPHs. We estimated the average binding energy between a pair of stickers as 96 kJ/mol using the Molecular Mechanics Poisson-Boltzmann Surface Area (MMPBSA) method.

Next, we adopt Monte Carlo simulations to describe the stochastic movement of IPHs under physiological conditions. IPHs are structured as strings of stickers and spacers and randomly placed in a three-dimensional simple cubic lattice (200×200×200) as a canonical ensemble. We perform 10⁵ order of hypothetical Monte Carlo movements as self-avoiding walks on the lattice to obtain energy minimized configuration using the Metropolis-Hastings algorithm as movement acceptance/rejection criteria. Then the radial distribution function is used to identify the phase boundaries of the system. The results provide insights about the propensity of the IPHs to phase separate.

In summary, the research will provide a theoretical framework for understanding the material requirement on the molecular and macromolecular level for the IPHs to form MO-like structures. It provides a fast and economical means to guide the design of synthetic materials for mimicking intrinsically disordered proteins.

Molecular assemblies of dye molecules, known as dye aggregates, are of great interest for applications in light harvesting, nanoscale computing, and energy conversion, to name a few. When dye molecules are situated in close (few nm) proximity, short-range interactions modify their electronic structure, which is observed via dramatic changes in their optical properties. Recently, researchers have used DNA as a scaffold to template dye aggregates, raising the prospect that DNA nanotechnology may facilitate the development of aggregates with tunable optical properties. While the electronic structure (i.e., optical properties) of a variety of DNA-templated aggregates has been investigated via steady-state spectroscopic methods, their excited state dynamics, which are critical to their application, remain largely unexplored. In this contribution, we present time-resolved measurements of the excited-state lifetimes of a series of DNA-templated dye aggregates containing a prototypical cyanine dye, Cy5. We demonstrate that for all of the aggregate structures studied, the excited-state lifetimes are considerably shortened relative to that of the Cy5 monomer, exhibiting up to 20-fold lifetime reductions. We attribute the reduced lifetimes to enhanced nonradiative decay. Additionally, we discuss possible mechanisms of the enhanced nonradiative decay and ways that the nonradiative decay process might either be enhanced further or suppressed in order to meet the demands of various applications.

Stability and efficiency remain as a critical hurdle limiting clinical application of gene therapeutics, where development of protective gene carrier system has a potential to solve existing problems. In cells, nucleic acid molecules together with intrinsically disordered proteins (IDP) are actively localized in specialized compartments known as membraneless organelles (MO), that serve to stabilize, protect, and regulate corresponding reactions of molecules inside. Inspired by following beneficial aspects of MOs, here we report a new method for encapsulation and enhancement of functional activity of RNA therapeutics using membraneless organelle biomimetic system, reconstructed from IDP-mimicking polymer-oligopeptide hybrid (IPH). IPH, designed to display weak molecular attractions and RNA-binding capability, forms membraneless droplets under physiological mimicking conditions and demonstrates range of biomimetic properties. A model gene therapeutic, hammerhead RNAzyme against TNF-α cytokine mRNA, was preferentially recruited into IPH-droplets, along with target mRNA, with up to 30-folds enrichment. Owing to the liquid-like nature of the droplet interior, both recruited nucleic acid molecules exhibited free diffusion within the droplet environment as indicated by FRAP. Notably, RNAzyme catalytic activity was enhanced in the presence of the artificial MOs, demonstrated by gel electrophoresis and confocal fluorescence microscopy, presumably owing to localized increase of RNAzyme concentration and distinct droplet interior. This result also seems to indicate that localization within the IPH-droplet supports RNA folding, essential for its reactivity. Furthermore, methods for delivering RNAzyme loaded IPH-droplets into a macrophage cell line will be explored, where upon successful delivery, biocompatibility, stability, and suppression level of TNF-α production will be investigated. Overall, IPH-based MO biomimetics investigated here offers a potential as a gene carrier and bioreactor module, which may be useful for a range of gene therapeutic strategies.

Bioinspired polymeric materials receive considerable attention due to significant advantages over their natural counterparts: the ability to tune their structures over a broad range of chemical and physical properties, increased stability and improved processability. In particular, polypeptoids, or poly N-substituted glycines, are a promising class of peptidomimetic polymers, which offer great unique properties for both fundamental research and applications in biotechnology. The polypeptoid possess identical backbones to the polypeptide, but the side chain is attached to the nitrogen instead of a-carbon. It thus eliminates the inter- and intrachain hydrogen bonding and the chirality in the main chain. The peptoid polymers with high molecular weights and large scale yields can be obtained by ring-opening polymerization technique. Many polypeptoid-based block copolymers have therefore been synthesized and studied. We synthesized a series of functional polypolypeptoids with stimuli responsive properties by a combination of ring-opening polymerization and thiol-yne click chemistry. The obtained polymers show either LCST-type or UCST-type behaviour depending on the side-chain functionalities. We further reported a facile approach to prepare functional nanostructures such as highly flexible 2D crystalline nanosheets and superbrushes. The obtained bioinspired nanostructures are potential candidates for applications in nanoscience and biomedicine.

Silk fibroins are a class of proteins produced by a variety of insects and arachnids that can surpass man-made materials in specific strength and toughness. From a macromolecular perspective, silk fibroins have a linear architecture predominantly consisting of regularly alternating beta-sheet forming peptide segments and flexible peptide segments, resulting in a supramolecular network structure with stiff crystalline domains reinforcing an amorphous matrix. In nature, silk fibroins undergo a complex self-assembly process during spinning, rapidly transitioning from a soluble protein to an insoluble, highly robust material. Our work leverages the self-assembly of silk fibroin and silk-like macromolecules as a bottom-up method to form functional biomedical coatings. In particular, we have observed that non-specific interactions of silk fibroin with surfaces during supramolecular self-assembly can lead to the formation of stable and adherent thin-film coatings. These coatings provide complete surface coverage and can grow to tens of nanometers thick, completely transforming the physicochemical properties of a surface without requiring covalent chemistry or substrate pre-activation. Our studies also demonstrate that silk fibroin coatings can be generated on a variety of substrates ranging from hydrophobic Teflon to hydrophilic TiO₂. Furthermore, these coatings can readily exhibit beneficial biomedical properties, such as decreasing bacterial attachment and increasing neurite extension. Our research moreover delves into the complex interplay of surface-protein and protein-protein interactions underlying coating formation to establish methods by which we can tune the coating process. Through these investigations, we reveal a novel mechanism of protein adsorption that enables continuous, indefinite growth of robust protein layers on a variety of surfaces, which forms the foundation of a new approach towards modifying biomedical surfaces.

Peptide-based amphiphilic biomaterials that self-assemble into nanostructures provide a path for designing materials such as hydrogels and drug delivery vehicles. The engineering of these materials hinges upon the precise characterization of the self-assembled structures such as those obtained through small angle scattering techniques. The interpretation of these scattering profiles typically relies on analytical models for conventional shapes that may not capture the system geometry at hand. This calls for a method that is able to tie scattering profile features directly to the molecular level details in complex nanostructures without needing off-the-shelf scattering models. To address this need, we present recent developments in extending Computational Reverse-Engineering Analysis for Scattering Experiments (CREASE) to a system of polymer-peptide conjugates that self-assemble into bilayer and vesicle structures. Taking in scattering intensity profiles and polymer chemistries as inputs, CREASE combines genetic algorithm and molecular reconstruction simulations to determine the peptide amphiphile bilayer composition and vesicle dimensions (e.g. core diameter, layer thicknesses) and molecular level packing within the nanostructure.

In this talk we present a new coarse-grained (CG) model for cellulose and cellulose derivatives (e.g., methylcellulose) that enables simulations of their assembly in experimentally relevant solution conditions. This model balances the incorporation of chemical details at the monomer level (e.g., β, 1-4 linkage, relevant placement of groups that can/cannot form hydrogen bonds, directional hydrogen bonding interactions) as well as the reduction in degrees of freedom needed to simulate experimentally relevant length scales and time scales associated with assembly of multiple cellulose or methylcellulose chains in solution at finite concentration. We will first validate this CG model by comparing the cellulose single chain structure observed with the CG molecular dynamics (MD) simulations to that seen in atomistic MD simulations. We also compare the hydrogen bonding pattern, interchain distance and interchain orientation seen in multi-chain CG MD simulations with those observed in experimental crystallographic studies. After validation of cellulose CG model, we extend the CG model to study impact of ‘silenced’ hydrogen bonding sites in order to simulate cellulose derivatives synthesized by substituting some of the hydrogen bonding -OH groups in cellulose with other non-hydrogen bonding groups (e.g., -OMe in methyl cellulose). We expect this type of CG model to be useful in predicting morphology of cellulose and its derivatives under a wide range of solution conditions and chemical modifications to the chains.

Natural chitin and chitinoid materials have outstanding physical and biological properties, which inspired us to develop a process for biomimetic chitinoid organic and hybrid organic-inorganic thin film growth by Molecular Layer Deposition (MLD).
Here, we present a new class of organic–inorganic hybrid polymers called "metallosaccharides", based on sugar-type precursors. For a controlled MLD growth, the hexosamine monosaccharide N-Acetyl-D-mannosamine (ManNAc) was coupled with trimethylaluminum (TMA) repetitively in a cyclic manner for the growth of the hybrid organic-inorganic alumochitin thin films.
The self-limiting behavior of the surface reactions and the growth rate were determined by in-situ quartz crystal microbalance (QCM) and X-ray reflectivity (XRR) studies. The QCM measurements revealed a linear mass increase with the number of MLD cycles, and a film growth rate of ∼20 ng/cm²/cycle at 115 °C. XRR studies showed a growth rate of ∼1.3 Å/cycle and a constant film density of ∼2.5 g/cm³. The chemical structures of the coatings were studied with ex-situ X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). Characterization of the film structure, morphology, and conformality were performed by High-resolution transmission electron microscopy (HR-TEM), showing uniform and conformal alumochitin films wrapping ZrO₂ nanoparticles (NPs).
The chemical interaction between ManNAc and TMA, and the possibility of hybrid alumochitin film formation were modeled by density functional theory (DFT). The computed interaction energies between TMA and ManNAc are negative, meaning that there’s a strong interaction between these precursors. Theoretical modeling revealed that the proposed reaction mechanism for the ManNAc/TMA MLD process is energetically favorable.
The evaluation of the antimicrobial activity of the alumochitin thin film against Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria was assessed. Bacteria attachment and proliferation on glass substrates, covered with MLD film, were analyzed by confocal microscopy. Both types of bacteria grow and proliferate on positive control samples, while neither Staphylococcus aureus nor E. coli bacteria attached to the surface of the alumochitin film. These results show a great antimicrobial activity of alumochitin against gram-positive and gram-negative bacteria, as well as its enormous application potential as bioactive surfaces.

This project has received funding from the European Unions Horizon 2020 research and innovation programme under the Marie Sklodowska -Curie grant agreement No 765378.

The study of natural and designer protein-based materials has enabled the development of ubiquitous modern technologies for applications in optics, electronics, bioengineering and even medicine. Within this context, unique cephalopod structural proteins called reflectins have garnered attention due to their technological potential for the development of biophotonic and bioelectronic devices. However, the development of reflectin-based materials has been impeded by an incomplete understanding of their structures and properties. Here we highlight the proteins’ structure, assembly and multi-faceted material properties within the context of biophotonic platforms. Specifically, we present the molecular-level structure of a model cephalopod protein, its tunable self-assembly, and the correlation between its structural characteristics and optical properties. Our findings not only provide useful insights into the structure-function relationships of reflectins but also underscore their potential as functional biomaterials and hold relevance for the development of cephalopod-inspired optical technologies.

Self-assembly of molecules is an attractive materials construction strategy due to its simplicity in application. By considering peptidic molecules in the bottom-up materials self-assembly design process, one can take advantage of inherently biomolecular attributes; intramolecular folding events, secondary structure, and electrostatic interactions; in addition to more traditional self-assembling molecular attributes such as amphiphilicty, to define hierarchical material structure and consequent properties. A new solution assembled system comprised of theoretically designed coiled coil bundle motifs, also known as ‘bundlemers’ will be introduced. The molecules and nanostructures are not natural sequences and provide opportunity for arbitrary nanostructure creation with peptides. With control of the display of all amino acid side chains (both natural and non-natural) throughout the peptide bundles, desired physical and covalent (through appropriate ‘click’ chemistry) interactions have been designed to produce one and two-dimensional nanostructures. One-dimensional nanostructures span exotically rigid rod molecules that produce a wide variety of liquid crystal phases to semi-flexible chains, the flexibility of which are controlled by the interbundle linking chemistry. The two dimensional nanostructure is formed by physical and covalent interactions and are also nanostructures not observed in nature. All of the assemblies are responsive to temperature since the individual bundle building blocks are physically stabilized coiled coil bundles that can be melted and reformed with temperature. Additional, novel nanostructures to be discussed include uniform nanotubes as well as the templated growth of metallic phases. Included in the discussion will be molecule design, hierarchical assembly pathway design and control, click chemistry reactions, and the characterization of nanostructure via electron microscopy, neutron and x-ray scattering, and rheological measurements, as well as inherent material properties (e.g. extreme stiffness, responsiveness to temperature and pH, stability in aqueous and organic solvents).

We are exploring the de novo design of proteins that self-assemble into 1D (fiber), 2D (array), or 3D (crystal) architectures. We have designed, with near-atomic accuracy, 1D helical filaments with a wide range of diameters that assemble into precisely ordered micron-scale fibers, as well as 2D hexagonal arrays that assemble rapidly upon mixing the two designed protein components. The arrays span multiple microns and are robust to fusion of a wide range of functional groups enabling. We have also extended these approaches to the design of protein-inorganic hybrid materials. Finally, we are pursuing the computational design of new mechanical systems made of proteins. With this work, we seek to create custom devices that can perform useful work at the nanoscale.

Proteins represent the most versatile building blocks available to living organisms or the laboratory scientist for constructing functional materials and molecular devices. Underlying this versatility is an immense structural and chemical heterogeneity that renders the programmable self-assembly of proteins a challenging design task. To circumvent the challenge of designing extensive non-covalent interfaces for controlling protein self-assembly, we have endeavoured to use bonding strategies based on fundamental principles of inorganic, supramolecular and polymer chemistry. These strategies have resulted in 0, 1, 2, and 3D protein assemblies that display high structural order over many length scales and possess emergent chemical, physical, functional and dynamic properties. In this talk, I will present some of the recent protein-based assemblies and materials constructed in our laboratory.

Driven by liquid-liquid phase separation (LLPS), an emerging universal intracellular organization mechanism, membraneless organelles (MOs) generally harbor intrinsically disordered proteins (IDPs) and RNAs. As a minimalist biomimetic synthetic pathway, we synthesized IDP-mimicking polymer-oligopeptide hybrid (IPH) by conjugating cysteine-terminated peptides to vinylsulfone-modified dextran via facile click chemistry pathway through Michael addition between thiol and vinylsulfone. Two peptide sequences, namely, cysteine-terminated low complexity domain-like peptide (CLCDP) and cysteine-terminated arginine-glycine-glycine-containing peptide (CRP), were designed to impart weak molecular attraction and RNA-binding capacity to IPH, respectively. Most intriguingly, IPH underwent LLPS under physiology-mimicking conditions in vitro, resulting in micron-sized compartmentalized droplets, which could recruit RNA to generate complexed coacervate, namely, artificial MOs (AMOs). Stoichiometry of RNA, represented by N/P ratio between IPH and RNA, could exert effect on viscoelastic properties (storage modulus, G^', as an indicator of stiffness) of AMOs in a dose-dependent fashion, as will be quantified by microrheology, whilst no appreciable change of sphericity of AMOs was observed even for long RNAs (up to ca. 2.78 kbs) with high incorporation (up to N/P=1/25). Moreover, mobility, indicated by diffusion coefficient (D) measured by fluorescence recovery after photobleaching (FRAP), was also significantly affected by incorporation of RNAs. As an intracellular structural analogue which has also been shown implication in MO formation, (single/double stranded) DNA-based AMOs were also constructed and investigated. In stark contrast to RNA-based MOs, DNA modulates stiffness of AMO much more drastically, as is indicated by significant decrease of sphericity even at low incorporation (as low as N/P=1/0.1, similar length as RNA counterpart), as well as with very short DNA (ca. 36 bp, N/P=1/10), which will be further quantified by microrheology. Additionally, FRAP will be leveraged to quantify D of DNA-based AMO, which is expected to be drastically different from RNA-based AMO owing to occurrence of irregular-shaped assemblies. We reason the disparity between effect of RNA and DNA (single/double stranded) originates from the difference of intrinsic rigidity, as well as their non-specific interactions with IPH, which will be further elucidated via a biophysical model.

Hierarchical biological materials, such as osteons and plant cell walls, are highly complex structures that are difficult to mimic. Here, we demonstrate that liquid crystal systems combined with polymerization techniques could be applied in confined spaces to develop complex structures. We report development of a highly ordered concentric chiral nematic polymeric fibers based on cellulose nanocrystals (CNCs).

CNCs are nano-sized needle-shaped crystalline cellulose particles obtained by treatment of cellulosic biomass with acids. CNC aqueous suspensions spontaneously form chiral nematic liquid crystalline structures above a critical concentration in water. Organization of CNC particles could be manipulated through confinement. In our experiments, CNC suspensions were mixed with polymeric precursors and confined within a glass capillary tube. The tube was aged for several days for the liquid crystalline structure to form, followed by UV-initiated polymerization to lock the structure. The resulting CNC/polymeric fiber could then be removed from the tube and shows a highly ordered single domain liquid crystalline structure throughout its length.

Polarized optical microscopy, electron microscopy, confocal microscopy and 2D X-ray diffraction showed highly uniform concentric rings throughout the length of the fiber. The concentric rings are formed by CNC particles arranging in a chiral nematic liquid crystalline order where the CNC particles’ director rotates along the fiber diameter. A good analogy to describe the fiber structure is a tree trunk with its annual rings. The distance between the concentric rings of the fiber is equal to half of the pitch of the chiral nematic CNC liquid crystal. We tracked the formation of this highly ordered structure over time and under different conditions in which we varied the tube orientation, CNC concentration, CNC type, and capillary tube size.

Tube orientation during liquid crystalline phase formation was important because gravity causes sedimentation of tactoids, a predecessor to the long-range ordered phase. Tactoids are liquid crystalline anisotropic droplets that spontaneously nucleate above a critical CNC concentration and are the intermediate state bridging the isotropic phase and the macroscopic liquid crystalline phase with longer range order. CNC concentration and type were shown to determine the distance between concentric rings of the fiber. The capillary tube inner diameter was also important, and a single-domain structure was only obtained inside small-diameter tubes, not large ones. Mechanical tests showed similar properties for the chiral nematic and a pseudo-nematic CNC/polymeric fiber, both of which had superior mechanical properties compared to a polymer-alone fiber.

The structure of the single-domain chiral nematic concentric CNC/polymeric fiber is very similar to biological hierarchical structures, such as twisted plywood architecture of collagen fibers in cortical bone or twisting cellulose microfibrils of wood cell units. Indeed, liquid crystal systems, confined spaces, and polymerization techniques could be combined to achieve complex structures. These highly ordered CNC/polymeric fibers could become a platform for many applications from photonics to developing complex hierarchical materials.

In this paper, lipophilically modified silica coated gold nanorods were developed to enhance the photoacoustic response of contrast agents. Photoacoustic imaging become a popular technique in the diagnostic imaging because it can utilize light at larger penetration depths and better resolution than optical coherence tomography or fluorescence imaging. In addition, photoacoustic imaging can augment optical microscopy to image in high scattering tissue. To boost signal, many exogenous contrast agents have been synthesized. However, these agents are still limited to a linear dependence of signal on laser fluence, which limits the benefits for imaging in scattering media. The ability of agents to induce cavitation events in response to laser irradiation would both increase signal and promote nonlinearity. In this work, silica coated gold nanorods with a longitudinal plasmon peak of 750-800 nm were lipophilically modified to facilitate the formation of cavitation nuclei on the rod’s surface. It was found that the lipophilically modified silica coated gold nanorods were able to achieve nonlinearity at pulse radiant exposures greater than 8 mJ/cm². At radiant exposures of 21 mJ/cm², the photoacoustic response was 13-15 times higher than unfunctionalized gold nanorods. The concentration of the samples was also investigated, and it was found that the photoacoustic response was greater for samples with higher concentrations than ones that were lower. Finally, the lipohilically modified silica coated gold nanorods were more resistant to etching in aqueous media, showing stability for more than one month in PBS.

Influx and efflux of water is important for polysaccharides in living organisms, e.g. directional control of water diffusion on vascular bundle and water retention on fruits. While, it is possible to artificially create spatial patterns through water evaporation under physicochemically controlled environments. In fact, based on fingering phenomena, we could successfully obtain spatio-temporal patterns by drying aqueous mixture of polysaccharides.¹ The pattern formation has been demonstrated using several kinds of viscous aqueous mixtures of polysaccharides. The spatial pattern is formed by meniscus splitting with ordered depositions of polysaccharide self-assembly, from one space into multiple spaces. Differing from previous dissipative structures transiently showing spatial patterns, we successfully immobilized the structure as polymer deposition with uniaxial orientation. In this study, to clarify the factors on specific deposition nucleation, the nucleus position is statistically analyzed by changing the initial polymer concentration and drying temperature. Furthermore, by introducing crosslinking points into the membrane, the swelling characteristics as an anisotropic hydrogel were investigated. Reference 1. Sci. Rep. 2017, 7, 5615; Polymer J. 2020, 52 1185.

Cellulose nanocrystals (CNCs) are an abundant biorenewable resource that spontaneously organize into chiral nematic liquid crystals with hierarchical structure. This chiral nematic organization is retained in dried films of CNCs, giving films with brilliant iridescent colors.¹ The introduction of polymers into a chiral nematic cellulose nanocrystal (CNC) matrix allows for the tuning of optical and mechanical properties, enabling the development of responsive photonic materials.² Previously, researchers have investigated CNCs added to hydroxypropyl cellulose (HPC), but not the effects of small amounts of HPC on CNC.^{3, 4} In this study,⁵ we explored the incorporation of HPC into a CNC film prepared by slow evaporation. In the composite CNC/HPC thin films, the CNCs adopt a chiral nematic structure, which can selectively reflect certain wavelengths of light to yield a colored film. The color could be tuned across the visible spectrum by changing concentration or molecular weight of the HPC. Importantly, the composite films were more flexible than pure CNC films with up to a ten-fold increase in elasticity and a decrease in stiffness and tensile strength of up to six-times and four-times, respectively. Surface modification of the films with methacrylate groups increased the hydrophobicity of the films and therefore the water stability of these materials was also improved.


References:

1. Revol, J.-F.; Godbout, L.; Gray, D., Solid self-assembled films of cellulose with chiral nematic order and optically variable properties. J. Pulp Pap. Sci. 1998, 24, 146-149.
2. Tran, A.; Boott, C. E.; MacLachlan, M. J., Understanding the Self-Assembly of Cellulose Nanocrystals—Toward Chiral Photonic Materials. Adv. Mater. 2019, 32, 1905876.
3. Ma, L.; Wang, L.; Wu, L.; Zhuo, D.; Weng, Z.; Ren, R., Cellulosic nanocomposite membranes from hydroxypropyl cellulose reinforced by cellulose nanocrystals. Cellulose 2014, 21, 4443-4454.
4. Fernandes, S. N.; Geng, Y.; Vignolini, S.; Glover, B. J.; Trindade, A. C.; Canejo, J. P.; Almeida, P. L.; Brogueira, P.; Godinho, M. H., Structural Color and Iridescence in Transparent Sheared Cellulosic Films. Macromol Chem Phys 2013, 214, 25-32.
5. Walters, C. M.; Boott, C. E.; Nguyen, T.-D.; Hamad, W. Y.; MacLachlan, M. J., Iridescent Cellulose Nanocrystal Films Modified with Hydroxypropyl Cellulose. Biomacromolecules 2020, 21, 1295–1302.

Spiders can produce up to seven different types of silk fibers with varying mechanical properties and functions to support their survival. Some of their most characteristic properties that do not exist in other natural fibers are flat-stress strain behavior (tubuliform silk), supercontraction (dragline), and water collection (capture silk). These interesting properties can serve the requirements for smart functionality of materials for various applications. However, unlike silkworm silk spiders cannot be farmed due to their cannibalistic nature. This limits utilization of spider silks in their natural form for real world applications. The understanding of molecular structure of silks has inspired research by utilizing the repeating modules of spider silks with different gene sequence motifs to develop biomimic, novel and high performance materials. There are so far a range of recombinant spider silk proteins, namely, spidrions, being genetically produced by a variety of host organisms. Although such produced spidroins have been shown to be versatile proteins with the capability to be processed into diffeent morphologies, fibrous materials are still one of the most attractive incentives since its natural counerparts due to the above reasons. This talk will present several examples of biomimetic fibrous materials with different properties including shape memory/supercontraction, mechanical toughness and directional water collection by using spidroins made from different gene motifs expressed in E. Coli.

Tubuliform spidroin 1, from a black widow spider-Lactrodectus Mactans, was first genetically engineered by using the single repeat unit and abbreviated as eTuSp1 for flat-stress-strain mechanical properties. In this work, in good agreement with previous studies, spherical aggregates were considered as intermediates and could be induced into β-sheet-rich silk fibers by the shear and elongation. The underlying mechanism for the assembly of silk spheres and fibers were demonstrated by the micelle theory. To investigate mechanical properties, individual spheres were subjected to the AFM indentation and the corresponding compressive modulus was determined by using Hertz model. In the tensile test, the modulus of silk fibers could be flexibly regulated in accordance to different post-spin drawing ratios. We also prepared an engineered major ampullate spidroin 2 (eMaSp2) by using N & C terminal domains from spidroins MaSp1 of Euprosthenops australis and MiSp1 (minor ampullate spidroin) of Araneus ventricosus respectively for shape and stress memory fibers. Revealed by CD spectrum, eMaSp2 formed a dimer in the solution and predominantly obtained a α-helix structure. Upon exposure to the elevated temperature from 25 oC to 70 oC, a permanent transition from α-helix to β-sheet was observed. Followed by a biomimetic wet-spinning approach, eMaSp2 fiber was prepared and later displayed β-sheet-rich structure similar to natural counterpart.

Moreover, to obtain fibers to perform as a spider capture silk in spider web to collect water for recovering the daytime-distorted shape during night through water-sensitive shape memory effect. Different from using synthetic materials, an all silk-protein fiber (ASPF) with periodic knots to endow extremely high volume-to-mass water collection capability. This fiber has a main body of B. mori degummed silk coated with recombinant eMaSp2 of spider dragline silk. It is 252 times lighter than synthetic polymer coated nylon fibers that once was reported to have the highest water collection performance. The ASPF collected a volume of 6.6 µL of water and has 100 times higher water collection efficiency compared to existing best water collection artificial fibers in terms of volume-to-mass index (VTMI) at the shortest length (0.8 mm) of three phase contact line (TCL). Since silkworm silks are available abundantly, effective use of recombinant spidroins tandemly shows great potential for scalability.

Possessing an amphiphilic character, proteins are commonly used to stabilize the oil-water interface of the food-grade emulsions. Soybeans are a particularly good source of edible proteins because of their relative abundance, sustainable supply, and low cost. Soy proteins can be isolated from other components of the beans and converted into functional ingredients using commercially viable extraction and purification methods. The major fractions in soy protein are globulins, namely β-conglycinin (a 7S globulin) and glycinin (an 11S globulin). These protein globulins are one of the most commonly used plant proteins for the fabrication of food-grade particles as Pickering emulsion stabilizers. As the use of soy protein isolates in complex food systems such as emulsions and suspensions, gains more momentum, it is important to fully understand the amphiphilic properties of these protein globulins and study their adsorbance at the oil-water interface.
Diffusing away from the aqueous phase, soy protein (SPI) globulins adsorbed at the water/oil interface. For this film of adsorbed SPI, the viscoelastic effects were investigated using a rotational rheometer equipped with the double-wall ring geometry (DWR). Steady-shear time sweeps using DWR revealed an increase in the interfacial viscosity similar to the Kelvin-Voigt model. The relaxation time (as a measure of the initial adsorbance rate) scaled linearly with the SPI bulk concentration (E/eta~c^1.0). It was concluded that perhaps, at the early stages of SPI adsorbance, the transport mechanism is driven by the concentration gradient between the layer adjacent to the interface and the interface itself (c/2*Rh, with Rh being the hydrodynamic radius of the SPI globulins). Moreover, frequency sweeps (at 0.01-100 rad/s) from the DWR indicated a highly entangled layer of SPI globulins at the interface. However, pressure-driven flow through a pipe at high shear rates (steady flow at ~10-1000 1/s with zero interface) showed Newtonian flow behavior (n~1.0). This was attributed to the difference in conformation for the SPI chain at the oil/water interface vs in the aqueous bulk, causing the SPI globulin to unfold in the former case.