Designing Multifunctional Biomaterials via Protein Self-Assembly

Protein self-assembly is a fundamental biological process where proteins spontaneously organize into complex and functional structures without external direction. This process is crucial for the formation of various biological functionalities. However, when protein self-assembly fails, it can trigger the development of multiple disorders, thus making understanding this phenomenon extremely important. Up until recently, protein self-assembly has been solely linked either to biological function or malfunction; however, in the past decade or two it has also been found to hold promising potential as an alternative route for fabricating materials for biomedical applications. It is therefore necessary and timely to summarize the key aspects of protein self-assembly: how the protein structure and self-assembly conditions (chemical environments, kinetics, and the physicochemical characteristics of protein complexes) can be utilized to design biomaterials. This minireview focuses on the basic concepts of forming supramolecular structures, and the existing routes for modifications. We then compare the applicability of different approaches, including compartmentalization and self-assembly monitoring. Finally, based on the cutting-edge progress made during the last years, we summarize the current knowledge about tailoring a final function by introducing changes in self-assembly and link it to biomaterials' performance.

From Basic Principles of Protein-Polysaccharide Association to the Rational Design of Thermally Sensitive Materials

Biology resolves design requirements toward functional materials by creating nanostructured composites, where individual components are combined to maximize the macroscale material performance. A major challenge in utilizing such design principles is the trade-off between the preservation of individual component properties and emerging composite functionalities. Here, polysaccharide pectin and silk fibroin were investigated in their composite form with pectin as a thermal-responsive ion conductor and fibroin with exceptional mechanical strength. We show that segregative phase separation occurs upon mixing, and within a limited compositional range, domains ∼50 nm in size are formed and distributed homogeneously so that decent matrix collective properties are established. The composite is characterized by slight conformational changes in the silk domains, sequestering the hydrogen-bonded β-sheets as well as the emergence of randomized pectin orientations. However, most dominant in the composite's properties is the introduction of dense domain interfaces, leading to increased hydration, surface hydrophilicity, and increased strain of the composite material. Using controlled surface charging in X-ray photoelectron spectroscopy, we further demonstrate Ca ions (Ca2+) diffusion in the pectin domains, with which the fingerprints of interactions at domain interfaces are revealed. Both the thermal response and the electrical conductance were found to be strongly dependent on the degree of composite hydration. Our results provide a fundamental understanding of the role of interfacial interactions and their potential applications in the design of material properties, polysaccharide-protein composites in particular.

Protein Compartments Modulate Fibrillar Self-Assembly

A notable feature of complex cellular environments is protein-rich compartments that are formed via liquid-liquid phase separation. Recent studies have shown that these biomolecular condensates can play both promoting and inhibitory roles in fibrillar protein self-assembly, a process that is linked to Alzheimer's, Parkinson's, Huntington's, and various prion diseases. Yet, the exact regulatory role of these condensates in protein aggregation remains unknown. By employing microfluidics to create artificial protein compartments, the self-assembly behavior of the fibrillar protein lysozyme within them can be characterized. It is observed that the volumetric parameters of protein-rich compartments can change the kinetics of protein self-assembly. Depending on the change in compartment parameters, the lysozyme fibrillation process either accelerated or decelerated. Furthermore, the results confirm that the volumetric parameters govern not only the nucleation and growth phases of the fibrillar aggregates but also affect the crosstalk between the protein-rich and protein-poor phases. The appearance of phase-separated compartments in the vicinity of natively folded protein complexes triggers their abrupt percolation into the compartments' core and further accelerates protein aggregation. Overall, the results of the study shed more light on the complex behavior and functions of protein-rich phases and, importantly, on their interaction with the surrounding environment.

Effects of sound energy on proteins and their complexes

Mechanical energy in the form of ultrasound and protein complexes intuitively have been considered as two distinct unrelated topics. However, in the past few years, increasingly more attention has been paid to the ability of ultrasound to induce chemical modifications on protein molecules that further change protein-protein interaction and protein self-assembling behavior. Despite efforts to decipher the exact structure and the behavior-modifying effects of ultrasound on proteins, our current understanding of these aspects remains limited. The limitation arises from the complexity of both phenomena. Ultrasound produces multiple chemical, mechanical, and thermal effects in aqueous media. Proteins are dynamic molecules with diverse complexation mechanisms. This review provides an exhaustive analysis of the progress made in better understanding the role of ultrasound in protein complexation. It describes in detail how ultrasound affects an aqueous environment and the impact of each effect separately and when combined with the protein structure and fold, the protein-protein interaction, and finally the protein self-assembly. It specifically focuses on modifying role of ultrasound in amyloid self-assembly, where the latter is associated with multiple neurodegenerative disorders.

Sound-mediated nucleation and growth of amyloid fibrils

Mechanical energy, specifically in the form of ultrasound, can induce pressure variations and temperature fluctuations when applied to an aqueous media. These conditions can both positively and negatively affect protein complexes, influencing their stability, folding patterns, and self-assembling behavior. Regarding understanding the effects of ultrasound on the self-assembly of amyloidogenic proteins, our knowledge remains quite limited. In our recent work, we established the boundary conditions under which sound energy can either cause damage or induce only negligible changes in the structure of protein species. In the present study, we demonstrate that when the delivered ultrasonic energy is sufficiently low, it can induce refolding of specific motifs in protein monomers, as it has been revealed by MD, which is sufficient for primary nucleation, characterized by adopting a hydrogen-bonded β -sheet-rich structure. These structural changes are initiated by pressure perturbations and are accelerated by a temperature factor. Furthermore, the prolonged action of low-amplitude ultrasound enables the elongation of amyloid protein nanofibrils directly from monomeric lysozyme proteins, in a controlled manner, until they reach a critical length. Using solution X-ray scattering, we determined that nanofibrillar assemblies, formed under the influence of ultrasound energy and natively fibrillated lysozyme, share identical structural characteristics. Thus, these results contribute to our understanding of the effects of ultrasound on fibrillar protein self-assembly and lay the foundation for the potential exploitation of sound energy in a protein chemistry environment.

Microcompartmentalization Controls Silk Feedstock Rheology

The rheological characteristics of pre-spun native silk protein, which is stored as a viscous pulp inside the silk gland, are the key factors that determine the mechanical performance of the endpoint material: the spun silk fibers. In silkworms and arthropods, microcompartmentalization was shown to play an important regulatory role in storing and stabilizing the aggregation-prone silk and in initiating the fibrillar self-assembly process. However, our current understanding of the mechanism of stabilization of the highly unstable protein pulp in its soluble state inside the microcompartments and of the conditions required for initiating the structural transition in protein inside the microcompartments remains limited. Here, we exploited the power of droplet microfluidics to mimic the silk protein's microcompartmentalization event; we introduced changes in the chemical environment and analyzed the storage-to-spinning transition as well as the accompanying structural changes in silk fibroin protein, from its native fold into an aggregative β-sheet-rich structure. Through a combination of experimental and computational simulations, we established the conditions under which the structural transition in microcompartmentalized silk protein is initiated, which, in turn, is reflected in changes in the silk-rich fluid behavior. Overall, our study sheds light on the role of the independent parameters of a dynamically changing chemical environment, changes in fluid viscosity, and the shear forces that act to balance silk protein self-assembly, and thus, facilitate new exploratory avenues in the field of biomaterials.

Polymer Gel with Tunable Conductive Properties: A Material for Thermal Energy Harvesting

The spontaneous gelation of poly(4-vinyl pyridine)/pyridine solution produces materials with conductive properties that are suitable for various energy conversion technologies. The gel is a thermoelectric material with a conductivity of 2.2-5.0 × 10^-6 S m^-1 and dielectric constant ε = 11.3. On the molecular scale, the gel contains various types of hydrogen bonding, which are formed via self-protonation of the pyridine side chains. Our measurements and calculations revealed that the gelation process produces bias-dependent polymer complexes: quasi-symmetric, strongly hydrogen-bonded species, and weakly bound protonated structures. Under an applied DC bias, the gelled complexes differ in their capacitance/conductive characteristics. In this work, we exploited the bias-responsive characteristics of poly(4-vinyl pyridine) gelled complexes to develop a prototype of a thermal energy harvesting device. The measured device efficiency is S = ΔV/ΔT = 0.18 mV/K within the temperature range of 296-360 K. Investigation of the mechanism underlying the conversion of thermal energy into electric charge showed that the heat-controlled proton diffusion (the Soret effect) produces thermogalvanic redox reactions of hydrogen ions on the anode. The charge can be stored in an external capacitor for heat energy harvesting. These results advance our understanding of the molecular mechanisms underlying thermal energy conversion in the poly(4-vinyl pyridine)/pyridine gel. A device prototype, enabling thermal energy harvesting, successfully demonstrates a simple path toward the development of inexpensive, low-energy thermoelectric generators.

Micro and nano-scale compartments guide the structural transition of silk protein monomers into silk fibers

Silk is a unique, remarkably strong biomaterial made of simple protein building blocks. To date, no synthetic method has come close to reproducing the properties of natural silk, due to the complexity and insufficient understanding of the mechanism of the silk fiber formation. Here, we use a combination of bulk analytical techniques and nanoscale analytical methods, including nano-infrared spectroscopy coupled with atomic force microscopy, to probe the structural characteristics directly, transitions, and evolution of the associated mechanical properties of silk protein species corresponding to the supramolecular phase states inside the silkworm's silk gland. We found that the key step in silk-fiber production is the formation of nanoscale compartments that guide the structural transition of proteins from their native fold into crystalline β-sheets. Remarkably, this process is reversible. Such reversibility enables the remodeling of the final mechanical characteristics of silk materials. These results open a new route for tailoring silk processing for a wide range of new material formats by controlling the structural transitions and self-assembly of the silk protein's supramolecular phases.

Dataset for the Synthesis of Boron-Dipyrrin Dyes, their fluorescent properties, their interaction with proteins, Triton-X-based surfactants, and micellar clusterization approaches to validation based on fluorescent dyes

The data presented here refer to the research article by Aleksei V. Solomonov, Yuriy S. Marfin, Alexander B. Tesler, Dmitry A. Merkushev, Elizaveta A. Bogatyreva, Elena V. Antina, Evgeniy V. Rumyantsev, and Ulyana Shimanovich "Spanning BODIPY fluorescence with self-assembled micellar clusters", Colloids and Surfaces B: Biointerfaces, 216, 2022, 112532. The present article provides details on optical characterization for a set of meso- and tetra-substituted boron-dipyrrin (BODIPY) complexes encapsulated inside of self-assembled Triton-X-based micellar coordination clusters (MCCs), based on Triton-X family surfactants. Changes in the optical properties of the BODIPY complexes upon interaction with bovine serum albumin, in a binary mixture of THF:H2O and titrated with Triton TX-114, were evaluated. The optical properties and the formation kinetics of the BODIPY-based MCCs and the BODIPY-supported micelle chelator aggregates (MCAs) are presented as well. The presented data provide additional insights into the structural and formation aspects of both the traditional and newly obtained micellar coordination clusters for their future optimization, control, and application. The synthetic procedures for the synthesis of a set of meso- and tetra-substituted BODIPY complexes and their optical properties in different media are also presented. The research is related to the paper (Solomonov et al., 2022).

Light-Induced Reactions within Poly(4-vinyl pyridine)/Pyridine Gels: The 1,6-Polyazaacetylene Oligomers Formation

Cyclic 6-membered aromatic compounds such as benzene and azabenzenes (pyridine, pyridazine, and pyrazine) are known to be light-sensitive, affording, in particular, the Dewar benzene type of intermediates. Pyridine is known to provide the only Dewar pyridine intermediate that undergoes reversible ring-opening. We found that irradiation of photosensitive gels prepared from poly(4-vinyl pyridine) and pyridine at 254 or 312 nm leads to pyridine ring-opening and subsequent formation of 5-amino-2,4-pentadienals. We show that this light-induced process is only partially reversible, and that the photogenerated aminoaldehyde and aminoaldehyde-pending groups undergo self-condensation to produce cross-linked, conjugated oligomers that absorb light in the visible spectrum up to the near-infrared range. Such a sequence of chemical reactions results in the formation of gel with two distinct morphologies: spheres and fiber-like matrices. To gain deeper insight into this process, we prepared poly(4-vinyl pyridine) with low molecular weight (about 2000 g/mol) and monitored the respective changes in absorption, fluorescence, 1H-NMR spectra, and electrical conductivity. The conductivity of the polymer gel upon irradiation changes from ionic to electronic, indicative of a conjugated molecular wire behavior. Quantum mechanical calculations confirmed the feasibility of the proposed polycondensation process. This new polyacetylene analog has potential in thermal energy-harvesting and sensor applications.

pH-Responsive Capsules with a Fibril Scaffold Shell Assembled from an Amyloidogenic Peptide

Peptides and proteins have evolved to self-assemble into supramolecular entities through a set of non-covalent interactions. Such structures and materials provide the functional basis of life. Crucially, biomolecular assembly processes can be highly sensitive to and modulated by environmental conditions, including temperature, light, ionic strength and pH, providing the inspiration for the development of new classes of responsive functional materials based on peptide building blocks. Here, it is shown that the stimuli-responsive assembly of amyloidogenic peptide can be used as the basis of environmentally responsive microcapsules which exhibit release characteristics triggered by a change in pH. The microcapsules are biocompatible and biodegradable and may act as vehicles for controlled release of a wide range of biomolecules. Cryo-SEM images reveal the formation of a fibrillar network of the capsule interior with discrete compartments in which cargo molecules can be stored. In addition, the reversible formation of these microcapsules by modulating the solution pH is investigated and their potential application for the controlled release of encapsulated cargo molecules, including antibodies, is shown. These results suggest that the approach described here represents a promising venue for generating pH-responsive functional peptide-based materials for a wide range of potential applications for molecular encapsulation, storage, and release.

Protein nanofibril design via manipulation of hydrogen bonds

The process of amyloid nanofibril formation has broad implications including the generation of the strongest natural materials, namely silk fibers, and their major contribution to the progression of many degenerative diseases. The key question that remains unanswered is whether the amyloidogenic nature, which includes the characteristic H-bonded β-sheet structure and physical characteristics of protein assemblies, can be modified via controlled intervention of the molecular interactions. Here we show that tailored changes in molecular interactions, specifically in the H-bonded network, do not affect the nature of amyloidogenic fibrillation, and even have minimal effect on the initial nucleation events of self-assembly. However, they do trigger changes in networks at a higher hierarchical level, namely enhanced 2D packaging which is rationalized by the 3D hierarchy of β-sheet assembly, leading to variations in fibril morphology, structural composition and, remarkably, nanomechanical properties. These results pave the way to a better understanding of the role of molecular interactions in sculpting the structural and physical properties of protein supramolecular constructs.

Fibrous Protein Self-Assembly in Biomimetic Materials

Protein self-assembly processes, by which polypeptides interact and independently form multimeric structures, lead to a wide array of different endpoints. Structures formed range from highly ordered molecular crystals to amorphous aggregates. Order arises in the system from a balance between many low-energy processes occurring due to a set of interactions between residues in a chain, between residues in different chains, and between solute and solvent. In Nature, self-assembling protein systems have evolved over millions of years to organize into supramolecular structures, optimized for specific functions, with this propensity determined by the sequence of their constituent amino acids, of which only 20 are encoded in DNA. The structural materials that arise from biological self-assembly can display remarkable mechanical properties, often as a result of hierarchical structure on the nano- and microscales, and much research has been devoted to mimicking and exploiting these properties for a variety of end uses. This work presents a review of a range of studies in which biological functions are effectively reproduced through the design of self-assembling fibrous protein systems.

Biophotonics of Native Silk Fibrils

Native silk fibroin (NSF) is a unique biomaterial with extraordinary mechanical and biochemical properties. These key characteristics are directly associated with the physical transformation of unstructured, soluble NSF into highly organized nano- and microscale fibrils rich in β-sheet content. Here, it is shown that this NSF fibrillation process is accompanied by the development of intrinsic fluorescence in the visible range, upon near-UV excitation, a phenomenon that has not been investigated in detail to date. Here, the optical and fluorescence characteristics of NSF fibrils are probed and a route for potential applications in the field of self-assembled optically active biomaterials and systems is explored. In particular, it is demonstrated that NSF can be structured into autofluorescent microcapsules with a controllable level of β-sheet content and fluorescence properties. Furthermore, a facile and efficient fabrication route that permits arbitrary patterns of NSF microcapsules to be deposited on substrates under ambient conditions is shown. The resulting fluorescent NSF patterns display a high level of photostability. These results demonstrate the potential of using native silk as a new class of biocompatible photonic material.

Sequential Release of Proteins from Structured Multishell Microcapsules

In nature, a wide range of functional materials is based on proteins. Increasing attention is also turning to the use of proteins as artificial biomaterials in the form of films, gels, particles, and fibrils that offer great potential for applications in areas ranging from molecular medicine to materials science. To date, however, most such applications have been limited to single component materials despite the fact that their natural analogues are composed of multiple types of proteins with a variety of functionalities that are coassembled in a highly organized manner on the micrometer scale, a process that is currently challenging to achieve in the laboratory. Here, we demonstrate the fabrication of multicomponent protein microcapsules where the different components are positioned in a controlled manner. We use molecular self-assembly to generate multicomponent structures on the nanometer scale and droplet microfluidics to bring together the different components on the micrometer scale. Using this approach, we synthesize a wide range of multiprotein microcapsules containing three well-characterized proteins: glucagon, insulin, and lysozyme. The localization of each protein component in multishell microcapsules has been detected by labeling protein molecules with different fluorophores, and the final three-dimensional microcapsule structure has been resolved by using confocal microscopy together with image analysis techniques. In addition, we show that these structures can be used to tailor the release of such functional proteins in a sequential manner. Moreover, our observations demonstrate that the protein release mechanism from multishell capsules is driven by the kinetic control of mass transport of the cargo and by the dissolution of the shells. The ability to generate artificial materials that incorporate a variety of different proteins with distinct functionalities increases the breadth of the potential applications of artificial protein-based materials and provides opportunities to design more refined functional protein delivery systems.

Fabrication of fibrillosomes from droplets stabilized by protein nanofibrils at all-aqueous interfaces

All-aqueous emulsions exploit spontaneous liquid-liquid separation and due to their water-based nature are particular advantageous for the biocompatible storage and processing of biomacromolecules. However, the ultralow interfacial tensions characteristic of all-aqueous interfaces represent an inherent limitation to the use of thermally adsorbed particles to achieve emulsion stability. Here, we use protein nanofibrils to generate colloidosome-like two-dimensional crosslinked networks of nanostructures templated by all-aqueous emulsions, which we term fibrillosomes. We show that this approach not only allows us to operate below the thermal limit at ultra-low surface tensions but also yields structures that are stable even in the complete absence of an interface. Moreover, we show that the growth and multilayer deposition of fibrils allows us to control the thickness of the capsule shells. These results open up the possibility of stabilizing aqueous two-phase systems using natural proteins, and creating self-standing protein capsules without the requirement for three-phase emulsions or water/oil interfaces.

Nanotechnology solutions to restore antibiotic activity

This review focuses on the development of nanoparticle systems that enables to enhance and restore the antibiotic activity for drug-resistant organisms. New and more aggressive antibiotic resistant bacteria and parasites calls for the development of new therapeutic strategies to overcome the inefficiency of conventional antibiotics and bypass treatment limitations related to these pathologies. Nanostructured biomaterials, nanoparticles in particular, have unique physicochemical properties such as ultra-small and controllable size, large surface area to mass ratio, high reactivity, and functionalizable structure. These properties can be applied to facilitate the administration of antimicrobial drugs, thereby overcoming some of the limitations in traditional antimicrobial therapeutics. Here the current progress and challenges in synthesizing nanoparticle platforms for restoring activity of various antimicrobial drugs are reviewed with an emphasis on antibiotics. We also call attention to the need to unite the shared interest between nanoengineers and microbiologists in developing nanotechnology for the treatment of microbial diseases.

Micro- and nanoscale hierarchical structure of core–shell protein microgels

In this work, we fabricate core–shell protein microgels stabilized by protein fibrillation with hierarchical structuring on scales ranging from a few nanometers to tens of microns.

Peptide Anchor for Folate-Targeted Liposomal Delivery

Specific folate receptors are abundantly overexpressed in chronically activated macrophages and in most cancer cells. Directed folate receptor targeting using liposomes is usually achieved using folate linked to a phospholipid or cholesterol anchor. This link is formed using a large spacer like polyethylene glycol. Here, we report an innovative strategy for targeted liposome delivery that uses a hydrophobic fragment of surfactant protein D linked to folate. Our proposed spacer is a small 4 amino acid residue linker. The peptide conjugate inserts deeply into the lipid bilayer without affecting liposomal integrity, with high stability and specificity. To compare the drug delivery potential of both liposomal targeting systems, we encapsulated the nuclear dye Hoechst 34580. The eventual increase in blue fluorescence would only be detectable upon liposome disruption, leading to specific binding of this dye to DNA. Our delivery system was proven to be more efficient (2-fold) in Caco-2 cells than classic systems where the folate moiety is linked to liposomes by polyethylene glycol.

Enzymatically Active Microgels from Self-Assembling Protein Nanofibrils for Microflow Chemistry

Amyloid fibrils represent a generic class of protein structure associated with both pathological states and with naturally occurring functional materials. This class of protein nanostructure has recently also emerged as an excellent foundation for sophisticated functional biocompatible materials including scaffolds and carriers for biologically active molecules. Protein-based materials offer the potential advantage that additional functions can be directly incorporated via gene fusion producing a single chimeric polypeptide that will both self-assemble and display the desired activity. To succeed, a chimeric protein system must self-assemble without the need for harsh triggering conditions which would damage the appended functional protein molecule. However, the micrometer to nanoscale patterning and morphological control of protein-based nanomaterials has remained challenging. This study demonstrates a general approach for overcoming these limitations through the microfluidic generation of enzymatically active microgels that are stabilized by amyloid nanofibrils. The use of scaffolds formed from biomaterials that self-assemble under mild conditions enables the formation of catalytic microgels while maintaining the integrity of the encapsulated enzyme. The enzymatically active microgel particles show robust material properties and their porous architecture allows diffusion in and out of reactants and products. In combination with microfluidic droplet trapping approaches, enzymatically active microgels illustrate the potential of self-assembling materials for enzyme immobilization and recycling, and for biological flow-chemistry. These design principles can be adopted to create countless other bioactive amyloid-based materials with diverse functions.

Tetracycline nanoparticles as antibacterial and gene-silencing agents

The spread of antibiotic-resistant bacteria and parasites calls for the development of new therapeutic strategies with could potentially reverse this trend. Here, a proposal is presented to exploit a sonochemical method to restore the antibiotic activity of tetracycline (TTCL) against resistant bacteria by converting the antibiotic into a nanoparticulate form. The demonstrated sonochemical method allows nanoscale TTCL assembly to be driven by supramolecular hydrogen bond formation, with no further modification to the antibiotic's chemical structure. It is shown that tetracycline nanoparticles (TTCL NPs) can act as antibacterial agents, both against TTCL sensitive and against resistant bacterial strains. Moreover, the synthesized antibiotic nanoparticles (NPs) can act as effective gene-silencing agents through the use of a TTCL repressor in Trypanosome brucei parasites. It is demonstrated that the NPs are nontoxic to human cells and T. brucei parasites and are able to release their monomer components in an active form in a manner that results in enhanced antimicrobial activity relative to a homogeneous solution of the precursor monomer. As the TTCL NPs are biocompatible and biodegradable, sonochemical formation of TTCL NPs represents a new promising approach for generation of pharmaceutically active nanomaterials.

Folic acid-tagged protein nanoemulsions loaded with CORM-2 enhance the survival of mice bearing subcutaneous A20 lymphoma tumors

Folic Acid (FA)-tagged protein nanoemulsions were found to be preferentially internalized on B-cell lymphoma cell line (A20 cell line), which, for the first time, is reported to express folate receptor (FR)-alpha. Carbon monoxide releasing molecule-2 (CORM-2) was incorporated in the oil phase of the initial formulation. FA-functionalized nanoemulsions loaded with CORM-2 exhibited a considerable antitumor effect and an increased survival of BALB/c mice bearing subcutaneous A20 lymphoma tumors. The developed nanoemulsions also demonstrated to be well tolerated by these immunocompetent mice. Thus, the results obtained in this study demonstrate that FA-tagged protein nanoemulsions can be successfully used in cancer therapy, with the important ability to delivery drugs intracellularly.

FROM THE CLINICAL EDITOR

In this research, the authors developed folic acid tagged nanoemulsions containing a carbon monoxide releasing protein molecule for targeted cancer cell treatment. In-vitro and in-vivo experiments showed efficacy against B-cell lymphoma cells. The same nanocarrier platform could be applied to other tumor cells expressing folate receptors on the cell surface.

Protein microgels from amyloid fibril networks

Nanofibrillar forms of proteins were initially recognized in the context of pathology, but more recently have been discovered in a range of functional roles in nature, including as active catalytic scaffolds and bacterial coatings. Here we show that protein nanofibrils can be used to form the basis of monodisperse microgels and gel shells composed of naturally occurring proteins. We explore the potential of these protein microgels to act as drug carrier agents, and demonstrate the controlled release of four different encapsulated drug-like small molecules, as well as the component proteins themselves. Furthermore, we show that protein nanofibril self-assembly can continue after the initial formation of the microgel particles, and that this process results in active materials with network densities that can be modulated in situ. We demonstrate that these materials are nontoxic to human cells and that they can be used to enhance the efficacy of antibiotics relative to delivery in homogeneous solution. Because of the biocompatibility and biodegradability of natural proteins used in the fabrication of the microgels, as well as their ability to control the release of small molecules and biopolymers, protein nanofibril microgels represent a promising class of functional artificial multiscale materials generated from natural building blocks.

Multiphase protein microgels

Peptides and proteins represent attractive building blocks for the development of new functional materials due to the biocompatibility and biodegradability of many naturally abundant proteins. In nature, sophisticated material functionality is commonly achieved through spatial control of protein localisation and structure on both the nano and micro scales. We approached this requirement in an artificial setting by exploiting the propensity of proteins to self-assemble into amyloid fibrils to achieve nano scale order, and utilised aqueous liquid/liquid phase separation to control the micron scale localization of the proteinaceous component under microconfinement. We show that in combination with droplet microfluidics, this strategy allows the synthesis of core-shell microgel particles composed of protein nanofibrils.

Self-Assembly of Amyloid Fibrils That Display Active Enzymes

Enzyme immobilization is an important strategy to enhance the stability and recoverability of enzymes and to facilitate the separation of enzymes from reaction products. However, enzyme purification followed by separate chemical steps to allow immobilization on a solid support reduces the efficiency and yield of the active enzyme. Here we describe polypeptide constructs that self-assemble spontaneously into nanofibrils with fused active enzyme subunits displayed on the amyloid fibril surface. We measured the steady-state kinetic parameters for the appended enzymes in situ within fibrils and compare these with the identical protein constructs in solution. Finally, we demonstrated that the fibrils can be recycled and reused in functional assays both in conventional batch processes and in a continuous-flow microreactor.

Nanoscale spatially resolved infrared spectra from single microdroplets

Droplet microfluidics has emerged as a powerful platform allowing a large number of individual reactions to be carried out in spatially distinct microcompartments. Due to their small size, however, the spectroscopic characterisation of species encapsulated in such systems remains challenging. In this paper, we demonstrate the acquisition of infrared spectra from single microdroplets containing aggregation-prone proteins. To this effect, droplets are generated in a microfluidic flow-focussing device and subsequently deposited in a square array onto a ZnSe prism using a micro stamp. After drying, the solutes present in the droplets are illuminated locally by an infrared laser through the prism, and their thermal expansion upon absorption of infrared radiation is measured with an atomic force microscopy tip, granting nanoscale resolution. Using this approach, we resolve structural differences in the amide bands of the spectra of monomeric and aggregated lysozyme from single microdroplets with picolitre volume.

Pre-miRNA expressing plasmid delivery for anti-cancer therapy

The premiR145/GFP expressing plasmid DNA was delivered into glioma cells and the transcripted miRNA145 efficiently decreases the expression of CTGF.

Protein micro- and nano-capsules for biomedical applications

Micro- and nano-scale systems have emerged as important tools for developing clinically useful drug delivery systems. In this tutorial review, we discuss the exploitation of biomacromolecules for this purpose, focusing on proteins, polypeptides, nucleic acids and polysaccharides and mixtures thereof as potential building blocks for novel drug delivery systems. We focus on the mechanisms of formation of micro- and nano-scale protein-based capsules and shells, as well as on the functionalization of such structures for use in targeted delivery of bioactive materials. We summarise existing methods for protein-based capsule synthesis and functionalization and highlight future challenges and opportunities for delivery strategies based on biomacromolecules.

Releasing dye encapsulated in proteinaceous microspheres on conductive fabrics by electric current

The current paper reports on the relase properties of conductive fabrics coated with proteinaceous microspheres containing a dye. The release of the dye was achieved by passing an electric current through the fabric. The conductivity of the polyester fibers resulted from nanosilver (Ag NPs) coated on the surface of these fibers. Both types of coatings (nanosilver coating and the coating of the proteinaceous microspheres) were performed using high-intensity ultrasonic waves. Two different types of dyes, hydrophilic RBBR (Remazol Brilliant Blue R) and hydrophobic ORO (Oil Red O), were encapsulated inside the microspheres (attached to the surface of polyester) and then released by applying an electric current. The Proteinaceous Microsphere (PM)-coated conductive fabrics could be used in medicine for drug release. The encapsulated dye can be replaced with a drug that could be released from the surface of fabrics by applying a low voltage.

Sonochemical coating of cotton and polyester fabrics with "antibacterial" BSA and casein spheres

A novel antibacterial coating for cotton and polyester fabrics has been developed by using drug-loaded proteinaceous microspheres made of bovine serum albumin and casein proteins. The microbubbles were created and anchored onto the fabrics (see figure) in a one-step reaction that lasts 3 min. The sonochemically produced "antibacterial fabrics" have been characterized. The efficiency of the sonochemical process in converting the native proteins into microspheres, encapsulating the drug, and coating the fabric has also been studied.

Stabilizing RNA by the sonochemical formation of RNA nanospheres

Biological macromolecules, including DNA, RNA, and proteins, have intrinsic features that make them potential building blocks for the bottom-up fabrication of nanodevices. Unlike DNA, RNA is a more versatile molecule whose range in the cell is from 21 to thousands of nucleotides and is usually folded into stem and loop structures. RNA is unique in nanoscale fabrication due to its diversity in size, function, and structure. Because gene expression analysis is becoming a clinical reality and there is a need to collect RNA in minute amounts from clinical samples, keeping the RNA intact is a growing challenge. RNA samples are notoriously difficult to handle because of their highly labile nature and tendency to degrade even under controlled RNase-free conditions and maintenance in the cold. Silencing the RNA that induces the RNA interference is viewed as the next generation of therapeutics. The stabilization and delivery of RNA to cells are the major concerns in making siRNAs usable drugs. For the first time, ultrasonic waves are shown to convert native RNA molecules to RNA nanospheres. The creation of the nanobubbles is performed by a one-step reaction. The RNA nanospheres are stable at room temperature for at least one month. Additionally, the nanospheres can be inserted into mammalian cancer cells (U2OS). This research achieves: 1) a solution to RNA storage; and 2) a way to convert RNA molecules to RNA particles. RNA nanosphere formation is a reversible process, and by using denaturing conditions, the RNA can be refolded into intact molecules.