Natural Spider Silk Research Articles

Fibers Made of Recombinant Spidroins—A Brief Review

Spider silk is a promising biomaterial, with a wide range of potential applications in the medical, military, and commercial sectors. In the past decade, researchers have been developing recombinant spider silk (RSS) proteins with the help of advanced genetic engineering techniques, including gene design, cloning, and protein expression in different foreign hosts. The extraordinary strength and extensibility of natural spider silk fiber are constituted from the tandemly repeated amino acid sequences and antiparallel crystalline β-sheet segments formed by polyalanine motifs. Additionally, mechanical properties are also influenced by extrusion and drawing of fibers in the natural spinning process. To date, the wet spinning process was found to be a commercially successful method for spinning recombinant silks with properties comparable to their natural counterparts.

Structure Design and Property of Spider silk-Inspired Shape Memory Materials

Abstract Study on biomimetic materials inspired by natural spider silk has been a hot topic. Inspired by the shape memory behavior of spider silk, thermo-responsive shape memory polypeptide with β-sheet structure was reported, and silk fibroin with β-sheet structure is incorporated into poly(vinyl alcohol) to develop a novel water-sensitive two-way shape memory material. The β-sheet structures act as netpoints responsible for the achievement of good shape recovery ability and high shape fixity. These materials not only possess biocompatibility and nontoxicity, but also have ease to be fabricated, which will be used in many biomedical applications. This study not only provides a new idea for designing intelligent materials, expands the development of bionic and intelligent materials, but also helps to improve the establishment of shape memory theory system and lay a solid theoretical foundation for the further development of shape-memory polymer materials.

High strength structural protein material derived from natural spider silk

High strength structural protein material derived from natural spider silk

Hierarchical fibers for water collection inspired by spider silk

Water scarcity plagues two-thirds of the global population. Interestingly, researchers have found that spider silk exhibits excellent water-collection ability owing to its unique structure and chemical components. Based on this characteristic, numerous bioinspired fibers have been fabricated for water collection. Herein, we review the water-collection process for spider silk and recent vital advances in bioinspired fibriform materials, focusing on the water-collection mechanisms of spindle-knot fibers, which exhibit directional droplet transport, hanging mechanism and hanging ability. Also, we evaluated their water-collection abilities on a micro- and macro-scale, which gave a better view for the design of bioinspired water-collection materials. These advances enable the significant use of bioinspired fibers in water collection, which may be applied in several other fields, such as directional transport, tissue engineering, oil-water separation and biosensors.

Biomimetic Supertough and Strong Biodegradable Polymeric Materials with Improved Thermal Properties and Excellent UV‐Blocking Performance

AbstractThe preparation of biodegradable polymeric materials with both great strength and toughness remains a huge challenge. The natural spider silk exhibits a combined super high tensile strength and high fracture toughness (150–190 J g−1), attributing to the hierarchically assembled nanophase separation and the densely organized sacrificial hydrogen bonds confined in the nanoscale granules. Herein, inspired by natural spider silk, a facile strategy is reported for the preparation of nanostructured biomimetic polymeric material by incorporating biomass‐derived lignosulfonic acid (LA) as interspersed nanoparticles into a biodegradable poly(vinyl alcohol) (PVA) matrix. The fabricated PVA/LA nanocomposite film exhibits the world's highest toughness of 172 (±5) J g−1 among the PVA materials, as well as a powerful tensile strength of 98.2 MPa and a large breaking strain of 282%. The outstanding performance is attributed to the strain‐induced scattering of LA nanoparticles in the PVA matrix and the strong intermolecular sacrificial hydrogen bonds confined in the interphase. Moreover, after introducing the easily available green biomass LA, the prepared biomimetic polymer films show excellent ultraviolet‐blocking performance and good thermal stability. As both PVA and LA are biodegradable, this work presents an innovative design strategy for fully biodegradable robust polymeric materials with integrated strength and toughness.

Strength of Recluse Spider's Silk Originates from Nanofibrils.

Spider silk exhibits a combination of outstanding tensile strength and extensibility unique among all synthetic and biogenic polymer fibers. It has thus generated great interest to understand protein-based high-toughness materials and inspired the design of similar synthetic materials. The unrivaled properties of silk fibers have been recognized to be intimately related to their hierarchical structure. However, in the absence of unambiguous experimental evidence, competing and incompatible structural models of natural silk fibers have been proposed, some of them including various types of fibrillar components. Here we show that the fibers of the recluse (Loxosceles) spider exhibit the typical tensile properties of a very good spider silk and are entirely composed of 20 nm diameter protein fibrils that are more than 1 μm long. Based on these findings, we developed the most detailed structural model for any silk directly supported by experimental evidence. Our work suggests that all the key properties of a spider silk are implemented within a single nanofibril, and we have isolated and imaged such a nanofibril from a native spider silk fiber. The nanofibril breaking force was estimated to be ≈120 nN. Our work underlines the importance of nanofibrils and furthers the understanding of the structure-property relationships of silk, with wide-ranging implications for silk research and the design of silk-inspired high-performance materials.

Major ampullate silk gland transcriptomes and fibre proteomes of the golden orb-weavers, Nephila plumipes and Nephila pilipes (Araneae: Nephilidae).

Natural spider silk is one of the world’s toughest proteinaceous materials, yet a truly biomimetic spider silk is elusive even after several decades of intense focus. In this study, Next-Generation Sequencing was utilised to produce transcriptomes of the major ampullate gland of two Australian golden orb-weavers, Nephila plumipes and Nephila pilipes, in order to identify highly expressed predicted proteins that may co-factor in the construction of the final polymer. Furthermore, proteomics was performed by liquid chromatography tandem-mass spectroscopy to analyse the natural solid silk fibre of each species to confirm highly expressed predicted proteins within the silk gland are present in the final silk product. We assembled the silk gland transcriptomes of N. plumipes and N. pilipes into 69,812 and 70,123 contigs, respectively. Gene expression analysis revealed that silk gene sequences were among the most highly expressed and we were able to procure silk sequences from both species in excess of 1,300 amino acids. However, some of the genes with the highest expression values were not able to be identified from our proteomic analysis. Proteome analysis of “reeled” silk fibres of N. plumipes and N. pilipes revealed 29 and 18 proteins, respectively, most of which were identified as silk fibre proteins. This study is the first silk gland specific transcriptome and proteome analysis for these species and will assist in the future development of a biomimetic spider silk.

Recombinant Spidroins Fully Replicate Primary Mechanical Properties of Natural Spider Silk.

Despite significant efforts to engineer their heterologous production, recombinant spider silk proteins (spidroins) have yet to replicate the unparalleled combination of high strength and toughness exhibited by natural spider silks, preventing their use in numerous mechanically demanding applications. To overcome this long-standing challenge, we have developed a synthetic biology approach combining standardized DNA part assembly and split intein-mediated ligation to produce recombinant spidroins of previously unobtainable size (556 kDa), containing 192 repeat motifs of the Nephila clavipes dragline spidroin. Fibers spun from our synthetic spidroins are the first to fully replicate the mechanical performance of their natural counterparts by all common metrics, i.e., tensile strength (1.03 ± 0.11 GPa), modulus (13.7 ± 3.0 GPa), extensibility (18 ± 6%), and toughness (114 ± 51 MJ/m3). The developed process reveals a path to more dependable production of high-performance silks for mechanically demanding applications while also providing a platform to facilitate production of other high-performance natural materials.

Feasibility Study of Selecting Soft Components of Body Armor

A body armor is vital for users in combat filed. Normally, the body armor have two components: soft and hard ones. This paper proposes feasibility assessment technique to evaluate contemporary materials: Kevlar, natural spider silk, and human hair, for making soft component of the body armor. There are four criteria: technical, economic, legal, and operational feasibilities to generate the feasibility assessment matrix. The optimal material in question is human hair which has highest rank at 82%.

Preliminary investigations of spider silk in wounds in vivo — Implications for an innovative wound dressing

The ideal wound dressing in particular for burn wounds has not been found yet. The aim of this study was to investigate native spider silk as a novel wound dressing.Release of inflammatory cytokines of macrophages and neutrophile granulocytes was determined via ELISA after exposure to spider silk. Migration of dermal cells as well as angiogenesis on spider silk was visualized with live video microscopy or chorioallantois membrane model, respectively. Native spider silk was placed in full-thickness skin wounds in a sheep in vivo-model and wounds were evaluated after 2, 4, 6, and 8weeks histologically as well as per quantitative real-time PCR.Minimal inflammatory cytokine release could be seen for spider silk. Ingrowth of single capillaries into bundles of spider silk and migration of keratinocytes as well as fibroblasts on spider silk fibres was proven. Macroscopically, a comparable wound closure could be seen in spider silk and in sham controls. In histological evaluation, a thicker epidermis was observed in spider silk treated wounds while collagen III/I expression ratio was comparable in both groups.As native spider silk has been described as highly biocompatible, it might represent an innovative alternative to common wound dressings.

Polymorphic regenerated silk fibers assembled through bioinspired spinning

A variety of artificial spinning methods have been applied to produce regenerated silk fibers; however, how to spin regenerated silk fibers that retain the advantages of natural silks in terms of structural hierarchy and mechanical properties remains challenging. Here, we show a bioinspired approach to spin regenerated silk fibers. First, we develop a nematic silk microfibril solution, highly viscous and stable, by partially dissolving silk fibers into microfibrils. This solution maintains the hierarchical structures in natural silks and serves as spinning dope. It is then spun into regenerated silk fibers by direct extrusion in the air, offering a useful route to generate polymorphic and hierarchical regenerated silk fibers with physical properties beyond natural fiber construction. The materials maintain the structural hierarchy and mechanical properties of natural silks, including a modulus of 11 ± 4 GPa, even higher than natural spider silk. It can further be functionalized with a conductive silk/carbon nanotube coating, responsive to changes in humidity and temperature.

Foundation of the Outstanding Toughness in Biomimetic and Natural Spider Silk.

Spider dragline silk is distinguished through the highest toughness of all natural as well as artificial fiber materials. To unravel the toughness's molecular foundation and to enable manufacturing biomimetic analogues, we investigated the morphological and functional structure of recombinant fibers, which exhibit toughness similar to that of the natural template, on the molecular scale by means of vibrational spectroscopy and on the mesoscale by X-ray scattering. Whereas the former was used to identify protein secondary structures and their alignment in the natural as well as artificial silks, the latter revealed nanometer-sized crystallites on the higher structural level. Furthermore, a spectral red shift of a crystal-specific absorption band demonstrated that macroscopically applied stress is directly transferred to the molecular scale, where it is finally dissipated. Concerning this feature, both the natural as well as the biomimetic fibers are almost indistinguishable, giving rise to the toughness of both fiber materials.

Exploring the Use of Native Spider Silk as an Optical Fiber for Chemical Sensing

A spider uses up to seven different types of silk, all having specific functions, as building material, weapon, and sensory organ to detect the presence of preys on its web. Recently, scientists have put under the limelight the extraordinary properties of this ancient material. Indeed, native silk, directly extracted from spiders, is a tough, biodegradable, and biocompatible thread used mainly for tissue engineering and textile applications. Blessed with outstanding optical properties, this protein strand can also be used as a bioresorbable optical fiber and is, moreover, intrinsically sensitive to chemical compounds. In this communication, the waveguiding properties of native dragline silk are assessed and a pioneering proof-of-concept experiment using pristine spider silk as an optical fiber to measure humidity content is demonstrated. The feasibility of using silk-based optical fiber chemical sensors is also discussed.

Spider silk foam coating of fabric

Abstract Silks are well known natural fibers used for textile applications and have got for the first time available upon sericulture of silkworms (Bombyx mori) several thousand years ago in China. In contrast to silkworm silk, spider silks offer better mechanical properties such as higher tensile strength and much better toughness, but natural spider silk is less accessible due to the cannibalistic behavior of spiders prohibiting large scale farming, and therefore has not been employed in textile industry yet. In this study, a biotechnologically produced spider silk protein was introduced as a new material for textile applications in form of foam coating material. The spider silk foam coating was developed to increase the abrasion behavior of natural and polymeric furniture textiles. Modern textiles are high-tech materials and optimized concerning yarn design and fabric weave to fit a wide range of applications. Often hydrofluorocarbons based coatings are used to enhance textile performances. Upon coating with sustainable spider silk, yarn fraying was significantly reduced lowering the tendency to form knots and loops. Further, the textile abrasion resistance, analyzed by pilling tests, was improved significantly (17–200%) for all tested types of fabrics, in particular long term strain pilling was minimized.

Influence of direct or indirect contact for the cytotoxicity and blood compatibility of spider silk.

Spider silk became one of the most-researched biomaterials in the last years due to its unique mechanical strength and most favourable chemical composition for tissue engineering purposes. However, standardized analysis of cytocompatibility is missing. Therefore, the aim of this study was to investigate hemolysis, cytotoxicity of native spider silk as well as influences on the cell culture medium. Changes of cell culture medium composition, osmolarity as well as glucose and lactate content were determined via ELISA measurement. Possible hemolysis and cytotoxicity in vitro of spider silk were performed via measurement of hemoglobin release of human red blood cells or relative metabolic activity of L929 fibroblasts, respectively, according to international standard procedures. In ELISA measurement, no significant changes in medium composition could be found in this study. Spider silk was not hemolytic in direct and indirect testing. However, a borderline cytotoxicity according to definitions was found in indirect cytotoxicity testing. Nevertheless, in direct cytotoxicity testing, relative metabolic activity measurement revealed that spider silk is not cytotoxic under these conditions. This is the first study to conduct standardized tests regarding cytotoxicity and hemolysis of native spider silk, which might be considered inert in cell culture. As neither hemolysis nor cytotoxicity was found in direct contact in standardized procedures, safety in biomedical applications may be assumed. The indirect cytotoxicity seems to play a minor role in vivo. However, a borderline toxicity was revealed, suggesting potential leachables not yet identified. Displays one of the weaving frames used in this study after seeding with the single drop technique described herein.

A Leishmania secretion system for the expression of major ampullate spidroin mimics.

Spider major ampullate silk fibers have been shown to display a unique combination of relatively high fracture strength and toughness compared to other fibers and show potential for tissue engineering scaffolds. While it is not possible to mass produce native spider silks, the potential ability to produce fibers from recombinant spider silk fibers could allow for an increased innovation rate within tissue engineering and regenerative medicine. In this pilot study, we improved upon a prior fabrication route by both changing the expression host and additives to the fiber pulling precursor solution to improve the performance of fibers. The new expression host for producing spidroin protein mimics, protozoan parasite Leishmania tarentolae, has numerous advantages including a relatively low cost of culture, rapid growth rate and a tractable secretion pathway. Tensile testing of hand pulled fibers produced from these spidroin-like proteins demonstrated that additives could significantly modify the fiber’s mechanical and/or antimicrobial properties. Cross-linking the proteins with glutaraldehyde before fiber pulling resulted in a relative increase in tensile strength and decrease in ductility. The addition of ampicillin into the spinning solution resulted in the fibers being able to inhibit bacterial growth.

Synthetic Engineering of Spider Silk Fiber as Implantable Optical Waveguides for Low-Loss Light Guiding.

A variety of devices used for biomedical engineering have been fabricated using protein polymer because of their excellent properties, such as strength, toughness, biocompatibility, and biodegradability. In this study, we fabricated an optical waveguide using genetically engineered spider silk protein. This method has two significant advantages: (1) recombinant spider silk optical waveguide exhibits excellent optical and biological properties and (2) biosynthesis of spider silk protein can overcome the limitation to the research on spider silk optical waveguide due to the low yield of natural spider silk. In detail, two kinds of protein-based optical waveguides made from recombinant spider silk protein and regenerative silkworm silk protein were successfully prepared. Results suggested that the recombinant spider silk optical waveguide showed a smoother surface and a higher refractive index when compared with regenerative silkworm silk protein. The optical loss of recombinant spider silk optical waveguide was 0.8 ± 0.1 dB/cm in air and 1.9 ± 0.3 dB/cm in mouse muscles, which were significantly lower than those of regenerative silkworm silk optical waveguide. Moreover, recombinant spider silk optical waveguide can meet the demand to guide and efficiently deliver light through biological tissue. In addition, recombinant spider silk optical waveguide showed low toxicity to cells in vitro and low-level inflammatory reaction with surrounding tissue in vivo. Therefore, recombinant spider silk optical waveguide is a promising implantable device to guide and deliver light with low loss.

Thermal characterization of natural and synthetic spider silks by both the 3ω and transient electrothermal methods

Thermal conductivity, thermal diffusivity, and volumetric heat capacity of three spider silks are measured in this paper as a benchmark for further studies. These silks include the major and minor ampullate silks of the Nephila clavipes spider, and a synthetic spider silk fiber made from recombinant dragline silk proteins purified from transgenic goats' milk. Two complementary measurement techniques are employed in the thermal characterization of these microscale single fibers for self-verification. One is the transient electrothermal technique (TET) and the other is the 3ω method. Experimental measurements indicate that thermal properties of the dragline silk are very close to those of the minor ampullate silk, whereas the ones for the synthetic silk are much lower due in part to its low crystallinity. The directly measured thermal conductivity, thermal diffusivity, and volumetric heat capacity of the major and minor ampullate silks are 1.2–1.26Wm−1K−1, 5.7–6×10−7m2s−1, and 2–2.17 MJm−3K−1, respectively. The thermal conductivity and thermal diffusivity of the as-spun synthetic silk are 0.24Wm−1K−1 and 1.6×10−7m2s−1 respectively. As part of this study, a detailed comparison of the TET and 3ω methods is provided showing the complementary nature of the techniques and illustrating the strengths and weaknesses of each.

Biomimetic spinning of artificial spider silk from a chimeric minispidroin.

Herein we present a chimeric recombinant spider silk protein (spidroin) whose aqueous solubility equals that of native spider silk dope and a spinning device that is based solely on aqueous buffers, shear forces and lowered pH. The process recapitulates the complex molecular mechanisms that dictate native spider silk spinning and is highly efficient; spidroin from one liter of bacterial shake-flask culture is enough to spin a kilometer of the hitherto toughest as-spun artificial spider silk fiber.

Recombinant spider silk from aqueous solutions via a bio-inspired microfluidic chip.

Spiders achieve superior silk fibres by controlling the molecular assembly of silk proteins and the hierarchical structure of fibres. However, current wet-spinning process for recombinant spidroins oversimplifies the natural spinning process. Here, water-soluble recombinant spider dragline silk protein (with a low molecular weight of 47 kDa) was adopted to prepare aqueous spinning dope. Artificial spider silks were spun via microfluidic wet-spinning, using a continuous post-spin drawing process (WS-PSD). By mimicking the natural spinning apparatus, shearing and elongational sections were integrated in the microfluidic spinning chip to induce assembly, orientation of spidroins, and fibril structure formation. The additional post-spin drawing process following the wet-spinning section partially mimics the spinning process of natural spider silk and substantially contributes to the compact aggregation of microfibrils. Subsequent post-stretching further improves the hierarchical structure of the fibres, including the crystalline structure, orientation, and fibril melting. The tensile strength and elongation of post-treated fibres reached up to 510 MPa and 15%, respectively.