Polymorphic regenerated silk fibers assembled through bioinspired spinning

An in-situ assembled cobweb-like adhesive with high processability

Low temperature tolerant adhesive with high flexibility and adhesion strength is highly desired yet challenging owing to the presence of obvious volume shrinkage, increased brittleness, and reduced transmission of mechanical stress at low temperature. Inspired by the cobweb, we hereby develop a kind of flexible adhesive that can be used at low temperature by in-situ polymerization of disulfide bond-based polymer with polyoxometalate. This low-temperature tolerant adhesive presents high flexibility and adhesion strength, good processability and reversible adhesion ability, a wide tolerable temperature range (i.e., -196 to 50 °C), and a long-lasting adhesion effect (>80 days, -196 °C) that is significantly better than commercial solvent-free adhesives. The adhesive can be processed into high-strength cobwebs, injected into tiny tube models, and adhered onto complicated interfaces. Notably, it enables to be kilogram-scale produced through a solvent-free method, holding promise for potential utilization in fields like repairing artifacts or precision instruments with micro-fractures at low temperature.

Hierarchical design of silkworm silk for functional composites

Silk-reinforced composites (SRCs) manifest the unique properties of silkworm silk fibers, offering enhanced mechanical strength, biocompatibility, and biodegradability. These composites present an eco-friendly alternative to conventional synthetic materials, with applications expanding beyond biomedical engineering, flexible electronics, and environmental filtration. This review explores the diverse forms of silkworm silk fibers including fabrics, long fibers, and nanofibrils, for functional composites. It highlights advancements in composite design and processing techniques that allow precise engineering of mechanical and functional performance. Despite substantial progress, challenges remain in making optimally functionalized SRCs with multi-faceted performance and understanding the mechanics for reverse-design of SRCs. Future research should focus on the unique sustainable, biodegradable and biocompatible advantages and embrace advanced processing technology, as well as artificial intelligence-assisted material design to exploit the full potential of SRCs. This review on SRCs will offer a foundation for future advancements in multifunctional and high-performance silk-based composites.

Biopolymer based Fibrous Aggregate Materials for Diagnosis and Treatment: Design, Manufacturing, and Applications

Biopolymer-based fibrous aggregate materials (BFAMs) have gained increasing attention in biomedicine due to their excellent biocompatibility, processability, biodegradability, and multifunctionality. Especially, the medical applications of BFAMs demand advanced structure, performance, and function, which conventional trial-and-error methods struggle to provide. This necessitates the rational selection of materials and manufacturing methods to design BFAMs with various intended functions and structures. This review summarizes the current progress in raw material selection, structural and functional design, processing technology, and application of BFAMs. Additionally, the challenges encountered during the development of BFAMs are discussed, along with perspectives for future research offered.

Molecular Dynamics Simulation of Self-Assembly and Tensile Deformation of Silk-Mimetic Polymers

Silk is a natural biopolymer with outstanding mechanical properties due to its nanocomposite microstructure of crystalline β-sheets in an amorphous matrix. However, there remains a lack of understanding of the relationship between amino acid sequence, supramolecular structure formation, and mechanical properties. In this work, we developed a reactive coarse-grained molecular dynamics model to simulate the self-assembly, tensile deformation, and fracture of a segmented copolymer based on the repetitive core domain of spider dragline spidroins. We find that the β-sheet nanocrystal content is determined by the length ratio of β-sheet to non-β-sheet segments. We reveal that the chain length affects the chain-to-chain network connectivity between the nanocrystals. High nanocrystal content and high connectivity improve the strength and stiffness at the cost of extensibility. Toughness does not continue to increase past a threshold β-sheet-to-non-sheet segment ratio. Our findings provide important insights to guide the rational molecular design of silk-mimetic materials.

Photo-synthesis of sensing silk fibroin fibers with double-network structures

Toughened fibers are highly desirable for a wide range of practical applications, particularly in biomedical and textile industries. Herein, robust silk fibroin fibers with a double-network (DN) structure were successfully fabricated using an in situ photo-polymerization process after swelling. The DN fibers were characterized in terms of morphology, secondary structure, alkali resistance, and tensile properties. These fibers demonstrated remarkable tensile strength in both dry and wet states, along with enhanced alkali resistance, making them highly suitable for demanding environments. Another key advancement in this study is the incorporation of a chromatic biosensor into the DN silk suture, enabling the fibers to undergo a visible blue-to-red color change upon exposure to bacterial strains, both to the naked eye and under a microscope. This color change is essential for bacterial sensing, enabling real-time detection and providing an effective tool for infection monitoring and biosensors in surgical sutures.

Manipulating the Assembly and Architecture of Fibrillar Silk

Silk is a unique and exceptionally strong biological material. However, no synthetic method has yet come close to replicating the properties of natural silk. This shortfall is attributed to an insufficient understanding of both silk nanofibril structure and the mechanism of formation. Here in situ atomic force microscopy (AFM) and photo-induced force microscopy (PiFM) is utilized to investigate the formation process and define the basic structural paradigm of individual silk nanofibrils. By visualizing the multistage process of silk nanofibril formation, the importance of conformational transformations along the assembly pathway is revealed. Unfolded silk structures initially accumulate into amorphous clusters, which then evolve into crystal nuclei via conformational transformation into β-crystallites. Nanofibril elongation then occurs through the attachment of silk molecules at a single end of the nanofibril tip; this is facilitated through the formation of a new amorphous cluster that then repeats the aforementioned conformational transformation. However, enzymatic digestion of the amorphous regions leads to direct, rapid elongation of β-crystalline fibers. These findings imply that the energy landscape is characterized by shallow minima associated with intermediate states, which can be eliminated by introducing β-crystallites, and motivate research into the directed modification of the silk assembly pathway to select for features beneficial to specific applications.

High-Efficiency Dry-Jet Wet Spinning of Ultratoughness Regenerated Wool Keratin Fibers

Regenerated wool keratin fibers (RWKFs) featuring their ecofriendliness, ample resources, and intrinsic biocompatibility have attracted significant interest, while their high-value-added applications are still severely limited by inadequate mechanical properties and complex fabrication processes. Herein, a straightforward dry-jet wet spinning technique without post-treatment processes is proposed to prepare ultratoughness RWKFs. The as-spun fibers achieve a macroscale hierarchical structure due to the preorientation of nanoscale α-keratin protofibrils in air-gap drawing of dry-jet wet spinning, while α-keratins are preserved in large quantities because of no additional post-treatment stretching. As a result, the fabricated RWKFs achieve a tensile strength of ∼142.7 MPa, an outstanding elongation of ∼171.7%, and a record high toughness of ∼176.3 MJ m-3, outperforming natural wool and previously reported regenerated keratin fibers. Moreover, the reported RWKFs' dyeability, moisture-induced shape-memory capacity, and electric generation performance remarkably expand their applications in textiles or even smart apparel.

Advances in arthropod-inspired bionic materials for wound healing

Arthropods contain lots of valuable bionic information from the composition to the special structure of the body. In particular, the rapid self-healing ability and antibacterial properties are amazing. Biomimetic materials for arthropods have been helpful methods for wound management. Here, we have identified four major dimensions needed to create biomimetic materials for arthropods, including ingredient, behavior, structure and internal reaction. According to different dimensions, we classify and introduce the reported arthropod biomimetic materials. Antibacterial, hemostatic and healing promotion are the main functions of the active compositions of arthropods developed by humans, and most of them play a drug effect. We believe that an ideal biomimetic material of arthropod should have the effect on promoting wound healing through the advantages of structure and composition. The special macroscopic and microscopic structure of the epidermis may provide good mechanical support for biomimetic materials. The drug release regularity in the bionic materials can be referred to the aggressive and secretory behavior of arthropods. The synthesis of substances in arthropods is also noteworthy, and we can learn these special reactions to complete the fast preparation of materials. Arthropod-inspired bionic materials have broad innovation and application prospects in the field of wound repair.

Strong Silkworm Silk Fibers through CNT-Feeding and Forced Reeling

High-performance silk fibers, with their eco-friendly degradability and renewability, have long captivated researchers as an alternative to synthetic fibers. Spider dragline silk, renowned for its exceptional strength (>1 GPa), has an extremely low yield, hindering its widespread use. While domesticated silkworms (Bombyx mori) can produce silk fibers industrially, their moderate strength (≈0.5 GPa) pales in comparison to the formidable spider dragline silk. In this study, naturally produced strong silkworm silk fibers are reported with a tensile strength of ≈1.2 GPa achieved through combining feeding carbon nanotubes (CNTs) to silkworms and in situ forced reeling for alignment. Molecular dynamics simulations confirm the interaction between the CNTs and silk fibroin, while the forced reeling process aligns these reinforcing fillers and the silk fibroin β-sheet nanocrystals along the fiber axis. Structural analysis reveals a significant enhancement in the content and alignment of β-sheet nanocrystals within the silk fibers, accounting for their superior mechanical properties, including tensile strength of ≈1.2 GPa and Young's modulus of 24.4 GPa, surpassing various types of silkworm silk and spider silk. This advancement addresses the historical trade-off between the strength and scalability of silk, potentially paving the way for eco-friendly, biodegradable, and renewable alternatives to synthetic fibers in a variety of applications.

Synthesis and In Situ Thermal Induction of β-Sheet Nanocrystals in Spider Silk-Inspired Copolypeptides

Spider silk, known for its exceptional tensile strength, extensibility, and toughness, continues to inspire advancements in polymer and materials science. Despite extensive research, synthesizing materials that encompass all these properties remains a significant challenge. This study addresses this challenge by developing high molecular-weight multiblock synthetic copolypeptides that mimic the hierarchical structure and mechanical properties of spider silk. Using autoaccelerated ring-opening polymerization of N-carboxyanhydrides, we synthesized copolypeptides featuring transformable β-sheet blocks. These blocks retain a helical structure during synthesis but transition into β-sheet nanocrystals in situ during solvent-free thermal mechanical processing. Compression molding was employed to induce hierarchical ordering within the copolypeptide films, resulting in a solid "liquid crystalline" structure that undergoes a temperature-induced α-to-β structural transformation. This transformation integrates β-sheet nanocrystals throughout the helical block matrix, significantly enhancing the material's mechanical performance. Our innovative synthesis and processing strategy, which involves alternating sequences of α-helical and β-sheet blocks with various β-sheet-forming NCAs, enables the customization of diverse mechanical characteristics. These advancements not only deepen our understanding of the fundamental design principles of spider silk but also pave the way for a new generation of high-performance, silk-inspired synthetic copolypeptides with broad application potential.

Overexpressed Artificial Spidroin Based Microneedle Spinneret for 3D Air Spinning of Hybrid Spider Silk

Efforts have been devoted to developing strategies for converting spider silk proteins (spidroins) into functional silk materials. However, studies mimicking the exact natural spinning process of spiders encounter arduous challenges. In this paper, consistent with the natural spinning process of spiders, we report a high-efficient spinning strategy that enables the mass preparation of multifunctional artificial spider silk at different scales. By simulating the structural stability mechanism of the cross-β-spine of the amyloid polypeptide by computer dynamics, we designed and obtained an artificial amyloid spidroin with a significantly increased yield (13.5 g/L). Using the obtained artificial amyloid spidroin, we fabricated artificial spiders with artificial spinning glands (hollow MNs). Notably, by combining artificial spiders with 3D printing, we perform patterned air spinning at the macro- and microscales, and the resulting patterned artificial spider silk has excellent pump-free liquid flow and conductive and frictional electrical properties. Based on these findings, we used macroscale artificial spider silk to treat rheumatoid arthritis in mice and micro artificial spider silk to prepare wound dressings for diabetic mice. We believe that artificial spider silk based on an exact spinning strategy will provide a high-efficient way to construct and modulate the next generation of smart materials.

Engineered Microfibers for Tissue Engineering

Hydrogel microfibers are hydrogel materials engineered into fiber structures. Techniques such as wet spinning, microfluidic spinning, and 3D bioprinting are often used to prepare microfibers due to their ability to precisely control the size, morphology, and structure of the microfibers. Microfibers with different structural morphologies have different functions; they provide a flow-through culture environment for cells to improve viability, and can also be used to induce the differentiation of cells such as skeletal muscle and cardiac muscle cells to eventually form functional organs in vitro through special morphologies. This Review introduces recent advances in microfluidics, 3D bioprinting, and wet spinning in the preparation of microfibers, focusing on the materials and fabrication methods. The applications of microfibers in tissue engineering are highlighted by summarizing their contributions in engineering biomimetic blood vessels, vascularized tissues, bone, heart, pancreas, kidney, liver, and fat. Furthermore, applications of engineered fibers in tissue repair and drug screening are also discussed.

Natural Deep Eutectic Solvent-Assisted Construction of Silk Nanofibrils/Boron Nitride Nanosheets Membranes with Enhanced Heat-Dissipating Efficiency

Natural polymer-derived nanofibrils have gained significant interest in diverse fields. However, production of bio-nanofibrils with the hierarchical structures such as fibrillar structures and crystalline features remains a great challenge. Herein, an all-natural strategy for simple, green, and scalable top-down exfoliation silk nanofibrils (SNFs) in novel renewable deep eutectic solvent (DES) composed by amino acids and D-sorbitol is innovatively developed. The DES-exfoliated SNFs with a controllable fibrillar structures and intact crystalline features, novelty preserving the hierarchical structure of natural silk fibers. Owing to the amphiphilic nature, the DES-exfoliated SNFs show excellent capacity of assisting the exfoliation of several 2D-layered materials, i.e., h-BN, MoS2, and WS2. More importantly, the SNFs-assisted dispersion of BNNSs with a concentration of 59.3% can be employed to construct SNFs/BNNSs nanocomposite membranes with excellent mechanical properties (tensile strength of 416.7 MPa, tensile modulus of 3.86 GPa and toughness of 1295.4 KJ·m-3) and thermal conductivity (in-plane thermal conductivity coefficient of 3.84 W·m-1·K-1), enabling it to possess superior cooling efficiency compared with the commercial silicone pad.

A Hydroxylamine-Mediated Amidination of Lysine Residues That Retains the Protein's Positive Charge

Lysine-specific peptide and protein modification strategies are widely used to study charge-related functions and applications. However, these strategies often result in the loss of the positive charge on lysine, significantly impacting the charge-related properties of proteins. Herein, we report a strategy to preserve the positive charge and selectively convert amines in lysine side chains to amidines using nitriles and hydroxylamine under aqueous conditions. Various unprotected peptides and proteins were successfully modified with a high conversion rate. Moreover, the reactive amidine moiety and derived modification site enable subsequent secondary modifications. Notably, positive charges were retained during the modification. Therefore, positive charge-related protein properties, such as liquid-liquid phase separation behaviour of α-synuclein, were not affected. This strategy was subsequently applied to a lysine rich protein to develop an amidine-containing coacervate DNA complex with outstanding mechanical properties. Overall, our innovative strategy provides a new avenue to explore the characteristics of positively charged proteins.

ATPSpin: A Single Microfluidic Platform that Produces Diversified ATPS-Alginate Microfibers

Microfluidic spinning is emerging as a useful technique in the fabrication of alginate fibers, enabling applications in drug screening, disease modeling, and disease diagnostics. In this paper, by capitalizing on the benefits of aqueous two-phase systems (ATPS) to produce diverse alginate fiber forms, we introduce an ATPS-Spinning platform (ATPSpin). This ATPS-enabled method efficiently circumvents the rapid clogging challenges inherent to traditional fiber production techniques by regulating the interaction between alginate and cross-linking agents like Ba2+ ions. By varying system parameters under the guidance of a regime map, our system produces several fiber forms─solid, hollow, and droplet-filled─consistently and reproducibly from a single device. We demonstrate that the resulting alginate fibers possess distinct features, including biocompatibility. We also encapsulate HEK293 cells in the microfibers as a proof-of-concept that this versatile microfluidic fiber generation platform may have utility in tissue engineering and regenerative medicine applications.

Modular Protein Fibers with Outstanding High-Strength and Acid-Resistance Performance Mediated by Copper Ion Binding and Imine Networking

Engineered protein fibers are promising biomaterials with diverse applications due to their tunable protein structure and outstanding mechanical properties. However, it remains challenging at the molecular level to achieve satisfied mechanical properties and environmental tolerance simultaneously, especially under extreme acid conditions. Herein, the construction of artificial fibers comprising chimeric proteins made of rigid amyloid peptide and flexible cationic elastin-like protein (ELP) module is reported. The amyloid peptide readily assembles into highly organized β-sheet structures that can be further strengthened by the coordination of Cu2+, while the flexible ELP module allows the formation of imine-based crosslinking networks. These double networks synergistically enhance the mechanical properties of the fibers, leading to a high tensile strength and toughness, overwhelming many reported recombinant spidroin fibers. Notably, the coordination of Cu2+ with serine residues could stabilize β-sheet structures in the fibers under acidic conditions, which makes the fibers robust against acid, thus enabling their successful utilization in gastric perforation suturing. This work highlights the customization of double networks at the molecular level to create tailored high-performance protein fibers for various application scenarios.

In-situ observation of silk nanofibril assembly via graphene plasmonic infrared sensor

Silk nanofibrils (SNFs), the fundamental building blocks of silk fibers, endow them with exceptional properties. However, the intricate mechanism governing SNF assembly, a process involving both protein conformational transitions and protein molecule conjunctions, remains elusive. This lack of understanding has hindered the development of artificial silk spinning techniques. In this study, we address this challenge by employing a graphene plasmonic infrared sensor in conjunction with multi-scale molecular dynamics (MD). This unique approach allows us to probe the secondary structure of nanoscale assembly intermediates (0.8-6.2 nm) and their morphological evolution. It also provides insights into the dynamics of silk fibroin (SF) over extended molecular timeframes. Our novel findings reveal that amorphous SFs undergo a conformational transition towards β-sheet-rich oligomers on graphene. These oligomers then connect to evolve into SNFs. These insights provide a comprehensive picture of SNF assembly, paving the way for advancements in biomimetic silk spinning.

Redefining Surgical Materials: Applications of Silk Fibroin in Osteofixation and Fracture Repair

Silk and silk derivatives have emerged as a possible alternative in surgical device development, offering mechanical strength, biocompatibility, and environmental sustainability. Through a systematic review following PRISMA guidelines, this study evaluated silk fibroin's application across pre-clinical and clinical settings, focusing on its role as screws and plates for osteofixation. A comprehensive search yielded 245 studies, with 33 subjected to full-text review and 15 ultimately included for qualitative analysis. The findings underscore silk fibroin's superior properties, including its tunable degradation rates and ability to be functionalized with therapeutic agents. In vivo and in vitro studies demonstrated its efficacy in enhancing bone healing, offering improved outcomes in osteofixation, particularly for craniofacial defects. Silk fibroin's remarkable attributes in biodegradation and drug release capabilities underscore its potential to enhance patient care. Ultimately, silk fibroin's integration into surgical practices promises a revolution in patient outcomes and environmental sustainability. Its versatility, coupled with the continuous progress in fabrication techniques, signals a promising horizon for its widespread acceptance in the medical field, potentially establishing a new benchmark in surgical treatment. Further research is expected to solidify the transition of silk products from basic science to patient care, paving the way for widespread use in various surgical applications.

Overexpression of bond-forming active protein for efficient production of silk with structural changes and properties enhanced in silkworm

Silkworm silk exhibits excellent mechanical properties, biocompatibility, and has potential applications in the biomedical sector. This study focused on enhancing the mechanical properties of Bombyx mori silk by overexpressing three bond-forming active proteins (BFAPs): AFP, HSP, and CRP in the silk glands of silkworms. Rheological tests confirmed increased viscoelasticity in the liquid fibroin stock solution of transgenic silkworms, and dynamic mechanical thermal analysis (DMTA) indicated that all three BFAPs participated in the interactions between fibroin molecular networks in transgenic silk. The mechanical property assay indicated that all three BFAPs improved the mechanical characteristics of transgenic silk, with AFP and HSP having the most significant effects. A synchrotron radiation Fourier transform infrared spectroscopy assay showed that all three BFAPs increased the β-sheet content of transgenic silk. Synchrotron radiation wide-angle X-ray diffraction assay showed that all three BFAPs changed the crystallinity, crystal size, and orientation factor of the silk. AFP and HSP significantly improved the mechanical attributes of transgenic silk through increased crystallinity, refined crystal size, and a slight decrease in orientation. This study opens new possibilities for modifying silk and other fiber materials.

Versatile, durable conductive networks assembled from MXene and sericin-modified carbon nanotube on polylactic acid textile micro-etched via deep eutectic solvent

Integration of polylactic acid (PLA) textiles with conductive MXene holds great promise for fabricating green electronic textiles (e-textiles) and reducing the risk of electronic waste. However, constructing robust conductive networks on PLA fibers remains challenging due to the susceptibility of MXene to oxidation and the hydrophobicity of PLA fibers. Here, we demonstrate a versatile, degradable, and durable e-textile by decorating the deep eutectic solvent (DES) micro-etched PLA textile with MXene and sericin-modified carbon nanotube hybrid (MXene@SSCNT). The co-assembly of MXene with SSCNT in water not only enhanced its oxidative stability but also formed synergistic conductive networks with biomimetic leaf-like nanostructures on PLA fiber. Consequently, the MXene@SSCNT coated PLA textile (MCP-textile) exhibited high electrical conductivity (5.5 Ω·sq-1), high electromagnetic interference (EMI) shielding efficiency (34.20 dB over X-band), excellent electrical heating performance (66.8 ℃, 5 V), and sensitive humidity response. Importantly, the interfacial bonding between the MXene@SSCNT and fibers was significantly enhanced by DES micro-etching, resulting in superior wash durability of MCP-textile. Furthermore, the MCP-textile also showed satisfactory breathability, flame retardancy, and degradability. Given these outstanding features, MCP-textile can serve as a green and versatile e-textile with tremendous potential in EMI shielding, personal thermal management, and respiratory monitoring.

Influence of Spider Silk Protein Structure on Mechanical and Biological Properties for Energetic Material Detection

Spider silk protein, renowned for its excellent mechanical properties, biodegradability, chemical stability, and low immune and inflammatory response activation, consists of a core domain with a repeat sequence and non-repeating sequences at the N-terminal and C-terminal. In this review, we focus on the relationship between the silk structure and its mechanical properties, exploring the potential applications of spider silk materials in the detection of energetic materials.

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.

Mucosa-Inspired Electro-Responsive Lubricating Supramolecular-Covalent Hydrogel

Enabling the living capability of secreting liquids dynamically triggered by external stimuli while maintaining the bulk frame is a significant challenge for mucosa-inspired hydrogels. A mucosa-inspired electro-responsive hydrogel is developed in this study using the synergy between electro-responsive silk fibroin supramolecular non-covalent networks and covalent polyacrylamide and polyvinyl alcohol polymer networks. The formed supramolecular-covalent hydrogel exhibits a partial gel-sol transition upon the application of an electric field, and the liquid layer on the hydrogel surface near the cathode is used to mimic the mucus-secreting capability to regulate lubrication. The electro-responsive lubricating process can operate under a safe voltage and exhibits good reversibility. It is also a universal strategy to construct an electro-responsive hydrogel by introducing an electro-responsive supramolecular network into the polymer network. This mucosa-inspired electro-responsive supramolecular-covalent hydrogel offers a promising method for designing soft actuators or robots that can regulate lubrication using an electric strategy.

Pulling and analyzing silk fibers from aqueous solution using a robotic device

Spiders, silkworms, and many other animals can spin silk with exceptional properties. However, artificially spun fibers often fall short of their natural counterparts partly due sub-optimal production methods. A variety of methods, such as wet-, dry-, and biomimetic spinning have been used. The methods are based on extrusion, whereas natural spinning also involves pulling. Another shortcoming is that there is a lack feedback control during extension. Here we demonstrate a robotic fiber pulling device that enables controlled pulling of silk fibers and in situ measurement of extensional forces during the pulling and tensile testing of the pulled fibers. The pulling device was used to study two types of silk-one recombinant spider silk (a structural variant of ADF3) and one regenerated silk fibroin. Also, dextran-a branched polysaccharide-was used as a reference material for the procedure due to its straightforward preparation and storage. No post-treatments were applied. The pulled regenerated silk fibroin fibers achieved high tensile strength in comparison to similar extrusion-based methods. The mechanical properties of the recombinant spider silk fibers seemed to be affected by the liquid-liquid phase separation of the silk proteins.

Radiative cooling and anisotropic wettability in E-textile for comfortable biofluid monitoring

Long-term wearing comfort is essential for future advanced electronic textiles (e-textiles). Herein, we fabricate a skin-comfortable e-textile for long-term wearing experience on human epidermis. Such e-textile was simply fabricated through two different dip coating methods and single-side air plasma treatment, which couples radiative thermal and moisture management for biofluid monitoring. The silk-based substrate with improved optical properties and anisotropic wettability can provide a temperature drop of 1.4 °C under strong sunlight. Moreover, the anisotropic wettability of the e-textile can provide a dryer skin microenvironment by comparing with traditional fabric. The fiber electrodes weaving into the inner side of the substrate can noninvasively monitor multiple sweat biomarkers (i.e., pH, uric acid, and Na+). Such a synergistic strategy may pave a new path to design next-generation e-textiles with significantly improved comfort.

Biomimetic Silk Architectures Outperform Animal Horns in Strength and Toughness

Structural biomimicry is an intelligent approach for developing lightweight, strong, and tough materials (LSTMs). Current fabrication technologies, such as 3D printing and two-photon lithography often face challenges in constructing complex interlaced structures, such as the sinusoidal crossed herringbone structure that contributes to the ultrahigh strength and fracture toughness of the dactyl club of peacock mantis shrimps. Herein, bioinspired LSTMs with laminated or herringbone structures is reported, by combining textile processing and silk fiber "welding" techniques. The resulting biomimetic silk LSTMs (BS-LSTMs) exhibit a remarkable combination of lightweight with a density of 0.6-0.9 g cm-3 , while also being 1.5 times stronger and 16 times more durable than animal horns. These findings demonstrate that BS-LSTMs are among the toughest natural materials made from silk proteins. Finite element simulations further reveal that the fortification and hardening of BS-LSTMs arise primarily from the hierarchical organization of silk fibers and mechanically transferable meso-interfaces. This study highlights the rational, cost-effective, controllable mesostructure, and transferable strategy of integrating textile processing and fiber "welding" techniques for the fabrication of BS-LSTMs with advantageous structural and mechanical properties. These findings have significant implications for a wide range of applications in biomedicine, mechanical engineering, intelligent textiles, aerospace industries, and beyond.

Protein fibers with self-recoverable mechanical properties via dynamic imine chemistry

The manipulation of internal interactions at the molecular level within biological fibers is of particular importance but challenging, severely limiting their tunability in macroscopic performances and applications. It thus becomes imperative to explore new approaches to enhance biological fibers' stability and environmental tolerance and to impart them with diverse functionalities, such as mechanical recoverability and stimulus-triggered responses. Herein, we develop a dynamic imine fiber chemistry (DIFC) approach to engineer molecular interactions to fabricate strong and tough protein fibers with recoverability and actuating behaviors. The resulting DIF fibers exhibit extraordinary mechanical performances, outperforming many recombinant silks and synthetic polymer fibers. Remarkably, impaired DIF fibers caused by fatigue or strong acid treatment are quickly recovered in water directed by the DIFC strategy. Reproducible mechanical performance is thus observed. The DIF fibers also exhibit exotic mechanical stability at extreme temperatures (e.g., -196 °C and 150 °C). When triggered by humidity, the DIFC endows the protein fibers with diverse actuation behaviors, such as self-folding, self-stretching, and self-contracting. Therefore, the established DIFC represents an alternative strategy to strengthen biological fibers and may pave the way for their high-tech applications.

Mulberry Leaves (Morus Rubra)-Derived Blue-Emissive Carbon Dots Fed to Silkworms to Produce Augmented Silk Applicable for the Ratiometric Detection of Dopamine

Silk fibers (SF) reeled from silkworms are constituted by natural proteins, and their characteristic structural features render them applicable as materials for textiles and packaging. Modification of SF with functional materials can facilitate their applications in additional areas. In this work, the preparation of functional SF embedded with carbon dots (CD) is reported through the direct feeding of a CD-modified diet to silkworms. Fluorescent and mechanically robust SF are obtained from silkworms (Bombyx mori) that are fed on CDs synthesized from the Morus rubra variant of mulberry leaves (MB-CDs). MB-CDs are introduced to silkworms from the third instar by spraying them on the silkworm feed, the mulberry leaves. MB-CDs are synthesized hydrothermally without adding surface passivating agents and are observed to have a quantum yield of 22%. With sizes of ≈4 nm, MB-CDs exhibited blue fluorescence, and they can be used as efficient fluorophores to detect Dopamine (DA) up to the limit of 4.39 nM. The nanostructures and physical characteristics of SF weren't altered when the SF are infused with MB-CDs. Also, a novel DA sensing application based on fluorescence with the MB-CD incorporated SF is demonstrated.

Biomimetic Spun Silk Ionotronic Fibers for Intelligent Discrimination of Motions and Tactile Stimuli

Innovation in the ionotronics field has significantly accelerated the development of ultraflexible devices and machines. However, it is still challenging to develop efficient ionotronic-based fibers with necessary stretchability, resilience, and conductivity due to inherent conflict in producing spinning dopes with both high polymer and ion concentrations and low viscosities. Inspired by the liquid crystalline spinning of animal silk, this study circumvents the inherent tradeoff in other spinning methods by dry spinning a nematic silk microfibril dope solution. The liquid crystalline texture allows the spinning dope to flow through the spinneret and form free-standing fibers under minimal external forces. The resultant silk-sourced ionotronic fibers (SSIFs) are highly stretchable, tough, resilient, and fatigue-resistant. These mechanical advantages ensure a rapid and recoverable electromechanical response of SSIFs to kinematic deformations. Further, the incorporation of SSIFs into core-shell triboelectric nanogenerator fibers provides outstanding stable and sensitive triboelectric response to precisely and sensitively perceive small pressures. Moreover, by implementing a combination of machine learning and Internet of Things techniques, the SSIFs can sort objects made of different materials. With these structural, processing, performance, and functional merits, the SSIFs prepared herein are expected to be applied in human-machine interfaces.

Pressure-driven distillation using air-trapping membranes for fast and selective water purification

Membrane technologies that enable the efficient purification of impaired water sources are needed to address growing water scarcity. However, state-of-the-art engineered membranes are constrained by a universal, deleterious trade-off where membranes with high water permeability lack selectivity. Current membranes also poorly remove low-molecular weight neutral solutes and are vulnerable to degradation from oxidants used in water treatment. We report a water desalination technology that uses applied pressure to drive vapor transport through membranes with an entrapped air layer. Since separation occurs due to a gas-liquid phase change, near-complete rejection of dissolved solutes including sodium chloride, boron, urea, and N-nitrosodimethylamine is observed. Membranes fabricated with sub-200-nm-thick air layers showed water permeabilities that exceed those of commercial membranes without sacrificing salt rejection. We also find the air-trapping membranes tolerate exposure to chlorine and ozone oxidants. The results advance our understanding of evaporation behavior and facilitate high-throughput ultraselective separations.

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.

Silk-based conductive materials for smart biointerfaces

Silk-based conductive materials are widely used in biointerface applications, such as artificial epidermal sensors, soft and implantable bioelectronics, and tissue/cell scaffolds. Such biointerface materials require coordinated physicochemical, biological, and mechanical properties to meet current practical needs and future sophisticated demands. However, it remains a challenge to formulate silk-based advanced materials with high electrical conductivity, good biocompatibility, mechanical robustness, and in some cases, tissue adhesion ability without compromising other physicochemical properties. In this review, we highlight recent progress in the development of functional conductive silk-based advanced materials with different morphologies. Then, we reviewed the advanced paradigms of these silk materials applied as wearable flexible sensors, implantable electronics, and tissue/cell engineering with perspectives on the application challenges. Silk-based conductive materials can serve as promising building blocks for biomedical devices in personalized healthcare and other fields of bioengineering.

Instantaneous Formation of Silk Protein Aerosols and Fibers with a Portable Spray Device Under Ambient Conditions

A variety of artificial silk spinning approaches have been attempted to mimic the natural spinning process found in silkworms and spiders, yet instantaneous silk fiber formation with hierarchical structure under physiological and ambient conditions without post-treatment procedures remains unaddressed. Here, we report a new strategy to fabricate silk protein-based aerosols and silk fibers instantaneously (< 1 s) in situ using a simple, portable, spray device, avoiding complicated and costly advanced manufacturing techniques. The key to success is the instantaneous conformational transition of silk fibroin from random coil to β-sheet right before spraying by mixing silk and polyethylene glycol (PEG) solutions in the spray device, allowing aerosols and silk fibers to be sprayed in situ, with further control achieved via the molecular weight of silk. The spinning process of the spray device is based on the use of green solvents, i.e., all steps of instant conformational transition of silk fibroin are carried out in aqueous conditions or with buffers at ambient conditions, in combination with shear and elongational flow caused by the hydraulic pressure generated in the spray container. The system supports a portable and user-friendly system that could be used for drug delivery carriers, wound coating materials and rapid silk fiber conformal coatings on surfaces.

In Situ Mineralizing Spinning of Strong and Tough Silk Fibers for Optical Waveguides

Biopolymer-based optical waveguides with low-loss light guiding performance and good biocompatibility are highly desired for applications in biomedical photonic devices. Herein, we report the preparation of silk optical fiber waveguides through bioinspired in situ mineralizing spinning, which possess excellent mechanical properties and low light loss. Natural silk fibroin was used as the main precursor for the wet spinning of the regenerated silk fibroin (RSF) fibers. Calcium carbonate nanocrystals (CaCO₃ NCs) were in situ grown in the RSF network and served as nucleation templates for mineralization during the spinning, leading to the formation of strong and tough fibers. CaCO₃ NCs can guide the structure transformation of silk fibroin from random coils to β-sheets, contributing to enhanced mechanical properties. The tensile strength and toughness of the obtained fibers are up to 0.83 ± 0.15 GPa and 181.98 ± 52.42 MJ·m^-3, obviously higher than those of natural silkworm silks and even comparable to spider silks. We further investigated the performance of the fibers as optical waveguides and observed a low light loss of 0.46 dB·cm^-1, which is much lower than natural silk fibers. We believed that these silk-based fibers with excellent mechanical and light propagation properties are promising for applications in biomedical light imaging and therapy.

Nanosilk Template-Guided/Induced Construction of Brush-/Flower-like 3D Nanostructures

Biomaterials with natural hierarchical structures typically exhibit extraordinary properties because of their multilevel structural designs. They offer many templates and models as well as inspiration for material design, particularly for fabricating structure-regulated, performance-enhanced, and function-enriched materials. Biopolymer-based nanocomposites with ingenious nanostructures constructed through ecofriendly and sustainable approaches are highly desirable to meet the multifunctional requirements of developing bioinspired materials. Herein, an all-silk fibroin-based nanocomposite with a brush-like nanostructure was constructed for the first time using a nanotemplate-guided assembly approach in which dissolved silk assembled directly on a silk nanowhisker (SNW) backbone to form peculiar nanobrushes based on the classical micelle model. Three-dimensional spider-like or centipede-like silk nanobrushes (SNBs) were fabricated by varying the SNW backbone length from 0.16 to 6 μm. The branches with average lengths of 32-290 nm were also adjustable. SNBs were further designed to regulate and induce biomineralization of hydroxyapatite (HAP) to form interesting flower-like nanostructures, in which the HAP nanosphere (diameters ∼16 nm) "core" was covered by SNBs with branches extending to form a "shell" (∼101 nm in length). Based on such protein nanotemplate-guided formation of nanoscale structures, practical hollow conduits with remarkable mechanical properties, biocompatibility, shape memory behavior, and bone engineering potential were fabricated. This study inspires the design of polymorphous biopolymer-based nanostructures with enhanced performance at multiple length scales where the weaknesses of individual building blocks are offset.

Structurally Tailoring Clay Nanosheets to Design Emerging Macrofibers with Tunable Mechanical Properties and Thermal Behavior

Bio-derived nanomaterials are promising candidates for spinning high-performance sustainable textiles, but the inherent flammability of biomass-based fibers seriously limits their applications. There is still an urgent need to improve fiber flame retardancy while maintaining excellent mechanical performance. Here, inspired by the structural properties of layered nanoclay, we report a novel and efficient strategy to synthesize the strong, super tough, and flame-retardant nanocellulose/clay/sodium alginate (CRS) macrofibers via wet-spinning and directional drying. Benefiting from the precise modulation of arrangement and orientation of nanoclay in macrofibers, the new inorganic structure exhibits excellent mechanical and thermal functional properties. The anisotropic structure contributes to high toughness: the tensile strength was 373.3 MPa and the toughness was 26.92 MJ·m^-3. Remarkably, rectorite nanosheets as a thermal and qualitative insulator significantly improve the flame retardancy of the CRS fibers with a heat release rate as low as 6.07 W/g, thermal conductivity of 90.5 mW/(m·K), and good temperature tolerance (ranging from -196 to 100 °C). This facile and high-efficiency strategy may have great scalability in manufacturing high-strength, super tough, and flame-retardant fibers for emerging biodegradable next-generation artificial fibers.

Drosophila melanogaster resilin improves the mechanical properties of transgenic silk

Resilin is a natural protein with high extensibility and resilience that plays a key role in the biological processes of insects, such as flight, bouncing, and vocalization. This study used piggyBac-mediated transgenic technology to stably insert the Drosophila melanogaster resilin gene into the silkworm genome to investigate whether exogenous protein structures improve the mechanical properties of silkworm silk. Molecular detection showed that recombinant resilin was expressed and secreted into silk. Secondary structure and mechanical property analysis showed that the β-sheet content in silk from transgenic silkworms was higher than in wild-type silk. The fracture strength of silk fused with resilin protein was 7.2% higher than wild-type silk. The resilience of recombinant silk after one-time stretching and cyclic stretching was 20.5% and 18.7% higher than wild-type silk, respectively. In summary, Drosophila resilin can enhance the mechanical properties of silk, and this study is the first to improve the mechanical properties of silk using proteins other than spider silk, which broadens the possibilities for the design and application of biomimetic silk materials.

Hierarchically structured bioinspired nanocomposites

Next-generation structural materials are expected to be lightweight, high-strength and tough composites with embedded functionalities to sense, adapt, self-repair, morph and restore. This Review highlights recent developments and concepts in bioinspired nanocomposites, emphasizing tailoring of the architecture, interphases and confinement to achieve dynamic and synergetic responses. We highlight cornerstone examples from natural materials with unique mechanical property combinations based on relatively simple building blocks produced in aqueous environments under ambient conditions. A particular focus is on structural hierarchies across multiple length scales to achieve multifunctionality and robustness. We further discuss recent advances, trends and emerging opportunities for combining biological and synthetic components, state-of-the-art characterization and modelling approaches to assess the physical principles underlying nature-inspired design and mechanical responses at multiple length scales. These multidisciplinary approaches promote the synergetic enhancement of individual materials properties and an improved predictive and prescriptive design of the next era of structural materials at multilength scales for a wide range of applications.

Tailoring micro/nano-fibers for biomedical applications

Nano/micro fibers have evoked much attention of scientists and have been researched as cutting edge and hotspot in the area of fiber science in recent years due to the rapid development of various advanced manufacturing technologies, and the appearance of fascinating and special functions and properties, such as the enhanced mechanical strength, high surface area to volume ratio and special functionalities shown in the surface, triggered by the nano or micro-scale dimensions. In addition, these outstanding and special characteristics of the nano/micro fibers impart fiber-based materials with wide applications, such as environmental engineering, electronic and biomedical fields. This review mainly focuses on the recent development in the various nano/micro fibers fabrication strategies and corresponding applications in the biomedical fields, including tissue engineering scaffolds, drug delivery, wound healing, and biosensors. Moreover, the challenges for the fabrications and applications and future perspectives are presented.

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

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

Design of Volumetric Nanolayers via Rapid Proteolysis of Silk Fibroin for Tissue Engineering

Various methods have been studied to make a regenerated silk fibroin solution. However, most of them take too much time and effort to liquefy. Here, we report that a regenerated silk fibroin solution could be prepared within seconds through acid proteolysis for the first time. The solubilized fibroin could be applied to advanced tissue engineering. Our method shortened the production time to one day (more than 10 times) compared to the general fibroin solution preparation method. It was confirmed that the initial protein affinity nearly doubled from 0.028 to 0.076 μg·mm^-2 in FF(ac) compared to FF(aq). A fibroin nanofiber layer having a volumetric hierarchical structure was prepared by electrospinning an acid-proteolyzed fibroin solution, followed by gas foaming. In vitro results of cell adhesion and proliferation capacity of the gas-foamed scaffold were not significantly different compared to the two-dimensional (2D) fibroin nanofiber membrane, overcoming the limitations of volumetric nanofiber scaffolds. We are confident that our research will greatly contribute to the development of regenerative engineering using other proteins.

Bioinspired gelatin nano-film implanted into composite scaffold exhibiting both expandable adhesion and enhanced proliferation

Tissue engineering technology provides a new treatment to the cartilage damage. Recent progress has focused on coating strategies with the printed scaffold surface, using various materials such as bioactive nanocomposites. However, the fracture and exfoliation of printed scaffolds remain challenges due to their poor adhesion on smooth substrates. These limitations can be offset by developing a versatile film. Here, inspired by the mechanism of the wet adhesion of snails, we introduced a biomimetic nanoscale gelatin film between a smooth conductive slide and a scaffold, which enhanced early cell adhesion rates through water absorption, swelling and adhesion. A bionic technique of preparing gelatin nanofilms and PVP/PCL 3D scaffolds, which involved E-Jet atomization deposition and E-Jet printing techniques based on the electrohydrodynamic effect, was investigated. It is found that the composite scaffold with 400 nm gelatin nanofilm significantly enhances cell attachment (from 62 % to 87 %) and proliferation (increased 6.5 times in 7 days). Collectively, this study highlights the combination of biomimetic nanoscale adhesive film in promoting cell adhesion and cartilage differentiation, which benefiting from water absorption and swelling of gelatin nanofilm. This work provides a new idea for the potential application in the orthopedics field.

Unexpected high toughness of Samia cynthia ricini silk gut

Silk gut fibers were produced from the silkworm Samia cynthia ricini silk glands by the usual procedure of immersion in a mildly acidic solution and subsequent stretching. The morphology of the silk guts was assessed by scanning electron microscopy, and their microstructure was assessed by infrared spectroscopy and X-ray diffraction. It was found that both naturally spun and Samia silk guts share a common semicrystalline microstructure. The mechanical characterization of the silk guts revealed that these fibers show an elastomeric behavior when tested in water, and exhibit a genuine ground state to which the fiber may revert independently of its previous loading history. In spite of its large cross-sectional area compared with naturally spun silk fibers, Samia silk guts show values of work to fracture up to 160 MJ m^-3, much larger than those of most of their natural counterparts, and establish a new record value for this parameter in silk guts.

Bioengineered Silkworm for Producing Cocoons with High Fibroin Content for Regenerated Fibroin Biomaterial-Based Applications

Silk fibroin exhibits high biocompatibility and biodegradability, making it a versatile biomaterial for medical applications. However, contaminated silkworm-derived substances in remnant sericin from the filature and degumming process can result in undesired immune reactions and silk allergy, limiting the widespread use of fibroin. Here, we established transgenic silkworms with modified middle silk glands, in which sericin expression was repressed by the ectopic expression of cabbage butterfly-derived cytotoxin pierisin-1A, to produce cocoons composed solely of fibroin. Intact, nondegraded fibroin can be prepared from the transgenic cocoons without the need for sericin removal by the filature and degumming steps that cause fibroin degradation. A wide-angle X-ray diffraction analysis revealed low crystallinity in the transgenic cocoons. However, nondegraded fibroin obtained from transgenic cocoons enabled the formation of fibroin sponges with varying densities by using 1–5% (v/v) alcohol. The effective chondrogenic differentiation of ATDC5 cells was induced following their cultivation on substrates coated with intact fibroin. Our results showed that intact, allergen-free fibroin can be obtained from transgenic cocoons without the need for sericin removal, providing a method to produce fibroin-based materials with high biocompatibility for biomedical uses.

A Protein-Like Nanogel for Spinning Hierarchically Structured Artificial Spider Silk

Spider dragline silk is draw-spun from soluble, β-sheet-crosslinked spidroin in aqueous solution. This spider silk has an excellent combination of strength and toughness, which originates from the hierarchical structure containing β-sheet crosslinking points, spiral nanoassemblies, a rigid sheath, and a soft core. Inspired by the spidroin structure and spider spinning process, a soluble and crosslinked nanogel is prepared and crosslinked fibers are drew spun with spider-silk-like hierarchical structures containing cross-links, aligned nanoassemblies, and sheath-core structures. Introducing nucleation seeds in the nanogel solution, and applying prestretch and a spiral architecture in the nanogel fiber, further tunes the alignment and assembly of the polymer chains, and enhances the breaking strength (1.27 GPa) and toughness (383 MJ m^-3 ) to approach those of the best dragline silk. Theoretical modeling provides understanding for the dependence of the fiber's spinning capacity on the nanogel size. This work provides a new strategy for the direct spinning of tough fiber materials.

Engineering High Strength and Super-Toughness of Unfolded Structural Proteins and their Extraordinary Anti-Adhesion Performance for Abdominal Hernia Repair

The utility of unfolded structural proteins with diverse sequences offers multiple potentials to create functional biomaterials. However, it is challenging to overcome their structural defects for the development of biological fibers with a combination of high strength and high toughness. Herein, robust fibers from a recombinant unfolded protein consisting of resilin and supercharged polypeptide are fabricated via wet-spinning approaches. Particularly, the highly ordered structures induced by supramolecular complexation significantly improve the fiber's mechanical performance. In contrast to chemical fibers with high strength and low toughness (or vice versa), the present fibers demonstrate exceptional high strength and super-toughness, showing a breaking strength of ≈550 MPa and a toughness of ≈250 MJ m^-3 , respectively, surpassing many polymers and artificial protein fibers. Remarkably, the outstanding biocompatibility and superior mechanical properties allow application of the constructed fiber patches for efficient abdominal hernia repair in rat models. In stark contrast to clinical patches, there is no observed tissue adhesion by this treatment. Therefore, this work provides a new type of engineered protein material for surgical applications.

Silkworm Gut Fibres from Silk Glands of Samia cynthia ricini-Potential Use as a Scaffold in Tissue Engineering

High-performance fibroin fibres are ideal candidates for the manufacture of scaffolds with applications in tissue engineering due to the excellent mechanical properties and optimal biocompatibility of this protein. In this work, the manufacture of high-strength fibres made from the silk glands of Samia cynthia ricini is explored. The glands were subjected to soaking in aqueous dissolutions of acetic acid and stretched to manufacture the fibres. The materials produced were widely characterized, in terms of morphology, mechanical properties, crystallinity and content of secondary structures, comparing them with those produced by the standard procedure published for Bombyx mori. In addition, mechanical properties and biocompatibility of a braided scaffold produced from these fibres was evaluated. The results obtained show that the fibres from B. mori present a higher degree of crystallinity than those from S. c. ricini, which is reflected in higher values of elastic modulus and lower values of strain at break. Moreover, a decrease in the elongation values of the fibres from S. c. ricini was observed as the concentration of acetic acid was increased during the manufacture. On the other hand, the study of the braided scaffolds showed higher values of tensile strength and strain at break in the case of S. c. ricini materials and similar values of elastic modulus, compared to those of B. mori, displaying both scaffolds optimal biocompatibility using a fibroblast cell line.

Mechanically Reinforced Silkworm Silk Fiber by Hot Stretching

Silkworm silk, which is obtained from domesticated Bombyx mori (B. mori), can be produced in a large scale. However, the mechanical properties of silkworm silk are inferior to its counterpart, spider dragline silk. Therefore, researchers are continuously exploring approaches to reinforce silkworm silk. Herein, we report a facile and scalable hot stretching process to reinforce natural silk fibers obtained from silkworm cocoons. Experimental results show that the obtained hot-stretched silk fibers (HSSFs) retain the chemical components of the original silk fibers while being endowed with increased β-sheet nanocrystal content and crystalline orientation, leading to enhanced mechanical properties. Significantly, the average modulus of the HSSFs reaches 21.6 ± 2.8 GPa, which is about twice that of pristine silkworm silk fibers (11.0 ± 1.7 GPa). Besides, the tensile strength of the HSSFs reaches 0.77 ± 0.13 GPa, which is also obviously higher than that of the pristine silk (0.56 ± 0.08 GPa). The results show that the hot stretching treatment is effective and efficient for producing superstiff, strong, and tough silkworm silk fibers. We anticipate this approach may be also effective for reinforcing other natural or artificial polymer fibers or films containing abundant hydrogen bonds.

Facile One-Pot Method for All Aqueous Green Formation of Biocompatible Silk Fibroin-Poly(Ethylene Oxide) Fibers for Use in Tissue Engineering

Silk fibroin (SF) fibers are highly regarded in tissue engineering because of their outstanding biocompatibility and tunable properties. A challenge remains in overcoming the trade-off between functioning and biocompatible fibers and the use of cytotoxic, environmentally harmful organic solvents in their processing and formation. The aim of this research was to produce biocompatible SF fibers without the use of cytotoxic solvents, via pressurized gyration (PG). Aqueous SF was blended with poly(ethylene oxide) (PEO) in ratios of 80:20 (labeled SF-PEO 80:20) and 90:10 (labeled SF-PEO 90:10) and spun into fibers using PG, assisted by a range of applied pressures and heat. Pure PEO (labeled PEO-Aq) and SF solubilized in hexafluoro-isopropanol (HFIP) (labeled SF-HFIP) and aqueous SF (labeled SF-Aq) were also prepared for comparison. The resulting fibers were characterized using SEM, TGA, and FTIR. Their in vitro cell behavior was analyzed using a Live/Dead assay and cell proliferation studies with the SaOS-2 human bone osteosarcoma cell line (ATCC, HTB-85) and human fetal osteoblast cells (hFob) (ATCC, CRL-11372) in 2D culture conditions. Fibers in the micrometer range were successfully produced using SF-PEO blends, SF-HFIP, and PEO-Aq. The fiber thickness ranged from 0.71 ± 0.17 μm for fibers produced using SF-PEO 90:10 with no applied pressure to 2.10 ± 0.78 μm for fibers produced using SF-PEO 80:10 with 0.3 MPa applied pressure. FTIR confirmed the presence of SF via amide I and amide II bands in the blend fibers because of a change in structural conformation. No difference was observed in thermogravimetric properties among varying pressures and no significant difference in fiber diameters for pressures. SaOS-2 cells and hFOb cell studies demonstrated higher cell densities and greater live cells on SF-PEO blends when compared to SF-HFIP. This research demonstrates a scalable and green method of producing SF-based constructs for use in bone-tissue engineering applications.