Nanostructured, Self-Assembled Spider Silk Materials for Biomedical Applications

Spider minor ampullate silk protein nanoparticles: an effective protein delivery system capable of enhancing systemic immune responses

Spider silk proteins (spidroins) are particularly attractive due to their excellent biocompatibility. Spider can produce up to seven different types of spidroins, each with unique properties and functions. Spider minor ampullate silk protein (MiSp) might be particularly interesting for biomedical applications, as the constituent silk is mechanically strong and does not super-contract in water, attributed to its amino acid composition. In this study, we evaluate the potential of recombinant nanoparticles derived from Araneus ventricosus MiSp as a protein delivery carrier. The MiSp-based nanoparticles were able to serve as an effective delivery system, achieving nearly 100% efficiency in loading the model protein lysozyme, and displayed a sustained release profile at physiological pH. These nanoparticles could significantly improve the delivery efficacy of the model proteins through different administration routes. Furthermore, nanoparticles loaded with model protein antigen lysozyme after subcutaneous or intramuscular administration could enhance antigen-specific immune responses in mouse models, through a mechanism involving antigen-depot effects at the injection site, long-term antigen persistence, and efficient uptake by dendritic cells as well as internalization by lymph nodes. These findings highlight the transnational potential of MiSp-based nanoparticle system for protein drug and vaccine delivery.

MMPs-responsive silk spheres for controlled drug release within tumor microenvironment

Silk is a biocompatible and biodegradable material that enables the formation of various morphological forms, including nanospheres. The functionalization of bioengineered silk makes it possible to produce particles with specific properties. In addition to tumor cells, the tumor microenvironment (TME) includes stromal, immune, endothelial cells, signaling molecules, and the extracellular matrix (ECM). Matrix metalloproteinases (MMPs) are overexpressed in TME. We investigated bioengineered spider silks functionalized with MMP-responsive peptides to obtain targeted drug release from spheres within TME. Soluble silks MS12.2MS1, MS12.9MS1, and MS22.9MS2 and the corresponding silk spheres carrying MMP-2 or MMP-2/9 responsive peptides were produced, loaded with doxorubicin (Dox), and analyzed for their susceptibility to MMP-2/9 digestion. Although all variants of functionalized silks and spheres were specifically degraded by MMP-2/9, the MS22.9MS2 nanospheres showed the highest levels of degradation and release of Dox after enzyme treatment. Moreover, functionalized spheres were degraded in the presence of cancer cells releasing MMP-2/9. In the 2D and 3D spheroid cancer models, the MMP-2/9-responsive substrate was degraded and released from spheres when loaded into MS22.9MS2 particles but not into the control MS2 spheres. The present study demonstrated that a silk-based MMP-responsive delivery system could be used for controlled drug release within the tumor microenvironment.

Rapid production of chimeric silkworm/spider silk with improved mechanical properties by infection of nonpermissive Bombyx mori with recombinant AcMNPV harboring native-size of spidroin genes

Spider silks with excellent mechanical properties attract more attention from scientists worldwide, and the dragline silk that serves as the framework of the spider's web is considered one of the strongest fibers. However, it is unfeasible for large-scale production of spider silk due to its highly territorial, cannibalistic, predatory, and solitary behavior. Herein, to alleviate some of these problems and explore aneasy way to produce spider fibers, we constructed recombinant baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV) simultaneously expressing Trichonephila clavipes native ampullate spidroin 2 (MaSp-G) and spidroin 1 (MaSp-C) driven by the promoters of silkworm fibroin genes, to infect the nonpermissive Bombyx mori larvae at the fifth instar. MaSp-G and MaSp-C were co-expressed in the posterior silk glands (PSGs) of infected silkworms and successfully secreted into the lumen of the silk gland for fibroin globule assembly. The integration of MaSp-G and MaSp-C into silkworm silk fibers significantly improved the mechanical properties of these chimeric silk fibers, especially the strength and extensibility, which may be caused by the increment of β-sheet in the chimeric silkworm/spider silk fiber. These results demonstrated that silkworms could be developed as the nonpermissive heterologous host for the mass production of chimeric silkworm/spider silk fibers via the recombinant baculovirus AcMNPV.

Cooperative assembly of a designer peptide and silk fibroin into hybrid nanofiber gels for neural regeneration after spinal cord injury

Local reconstruction of a permissive environment with biomaterials is a promising strategy to treat spinal cord injury (SCI). We reported a hybrid hydrogel fabricated from a small functional self-assembling peptide (F-SAP) and large silk fibroin (SF). The diffusion of SF micelles into F-SAP solution was driven by the dynamic synergy between osmotic pressure and F-SAP/SF electrostatic interactions, resulting in the rearrangement of SF micelles and the formation of rod-like filaments with axes nearly perpendicular to F-SAP nanofibers. Spectroscopy analysis, including circular dichroism, Raman and fluorescence, indicated conformation changes of SF from random coil to β sheet, which contributed to enhanced mechanical properties of the resultant hybrid hydrogel. Furthermore, the F-SAP/SF hybrid hydrogel coupled with controlled release of NT-3 provided a permissive environment for neural regeneration by providing nanofibrous substrates for regenerating axons, inflammatory modulation and remyelination, consequently resulting in improved locomotion and electrophysiological properties. This hydrogel could be used as a long-term stent in vivo for the treatment of SCI.

Characteristic Evaluation of Recombinant MiSp/Poly(lactic-co-glycolic) Acid (PLGA) Nanofiber Scaffolds as Potential Scaffolds for Bone Tissue Engineering

Biomaterial-based nanofibrous scaffolds are the most effective alternative to bone transplantation therapy. Here, two recombinant minor ampullate spidroins (spider silk proteins), R1SR2 and NR1SR2C, were blended with Poly(lactic-co-glycolic) Acid (PLGA), respectively, to generate nanofiber scaffolds by electrospinning. The N-terminal (N), C-terminal (C), repeating (R1 and R2) and spacer (S) modules were all derived from the minor ampullate spidroins (MiSp). The physical properties and structures of the blended scaffolds were measured by scanning electron microscopy (SEM), water contact angle measurement, Fourier transform infrared spectroscopy (FTIR), Differential scanning calorimetry (DSC), and Tensile mechanical testing. The results showed that blending of MiSp (R1SR2 and NR1SR2C) reduced the diameter of nanofibers, increased the porosity and glass transition temperatures of nanofibrous scaffolds, and effectively improved the hydrophilicity and ultimate strain of scaffolds. It is worth noting that the above changes were more significant in the presence of the N- and C-termini of MiSp. In cell culture assays, human bone mesenchymal stem cells (HBMSCs) grown on NR1SR2C/PLGA (20/80) scaffolds displayed markedly enhanced proliferative and adhesive abilities compared with counterparts grown on pure PLGA scaffolds. Jointly, these findings indicated recombinant MiSp/PLGA, particularly NR1SR2C/PLGA (20/80) blend nanofibrous scaffolds, is promising for bone tissue engineering.

High Performance Marine and Terrestrial Bioadhesives and the Biomedical Applications They Have Inspired

This study has reviewed the naturally occurring bioadhesives produced in marine and freshwater aqueous environments and in the mucinous exudates of some terrestrial animals which have remarkable properties providing adhesion under difficult environmental conditions. These bioadhesives have inspired the development of medical bioadhesives with impressive properties that provide an effective alternative to suturing surgical wounds improving closure and healing of wounds in technically demanding tissues such as the heart, lung and soft tissues like the brain and intestinal mucosa. The Gecko has developed a dry-adhesive system of exceptional performance and has inspired the development of new generation re-usable tapes applicable to many medical procedures. The silk of spider webs has been equally inspiring to structural engineers and materials scientists and has revealed innovative properties which have led to new generation technologies in photonics, phononics and micro-electronics in the development of wearable biosensors. Man made products designed to emulate the performance of these natural bioadhesive molecules are improving wound closure and healing of problematic lesions such as diabetic foot ulcers which are notoriously painful and have also found application in many other areas in biomedicine. Armed with information on the mechanistic properties of these impressive biomolecules major advances are expected in biomedicine, micro-electronics, photonics, materials science, artificial intelligence and robotics technology.

Systemic and Local Silk-Based Drug Delivery Systems for Cancer Therapy

For years, surgery, radiotherapy, and chemotherapy have been the gold standards to treat cancer, although continuing research has sought a more effective approach. While advances can be seen in the development of anticancer drugs, the tools that can improve their delivery remain a challenge. As anticancer drugs can affect the entire body, the control of their distribution is desirable to prevent systemic toxicity. The application of a suitable drug delivery platform may resolve this problem. Among other materials, silks offer many advantageous properties, including biodegradability, biocompatibility, and the possibility of obtaining a variety of morphological structures. These characteristics allow the exploration of silk for biomedical applications and as a platform for drug delivery. We have reviewed silk structures that can be used for local and systemic drug delivery for use in cancer therapy. After a short description of the most studied silks, we discuss the advantages of using silk for drug delivery. The tables summarize the descriptions of silk structures for the local and systemic transport of anticancer drugs. The most popular techniques for silk particle preparation are presented. Further prospects for using silk as a drug carrier are considered. The application of various silk biomaterials can improve cancer treatment by the controllable delivery of chemotherapeutics, immunotherapeutics, photosensitizers, hormones, nucleotherapeutics, targeted therapeutics (e.g., kinase inhibitors), and inorganic nanoparticles, among others.

Characteristics of electrospun membranes in different spidroin/PCL ratios

Spider silk is a protein fiber with the highest strength and elasticity known in nature, even higher than that of silkworm silk. It was a biological and technical reserve material with great potential. However, the low yield of natural spider silk limits the application of spider silk, and the development of genetic engineering provides opportunities for the mass production of spider silk. We constructed a mini-recombinant spidroin NRC based on spider silk gene fromAraneus ventricosusand successfully expressed it through Prokaryotic expression that provide a high production for application using electrospinning, which is a mature technique to produce micro-nano scale fibers as thin as natural spider silks. By blending the purified and lyophilized NRC with polycaprolactone (PCL) in different mass ratio for electrospinning, different electrospun membranes were obtained, and then characterized in terms of morphology, chemical structure, mechanical and Schwann cell proliferation. Compared the difference between polycaprolactone (PCL) and NRC, the fiber diameter decreased from 1.0779 μm to 0.5785 μm, water contact angel decreased from 104.1 ± 2° to 56.9 ± 5°, and elongation decreased from 240.97 ± 89% to 37.76 ± 13%, while tensile strength increased from 1.74 ± 1.2 MPa to 3.18 ± 0.9 MPa and Young's Module increased from 3.05 ± 1.6 MPa to 16.54 ± 6.7 MPa. In this study, we obtained a thinner fiber, hydrophilicity and high strengthen electrospinning spidroin contained membrane, which can also promote Schwann cell proliferation and adhesion.

Controlled self-assembly of plant proteins into high-performance multifunctional nanostructured films

The abundance of plant-derived proteins, as well as their biodegradability and low environmental impact make them attractive polymeric feedstocks for next-generation functional materials to replace current petroleum-based systems. However, efforts to generate functional materials from plant-based proteins in a scalable manner have been hampered by the lack of efficient methods to induce and control their micro and nanoscale structure, key requirements for achieving advantageous material properties and tailoring their functionality. Here, we demonstrate a scalable approach for generating mechanically robust plant-based films on a metre-scale through controlled nanometre-scale self-assembly of water-insoluble plant proteins. The films produced using this method exhibit high optical transmittance, as well as robust mechanical properties comparable to engineering plastics. Furthermore, we demonstrate the ability to impart nano- and microscale patterning into such films through templating, leading to the formation of hydrophobic surfaces as well as structural colour by controlling the size of the patterned features.

Exogenic production of bioactive filamentous biopolymer by monogonant rotifers

The chemical ecology of rotifers has been little studied. A yet unknown property is presented within some monogonant rotifers, namely the ability to produce an exogenic filamentous biopolymer, named 'Rotimer'. This rotifer-specific viscoelastic fiber was observed in six different freshwater monogonants (Euchlanis dilatata, Lecane bulla, Lepadella patella, Itura aurita, Colurella adriatica and Trichocerca iernis) in exception of four species. Induction of Rotimer secretion can only be achieved by mechanically irritating rotifer ciliate with administering different types (yeast cell skeleton, denatured BSA, epoxy, Carmine or urea crystals and micro-cellulose) and sizes (approx. from 2.5 to 50 µm diameter) of inert particles, as inductors or visualization by adhering particles. The thickness of this Rotimer is 33 ± 3 nm, detected by scanning electron microscope. This material has two structural formations (fiber or gluelike) in nano dimension. The existence of the novel adherent natural product becomes visible by forming a 'Rotimer-Inductor Conglomerate' (RIC) web structure within a few minutes. The RIC-producing capacity of animals, depends on viability, is significantly modified according to physiological- (depletion), drug- (toxin or stimulator) and environmental (temperature, salt content and pH) effects. The E. dilatata-produced RIC is affected by protein disruptors but is resistant to several chemical influences and its Rotimer component has an overwhelming cell (algae, yeast and human neuroblastoma) motility inhibitory effect, associated with low toxicity. This biopolymer-secretion-capacity is protective of rotifers against human-type beta-amyloid aggregates.

Bioengineered elastin- and silk-biomaterials for drug and gene delivery

Advances in medical science have led to diverse new therapeutic modalities, as well as enhanced understanding of the progression of various disease states. These findings facilitate the design and development of more customized and exquisite drug delivery systems that aim to improve therapeutic indices of drugs to treat a variety of conditions. Synthetic polymer-based drug carriers have often been the focus of such research. However, these structures suffer from challenges with heterogeneity of the starting material, limited chemical features, complex functionalization methods, and in some cases a lack of biocompatibility. Consequently, protein-based polymers have garnered much attention in recent years due to their monodisperse features, ease of production and functionalization, and biocompatibility. Genetic engineering techniques enable the advancement of protein-based drug delivery systems with finely tuned physicochemical properties, and thus an expanded level of customization unavailable with synthetic polymers. Of these genetically engineered proteins, elastin-like proteins (ELP), silk-like proteins (SLP), and silk-elastin-like proteins (SELP) provide a unique set of alternatives for designing drug delivery systems due to their inherent chemical and physical properties and ease of engineering afforded by recombinant DNA technologies. In this review we examine the advantages of genetically engineered drug delivery systems with emphasis on ELP and SLP constructions. Methods for fabrication and relevant biomedical applications will also be discussed.

Surface Modification by Nano-Structures Reduces Viable Bacterial Biofilm in Aerobic and Anaerobic Environments

Bacterial biofilm formation on wet surfaces represents a significant problem in medicine and environmental sciences. One of the strategies to prevent or eliminate surface adhesion of organisms is surface modification and coating. However, the current coating technologies possess several drawbacks, including limited durability, low biocompatibility and high cost. Here, we present a simple antibacterial modification of titanium, mica and glass surfaces using self-assembling nano-structures. We have designed two different nano-structure coatings composed of fluorinated phenylalanine via the drop-cast coating technique. We investigated and characterized the modified surfaces by scanning electron microscopy, X-ray diffraction and wettability analyses. Exploiting the antimicrobial property of the nano-structures, we successfully hindered the viability of Streptococcus mutans and Enterococcus faecalis on the coated surfaces in both aerobic and anaerobic conditions. Notably, we found lower bacteria adherence to the coated surfaces and a reduction of 86–99% in the total metabolic activity of the bacteria. Our results emphasize the interplay between self-assembly and antimicrobial activity of small self-assembling molecules, thus highlighting a new approach of biofilm control for implementation in biomedicine and other fields.

Expanding Canonical Spider Silk Properties through a DNA Combinatorial Approach

The properties of native spider silk vary within and across species due to the presence of different genes containing conserved repetitive core domains encoding a variety of silk proteins. Previous studies seeking to understand the function and material properties of these domains focused primarily on the analysis of dragline silk proteins, MaSp1 and MaSp2. Our work seeks to broaden the mechanical properties of silk-based biomaterials by establishing two libraries containing genes from the repetitive core region of the native Latrodectus hesperus silk genome (Library A: genes masp1, masp2, tusp1, acsp1; Library B: genes acsp1, pysp1, misp1, flag). The expressed and purified proteins were analyzed through Fourier Transform Infrared Spectrometry (FTIR). Some of these new proteins revealed a higher portion of β-sheet content in recombinant proteins produced from gene constructs containing a combination of masp1/masp2 and acsp1/tusp1 genes than recombinant proteins which consisted solely of dragline silk genes (Library A). A higher portion of β-turn and random coil content was identified in recombinant proteins from pysp1 and flag genes (Library B). Mechanical characterization of selected proteins purified from Library A and Library B formed into films was assessed by Atomic Force Microscopy (AFM) and suggested Library A recombinant proteins had higher elastic moduli when compared to Library B recombinant proteins. Both libraries had higher elastic moduli when compared to native spider silk proteins. The preliminary approach demonstrated here suggests that repetitive core regions of the aforementioned genes can be used as building blocks for new silk-based biomaterials with varying mechanical properties.

Structural Basis of Oligomerization of N-Terminal Domain of Spider Aciniform Silk Protein

Spider silk is self-assembled from water-soluble silk proteins through changes in the environment, including pH, salt concentrations, and shear force. The N-terminal domains of major and minor ampullate silk proteins have been found to play an important role in the assembly process through salt- and pH-dependent dimerization. Here, we identified the sequences of the N-terminal domains of aciniform silk protein (AcSpN) and major ampullate silk protein (MaSpN) from Nephila antipodiana (NA). Different from MaSpN, our biophysical characterization indicated that AcSpN assembles to form large oligomers, instead of a dimer, upon condition changes from neutral to acidic pH and/or from a high to low salt concentration. Our structural studies, by nuclear magnetic resonance spectroscopy and homology modelling, revealed that AcSpN and MaSpN monomers adopt similar overall structures, but have very different charge distributions contributing to the differential self-association features. The intermolecular interaction interfaces for AcSp oligomers were identified using hydrogen–deuterium exchange mass spectrometry and mutagenesis. On the basis of the monomeric structure and identified interfaces, the oligomeric structures of AcSpN were modelled. The structural information obtained will facilitate an understanding of silk fiber formation mechanisms for aciniform silk protein.