Spider Silk Research Articles

Deformation and failure mechanisms in spider silk fibers

Spider silk fibers are protein materials that exhibit high strength and toughness thanks to a unique microstructure. In this work, a microscopically motivated model that sheds light on the underlying mechanisms behind the mechanical response of silk fibers is developed. The governing deformation mechanisms are as follows: initial stretching is enabled by the distortion of intermolecular hydrogen bonds that restrict the mobility of polypeptide chains. Once a sufficient force is applied, these bonds dissociate and the external load is transferred to the chains. Next, intramolecular β-sheets in the chains and/or the crystalline domains dissociate to provide additional chain length, thereby resulting in a macroscopic softening. Further deformation is enabled by the entropic elasticity of the chains, which stiffen with stretch. Based on the model, an algorithm to determine the overall constitutive response of silk fibers as a function of the initial distribution of chains and their composition is introduced. Experiments have shown that these two quantities can be controlled by supercontracting and dehydrating fibers under load. The model is validated through a comparison to various experimental findings at different alignment parameters. The merit of the model is three-fold: (1) it captures the microstructural evolution of the network as the fiber experiences stretch and reveals the role of key microstructural quantities such as chain-density, chain alignment, and chain composition, (2) it enables to compare between the microstructures of silk fibers produced by different spider species, and (3) it provides a platform for the microstructural design of biomimetic synthetic fibers with tunable properties.

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Spider silk is made of natural protein polymers and is known for its tradeoff between mutually exclusive strength and toughness. To simulate the spinning process of spiders in nature, the strong fibers are prepared by gene protein biotechnology and chemical synthesis. With their excellent properties, artificial spider silks can realize potential applications in biomedicine, smart wearables, artificial muscles and sensors, and aerospace. More details are discussed in the article by Liu et al. on page 3401—3418.image

Force-Induced Structural Changes in Spider Silk Fibers Introduced by ATR-FTIR Spectroscopy

Force-Induced Structural Changes in Spider Silk Fibers Introduced by ATR-FTIR Spectroscopy

Spider Silk-Inspired Binder Design for Flexible Lithium-Ion Battery with High Durability.

The development of flexible lithium-ion batteries (LIBs) imposes demands on energy density and high mechanical durability simultaneously. Due to the limited deformability of electrodes, as well as the flat and smooth surface of the metal current collectors, stable/durable/reliable contact between electrode materials and the current collectors remains a challenge, in particular, for electrodes with high loading mass and heavily deformed batteries. Binders play an essential role in binding particles of electrode materials and adhering them to current collectors. Herein, inspired by spider silk, a binder for flexible LIBs is developed, which equips a cross-linked supramolecular poly(urethane-urea) to the polyacrylic acid. The binder imparts super high elastic restorability originating from the meticulously engineered hydrogen-bonding segments as well as extraordinary adhesion. The developed binder provides excellent flexibility and intact electrode morphologies without disintegration even when the electrode is largely deformed, enabling a stable cycling and voltage output even when the batteries are put under tough dynamic deformation tests. The flexible LIBs exhibit a high energy density of 420WhL-1 , which is remarkably higher than reported numbers. The unique binder design is greatly promising and offers a valuable material solution for LIBs with high-loading mass and flexible designs.

Long-Jawed Spider Moves across Water with and without the Use of Silk

Among spiders, movement in aquatic environments, including below the water’s surface or on the surface film, is completed using a variety of techniques that do not involve the use of silk, including swimming, walking, and rowing. The use of silk to assist with aquatic locomotion has been explored only to a limited extent. In this study, we report on observations of a long-jawed spider (Family: Tetragnathidae) from Australia, Tetragnatha nitens, moving across the surface film in two different manners, one of which involves the use of silk. The first observation was of a female T. nitens walking across the water’s surface when prompted by a predation attempt: the spider used its front three pairs of legs for propulsion while the back pair remained motionless on the water, likely for stabilization. The second observation featured a male T. nitens utilizing a silk line to reel itself towards emergent vegetation while gliding across the water. Our findings support work on other long-jawed spiders, revealing that individual species can exploit several strategies for moving across water, including those that involve the use of silk. This study sheds light on the remarkable adaptability of spider silk and its potential use in aquatic systems.

Dynamics of Nanocomposite Hydrogel Alignment during 3D Printing to Develop Tissue Engineering Technology.

Taking inspiration from spider silk protein spinning, we developed a method to produce tough filaments using extrusion-based 3D bioprinting and salting-out of the protein. To enhance both stiffness and ductility, we have designed a blend of partially crystalline, thermally sensitive natural polymer gelatin and viscoelastic G-polymer networks, mimicking the components of spider silk. Additionally, we have incorporated inorganic nanoparticles as a rheological modifier to fine-tune the 3D printing properties. This self-healing nanocomposite hydrogel exhibits exceptional mechanical properties, biocompatibility, shear thinning behavior, and a well-controlled gelation mechanism for 3D printing.

Domain swap facilitates structural transitions of spider silk protein C-terminal domains.

Domain swap is a mechanism of protein dimerization where the two interacting domains exchange parts of their structure. Web spiders make use of the process in the connection of C-terminal domains (CTDs) of spidroins, the soluble protein building blocks that form tough silk fibers. Besides providing connectivity and solubility, spidroin CTDs are responsible for inducing structural transitions during passage through an acidified assembly zone within spinning ducts. The underlying molecular mechanisms are elusive. Here, we studied the folding of five homologous spidroin CTDs from different spider species or glands. Four of these are domain-swapped dimers formed by five-helix bundles from spidroins of major and minor ampullate glands. The fifth is a dimer that lacks domain swap, formed by four-helix bundles from a spidroin of a flagelliform gland. Spidroins from this gland do not undergo structural transitions whereas the others do. We found a three-state mechanism of folding and dimerization that was conserved across homologues. In chemical denaturation experiments the native CTD dimer unfolded to a dimeric, partially structured intermediate, followed by full unfolding to denatured monomers. The energetics of the individual folding steps varied between homologues. Contrary to the common belief that domain swap stabilizes protein assemblies, the non-swapped homologue was most stable and folded four orders of magnitude faster than a swapped variant. Domain swap of spidroin CTDs induces an entropic penalty to the folding of peripheral helices, thus unfastening them for acid-induced unfolding within a spinning duct, which primes them for refolding into alternative structures during silk formation.

Engineering Spider Genes for high-Tensile Silk and Patenting Challenges

This paper is a techno- legal review of existing scientific research, which explores the exciting field of genetic engineering and its potential in enhancing the tensile strength of spider silk through targeted modification of spider silk genes. Spider silk is renowned for its remarkable strength and flexibility, rendering it a highly coveted substance for many applications encompassing textiles, medical devices, and construction materials. However, its production on a large scale has been limited by the challenges of obtaining sufficient spider silk quantities. To overcome this limitation, researchers have turned to genetic engineering techniques to modify the genes responsible for spider silk production. This research delves into the development of novel techniques that enable precise and targeted modifications of these genes, aiming to enhance the tensile strength of spider silk even further. Additionally, this paper also addresses the legal challenges associated with patenting genetic modifications of spider silk genes. The unique nature of genetic engineering raises questions regarding patent eligibility, ownership, and potential infringement issues. This study discusses the current legal landscape surrounding patenting genetic modifications, including the criteria for patentability and the ethical considerations. By combining scientific advancements with legal insights, this research aims to contribute to the growing body of knowledge in the field of genetic engineering and provide a comprehensive understanding of the potential challenges and opportunities in enhancing spider silk's tensile strength and protecting intellectual property rights.

Strategies for Making High-Performance Artificial Spider Silk Fibers.

Artificial spider silk is an attractive material for many technical applications since it is a biobased fiber that can be produced under ambient conditions but still outcompetes synthetic fibers (e.g., Kevlar) in terms of toughness. Industrial use of this material requires bulk-scale production of recombinant spider silk proteins in heterologous host and replication of the pristine fiber's mechanical properties. High molecular weight spider silk proteins can be spun into fibers with impressive mechanical properties, but the production levels are too low to allow commercialization of the material. Small spider silk proteins, on the other hand, can be produced at yields that are compatible with industrial use, but the mechanical properties of such fibers need to be improved. Here, the literature on wet-spinning of artificial spider silk fibers is summarized and analyzed with a focus on mechanical performance. Furthermore, several strategies for how to improve the properties of such fibers, including optimized protein composition, smarter spinning setups, innovative protein engineering, chemical and physical crosslinking as well as the incorporation of nanomaterials in composite fibers, are outlined and discussed.

Steady Q-switched erbium-doped fiber laser pulse generation by exploiting spider silk as a passive saturable absorber

Spider silk is a biomaterial composed of natural protein that possesses unique strength and biocompatibility. Spider silk was explored for the first time that act as a potential saturable absorber (SA) for steady Q-switched erbium-doped fiber laser pulse generation around 1569 nm. The biocompatibility of spider silk SA will lead to the realization of an environment that is free from hazardous precursors and undesirable byproducts. In this study, spider silk was directly deposited onto the end face of the fiber ferrule to complete the fiberized SA assembly. In optical characteristic context, the modulation depth of spider silk SA used was 26 % and its saturation intensity was 0.02 MW/cm2. Results showed that self-started Q-switched at 30 mW threshold pump power was achieved. It was also interesting to find that the repetition rate of spider silk SA increased from 7 kHz to 29 kHz while the pulse width decreased from 32 µs to 10 µs. The signal-to-noise ratio (SNR) of the fundamental frequency was 54 dB, confirming the good stability of the pulsed laser. The highest output power and pulse energy measured at the pump power of 200 mW were 0.04 mW and 1.4 nJ respectively. In a nutshell, these results indicate that spider silk can be a viable alternative to real SA for producing laser at the 1570 nm region and spider silk-based SA can be equally with or even superior to the commonly employed SAs, which then opens up new possibilities for pulsed laser source applications.

The role of flow in the self-assembly of dragline spider silk proteins

Hydrodynamic flow in the spider duct induces conformational changes in dragline spider silk proteins (spidroins) and drives their assembly, but the underlying physical mechanisms are still elusive. Here we address this challenging multiscale problem with a complementary strategy of atomistic and coarse-grained molecular dynamics simulations with uniform flow. The conformational changes at the molecular level were analyzed for single-tethered spider silk peptides. Uniform flow leads to coiled-to-stretch transitions and pushes alanine residues into β sheet and poly-proline II conformations. Coarse-grained simulations of the assembly process of multiple semi-flexible block copolymers using multi-particle collision dynamics reveal that the spidroins aggregate faster but into low-order assemblies when they are less extended. At medium-to-large peptide extensions (50%–80%), assembly slows down and becomes reversible with frequent association and dissociation events, whereas spidroin alignment increases and alanine repeats form ordered regions. Our work highlights the role of flow in guiding silk self-assembly into tough fibers by enhancing alignment and kinetic reversibility, a mechanism likely relevant also for other proteins whose function depends on hydrodynamic flow.

Preparation of Strong and Thermally Conductive, Spider Silk-Inspired, Soybean Protein-Based Adhesive for Thermally Conductive Wood-Based Composites.

The development of formaldehyde-free functional wood composite materials through the preparation of strong and multifunctional soybean protein adhesives to replace formaldehyde-based resins is an important research area. However, ensuring the bonding performance of soybean protein adhesive while simultaneously developing thermally conductive adhesive and its corresponding wood composites is challenging. Taking inspiration from the microphase separation structure of spider silk, boron nitride (BN) and soy protein isolate (SPI) were mixed by ball milling to obtain a BN@SPI matrix and combined with the self-synthesized hyperbranched reactive substrates as amorphous region reinforcer and cross-linker triglycidylamine to prepare strong and thermally conductive soybean protein adhesive with cross-linked microphase separation structure. These findings indicate that mechanical ball milling can be employed to strip BN followed by combination with SPI, resulting in a tight bonded interface connection. Subsequently, the adhesive's dry and wet shear strengths increased by 14.3% and 90.5% to 1.83 and 1.05 MPa, respectively. The resultant adhesive also possesses a good thermal conductivity (0.363 W/mK). Impressively, because hot-pressing helps the resultant adhesive to establish a thermal conduction pathway, the thermal conductivity of the resulting wood-based composite is 10 times higher than that of the SPI adhesive, which shows a thermal conductivity similar to that of ceramic tile and has excellent potential for developing biothermal conductivity materials, geothermal floors, and energy storage materials. Moreover, the adhesive possessed effective flame retardancy (limit oxygen index = 36.5%) and mildew resistance (>50 days). This bionic design represents an efficient technique for developing multifunctional biomass adhesives and composites.

Designed Multifunctional Spider Silk Enabled by Genetically Encoded Click Chemistry (Adv. Funct. Mater. 43/2023)

Designed Multifunctional Spider Silk Enabled by Genetically Encoded Click Chemistry (Adv. Funct. Mater. 43/2023)

A bioinspired synthetic fused protein adhesive from barnacle cement and spider dragline for potential biomedical materials

Biomaterials with excellent biocompatibility, mechanical performance, and self-recovery properties are urgently needed for tissue regeneration. Inspired by barnacle cement and spider silk, we genetically designed and overexpressed a fused protein (cp19k-MaSp1) composed of Megabalanus rosa (cp19k) and Nephila clavata dragline silk protein (MaSp1) in Pichia pastoris. The recombinant cp19k-MaSp1 exhibited enhanced adhesion capability beyond those of the individual proteins in both aqueous and non-aqueous conditions. cp19k-MaSp1 protein fiber scaffolds prepared through electrospinning have adequate hydrophilicity compared to cp19k and MaSp1 protein fiber scaffolds, and offer improved overall porosity compared to MaSp1 protein fiber scaffolds. The cp19k-MaSp1 protein fiber scaffolds showed excellent proteolytically stable properties because of only 9.6 % depletion after incubation in a biodegradation solution for 56 d. The cp19k-MaSp1 protein fiber scaffolds present remarkably high extreme tensile strength (112.7 ± 11.6 MPa) and superior ductility (438.4 ± 43.9 %) compared with cp19k (34.4 ± 8.1 MPa, 115.4 ± 32.7 %) and MaSp1 protein fiber scaffolds (65.8 ± 9.3 MPa, 409.6 ± 23.1 %), also 68.4 % of tensile strength was recovered by incubation in K+ buffer after multiple stretches, which create a favorable cell adhesion, growth, and proliferation environment for human umbilical vein endothelial cells (HUVECs). The improved biocompatibility, extensive adhesion, mechanical strength, and self-recovery properties make the bioinspired synthetic cp19k-MaSp1 a potential candidate for biomedical tissue reconstruction.

Could an Anterior Cruciate Ligament Be Tissue-Engineered from Silk?

Silk has a long history as an exclusive textile, but also as a suture thread in medicine; nowadays, diverse cell carriers are manufactured from silk. Its advantages are manifold, including high biocompatibility, biomechanical strength and processability (approved for nearly all manufacturing techniques). Silk's limitations, such as scarcity and batch to batch variations, are overcome by gene technology, which allows for the upscaled production of recombinant "designed" silk proteins. For processing thin fibroin filaments, the sericin component is generally removed (degumming). In contrast to many synthetic biomaterials, fibroin allows for superior cell adherence and growth. In addition, silk grafts demonstrate superior mechanical performance and long-term stability, making them attractive for anterior cruciate ligament (ACL) tissue engineering. Looking at these promising properties, this review focusses on the responses of cell types to silk variants, as well as their biomechanical properties, which are relevant for ACL tissue engineering. Meanwhile, sericin has also attracted increasing interest and has been proposed as a bioactive biomaterial with antimicrobial properties. But so far, fibroin was exclusively used for experimental ACL tissue engineering approaches, and fibroin from spider silk also seems not to have been applied. To improve the bone integration of ACL grafts, silk scaffolds with osteogenic functionalization, silk-based tunnel fillers and interference screws have been developed. Nevertheless, signaling pathways stimulated by silk components remain barely elucidated, but need to be considered during the development of optimized silk cell carriers for ACL tissue engineering.

Highly strong and tough silk by feeding silkworms with rare earth ion-modified diets

Nature-derived silk fibers possess excellent biocompatibility, sustainability, and mechanical properties, yet producing strong and tough silk fibers in a facile and large-scale manner remains a significant challenge. Herein, we report a simple method for preparing strong and tough silk fibers by feeding silkworms rare earth ion-modified diets. The resulting silk fibers exhibit significantly increased tensile strength and toughness, with average values of 0.85 ± 0.07 GPa and 156 ± 13 MJ m−3, respectively, and maximum values of 0.97 ± 0.04 GPa and 188 ± 19 MJ m−3, approaching those of spider dragline silk. Our findings suggest that the incorporation of rare earth ions (La3+ or Eu3+) into the silk fibers contributes to this enhancement. Structure analysis reveals a reduction in content and an improvement in orientation of β-sheet nanocrystals in silk fibers. X-ray photoelectron spectroscopy analysis confirms the chemical interaction between rare earth ions with β-sheet nanocrystals. The structural evolution and chemical interactions lead to the simultaneous enhancement in both strength and toughness. This work presents a simple, scalable, and effective strategy for producing ultra-strong and tough silk fibers with potential applications in areas requiring super structural materials, such as personal protection and aerospace.

UV-curing polyurethane pressure-sensitive adhesive with high shear strength and good adhesion properties inspired by spider silk

It is a challenge to develop polyurethane pressure-sensitive adhesive (PU-PSA) simultaneously with good cohesion and adhesion properties. Inspired by the structure of multiple hydrogen bonds in spider silk, we introduced Acylsemicarbazide (ASCZ) moiety that can form multiple hydrogen bonds in the polymer network into PU-PSA. The characteristic absorption peaks of ester groups at 1600–1780 cm−1 were analyzed in FTIR testing, and the results showed that ASCZ formed multiple hydrogen bonds in PU-PSA, and the hydrogen bond content increased with the increase of ASCZ content. In particular, PUA-AD20% with 24.3 % hydrogen bond content showed higher shear strength (0.51 MPa) and debonding energy (3.3 KJ m−2). Rheological tests showed that PU-PSA storage modulus and loss modulus increased with increasing frequency, which was highly frequency dependent. Therefore, as dynamic and reversible sacrificial bonds, hydrogen bonds can dissipate energy efficiently and resist external forces. In addition, the ASCZ component also provided PU-PSA with the polar groups required for adhesion. Therefore, PUA-AD20% had excellent adhesion properties. Compared to PUA, PUA-AD20% tack and peel strength increased by 36.1 % and 146.8 %, with values of 4.9 N and 11.6 N, respectively. In summary, this work offered a simple and versatile approach to designing PU-PSA with outstanding overall performance.

High strength, high stiffness and toughness, defect‐tolerant waterborne polyurethane with healing and antibacterial abilities

AbstractThe nature creates many biomaterials such as spider silk which exhibits a combination of stiffness, strength and toughness. However, most of synthetic unfilled materials suffer from a trade‐off between toughness and stiffness. Inspired by the structure of spider silk but beyond it, we proposed a novel molecular design to achieve transparent unfilled waterborne polyurethane (WPU) with simultaneously enhanced stiffness (280.9 MPa), tensile strength (25.1 MPa) and toughness (140.0 MJ/m3) as well as good elasticity (710%). The designed WPU comprised homogeneous continuous phase (soft segments) and diverse H‐bonds (hard segments) dispersed in it. The increase of rigid molecular chain content and H‐bonds contributed to the high stiffness of WPU. Furthermore, the mismatch of stiffness between hard domains and soft segments might promote crack deflection and branching, which endowed the robust WPU with fracture energy of 81.16 kJ/m2. The robust WPU film could be healed to recover most of its original mechanical properties (strength for 24.4 MPa and elongation for 610%) under heating. In addition, the WPU films demonstrated good antibacterial performance against Staphylococcus aureus and Escherichia coli after chlorination.

High-strength and ultra-tough whole spider silk fibers spun from transgenic silkworms

High-strength and ultra-tough whole spider silk fibers spun from transgenic silkworms

Research Progress on Spider‐Inspired Tough Fibers†

Comprehensive SummarySpider silk has attracted increasing attention due to its fascinating combination of ultra‐high tenacity high strength, and excellent elasticity. Based on the fundamental biological studies on spider silk, significant research efforts have been devoted to biotechnology and chemical synthesis to mimic or even exceed the properties of natural spider silk fibers. Moreover, the natural spider silk fiber has been simulated with the burgeoning development of numerous spinning technologies, including wet spinning, dry spinning, electrostatic spinning, and microfluidic spinning, which continuously help to optimize the properties of synthetic spider silk. The unique characteristics of natural spider silk include high refraction transmission, heat resistance, antimicrobial properties, biocompatibility, and super shrinking. Biconical recreation of spider silk with special features and extraordinary capabilities demonstrates potential applications in biomedicine, smart wearables, artificial muscles and sensors, aerospace and other domains.