Symposium BM09 : Bioinspired Macromolecular Assembly and Inorganic Crystallization—From Tissue Scaffolds to Nanostructured Materials

Biological cells can inspire the creation of nanoparticles equipped to store and release hydrophobic drug molecules upon demand. Lipid vesicles impregnated with alpha-helical peptides have demonstrated the clustering of the peptides under equilibrium. The formation of thick, amphiphilic, transmembrane channels via the self-organization of the peptides could be potentially used for the on-demand release of small drug molecules from the hydrophobic core of a vesicle bilayer. We are interested in understanding the driving forces responsible for cluster formations and evaluating their effects using the Molecular Dynamics simulation technique. Coarse grained representations of the molecules are used to resolve the extended spatiotemporal scales relevant to the problem at hand. The bonded and non-bonded interactions between the particles is captured by the Martini force field. We investigate the role of peptide concentration and helical separation on the cluster formation. We find the cluster size to be dependent more on helical separation as compared to peptide concentration. Additionally, we test the role of hydrophobic mismatch to understand the effect of electrostatic interactions between the peptides and lipid molecules. Our results demonstrate negative mismatch to result in larger cluster sizes as compared to a zero hydrophobic mismatch condition due to larger perturbations in the vesicle monolayers.

Peptides that self-assemble into pore-like structures in lipid bilayers could have utility in a variety of biotechnological and clinical applications due to their ability to breach the barrier imposed by lipid bilayers. To empower such discoveries, we use rationally designed peptide libraries and high-throughput screens to select peptides based on a particular property, in this case macromolecular-size bilayer poration. Towards this goal, we designed a library based on the bee venom peptide melittin, and we developed a high throughput screen that reports on the passage of macromolecules across lipid bilayers. We identified two peptide families that efficiently assemble into large pore-like structures. One of the families is highly active at pH 7. The other peptide family is pH sensitive, as its self-assembly is triggered by low pH. The pH-triggered peptides could be used for endosomal release of uptaken polar molecules into the cell cytosol, upon endosomal acidification. They also could be used in cancer therapies to selectively permeabilize the plasma membranes of cancer cells, since the vicinity of solid tumors is often acidic. Additional generations can be screened to further fine-tune the properties of these peptides.

Self-assembly of biomolecules is a prominent issue explored in biomedical, biophysical, and bio-material research. Understanding how and why certain peptides/proteins prefer to self-assemble into larger networks can reveal the mechanism of amyloid formation and assist in bottom-up designs of supramolecular structures like gels and nanotubes. Some low molecular weight di- or tripeptides with aromatic residues and terminal groups have been shown to form gels. Contrary to expectations, we recently discovered that cationic glycylalanylglycine (GAG), a tripeptide of low hydrophobicity, forms a gel in 55 mol% ethanol/45 mol% water at room temperature if the concentration exceeds 200 mM. The underlying structure is comprised of unusually long crystalline fibrils (in the 10^-5m range), which do not exhibit the canonical β-sheet structure. Rheological data and vibrational circular dichroism spectra suggest the existence of two different gel phases, one formed between 15° and 35°C with left handed twisted fibrils and G’ values at ca. 2*10⁴ Pa and another one formed below 15°C with right handed twisted fibrils and G’ values close to 10⁵ Pa. Results from DFT calculations indicate that the two phases might be underlied by rather differently structured fibrils. The fluorescence kinetics probing the incorporation of thioflavin T into the hydrophobic interior of fibrils indicate a retarded diffusion of the fluorophore into fibrils that formed rather quickly after incubation above 15°C, while fluorescence increase, and gelation proceed on a similar time scale for the gel phase formed below this temperature. Upon increasing the temperature, it can preserve this capability until the melting temperature is reached, which suggests that this gel phase has all what it takes to function as a drug delivery system. The potential reformation process of the fibrils probed by UVCD, rheology, and microscopy show that after sitting for 16h above the melting temperature, the fibrils do not have the ability to grow back. Instead, microscopic images suggest the formation of a crystal-type structure that forms in its place. Our results therefore suggest that the gel phases are meta-stable states of the system that form more quickly at or below room temperature. We care currently working on optimizing the gelation/melting conditions for specific biotechnological applications of the gel as well as characterizing the observed crystal-type structure.

Peptide-based materials have drawn high interest for their use in biomedical applications such as drug delivery, cell encapsulation, and tissue regeneration. Particularly, self-assembling peptide hydrogels have shown promising properties as biomaterials since their properties and functionality are tunable by their peptide sequence. For example, they are inherently biocompatible and biodegradable, their nanofibrous structure resembles the extracellular matrix, and they form materials with high-water content. Generally, these peptides utilize ionic amino acids to control self-assembly by changing the pH or ionic strength. Included in these group are the self-assembling Multidomain Peptide nanofibers (MDP), composed of an amphiphilic β-sheet forming core and flanking charged domains, which increase peptide solubility and make the peptide material responsive to pH changes and the presence of ions.

It is known that the biological response and cell behavior is highly dependent on the chemistry of the materials. Positive polymers promote cell adhesion and proliferation while showing concentration-dependent cytotoxicity, whereas neutral polymers, such as PEG, are frequently inert, biocompatible and non-immunogenic. Previously, all MDPs were either positively or negatively charged; therefore, expanding the scope of MDPs to neutral, non-ionic peptides will make distinct biological properties available that are not present in highly charged peptides.

Strategies to control the self-assembly of non-ionic peptides is limited because these peptides tend to have low solubility, aggregate or precipitate in aqueous solutions, making the formation of finite supramolecular structures and self-assembled hydrogels challenging. In this project, we present an alternative mechanism to control the self-assembly of neutral, uncharged multidomain peptides by utilizing steric impediment. Through the study of a series of neutral peptides, we analyzed the effect of the steric interactions on the peptide solubility, aggregation, nanostructure, and hydrogelation. From the series, a novel neutral multidomain peptide hydrogel was developed, which is inert to pH variation and ionic strength. This novel material showed promising properties for biomedical, cell preservation and tissue regeneration applications.

Structurally defined materials on the nanometer length-scale have been historically the most challenging to rationally construct and the most difficult to structurally analyze. Sequence-specific biomolecules, i.e., proteins and nucleic acids, have advantages as design elements for construction of these types of nano-scale materials in that correlations can be drawn between sequence and higher order structure, potentially affording ordered assemblies in which functional properties can be controlled through the progression of structural hierarchy encoded at the molecular level. The predictable design of self-assembled structures requires precise structural control of the interfaces between peptide subunits (protomers). However, control of quaternary structure has proven to be challenging to reliably predict, as conservative changes in sequence can result in significant changes in higher order, i.e., supramolecular, structure. We have employed simple self-assembling peptides as building blocks for the construction of two-dimensional nano-scale assemblies. In contrast to filamentous assemblies (e.g., fibrils, ribbons, and tubes), protein-based two-dimensional assemblies occur relatively infrequently in native biological systems. We have demonstrated that extended and structurally defined two-dimensional assemblies can be constructed through lateral association of chiral rod-like subunits such as the collagen triple helix. The resultant assemblies can exhibit sequence-dependent control of structure, including growth in the lateral and/or axial dimensions. Moreover, the sheet-like assemblies can be integrated with other self-assembled biological structural motifs, such as DNA origami nano-tiles, to afford self-organized hybrid assemblies. Despite the potential for these two-dimensional assemblies as structurally defined nano-scale scaffolds, it remains challenging to reliably predict and control the structure of the assemblies based on sequence-structure correlations at present.

Supramolecular soft matter is a rapidly emerging field that encompasses the rational use of organic molecules to design function in materials. The most promising systems are “supramolecular polymers” since one-dimensional catenation of structural units is a critical feature to create mechanically robust macroscopic systems and directed transport of charge in aligned morphologies. Supramolecular polymers, in contrast to macromolecules in which structural units are linked through covalent bonds, supramolecular systems are designed using additive noncovalent bonds that are tunable over a very broad range of binding energies encoded in the molecular structure of the “mers”. Furthermore, a major gap in the design of synthetic soft matter is the rational integration of covalent and supramolecular polymers, a concept that is used to craft function in the structures of living organisms. This lecture will describe first entirely supramolecular systems based on peptides and nucleic acids in which dynamics of non-covalently bonded monomers can reversibly form superstructures linked to mechanical and biological functions. Within the domain of hybrid systems in which covalent macromolecules are integrated with supramolecular structures, the lecture will describe materials inspired by muscles that are capable of transducing thermal to mechanical energy, light to mechanical energy, and light to chemical energy in photocatalytic materials.

Macromolecular self-assembly in biological systems takes many forms and enables countless functions across multiple length scales. Often, the structure and function of these assembled structures are dictated by subtle changes in the composition of the molecular building blocks that make up these materials. For example, simple amino acid substitutions can impart significant changes in the structure and function of protein assemblies. Inspired by this theme, we explore here the self-assembly of an ABC triblock peptide-oligoethylene oxide amphiphile with hydrophilic A and C blocks and a hydrophobic B peptide block. By varying the amino acid side chain size and hydrophobicity within the B-block, we observe aqueous self-assembly into polymorphic cellular particles with hierarchical structure and porosity ranging from giant vesicles with foam-like membranes to porous tubular architectures. These structures are characterized microscopically and spectroscopically to determine the relationships between the varied peptide compositions, tunable intermolecular interactions, and the observed morphologies. Additional evaluation of these materials as vehicles for molecular encapsulation and as templates for secondary mineral templating reveal potential new strategies to control hierarchical materials synthesis and assembly through bio-inspired molecular building block design.
Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

Mucins – the glycoprotein building-blocks of mucus – play diverse and crucial roles in the body. These functions range from lubrication of articular joints and the eye, to the protection of stomach endothelium from the harsh environment of the lumen, to modulation of microflora populations in the digestive and respiratory systems. Despite this diversity, these functions are all attributed to slight modifications in a general structure shared by all mucins: a telechelic triblock polypeptide comprised of terminal association moieties and a heavily glycosylated core which forms a hydrated bottle brush center. In vivo, these versatile functions are achieved by altering glycosylation patterns, crosslinking density, and targeting affinity in a modular fashion.
Inspired by this adaptability, we have emulated this general architecture in a modular conjugate analogue mucin platform which engenders general structural features preserved among mucins which we, and others, have identified as key to their function. To recapitulate the mucin backbone, we genetically tether and co-express terminal binding modules with a lysine-rich, elastin-like polypeptide (ELP) central scaffold. Binding modules may include sequences designed to target surfaces of interest, to facilitate intramolecular associations, or to direct surface conformation of our construct. The regularly-spaced lysines in the ELP scaffold can be harnessed for grafting synthetic polymer bristles. Bristle chemistry may be chosen for a desired property (including non-fouling character and lubricity) independent of the binding and scaffold modules. Our platform is, to our knowledge, the first to adapt the modularity of the mucin architecture into a bio-synthetic platform technology.
To demonstrate the application of our platform to clinically-relevant problems, we have tailored our mCAMP to osteoarthritis and kidney stone disease, two conditions infamous for profound morbidity and high prevalence. In tailoring our analogue mucin to cartilage, we hope to rival the performance of lubricin, a natural mucin which provides lubrication and wear protection to articular joints. Moreover, we seek to harness the properties of natural mucins and apply them to systems not naturally protected by mucinous coatings. In doing so, we have adapted our platform to binding calcium oxalate kidney stones. Association modules are designed to direct assembly on mineral surfaces as well as inhibit further mineralization. Moreover, these modules are designed to form intramolecular associations, facilitating a robust surface coating. The inclusion of non-fouling synthetic polymer bristles provides a means by which to inhibit protein-mediated crystal aggregation. In this platform technology, we have begun to develop a means by which to replicate not only the in vivo function of mucins, but to harness that function to meet additional clinical needs.

Early investigations from The Medina Group identified that binding of cationic membrane-active peptides with negatively charged cell-surface glycans was a critical initiating step to potentiate the peptide’s lytic action. Inspired by this natural system, we have designed a family of biohybrid nanomaterials assembled via electrostatic association of cationic peptides and anionic carbohydrates. Screening a series of peptide-polysaccharide pairs under electrospray synthesis conditions identified that poly-L-lysine (PLL) and hyaluronic acid (HA) rapidly co-assemble to yield nano-scale gel-like particles, which we refer to as nanogels. Importantly, using peptide-carbohydrate co-assembly allowed for direct encapsulation of both small molecule drugs and protein cargo into the nanogel carrier under mild aqueous conditions conducive to sensitive biomolecules. Further, we found that modulating the ratio of PLL and HA utilized during particle assembly yielded nanogels with tunable swelling profiles and failure rates, thus allowing for controlled temporal release of loaded cargo. In vitro testing demonstrates that nanogels exhibit versatile and complimentary mechanisms of cargo delivery depending on the biologic context. In mammalian cells, nanogels can deliver membrane-impermeable protein cargo to the cytoplasm by rapid internalization via endocytosis, followed by endosomal escape. Likewise, chemotherapeutic-loaded nanogels were capable of enhancing the potency of loaded drug by up to an order of magnitude towards both chemo-sensitive and -resistant tumor cell lines. Remarkably, in the presence of bacterial pathogens, nanogels show a very different behavior. The carrier is able to recruit microbes and permeabilize their cell wall to sensitize pathogens to the action of loaded antibiotic. In a notable example, delivery of vancomycin from nanogels enhanced the drug’s potency by >15-fold towards a gram-positive strain. Even more surprising was the ability of nanogels to sensitize gram-negative pathogens to the action of vancomycin, which are otherwise innately resistant to the drug due to the low permeability of their cell wall. This adaptable bioactivity, in combination with their low toxicity towards human endothelial cells and erythrocytes, demonstrate that nanogels represent a versatile and bio-responsive carrier capable of augmenting and enhancing the utility of a broad range of biomolecular cargoes.

Phase-changing nanoparticles (PCNs) are a class of materials that undergo solid-liquid-gas transitions in response to various engineered stimuli, leading to their application in fields that include thermal energy storage, bioelectronics and precision medicine. In particular, liquid-shelled perfluorocarbon PCNs that can be vaporized upon exposure to ultrasound (US) are poised to open unprecedented opportunities in nanomedicine and molecular imaging. However, despite recent progress, challenges remain in controlling the material properties and acoustic activation of PCNs, as well as overcoming the poor loading efficiency and delivery of biologic cargo from the carrier. Here, we describe the design and synthesis of a new class of PCNs recently prepared via templated peptide assembly, which we refer to as ‘nano-peptisomes’. Nano-peptisome architecture develops from the spontaneous orientation of de novo designed peptide amphiphiles around an US-sensitive fluorinated droplet as the template. Utilizing peptide-assembly allows for facile particle synthesis, direct incorporation of bioactive sequences displayed from the peptide corona, and the ability to easily encapsulate biologics during particle preparation using a mild solvent exchange procedure. We find that nano-peptisome size can be precisely controlled by simply modulating the starting peptide and fluorinated solvent concentrations during synthesis, leading to programmable acoustic properties of the final carrier. Further, biomolecular cargo, including peptides and proteins, can be encapsulated within the particle core and directly delivered to the cytoplasm of cells upon US-mediated rupture of the carrier. Bio-imaging studies demonstrate that nano-peptisomes can be tracked and guided using diagnostic B-mode US, while Doppler imaging allows for real-time monitoring of particle activation and rupture in tissue mimetic gels. These results establish nanopeptisomes as a novel theranostic platform capable of image-guided delivery of bioactive macromolecules into cells with spatial and temporal precision.

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 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 interactions and are 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 nanoparticle on and in peptide nanostructures. Included in the discussion will be molecule design, hierarchical assembly pathway design and control, click chemistry reactions, and the characterization of nanostructure as well as inherent material properties (e.g. extreme stiffness, responsiveness to temperature and pH, stability in aqueous and organic solvents).

Life’s diverse molecular functions are largely based on only a small number of highly conserved building blocks- the twenty canonical amino acids. These building blocks are chemically simple, but when they are organized in three-dimensional structures of tremendous complexity, new properties emerge, giving rise to the extraordinary machinery of life. So, if just twenty simple building blocks- when appropriately assembled – give rise to the complexity and functionality that can sustain life- then this is clearly a very versatile construction set. Our overall goal is conceptually simple: to figure out how to make nanoscale systems and materials from biology’s building blocks, and to apply these materials to diverse problems, that require them to be interfaced, ideally seamlessly, with living systems, or the natural environment. Different from other research groups, we have an unbiased approach, that is not guided by copying biological systems, and we keep these systems as simple as possible, which lowers barriers to application. The talk will focus on our latest results in three areas: (i) directed discovery of peptide nanostructures with new functions, by searching the sequence space; (ii) application of peptide nanostructures as functional materials (including customizable melanin pigments). (iii) actively assembling systems, that continuously turn over chemical fuels, enabling dynamic changes in structure and function.

Hierarchical organization across length scales is ubiquitous in the superstructures of living organisms. These highly functional structures form through self-assembly, and have therefore inspired significant research activity on synthetic supramolecular materials over the past decade. We report here on a synthetic system containing two supramolecular nanoscale polymers, of very similar structure, that interestingly exhibit micron scale self-sorting. The two different supramolecular polymers are formed by peptide amphiphiles and each is labeled with a different small fluorescent dye, and based on earlier work were expected to undergo molecular exchange. We hypothesize that electrostatic charges on the nanofibers promote the self-organization of the fibers into micron scale hierarchical structures, which take the form of 2D crystals, in order to minimize charge repulsion. The propensity to self-sort is diminished when ions are present to screen the electrostatic charges thus disrupting the hierarchical structures. Our results provide insight on strategies to promote self-sorting superstructures versus co-assembly in supramolecular systems.

Biological channels are molecular gatekeepers that control cellular traffic across cell membrane. Realizing the functional principle of these systems through artificial transmembrane pores with molecularly defined structures is instrumental for future bionanotechnology applications. In this work, thermoresponsive synthetic channels based on supramolecular metal-organic complexes (MOCs) have been constructed to transport cell impermeable cargo across the membrane. The channels can be reversibly controlled as they collapse when the temperature is increased and are simultaneously regenerated when the system is cooled down to room temperature. These ON/OFF molecular valves could be used to overcome multidrug resistance (MDR) in cancer cells and as building blocks for artificial cells.

Extracellular matrix (ECM) properties are important regulators of cell function, particularly at early timepoints during bone healing. For example, physical and chemical properties of the ECM regulate cytoskeletal organization, proliferation, and migration of stem cells to the site of bone injuries for commencing repair. Controlling the presentation of such extracellular cues with molecularly engineered materials provides opportunities to direct bone regeneration. We hypothesize that engineering synthetic hydrogels to recapitulate aspects of the early stages of healing in healthy bone will promote stem cell invasion and remodeling processes toward improving bone regeneration of traumatic fractures or critical-sized defects. To test this, we have created well-defined materials to mimic the mechanical properties, biochemical content, and multiscale structure of native tissues, particularly the collagen-rich environment of the clot-like hematoma formed early in the wound healing process.

We have designed multifunctional collagen mimetic peptides (mfCMPs) that are variants of the Proline-Hydroxyproline-Glycine repeat unit of native collagen. Two variants of this peptide were synthesized: one promoting fibrillar assembly through ionic interactions using charged groups (CMP1a) and the other using hydrophobic interactions of aromatic groups on the C- and N-termini to promote end-to-end assembly (CMP2a). Circular dichroism was used to examine triple helical assembly of the peptides and measure associated melting temperatures, where melting temperatures of CMP1a and CMP2a were determined to be 45.0°C and 60.2°C, respectively. Further peptide assembly and fibril formation was investigated with transmission electron microscopy, where fibrils were observed that mimicked aspects of the hierarchical nanostructure of native collagen. For CMP1a, fibrils approximately 35 nm in width and on the order of 1 μm in length were observed, whereas for CMP2a, fibrils approximately 60 nm in width and on the order of 100 nm in length were observed. Toward studying cell response in vitro, these mfCMPs were covalently crosslinked within cell-degradable poly(ethylene glycol) hydrogels, and rheometry was used to characterize the resulting mechanical properties. Hydrogels with storage moduli in the range of 3500-4500 Pa were generated; further, good cell viability was observed within these unique matrices, with approximately 80% viable cells across conditions.

These studies support our hypothesis that incorporation of mfCMPs within a covalent hydrogel network captures aspects of the fibrillar structure of collagen on both the nano- and microscale toward providing a biomimetic matrix that recapitulates key cues found in ‘soft’ collagenous tissues. Ongoing studies of human mesenchymal stem cells within these materials support their relevance for multidimensional cell culture and suggest that the presence of mfCMPs influences cell-matrix interactions and observed cell response.

Cation-π interactions govern the assembly of many bio-macromolecules, including the adhesion proteins of marine organisms. Increasingly, cation-π interactions are also implicated in pathological processes, like the formation of neurodegenerative protein aggregates. Thus, developing molecular level approaches for engineering cation-π interactions is of both fundamental and technological importance. Although cation-π bonding has been extensively studied for gas phase ion-aromatic pairs, the energetics of cation-π adhesion in biological and biomineral interfaces, where many binding pairs are in close proximity, remains uncharted. In this seminar, I will discuss using molecular force spectroscopy, supplemented by solid-state NMR measurements, to show that the adhesive properties of simple aromatic- and lysine-rich peptides rival those of the adhesion proteins of the marine mussel. Surprisingly, we find that peptides with the aromatic amino acid phenylalanine, a functional group that is conspicuously rare in mussel proteins, exhibit adhesion that significantly exceeds that of analogous mussel-mimetic peptides. More broadly, we find that interfacial confinement fundamentally alters the energetics of cation-π mediated assembly, an insight that is relevant for diverse areas, from influencing bio-controlled crystal formation to engineering novel bioinspired medical adhesives.

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 the multiple-phenomena taking place at different scale levels during self-assembling. In this presentation, focused on the nanotech advancements in the field of nervous regeneration, we will see some multi-disciplinary researches and advances toward the regeneration of spinal cord injuries. This will bring us from coarse-grained molecular dynamics to electro-spinning of self-assembling peptides (SAPs), from cross-linking of SAPs to 3D high-denisty neural stem cells cultures. Lastly, in vivo tests of SAP prosthese in animal models of sub-acute and cronic SCI will be discussed.

Molecular self-assembly is a key direction in current nanotechnology based material science fields. In this approach, the physical properties of the formed assemblies are directed by the inherent characteristics of the specific building blocks used. Molecular co-assembly at varied stoichiometry substantially increases the structural and functional diversity of the formed assemblies, thus allowing tuning of both their architecture as well as their physical properties.
In particular, building blocks of short peptides and amino acids can form ordered assemblies such as nanotubes, nanospheres and 3D-hydrogels. These assemblies were shown to have unique mechanical, optical, piezoelectric and semiconductive properties. Yet, the control over the physical properties of the structure has remained challenging. For example, controlling nanotube length in solution is difficult, due to the inherent sequential self-assembly mechanism. Another example is the control of 3D-hydrogel scaffold’s physical properties, including mechanical strength, degradation profile and injectability, which are important for tissue engineering applications.
Here, in line with polymer chemistry paradigms, we applied a supramolecular polymer co-assembly methodology to modulate the physical properties of peptide nanotubes and hydrogel scaffolds. Utilizing this approach with peptide nanotubes, we achieved narrow nanotube length distribution by adjusting the molecular ratio between the two building blocks; the diphenylalanine assembly unit and its end-capped analogue. In addition, applying a co-assembly approach on hydrogel forming peptides resulted in a synergistic modulation of the mechanical properties, forming extraordinary rigid hydrogels. Furthermore, we designed organic-inorganic scaffold for bone tissue regeneration.
This work provides a conceptual framework for the utilization of co-assembly strategies to push the limits of nanostructures physical properties obtained through self-assembly.


References

Adler-Abramovich, L. et al. Controlling the Physical Dimensions of Peptide Nanotubes by Supramolecular Polymer Coassembly. ACS Nano 10, 7436-7442, (2016).
Halperin-Sternfeld, M., Ghosh, M., Sevostianov, R., Grogoriants, I. & Adler-Abramovich, L. Molecular Co-Assembly as a Strategy for Synergistic Improvement of the Mechanical Properties of Hydrogels. Chem. Comm. 53, 9586-9589, (2017).
Ghosh, M., Halperin-Sternfeld, M., Grigoriants, I., Lee, J., Nam, K. T. & Adler-Abramovich, L. Arginine-Presenting Peptide Hydrogels Decorated with Hydroxyapatite as Biomimetic Scaffolds for Bone Regeneration. Biomacromolecules, 18, 3541–3550, (2017).
Adler-Abramovich, L. et al. Bioinspired Flexible and Tough Layered Peptide Crystals. Adv. Mater. 30, 1704551, (2018).

Pathogens can thrive in an abundance of environments, and pose a significant threat to human health when irrigation or drinking sources become contaminated. The ability to detect the presence of pathogens or biomarkers, such as proteases, using a biosensing platform that is passive and requires no power can help monitor and prevent outbreaks of infectious diseases. We have developed a tunable protease-responsive platform that demonstrated a red-to-blue color shift for all target molecule concentrations between 20 nM and 4000 nM. Structurally colored particle hydrogels were fabricated by centrifuging monodisperse silica particles along with a 4-arm polyethylene glycol (PEG) and a protease-specific peptide linker into a close-packed microstructure, followed by UV irradiation to polymerize the composite. These films swelled in aqueous solutions, and color shift towards the red region of reflected visible light in response to the degree of swelling. Upon degradation of the peptide crosslink, the particles reassembled into a close-packed structure with interparticle spacing less than the initially centrifuged material. This reduction in particle spacing produced a 240 nm color change from the swollen state to the reassembled state of the material for 205 nm particle composites.

To elucidate the mechanism responsible for the color change, we investigated the role of particle size and charge, and polymer concentration in reassembly after degradation. Both particle size and surface functionalization were varied to produce composites with a range of observable structural colors. The reassembled materials reflected shorter wavelengths than their initially fabricated counterparts, indicating that the interparticle spacing had decreased as much as 45 nm for hydrogels with 230 nm particles. In addition, the reassembled composites reflected nearly identical wavelengths independent of the starting polymer weight fraction in the hydrogel. Ultra-small angle x-ray scattering confirmed that the interparticle spacing decreased and the spacing was the same for the reassembled composites. While the particle size or polymer content did not inhibit the reassembly process, particle surface charge was crucial to the reassembly mechanism. Only highly negative (-60mV) particles reassembled to produce structurally colored composites. PEGylated particle hydrogels did not reassemble, and the corresponding composites degraded into the protease solution. Composites with positively charged (+30mV) particle surfaces aggregated irreversibly into a material that appeared white due to incoherent scattering of visible light. Interaction potential models demonstrated that depletion forces provide necessary attraction for reassembly, with a range of up to 120 nm. These findings offer insight into the parameters that will enable passive monitoring of proteases with precise control of structurally colored particle hydrogel responses.

Bacterial communities, known as biofilms, cause multiple technological and health problems and represent an essential part of Earth’s ecosystem. The environmental resilience and sophisticated organization and of biofilms acting as a multicellular organism is enabled by extracellular matrix (ECM) that creates a protective network of biomolecules around the bacterial communities. The current antibiofilm agents can interfere with ECM production but, being based on small molecules, they can be degraded by bacteria and diffuse away from biofilms, which reduce their efficacy. Here we show that graphene quantum dots (GQDs) can effectively suppress the growth of Staphylococcus aureus biofilms by preventing the self-assembly of amyloid fibers - the essential component of ECM. Mimicking peptide-binding biomolecules, GQDs form supramolecular complexes with phenol soluble modulins (PSMs), the peptide monomers of amyloid fibers. Experimental and computational results show that GQDs dock at the N-terminal of the peptide and change the secondary structure of PSM, which disrupts their fibrillation. Concomitantly, the resulting free PSM monomers turn on biofilm dispersion signaling pathways that enhance the inhibitory effect. The two-prong anti-biofilm activity of GQDs offer a new strategy for manipulation of ECMs of bacterial communities.

Synthetic mechanical gradients based on synthetic and biocompatible hydrogels currently do not achieve the steep soft to hard transition found in many biological materials like squid beaks or osteochondral cartilage [1]. Indeed, it is difficult to obtain tight molecular packing and high crosslinking density using conventional polymeric building blocks. Here, we employ the recombinantly expressed protein HBP-1 found in the beak of squids, and make use of its folding in presence of polyelectrolytes to expel water and attain high packing density [2,3]. Under acidic pH and in the presence of chitosan, HBP-1 undergoes a conformational transition from predominantly random coil into ß-sheet-rich. At increased ionic strength, this conformation change leads to a phase separation from soluble to liquid droplets and a hydrogel-like phase. At a constant volume fraction of chitosan, the elastic modulus of the HBP-1/chitosan composite increases with the protein content. After drying and cross-linking using catechol chemistry, the resulting organic material shows similar trend under fully hydrated conditions. This observation is reminiscent to what is observed in the native squid beak. Furthermore, concentration gradients can be modeled based on molecular diffusion and phase separation. With this knowledge, gradients of controlled steepness can be obtained. The crosslinked gradient results in an increase of elastic modulus from 0.08 up to 1 GPa despite containing 60 vol% of water. The approach explored here may open new avenues for the fabrication of graded materials based solely on organic biomaterials with potential applications for orthopaedic devices and soft-to-hard attachment in hydrated environments.

[1] A. Miserez, T. Schneberk, C. Sun, F.W. Zok, J. H. Waite, The transition from stiff to compliant materials in squid beaks, Science, 319, 1816 (2008).

[2] Y. Tan, S. Hoon, P.A. Guerette, W.Wei, A. Ghadban, C. Hao, A. Miserez, J.H. Waite, Infiltration of chitin by protein coacervates defines the squid beak mechanical gradient, Nature Chemical Biology, 11, 488 (2015).

[3] H. Cai, B. Gabryelczyk, M.S.S. Manimekelai, G. Gruber, S. Salentinig, A. Miserez, Self-coacervation of modular squid beak proteins – a comparative study, Soft Matter, 13, 7740 (2017).

Macromolecular condensed phases such as protein crystals and gels bear great medical, scientific and industrial relevance, yet a molecular understanding of their initial stages of formation is still missing. Insights on the mechanism of nucleation have the potential to resolve one of the longest-standing questions of crystallization, i.e. polymorph selection. To gain control over the emerging polymorph one needs to have a molecular-level understanding of the pathways leading to the various macroscopic states and the underlying selection mechanisms that govern the process. Here we address the issue by capturing protein crystals at birth using time-resolved cryo-transmission electron microscopy and uncover at molecular resolution the nucleation pathways of the protein glucose isomerase into two crystalline and one gelled state. We show that polymorph selection takes place at the earliest stages of transformation and is based on the specific building blocks (monomers and nanorods) for each space group. Moreover, we demonstrate control over the system by selectively forming desired polymorphs through tuning of the directionality and specificity of inter-molecular bonding. These new insights on the mechanisms of nucleation and polymorph selection open new avenues towards the control of macromolecular phase transitions, which is crucial in the further development of protein-based drug delivery systems and macromolecular crystallography.

Leveraging self-assembly to pattern proteinaceous crystalline arrays in 2D and 3D offers a highly scalable, bottom up approach to develop nanomaterials with new catalytic, optical electronic or structural applications. However, introducing multiple sites of embellishment into existing 2D protein arrays currently utilizes weak interactions that are either sensitive to external conditions or challenging to re-engineer, limiting the ability to program in bifunctionality and new 3D configurations. Here we address these challenges by developing a means to introduce two orthogonal covalent linkages at multiple sites in a highly robust, thermostable 2D crystalline-forming protein. We first engineered the surface-layer (S-layer) protein SbsB from Geobacillus stearothermophilus to display SpyTag or SnoopTag at the C-terminal and two newly-identified locations within SbsB monomer. These regions were able to accommodate SpyTag or SnoopTag peptide tags without affecting the 2D lattice structure. The introduction of tags at distinct locations enabled orthogonal and covalent binding with high precision of SpyCatcher- or SnoopCatcher-protein fusions to micron-sized 2D sheets. By introducing different types of bifunctional crosslinkers, the dual functionalized nanosheets could be programmed to self-assemble into different 3D lamellae, all of which retain their nanoscale order. Additionally, these nanosheets can be functionalized to display two distinct nanomaterial, yielding nanomaterials with emergent optoelectronic properties. Thus, our work creates a modular protein platform that can be facilely programmed to create dual-functionalized 2D and lamellar 3D nanomaterials with novel catalytic, optoelectronic and mechanical properties.

There is currently a growing interest in biopolymer phase transitions, particularly those involving intrinsically disordered proteins/regions (IDPs/IDRs). It has been found that intracellular liquid-liquid phase separations underlie the assembly of many non-membranous organelles such as P granules, nucleoli, and stress granules. However, little is known about the physics of these organelles, including their internal molecular organization and feedback between their molecular and mesoscale properties. Progress on these questions has been hampered by the lack of detailed phase diagrams, which would elucidate how molecular interactions give rise to emergent droplet properties, particularly condensed-protein concentrations and their physical characteristics.

To answer these questions, we investigate the inter-molecular interaction strengths and the full binodal of a phase-separating disordered protein that induces in-vivo phase transitions, utilizing a novel technique, ultrafast-scanning fluorescence correlation spectroscopy. These measurements led to the recent discovery that phase-separated protein droplets have unusually low densities with large void volumes. The data demonstrate how sequence-encoded conformational fluctuations of IDRs give rise to low overlap volume fractions for driving phase separations. Using inter-molecular interactions of native non-membranous organelles, we develop an optogenetic platform that permits light activation of IDR-mediated phase transitions in living cells. Inter-molecular interaction strengths are quantified and demonstrated how IDR sequences determine intracellular phase separation. These studies can elucidate not only physiological phase transitions but also their links to pathological aggregates.

Our results provide a holistic picture of the dynamics and internal organization of phase separated organelles. By uncovering the relationship between molecular level interactions and emergent mesoscale material properties, this work is foundational for understanding the form, function and potential dysfunction of intracellular phase separated assemblies. Our study has significant impact for an extensive community of researchers, with interests spanning biomaterials, bio-inspired materials, macromolecular assembly, self-assembly, intracellular phase separation, disordered proteins dynamics, polymer chemistry, and bioengineering applications of synthesized intracellular biomimetic materials.

Protein 2D materials possess diverse sophisticated and synergistic structures, and inherent chemical and biological functions. Harnessing this paradigm of protein 2D materials for bottom-up biomaterial design, synthesis and application is an attractive task with promising perspectives in biomimetic and material science. Inspired by nature cases, various strategies have been developed to construct protein 2D crystals in bulk solution. Recently, computational protein design methodology has considerably improved the structural and functional complexities of protein 2D/3D supramolecular structures from scratch.[1, 2] Besides growth in solution, solid-liquid interface has also been used to template few-layer protein 2D materials. However, the solid-liquid interface that is used to artificially grow protein 2D supramolecular structures is generally limited to supported liquid bilayer. It is still not quite clear how solvent mediated protein-surface interactions to define protein thermodynamics, structure and function at solid-liquid interface. That is the obstacle for artificial design and functional applications of protein 2D crystalline arrays in future.
To address those issues, we assembled the variant of L-rhamnulose-1-phosphate aldolase (RhuA), ^C98RhuA[3], with incorporated Cys mutants, into crystalline 2D arrays on solid-liquid interface of mica. By carefully selecting cations and controlling their concentration, we create isotropic protein mono-/bi-layer 2D crystals with controlled packing patterns. It is surprising that the crystallizations of the first and second layers is bimodal that follows non-classical and classical pathways, respectively. We also proved that solvent mediated protein-surface interactions can alternate the energy-landscape of protein self-assembly from that in bulk to stabilize the original intermediate and quasi stable phase. ^C98RhuA can epitaxially grow on top of the surface that has different symmetry. All the findings inspire the novel strategy to synthesize protein crystalline 2D arrays at solid-liquid interface artificially. They also help to elucidate the growth modal of protein 2D architectures at solid-liquid interface. They remind us the importance of solvent mediated surface templating in the self-assembly of protein 2D structures both in nature and in human manner.

1. Huang, P.-S., S.E. Boyken, and D. Baker, The coming of age of de novo protein design. Nature, 2016. 537: p. 320.
2. Gonen, S., et al., Design of ordered two-dimensional arrays mediated by noncovalent protein-protein interfaces. Science, 2015. 348(6241): p. 1365.
3. Suzuki, Y., et al., Self-assembly of coherently dynamic, auxetic, two-dimensional protein crystals. Nature, 2016. 533(7603): p. 369-373.

Biological systems are highly complex and sophisticated with unparalleled structure-function correlations. Remarkably, biological systems produce materials with extraordinary properties and functions under ambient conditions, which is in total contrast to humans’ heat-beat-treat strategies. Thus, the capabilities of a technology by which biological networks of a cell can be programmed, offers tremendous potential as cellular factories and to produce biomaterials for various functional applications.

In this regard, we employ a novel technology entitled Biofilm-Integrated Nanofiber Display (BIND) that focuses on the curli system-the primary proteinaceous structural component of E. coli biofilms. Curli are highly robust functional amyloid nanofibers (diameter 4-7 nm) formed by the extracellular self-assembly of a small (13 kDa) secreted protein, CsgA. By genetic engineering, artificial peptide domains were grafted to the amyloid protein CsgA and the resulting CsgA fusion proteins were successfully secreted from the E. coli cells. Remarkably, these engineered fusion proteins were found to extracellularly self-assemble into amyloid nanofiber networks and also exhibited the characteristic functions of the grafted artificial peptide domains. By using BIND technology, E. coli biofilm matrix is conferred with several artificial functions for nanomedicinal, nanomechanical and nanoelectronics applications.

One of the key challenges in nanobiotechnology is the utilization of self-assembly systems wherein molecules spontaneously associate into reproducible aggregates and supromolecular structures. In this contribution, the basic principles of crystalline bacterial surface layers (S-layers) and their use as patterning elements will be described. The broad application potential of S-layers in nanobiotechnology is based on the specific intrinsic features of these monomolecular arrays which are composed of identical protein or glycoprotein subunits. Most important, physicochemical properties and functional groups on the protein lattice are arranged in well-defined positions. Many applications of S-layers depend on the capability of the isolated subunits to recrystallize into monomolecular arrays in suspension or on suitable surfaces (e.g. polymers, metals, silicon wafers) or interfaces (e.g. lipid films, liposomes, emulsomes). S-layers also represent a unique structural basis and patterning element for generating more complex supramolecular structures involving all major classes of biological molecules Thus, S-layers fulfil key requirements as building blocks for the production of new supramolecular materials and nanoscale devices as required in nanobiotechnology and synthetic biology.

Sleytr, U.B., Schuster, B., Egelseer, E.M., Pum, D. (2014) FEMS Microbiol Rev, 38, 823-864.
Pum, D., Toca-Herrera, J.L., Sleytr, U.B. (2014) Nanotechnology, 25, 312001.
Sleytr, U.B. 2016. Curiosity and Passion for Science and Art. World Scientific. ISBN 9813141816

We acknowledge the financial support by the Air Force Office of Scientific Research (AFOSR) (Grant FA9550-15-1-0459).

In nature, enzymes that catalyze multi-step reactions are often organized in close proximity to allow the efficient channeling of intermediates from one active site to another. Diverse synthetic scaffolds based on DNA and proteins have been designed to mimic such spatial control of enzymes, and have proven successful in facilitating cascade reactions. Recent studies revealed that such enhanced catalysis can also result from formation of enzyme agglomerates rather than direct channeling of intermediates between adjacent enzymes, highlighting the need to engineer the interactions that define metabolic clusters. Thus, there is a demand for scaffolds that can effectively crosslink with each other to form higher-order structures in a programmable manner, in addition to simply templating the enzymes.

The g-prefoldin (gPFD) is a filamentous protein isolated from the hyperthermophilic archaeon Methanocaldococcus jannaschii; its remarkable stability, unique modularity, and self-assembly into filaments with chaperone activity render it an ideal building block for the bottom-up construction of functionalized protein nanostructures. Here we propose a strategy to utilize the gPFD to build enzyme agglomerates in tunable fashion. Using the combinations of orthogonal protein-peptide bioconjugation pairs, the gPFD filaments displaying the peptide tags are first conjugated with the enzymes, and then crosslinked using the linker proteins. Thus, the extent of crosslinking is tunable through simply varying the stoichiometry between the scaffold and linker proteins.

We verified the gPFD scaffold’s ability to cluster enzymes in proximity using FRET analysis of the filaments containing fluorescent protein pairs. Subsequently, we investigated the effect of agglomerate formation on the catalytic activities of multi-step reactions using two different model system pairings: glucose oxidase (GOX)-horseradish peroxidase (HRP) and alcohol dehydrogenase (ADH)-aldehyde dehydrogenase (ALDH). Ultimately, the ability to fabricate enzyme-scaffold complexes with programmable stoichiometry and dimensions will enable better control over single- and multi-step enzymatic catalysis.

In this work, we demonstrate that assembly of macromolecules, such as proteins, can cause aqueous droplets to exhibit division, even in the absence of a cell membrane. The all-aqueous nature of the systems results in tunable interfacial tension, affinity partitioning and osmotic responses. The solubility of different types of macromolecules across the interfaces enables new strategies to assemble structures at the droplet interfaces. While the significantly lower interfacial tension can make stabilization of the interface difficult due to the slow adsorption dynamics by surfactants and particles, structures that have been assembled at the interfaces can be easily expelled. This contributes to the more sophisticated dynamics of the hierarhically structured all-aqueous droplets. These droplets have great potential to be utilized as templates for fabricating materials with novel properties.

Physiochemical irregularities within extracellular matrix (ECM) proteins such as collagen can lead to a wide range of connective tissue disorders including osteogenesis imperfecta and osteoarthritis. Current pharmaceutical regimens to treat such diseases suffer from off-target effects, suggesting that new approaches for targeted delivery are necessary. In the last decade, ECM-inspired polypeptide materials have garnered significant interest for their ability to selectively mimic specific matrix components such as collagens and elastins, offering new opportunities to control drug delivery within specific tissues. For example, triple helix forming collagen-like peptides (CLPs) comprising (Gly-Pro-Hyp)_n amino acid repeats can hybridize with high efficiency to denatured collagen proteins in the body via thermal annealing of peptide and protein single strands into a stable triple helix. Additionally, elastin-like peptides (ELPs) that consist of (Val-Pro-Gly-X_AA-Gly)_n (where X_AA is any amino acid with the exception of proline) amino acid repeats possess a lower critical solution temperature in which aggregation occurs upon heating above this temperature, making ELPs ideal candidates for on demand drug delivery behavior. Recently, our group has reported on the design of hybrid peptides with linked CLPs and ELPs, and the assembly of thermoresponsive, elastin-b-collagen-like peptide nanovesicles that are capable of dissociating at high temperature (70°C). These nanovesicles offer intriguing potential in drug delivery applications due to their dual thermoresponsivity and inherent ability to bind to degraded collagen protein. However, in order to make an ELP-CLP nanoparticle with optimal drug delivery properties such as physiologically relevant hybridization to degraded collagen protein, the critical parameters of their self-assembly must first be understood, specifically with respect to the CLP domain. To test the effects of the triple helical (CLP) melting temperature on temperature-dependent nanovesicle assembly and dissociation behavior a small library of ELP-CLP conjugates was made with varying numbers of CLP (G-X-Y) repeats and varied CLP sequences. These conjugates were characterized for their thermoresponsivity and their ability to form self-assembled structures. The melting temperature, repeat length, and overall hydrophilicity of the CLP domain were found to be of critical importance to nanoparticle formation.

As an excellent flexible biomaterial, Bombyx mori silk fibroin materials offer exquisite mechanical, optical, and electrical properties which are advantageous toward the development of next-generation biocompatible electronic devices. In this concern, to re-engineer the hierarchical structure of soft materials and to functionalize the materials are the two common approaches to achieve the functions. This requires the synergy of structures among different levels, which include the re-construction of the hierarchical structure of soft/SF materials at the mesoscale and or Mesoscopic Material Assembly (MMA), which is to add and bind some specific nanomaterials or molecule to the networks so as to acquire some additional functions without jeopardizing the original performance. In this talk, I will cover the principles and strategies of mesoscopic structural re-engineering and functionalization of SF materials, which allows in the design and integration of high-performance bio-integrated devices for future applications in consumer, biomedical diagnosis, and human–machine interfaces.

The materials-by-design approach to the development of functional materials requires new synthetic strategies that allow for material composition and structure to be independently controlled and tuned on demand. Although it is exceedingly difficult to control the complex interactions between atomic and molecular species in such a manner, interactions between nanoscale components can be encoded, independent of the nanoparticle structure and composition, through the ligands attached to their surface. DNA represents a powerful, programmable tool for bottom-up material design. The Mirkin Group has shown that DNA and other nucleic acids can be used as highly programmable surface ligands (“bonds”) to control the spacing and symmetry of nanoparticle building blocks (“atoms”) in structurally sophisticated materials, analogous to a nanoscale genetic code for material assembly. The sequence and length tunability of nucleic acid bonds has allowed us to define a powerful set of design rules for the construction of nanoparticle superlattices with more than 30 unique lattice symmetries, spanning over one order of magnitude of interparticle distances, with several well-defined crystal habits. Further, this control has enabled exploration of sophisticated symmetry breaking processes, including the body-centered tetragonal lattice as well as the clathrate lattice, the most structurally complex nanoparticle-based material to date (>20 particles per unit cell). The nucleic acid bond can also be programmed to respond to external biomolecular and chemical stimuli, allowing structure and properties to be dynamically tailored. Notably, this unique genetic approach to materials design affords functional nanoparticle architectures that can be used to catalyze chemical reactions, manipulate light-matter interactions, and improve our fundamental understanding of crystallization processes.

The programmability of DNA makes it an attractive structure-directing ligand for the assembly of nanoparticle superlattices with unique structure-dependent physical phenomena. While DNA base pairing has enabled the development of materials with nanometer-scale precision in nanoparticle placement and independent control over particle size, lattice parameters, and crystal symmetry, manipulating the macroscopic shape of the lattices remains challenging. By pairing this “bottom-up” assembly method with “top-down” lithographic techniques and assembling nanoparticle superlattices on a patterned substrate, complete control over crystal size, shape, orientation and unit cell structure can be realized. The key challenges in developing this technique are to first understand how different design factors affect the assembly process in this broken-symmetry system that is assembled at an interface, and subsequently develop structure-property relationships that correlate the above mentioned design parameters with the resulting overall material structure. Here, we examine both at-equilibrium deposition processes capable of generating single crystals with well-defined shapes, as well as post-deposition annealing to transform disordered particle arrangements into crystalline arrays. Using a combination of X-ray diffraction and electron microscopy techniques, both surface morphology and internal thin film structure are examined to provide an understanding of the mechanisms of particle crystallization under conditions where crystal growth is anisotropic due to a boundary condition. This novel method for controlling particle assembly draws several strong analogies to traditionally atomic epitaxy/heteroepitaxy, providing a useful tool for understanding thin film growth processes. As a result, we are able to realize 3D architectures of arbitrary domain geometry and size, thereby making materials with unprecedented precision across multiple length scales.

Functional nucleic acids, that can target cancer cells and realize stimuli-responsive drug-delivery in tumor microenvironment, have been widely applied for anti-cancer chemotherapy. The high cost, unsatisfactory biostability, and complicated fabrication process are the main limits for the development of DNA-based drug-delivery nanocarriers. Recently, a kind of DNA-MgPPi (magnesium pyrophosphate) composite nanoparticles has been produced from rolling circle amplification (RCA), which combine advantages of the designable and high-throughput isothermal amplification technique and the high stability of DNA condensation structures, quickly becoming an attractive biomedical material with great potentials. Herein, instead of using MgPPi, we found that only Mg²⁺ is sufficiently enough to stabilize the functional DNAs for chemotherapeutic applications. The very long single-stranded RCA product with a high charge density is more prone to form a stable condensation structures compared with a short oligonucleotide. Moreover, the dynamic electrostatic interactions between Mg²⁺ and DNA can better preserve the functions of DNA, which is more suitable for the design of drug-delivery system. A tumor-targeting Dox-delivery nanoparticle (~ 100 nm) was synthesized by the condensation of RCA products in the presence of an excessive amount of Mg²⁺, which showed good bio-stability in serum, considerable Dox loading capability, specific cancer-targeting ability, and pH-responsive sustained Dox release. The DNA nanoparticle not only has a simple composition, but also it will keep intact after the excessive exterior Mg²⁺ is removed, making it safe and ideal for in vivo application. Through cellular and in vivo experiments, we thoroughly demonstrated that this kind of Mg²⁺ stabilized multi-functional DNA nanoparticles can successfully realize tumor-targeted Dox delivery.

Photonic and electronic devices require precise control of functional components at the nanosacle. The development of DNA nanotechnology offers a fascinating platform to direct the assembly of nanoparticles into well-organized architectures with prescribed distances and spatial arrangements. Here, we combine DNA-based assembly and diblock copolymer self-assembly to realize the multi-layer assembly of gold nanoparticles into large-area, three-dimensional arrays. Specifically, the assembly of gold nanoparticles is directed through binding with DNA origami that forms arrays, and the array growth is controlled by patterns formed via diblock copolymer on the surface. In our approach, DNA-programmable nanoparticle lattices are sequentially assembled with registry of polymer pattern. We show the potential to assemble functional nanoparticles in layer-by-layer manner with controllable interlayer distance and in-plane arrangements through a combination of surface patterns and DNA nanostructures.

The ability to design and program complex molecular interactions between synthetic biomolecules (especially polynucleotides and polypeptides) has led to a revolution in artificial nanomaterials capable of self-assembly. For example, DNA-based nanotech entails the design of artificial nucleotide sequences capable of self-assembling into desired geometric shapes and patterns with nanometer-scale precision. These synthetic DNA nanostructures have been shown useful for organizing other materials including inorganic nanoparticles (metals and semiconductors), nucleic acid aptamers, and carbon nanostructures. We are working with DNA self- and directed-assembly to develop a general purpose molecular assembly toolbox useful for a wide variety of applications, especially in nanoelectronics and medicine. One promising future direction is the bottom-up fabrication of electronics components and devices including molecular assembly of wires and metal nanoparticles toward the construction of single-electron transistors, multicomponent devices, and artificial neural networks.

In recent years, a key direction in the field of electronics and electro-optics involves the transition from inorganic to organic components, including organic light emitting diodes (OLED), thus paving the way towards flexible and wearable electronic and light emitting devices. Bio-inspired organic materials may be the next-generation of organic optoelectronic devices based on self-organization principles, which allow facile synthesis, eco-friendliness, resistance to oxidation and no need for heavy metal doping.
Recent advances in bioorganic nanotechnology have established the notion that very simple building blocks, such as dipeptides, can form regular nanostructures with distinct mechanical, optical, piezoelectric and electronic properties. In particular, members of the diphenylalanine (FF) peptide archetypical family have been shown to form various morphologies and ordered nanostructures such as tubes, rods, fibrils, spheres, plates and macroscopic hydrogels with nano-scale order.
Several studies have explored the piezoelectric properties of the diphenylalanine (FF) peptide. In the presence of an external electric field, vertically aligned FF microrod arrays can be organized on a substrate, resulting in enhanced piezoelectric response.
Here we show the ability of FF and other similar peptide assemblies to be used in various electronics and optics application as new bioorganic materials. FF assemblies can act as an active optical waveguiding material, allowing locally excited states to propagate along the axis of the assemblies. In addition, Fmoc capped building blocks exhibit remarkable optical properties, such as quantum confinement and fluorescence. Other rod-like assemblies and toroid-like assemblies exhibit remarkable physicochemical features, including high thermal stability, metallic-like mechanical rigidity, luminescence, piezoelectricity and semi-conductivity.
The ability of FF to self-assemble into ordered structures was discovered by a systematic reductionist exploration of biological recognition modules in an amyloidogenic polypeptide. We are applying a similar reductionist approache to expand our search for minimal building blocks towards single amino acids as well as other metabolites such as nucleobases, demonstrating their self-assembly into various ordered structures. Doing this we are enlarging our library of biological building blocks which bear the potential to be novel bio-inspired supramolecular materials for Optics And Electronic applications.