Natural Spider Silk Research Articles

Spider Silk Protein Forms Amyloid-Like Nanofibrils through a Non-Nucleation-Dependent Polymerization Mechanism.

Amyloid fibrils-nanoscale fibrillar aggregates with high levels of order-are pathogenic in some today incurable human diseases; however, there are also many physiologically functioning amyloids in nature. The process of amyloid formation is typically nucleation-elongation-dependent, as exemplified by the pathogenic amyloid-β peptide (Aβ) that is associated with Alzheimer's disease. Spider silk, one of the toughest biomaterials, shares characteristics with amyloid. In this study, it is shown that forming amyloid-like nanofibrils is an inherent property preserved by various spider silk proteins (spidroins). Both spidroins and Aβ capped by spidroin N- and C-terminal domains, can assemble into macroscopic spider silk-like fibers that consist of straight nanofibrils parallel to the fiber axis as observed in native spider silk. While Aβ forms amyloid nanofibrils through a nucleation-dependent pathway and exhibits strong cytotoxicity and seeding effects, spidroins spontaneously and rapidly form amyloid-like nanofibrils via a non-nucleation-dependent polymerization pathway that involves lateral packing of fibrils. Spidroin nanofibrils share amyloid-like properties but lack strong cytotoxicity and the ability to self-seed or cross-seed human amyloidogenic peptides. These results suggest that spidroins´ unique primary structures have evolved to allow functional properties of amyloid, and at the same time direct their fibrillization pathways to avoid formation of cytotoxic intermediates.

Ambient-conditions spinning of functional soft fibers via engineering molecular chain networks and phase separation

Producing functional soft fibers via existing spinning methods is environmentally and economically costly due to the complexity of spinning equipment, involvement of copious solvents, intensive consumption of energy, and multi-step pre-/post-spinning treatments. We report a nonsolvent vapor-induced phase separation spinning approach under ambient conditions, which resembles the native spider silk fibrillation. It is enabled by the optimal rheological properties of dopes via engineering silver-coordinated molecular chain interactions and autonomous phase transition due to the nonsolvent vapor-induced phase separation effect. Fiber fibrillation under ambient conditions using a polyacrylonitrile-silver ion dope is demonstrated, along with detailed elucidations on tuning dope spinnability through rheological analysis. The obtained fibers are mechanically soft, stretchable, and electrically conductive, benefiting from elastic molecular chain networks via silver-based coordination complexes and in-situ reduced silver nanoparticles. Particularly, these fibers can be configured as wearable electronics for self-sensing and self-powering applications. Our ambient-conditions spinning approach provides a platform to create functional soft fibers with unified mechanical and electrical properties at a two-to-three order of magnitude less energy cost under ambient conditions.

Quartz-Enhanced Photoacoustic Spectroscopy-Conductance Spectroscopy for Gas Mixture Analysis.

A novel spectroscopic method, named quartz-enhanced photoacoustic spectroscopy-conductance spectroscopy (QEPAS-CS), was first developed for gas mixture analysis. In QEPAS-CS, the advantage of photoacoustic detection and conductance analysis was realized by a quartz tuning fork (QTF). Two-component gas analysis was done by photoacoustic detection and conductance detection. For an explicit application, natural spider silk was used as a water vapor transducer to modify the QTF, making a conductance sensing channel. A 2004 nm laser diode was used as an excitation source for a photoacoustic sensing channel. Such a QEPAS-CS sensor was used for H2O/CO2 gas mixture analysis in a cell incubator. This provides a solution to calibrate an infrared photoacoustic spectroscopy gas sensor. This example effectively confirms the capacity of multigas analysis by the QEPAS-CS sensor.

Dry-Spinning of Artificial Spider Silk Ribbons from Regenerated Natural Spidroin in an Organic Medium.

Natural spider silks with striking performances have achieved extensive investigations. Nonetheless, a lack of consensus over the mechanism of the natural spinning hinders the development of artificial spinning methods where the regenerated spider silks generally show poor performances compared with the natural fibers. As is known, the Plateau-Rayleigh instability tends to break solution column into droplets and has been considered as a main challenge during fiber-spinning. Here in this study, by harnessing the viscoelastic properties of the regenerated spidroin dope solution via organic salt-zinc acetate (ZA), we avoid this outcome and successfully realize dry-spinning of long and mechanically robust regenerated spider silk ribbons. The as obtained dry-spun spider silk ribbons show an enhanced modulus up to 14±4GPa and a toughness of around 51±9 MJm-3 after the post-stretching treatment, which is even better than the pristine spider silk fibers. Our facile and flexible strategy enriches the spinning methodologies which bypasses the bottleneck of precisely mimicking the complex natural environment of the glands in spiders, shining a light to the spider-silk-based textile industrial applications. This article is protected by copyright. All rights reserved.

Spider silk-inspired dynamic covalent polyurethane with fast repairing, shape memory, and strong dynamic adhesion via lignin enhanced microphase separation

Introducing microphase separation and dynamic bonds into the polymeric materials is an effective strategy to enhance the performance of polyurethane. Herein, a modified lignin-based polyol (MLOH) was developed via a facile one-step approach which greatly improved its reactivity and dispersibility compared to that of virgin lignin. Subsequently, inspired by the biphasic structure of natural spider silk, a high-performance modified lignin-based dynamic covalent polyurethane (MLPU) with lignin enhanced microphase separation was fabricated, exploiting the synthetic MLOH as the crosslinker and the dynamic oxime-carbamate bonds as the linkage. Besides possessing high repairing efficiency (3 min for 100%, 80 °C without pressure), and outstanding shape-memory capability, the optimized MLPU-2 demonstrated robust adhesive performance when applied as a polyurethane hot-melt adhesive, including a fast curing rate and high adhesive strength (10.50 MPa). Meanwhile, it also manifested remarkable solvent resistance, temperature tolerance from −30 °C to 60 °C, long-term durability for at least 3 months, on-demand debonding ability, and excellent reusability. The synergistic effect of lignin enhanced microphase separation and adjustable dynamic crosslinked structure endows the remarkable performance of this resultant dynamic covalent MLPU, which provides another way to develop green, sustainable polyurethane simultaneously with highly comprehensive performances for the potential practical application.

Crystallinity and Stiffness of Spider Silk Govern the Migration of Schwann Cells

Introduction: Nerve guidance conduits are a promising alternative to autologous nerve transplantation and conduits filled with fibrous materials have shown great potential in bridging nerve gaps. The application of spider silk as a filament material has led to results comparable to nerve autograft.1 However, the use of spider silk has been phenomenological so far and the reasons for its success are still not identified. The aim of this study is to elucidate the material properties of spider silk leading to its unique medical performance. This knowledge enables a targeted production of synthetic alternatives such as recombinant silk. Materials and Methods: In this work, various silk types were investigated.2 Schwann cells were seeded on the spider silks and monitored by live cell imaging and immunofluorescent staining. In addition, the silk fibers were inspected with an electron microscopy, Raman spectroscopy wide angle X-ray scattering, and tensile tests to determine morphology, secondary protein structure, crystallinity and stiffness, respectively. Results: It was found that the secondary protein structure and specifically the high content of β-sheets in the direction of silk’s axis gives the fiber its ability to act as a guiding element for Schwann cells. In addition, the results show that the crystallinity of the silk does not affect the proliferation of Schwann cells, while the directed movement of cells is affected by this material property. Conclusion: This direct comparison demonstrated the crucial role of the secondary protein structures and crystallinity of spider silk for the guidance properties of fibers during nerve regeneration. The crystalline structure of silk affects its stiffness, which in turn influences the directed migration of Schwann cells. These results should be considered during the targeted production of synthetic fibrous materials for nerve regeneration. 1. Kornfeld T, Nessler J, Helmer C, et al. Spider silk nerve graft promotes axonal regeneration on long distance nerve defect in a sheep model. Biomaterials 2021;271:120692. 2. Naghilou A, Pöttschacher L, Millesi F, et al. Correlating the secondary protein structure of natural spider silk with its guiding properties for Schwann cells. Mater Sci Eng C. 2020;116:111219.

Recent developments in artificial spider silk and functional gel fibers

AbstractIt is highly desirable to develop fiber materials with high strength and toughness while increasing fiber strength always results in a decrease in toughness. Spider silk is a natural fiber material with an excellent combination of high strength and toughness, which is produced from the spinning dope solution by gelation and drawing spinning process. This encourages people to prepare artificial fibers by mimicking the material, structure, and spinning of natural spider silk. In this review, we first summarized the preparation of artificial spider silk prepared via such a gelation process from different types of materials, including nonrecombinant proteins, recombinant proteins, polypeptides, synthetic polymers, and polymer nanocomposites. In addition, different spinning approaches for spinning artificial spider silk are also summarized. In the third section, some novel application scenarios of the artificial spider silk were summarized, such as artificial muscles, sensing, and smart fibers.

Tyrosine's Unique Role in the Hierarchical Assembly of Recombinant Spider Silk Proteins: From Spinning Dope to Fibers.

Producing recombinant spider silk fibers that exhibit mechanical properties approaching native spider silk is highly dependent on the constitution of the spinning dope. Previously published work has shown that recombinant spider silk fibers spun from dopes with phosphate-induced pre-assembly (biomimetic dopes) display a toughness approaching native spider silks far exceeding the mechanical properties of fibers spun from dopes without pre-assembly (classical dopes). Dynamic light scattering experiments comparing the two dopes reveal that biomimetic dope displays a systematic increase in assembly size over time, while light microscopy indicates liquid-liquid-phase separation (LLPS) as evidenced by the formation of micron-scale liquid droplets. Solution nuclear magnetic resonance (NMR) shows that the structural state in classical and biomimetic dopes displays a general random coil conformation in both cases; however, some subtle but distinct differences are observed, including a more ordered state for the biomimetic dope and small chemical shift perturbations indicating differences in hydrogen bonding of the protein in the different dopes with notable changes occurring for Tyr residues. Solid-state NMR demonstrates that the final wet-spun fibers from the two dopes display no structural differences of the poly(Ala) stretches, but biomimetic fibers display a significant difference in Tyr ring packing in non-β-sheet, disordered helical domains that can be traced back to differences in dope preparations. It is concluded that phosphate pre-orders the recombinant silk protein in biomimetic dopes resulting in LLPS and fibers that exhibit vastly improved toughness that could be due to aromatic ring packing differences in non-β-sheet domains that contain Tyr.

The Properties and Application of Natural Spider Silk: a Literature Review

Drag silk, which is produced by the main ampullate silk gland, is a kind of natural insect silk which outperforms some other kinds of silk. Given its exceptional mechanical characteristics and excellent biocompatibility, drag silk, a kind of spider silk, does have the potential to be utilized by humans. The excellent properties of natural spider silk make it useful in many fields. But due to the cannibalistic nature of spiders, spiders cannot be reared on a large scale to meet the huge demand for spider silk. The development of recombinant spider silk protein and artificial spider silk through research and development is vital for the commercialization of spider silk and its applications. This research outlines the possible applications of natural spider silk by examining its physical, biological, and characteristic features. Due to its extraordinary physical and biological properties, drag silk and its corresponding silk proteins have been found to have the potential for the applications in the aerospace industry and biomedical treatments.

Fabrication of spider silk-inspired bio-based polymeric materials under dynamic nanoconfinement as high-strong, ultra-tough, and multifunctional plastic substitutes

The preparation of degradable bio-based materials with superhigh strength and toughness persists an enormous challenge. The natural spider silk presents ultrahigh tensile strength along with fracture toughness, due to the nanoconfinement effect of hydrogen-bonded crystalline β-sheets on the soft amorphous protein matrix. Herein, under inspiration of nanoconfinement effect in spider silk, an ingenious approach is proposed for fabricating a high-strong and ultra-tough soy protein (SP)-based material with dynamic nanoconfinement phases induced by tannic acid (TA) as hydrogen bond (H-bond) cross-linkers between hyperbranched polyester (HBPE) plasticizer and SP matrix molecules. Due to H-bond crosslinked dynamic nanoconfinement, the fabricated SP/HBPE/TA film reveals a superior tensile strength of 44.6 MPa together with ultrahigh toughness of 44.7 MJ m−3, surpassing its kind and other bio-based, and its toughness even outperforms common plastic-based materials. Additionally, the reversibility of the H-bonds and hydrophobic structure in nanoconfinement results in film with excellent recyclability and water resistance. The final film exhibits antioxidant and antibacterial properties after incorporating of TA. In addition, it also shows effective UV-shielding performance. This work affords a novel biomimetic strategy for fabricating fully degradable and multifunctional bio-based materials with integrated outstanding strength and toughness, for potential application in plastic waste remediation.

Bioinspired Tough and Strong Fibers with Hierarchical Core–Shell Structure

AbstractStrong and tough bio‐based fibers are attractive for both fundamental research and practical applications. In this work, strong and tough hierarchical core–shell fibers with cellulose nanofibrils (CNFs) in the core and regenerated silk fibroins (RSFs) in the shell are designed and prepared, mimicking natural spider silks. CNF/RSF core–shell fibers with precisely controlled morphology are continuously wet‐spun using a co‐axial microfluidic device. Highly‐dense non‐covalent interactions are introduced between negatively‐charged CNFs in the core and positively‐charged RSFs in the shell, diminishing the core/shell interface and forming an integral hierarchical fiber. Meanwhile, shearing by microfluidic channels and post‐stretching induce a better ordering of CNFs in the core and RSFs in the shell, while ordered CNFs and RSFs are more densely packed, thus facilitating the formation of non‐covalent interactions within the fiber matrix. Therefore, CNF/RSF core–shell fibers demonstrate excellent mechanical performances; especially after post‐stretching, their tensile strength, tensile strain, Young's modulus, and toughness are up to 635 MPa, 22.4%, 24.0 GPa, and 110 MJ m−3, respectively. In addition, their mechanical properties are barely compromised even at −40 and 60 °C. Static load and dynamic impact tests suggest that CNF/RSF core–shell fibers are strong and tough, making them suitable for advanced structural materials.

Ultrahigh Mechanical Strength and Robust Room-Temperature Self-Healing Properties of a Polyurethane-Graphene Oxide Network Resulting from Multiple Dynamic Bonds.

Addressing the conflict between achieving high mechanical properties and room-temperature self-healing ability is extremely significant to achieving a breakthrough in the application of self-healing materials. Therefore, inspired by natural spider silk and nacre, a room-temperature self-healing supramolecular material with ultrahigh strength and toughness is developed by synergistically incorporating flexible disulfide bonds and dynamic sextuple hydrogen bonds (H-bonds) into polyurethanes (PUs). Simultaneously, abundant H-bonds are introduced at the interface between graphene oxide nanosheets with dynamic multiple H-bonds and the PU matrix to afford strong interfacial interactions. The resulting urea-containing PU material with an inverse artificial nacre structure has a record mechanical strength (78.3 MPa) and toughness (505.7 MJ m-3), superior tensile properties (1273.2% elongation at break), and rapid room-temperature self-healing abilities (88.6% at 25 °C for 24 h), forming the strongest room-temperature self-healing elastomer reported to date and thus upending the previous understanding of traditional self-healing materials. In addition, this bionic PU-graphene oxide network endows the fabricated flexible intelligent robot with functional repair and shape memory capabilities, thus providing prospects for the fabrication of flexible functional devices.

Protein secondary structure in spider silk nanofibrils

Nanofibrils play a pivotal role in spider silk and are responsible for many of the impressive properties of this unique natural material. However, little is known about the internal structure of these protein fibrils. We carry out polarized Raman and polarized Fourier-transform infrared spectroscopies on native spider silk nanofibrils and determine the concentrations of six distinct protein secondary structures, including β-sheets, and two types of helical structures, for which we also determine orientation distributions. Our advancements in peak assignments are in full agreement with the published silk vibrational spectroscopy literature. We further corroborate our findings with X-ray diffraction and magic-angle spinning nuclear magnetic resonance experiments. Based on the latter and on polypeptide Raman spectra, we assess the role of key amino acids in different secondary structures. For the recluse spider we develop a highly detailed structural model, featuring seven levels of structural hierarchy. The approaches we develop are directly applicable to other proteinaceous materials.

Synergistic enhancement on flexible solid-state supercapacitor based on redox-active Fe3+ions/natural spidroin modified vertically aligned carbon nanotube arrays

The conductive skeleton and aligned carbon nanotube array (CNTA) structure can greatly shorten the ion transfer path and promote the charge transfer speed, which makes the CNTA an ideal electrode material for energy storage application. However, poor mechanical stability and low specific capacitance greatly impede its practical utilization. Here, we introduce a promising flexible electrode material based on the natural spider silk protein (SSP) modified CNTA(SSP/CNTA) with improved hydrophilicity and mechanical flexibility. The redox-active Fe3+ doped SSP/CNTA flexible solid-state supercapacitor (FSSC) device with superior energy storage performance was assembled in a symmetric ‘sandwich-type’ structure. The synergetic interaction between Fe3+ ions and the SSP are proved to greatly enhance the electrochemical performance especially the long-term cyclic stability. The Fe3+ doped SSP/CNTA FSSCs device achieves an ultra-high volumetric capacitance of 4.92 F cm−3 at a sweep speed of 1 mV s−1. Meanwhile it exhibited an excellent cycling stability with an increased capacitance by 10% after 10 000 charge–discharge cycles. As a control, a Fe3+ doped CNTA composite device without SSP will lose over 74% of the capacitance after 10 000 cycles. The energy storage mechanism analysis confirms the dominated capacitive behavior of the device, which explained a considerable power density and rate performance. Our method thus provides a promising strategy to build up highly-efficient redox-enhanced FSSCs for next generation of wearable and implantable electronics.

Fluorescent Hybrid Material Based on Natural Spider Silk and Carbon Dots for Bioapplication.

Since the outcome of an operation largely depends on the quality of wound healing, it is one of the most challenging stages in surgery. Today, wound closure is mostly undertaken by means of a surgical suture. Good surgical sutures are biocompatible and biodegradable and possess excellent mechanical properties. Preferably, these sutures demonstrate optical activity for bacteria detection as there is a risk of surgical site infections. In this study, a solution, which fulfills all the requirements for manufacturing a multifunctional hybrid material, is proposed. In this work, a method for the in situ modification of spider silk with fluorescent carbon dots has been developed. The basic concept is the use of silk fibers as both the main framework for tissue regeneration and a carbon source during carbon dot synthesis. The resulting hybrid material exhibits strong photoluminescence in the red region of the spectrum (590 nm) when irradiated with blue light (480 nm). The proposed approach potentially allows for simultaneous wound closure and pathogen detection.

67. Silk-silk Conduits Filled with Native Spider Silk Fibers Successfully Promoted Nerve Regeneration in a 10 Mm Sciatic Nerve Defect in Rats

67. Silk-silk Conduits Filled with Native Spider Silk Fibers Successfully Promoted Nerve Regeneration in a 10 Mm Sciatic Nerve Defect in Rats

Cell Adhesion Behaviors on Spider Silk Fibers, Films, and Nanofibers

Silk-based materials have garnered attention for use as medical supplies due to their mechanical toughness and low cytotoxicity. Silkworm silk has been applied as surgical sutures for decades. In contrast, the utilization of spider silk is limited mainly because of its scarcity. Although the biomimicry of spider silk has been developed using recombinant protein expression systems with the use of genetic engineering, the product often results in lower molecular weight and a lack of the N- or C-terminal regions. The incomplete sequence of the spider silk-like protein prevents the objective evaluation of the native spider silk as a medical application and retards the development of spider silk-inspired materials. Here, we reeled the native spider silk directly from live spiders and investigated the cell adhesion behavior based on three kinds of surface topography of spider silk-based substrates, namely, fibers, films, and non-woven fabrics. The cell adhesion behavior was largely influenced by the surface micro/nanostructure rather than the wettability of the surface. This study will contribute to promote the utilization of spider silk in the medical field as a candidate for promising bio-based fibers in the context of sustainable development goals.

Bio-Inspired 4D Printing of Dynamic Spider Silks.

Spider silks exhibit excellent mechanical properties and have promising application prospects in engineering fields. Because natural spider silk fibers cannot be manufactured on a large scale, researchers have attempted to fabricate bio-inspired spider silks. However, the fabrication of bio-inspired spider silks with dynamically tunable mechanical properties and stimulation–response characteristics remains a challenge. Herein, the 4D printing of shape memory polyurethane is employed to produce dynamic bio-inspired spider silks. The bio-inspired spider silks have two types of energy-absorbing units that can be adjusted, one by means of 4D printing with predefined nodes, and the other through different stimulation methods to make the bio-inspired spider silks contract and undergo spiral deformation. The shape morphing behaviors of bio-inspired spider silks are programmed via pre-stress assemblies enabled by 4D printing. The energy-absorbing units of bio-inspired spider silks can be dynamically adjusted owing to stress release generated with the stimuli of temperature or humidity. Therefore, the mechanical properties of bio-inspired spider silks can be controlled to change dynamically. This can further help in developing applications of bio-inspired spider silks in engineering fields with dynamic changes of environment.

Electrospinning of spider silk‐based nanofibers

AbstractSpider silk has garnered attention as a structural material and a medical resource for next generation because it is tough, lightweight, and biodegradable. Nonwoven silk fabrics are emerging in research and industries owing to advanced electrospinning techniques. Several studies have reported nonwoven fabrics made of spider silk‐like proteins, which are originated from recombinant expression systems, with lower molecular weights than the natural counterpart. The lower molecular weight causes a lack of mechanical strength and durability, preventing the evaluation of industrial potential of the spider silk‐based nonwoven fabric to use as a structural and medical material. In this study, an electrospun nonwoven fabric is produced using native spider silk fibers forcibly reeled from live spiders. The spider silk‐based nonwoven fabrics demonstrate cell compatibility, and the mechanical properties are superior to the silkworm silk‐based nonwoven fabrics. The availability of spider silk‐based nonwoven fabrics introduces an unexplored set of potential uses, along with the context of sustainable development goals.

Spider-inspired regenerated silk fibroin fiber actuator via microfluidic spinning

Wild spider silks exhibit unique supercontraction and reversible contraction/expansion behavior with changes in humidity. These properties are highly desirable in applications such as mechanical actuators and artificial muscles. However, sources of such natural spider silk are insufficient for industrial and practical applications. Research on regenerated protein actuators is highly significant for the development of robotics in biological applications. Herein, we biomimick the novel humidity actuation of natural spider silks by regenerating the abundantly available silkworm silk fibroin using a microfluidic spinning technology. We successfully engineer the fibril alignment and diameter of the desired microfluidic-spun regenerated silk fibers (MRSFs) by controlling the dehydration and shearing of silk fibroins (SFs). These MRSFs exhibit a unique directional initial contraction property once exposed to humidity or organic solvents, which is caused by a transition of the mesoscopic hierarchical structure of SF molecules between the hydrophilic and hydrophobic domains. Further, the MRSFs can be directionally aligned on hydrophobic substrates, thus realizing the facile programming of the folding shapes and deformation manner. The MRSF actuators show a rapid response to humid conditions, as well as high stability and excellent repeatability. We apply the MRSF actuators to smart cargo carriage and convertible structural coloration, offering broad application prospects for biomedical, biocompatible, and biodegradable robotics.