Natural Silk Fibers Research Articles

Effects of Mini-Spidroin Repeat Region on the Mechanical Properties of Artificial Spider Silk Fibers.

Spiders can produce up to seven different types of silk, each with unique mechanical properties that stem from variations in the repetitive regions of spider silk proteins (spidroins). Artificial spider silk can be made from mini-spidroins in an all-aqueous-based spinning process, but the strongest fibers seldom reach more than 25% of the strength of native silk fibers. With the aim to improve the mechanical properties of silk fibers made from mini-spidroins and to understand the relationship between the protein design and the mechanical properties of the fibers, we designed 16 new spidroins, ranging from 31.7 to 59.5 kDa, that feature the globular spidroin N- and C-terminal domains, but harbor different repetitive sequences. We found that more than 50% of these constructs could be spun by extruding them into low-pH aqueous buffer and that the best fibers were produced from proteins whose repeat regions were derived from major ampullate spidroin 4 (MaSp4) and elastin. The mechanical properties differed between fiber types but did not correlate with the expected properties based on the origin of the repeats, suggesting that additional factors beyond protein design impact the properties of the fibers.

Natural Kapok Fiber-derived Two-Dimensional Carbonized Sheets as Sustainable Electrode Material

Natural biomass-derived carbon nanostructures have attracted research interest because of their unique surface and electrochemical properties. The present study embodied the carbonized micro-nano sheets derived from the low-cost natural source Kapok silk fiber. The material was obtained via a facile thermal pyrolysis process. Diffraction analysis showed a broad graphene structure-like peak, indicating the formation of graphene-like carbon nanosheets. Field emission scanning electron microscope (FESEM) and transmission electron microscopic (TEM) images confirmed the presence of fragmented carbon sheets, some of which were folded to form a tube-like structure. Raman study showed the presence of D and G band with the Id/Ig ratio of 0.96 which indicated the formation of few-layered carbon nanosheets. Furthermore, the electrochemical performance was evaluated for lithium-ion battery as well as supercapacitor. A specific capacity of 465 mAh.g-1 at 0.1 C rate for Li-ion battery and a specific capacitance of 473.61 F.g-1 for supercapacitor have been obtained with the capacitance retention of 95%. This study provides insights into a strategy for the sustainable production and utilization of natural fiber-based carbon in energy storage systems.

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 416.7MPa, tensile modulus of 3.86GPa 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.

Α {Silk@Gallic‐Acid} hybrid material with controllable antioxidant hydrogen‐atom‐transfer activity

AbstractSilk fiber, often acclaimed as the pinnacle of textile materials, finds contemporary applications in the textile industry, health, and cosmetics. Gallic acid (GA) is a well‐established natural antioxidant. In the present study, a novel hybrid material SFd@GA was conceptualized and produced via surface grafting of GA onto degummed silk‐fibers (SFd). Successful covalent‐grafting of gallic acid onto the silk fabric surface was confirmed through Fourier‐transform infrared, Raman, thermogravimetric analysis (TG‐DTA), and scanning electron microscopy (SEM). electron paramagnetic resonance spectroscopy demonstrates that gallic moieties grafted on SFd@GA retain their radical/redox activity. The antioxidant capacity of the hybrid material SFd@GA was validated by quantitative analysis of antioxidant hydrogen‐atom‐transfer (HAT) to DPPH radicals. Our data reveal a 550% increase in antioxidant‐HAT activity of SFd@GA versus natural intact silk fiber, and a 1400% increase in antioxidant‐HAT activity compared to the degummed silk fiber. The paramount discovery of the present work lies in the capacity for repeated utilization of the hybrid material SFd@GA, without any discernible compromise in its antioxidant‐HAT activity. Specifically, we show that SFd@GA can be employed for at least 15 consecutive cycles, retaining >98% of its HAT efficiency, for up to many days of storage under ambient conditions. We discuss this expositional performance via the controllable Hat‐activity process that we propose.

Effect of Phosphate on the Molecular Properties, Interactions, and Assembly of Engineered Spider Silk Proteins.

Phosphate plays a vital role in spider silk spinning and has been utilized in numerous artificial silk spinning attempts to replicate the remarkable mechanical properties of natural silk fiber. Its application in artificial processes has, however, yielded varying outcomes. It is thus necessary to investigate the origins and mechanisms behind these differences. By using recombinant silk protein SC-ADF3 derived from the garden spider Araneus diadematus, here, we describe its conformational changes under various conditions, elucidating the effect of phosphate on SC-ADF3 silk protein properties and interactions. Our results demonstrate that elevated phosphate levels induce the irreversible conformational conversion of SC-ADF3 from random coils to β-sheet structures, leading to decreased protein solubility over time. Furthermore, exposure of SC-ADF3 to phosphate stiffens already formed structures and reduces the ability to form new interactions. Our findings offer insights into the underlying mechanism through which phosphate-induced β-sheet structures in ADF3-related silk proteins impede fiber formation in the subsequent phases. From a broader perspective, our studies emphasize the significance of silk protein conformation for functional material formation, highlighting that the formation of β-sheet structures at the initial stages of protein assembly will affect the outcome of material forming processes.

Effect of natural silk fibers and synthetic fiber-reinforced composites on the cytotoxicity of fibroblast cell lines.

Synthetic fibers have many benefits in clinical practice; however, they cause microplastic pollution, and their unaffordable price increases treatment costs. Natural silk fibers require biocompatibility assessment. This study investigated the effects of natural and synthetic fiber-reinforced composites (FRCs) on the cytotoxicity of fibroblast cell lines. Three commercial synthetic fibers (polyethylene, quartz, and E-glass) and two silk fibers from Bombyx mori and Samia ricini cocoons were employed. These fibers were made into FRC samples (n=6) by impregnation in flowable composite using a brass mold (25×2×2 mm). NIH/3T3 mouse fibroblasts were cultured in Dulbecco's modified eagle medium, supplemented, and seeded in 2×104 cells/mL. They were stored at 37 °C under 5% CO2 for 24 hours. The FRC samples were made into powder, eluted in dimethylsulfoxide, continued with PBS, supplemented with Dulbecco's modified eagle medium (DMEM), and exposed to cells for 24 hours. Blank (medium only) and control (cells and medium) samples were included. Subsequently, MTT was added for 4 h and read by enzyme-linked immunosorbent assay (λ=570 nm). Cell viability (%) was calculated and analyzed using one-way ANOVA (α=0.05). All groups of FRCs showed>80% cell viability. One-way ANOVA showed no significant difference between FRC groups regarding the viability of fibroblast cell lines (P>0.05). Both natural silk and synthetic fibers exhibit low cytotoxicity to fibroblast cell lines. B. mori and S. ricini silk fibers showed the potential to be used as alternative synthetic fibers.

Regenerated Fiber's Ideal Target: Comparable to Natural Fiber.

The toughness of silk naturally obtained from spiders and silkworms exceeds that of all other natural and man-made fibers. These insects transform aqueous protein feedstocks into mechanically specialized materials, which represents an engineering phenomenon that has developed over millions of years of natural evolution. Silkworms have become a new research hotspot due to the difficulties in collecting spider silk and other challenges. According to continuous research on the natural spinning process of the silkworm, it is possible to divide the main aspects of bionic spinning into two main segments: the solvent and behavior. This work focuses on the various methods currently used for the spinning of artificial silk fibers to replicate natural silk fibers, providing new insights based on changes in the fiber properties and production processes over time.

Repercussion of natural silk fibers from spider and silkworms on the mechanical properties of composite materials

Costly synthetic fibers like kevlar, glass, and carbon lead to expensive production costs for products made from these materials, necessitating the development of alternate materials. As a more sustainable and affordable substitute for synthetic reinforcement materials like glass, carbon, and kevlar, natural fiber has gained popularity. Silk fiber obtained from spiders and silkworms is one type of natural fiber that has excellent mechanical properties such as tensile strength, tensile modulus, and breaking elongation. Its mechanical and biocompatibility characteristics are unmatched by those of other synthetic and natural fibers. This article discusses various silk fiber-related topics such as chemical composition, mechanical properties, and applications with respect to spiders and silkworms. Also, the requirement for silk fiber to be used as a reinforcement in composite materials is highlighted. Furthermore, the mechanical properties of silk fiber-reinforced composites (SFRCs) are also explored in this review. It is acceptable to draw the conclusion that the use of SFRCs in the creation of useful and possibly lucrative applications as novel materials in many industrial areas is inevitable.

Durability improvement strategies for wettable fog harvesting devices inspired by spider silk fibers: a review.

Water scarcity is a persistent challenge, and in this case, the freshwater content in the air and water collection phenomena observed in nature provide ideas for fog harvesting. The fog-harvesting capabilities of natural spider silk have long attracted attention. Thus, researchers have undertaken significant efforts for the preparation of wettable biomimetic knotted fibers. However, the fragility of their chemical coating and the susceptibility of spun fibers to damage often present substantial challenges in the durability of fog harvesting equipment. Herein, from a bioengineering perspective, we review the improvement strategies for enhancing the mechanical properties of wettable biomimetic spider silk fibers based on the dense nanoconfined hydrogen-bond array crystalline regions and uniformly embedded amorphous regions of natural wettable spider silk fibers. These strategies aim to achieve high tensile strength, good fracture toughness, and corrosion resistance. Additionally, by incorporating UV inhibitors during spinning, the effects of sunlight can be mitigated or shielded, thereby greatly enhancing the mechanical durability of fog-harvesting devices under harsh realistic conditions.

Silk-based intelligent fibers and textiles: structures, properties, and applications.

Multifunctional fibers represent a cornerstone of human civilization, playing a pivotal role in numerous aspects of societal development. Natural biomaterials, in contrast to synthetic alternatives, offer environmental sustainability, biocompatibility, and biodegradability. Among these biomaterials, natural silk is favored in biomedical applications and smart fiber technology due to its accessibility, superior mechanical properties, diverse functional groups, controllable structure, and exceptional biocompatibility. This review delves into the intricate structure and properties of natural silk fibers and their extensive applications in biomedicine and smart fiber technology. It highlights the critical significance of silk fibers in the development of multifunctional materials, emphasizing their mechanical strength, biocompatibility, and biodegradability. A detailed analysis of the hierarchical structure of silk fibers elucidates how these structural features contribute to their unique properties. The review also encompasses the biomedical applications of silk fibers, including surgical sutures, tissue engineering, and drug delivery systems, along with recent advancements in smart fiber applications such as sensing, optical technologies, and energy storage. The enhancement of functional properties of silk fibers through chemical or physical modifications is discussed, suggesting broader high-end applications. Additionally, the review addresses current challenges and future directions in the application of silk fibers in biomedicine and smart fiber technologies, underscoring silk's potential in driving contemporary technological innovations. The versatility and sustainability of silk fibers position them as pivotal elements in contemporary materials science and technology, fostering the development of next-generation smart materials.

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.

Impregnation of various fiber tapes toward mechanical properties of dental fiber-reinforced composites

Synthetic dental fiber tape for fiber reinforcement (FRC) restoration is relatively costly and its availability is still limited in Indonesia, so natural dental fibers have been used as an alternative material. The aim of this study was to assess the effect of impregnation of various fiber tape toward the flexural strength and hardness of FRC. The materials used were natural Bombyx mori silk fibers (Indonesia), dental polyethylene tape (Construct Kerr, USA), dental Quartz tape (Quartz Splint UD, France), dental E-glass tape (Everstick TM, GC, Japan), silane coupling agent (Ultradent, Jordan), and composite resin (Denfil-Flow, USA). Five groups of samples consisted of FRC with various fiber tapes were prepared: unidirectional-silk, braided-silk, quartz, polyethylene, and E-glass. The five groups of FRC were tested to determine the flexural strength and hardness. The results were analyzed by one-way ANOVA, followed by LSD test. The results showed that the highest flexural strength was in the quartz group (496.84 ± 109.14 MPa), while the lowest was in the braided-silk group (139.39 ± 4.30 MPa). The highest hardness property was in the unidirectional-silk group (141.29 ± 25.17 VHN), while the lowest was in the braided-silk group (139.39 ± 4.30 VHN). The ANOVA showed that various fiber tapes significantly influenced the flexural strength and hardness of FRC (p < 0.05). The LSD showed that the unidirectional-silk, braided-silk, and polyethylene groups demonstrated no significant difference. The LSD for hardness showed that the unidirectional-silk group had a significant difference with the other groups (p < 0.05). It can be concluded that various fiber tapes influenced the flexural strength and hardness of FRC. Natural silk fibers showed comparable flexural strength and hardness with the other fiber tapes.

Controllable Production of Natural Silk Nanofibrils for Reinforcing Silk-Based Orthopedic Screws

As a natural high-performance material with a unique hierarchical structure, silk is endowed with superior mechanical properties. However, the current approaches towards producing regenerated silk fibroin (SF) for the preparation of biomedical devices fail to fully exploit the mechanical potential of native silk materials. In this study, using a top-down approach, we exfoliated natural silk fibers into silk nanofibrils (SNFs), through the disintegration of interfibrillar binding forces. The as-prepared SNFs were employed to reinforce the regenerated SF solution to fabricate orthopedic screws with outstanding mechanical properties (compression modulus > 1.1 GPa in a hydrated state). Remarkably, these screws exhibited tunable biodegradation and high cytocompatibility. After 28 days of degradation in protease XIV solution, the weight loss of the screw was ~20% of the original weight. The screws offered a favorable microenvironment to human bone marrow mesenchymal stem cell growth and spread as determined by live/dead staining, F-action staining, and Alamar blue staining. The synergy between native structural components (SNFs) and regenerated SF solutions to form bionanocomposites provides a promising design strategy for the fabrication of biomedical devices with improved performance.

Wild Silkworm Cocoon Waste Conversion into Tough Regenerated Silk Fibers by Solution Spinning.

Wild silkworm silk fibers have garnered attention owing to their softness, natural color, lightweight, and excellent mechanical properties. Because most wild silkworm cocoons obtained are pierced or dirty after the eclosion process, it is difficult to reel the long filament from the pierced cocoons to use as textile materials. Therefore, damaged wild silkworm cocoons are typically removed during the industrial process. Artificial silk spinning has been developed to transform domesticated silkworm silk solutions into regenerated silk fibers. However, regenerated fibers derived from wild silkworm silk have not been reported. Here, we produced regenerated silk fibers using a dry-wet spinning method using a dope solution derived from wild silkworm silk cocoon wastes. These regenerated silk fibers have thick and uniform diameters, unlike native silk fibers, contributing to their usefulness for sterilization and handling in medical applications. Moreover, they exhibited the same level of mechanical strength as their native counterparts. The molecular orientation and crystallinity of the regenerated silk fibers were adjustable by the drawing process, enabling the realization of their various tensile properties. This study promotes the utilization of unused protein resources to produce mechanically stable and tough silk-based fibers.

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.

Enhanced interaction of dye molecules and fibers via bio-based acids for greener coloration of silk/polyamide fabric

Multi-component fabrics combined with natural silk fibers and man-made polyamide fibers are good choices for high-quality textile owing to the remarkable comfort and excellent resistance. The silk/polyamide fabric colored with reactive dyes generally shows good fastness, but the problems still remain that large dye effluent discharge, high chemical consumption, and long-time dyeing process. To counter these issues, herein we report a greener coloration method without any salt or alkali added for the coloration of silk/polyamide fabrics. Three bio-based acids like acetic acid, citric acid, and tannic acid were introduced into the dye solution to improve the interaction of dye molecules and fibers. Much of the focus has been given to understand the mechanism between the dye molecules, bio-based acids and fibers, which was determined through dynamic surface tension and UV–visible absorption spectrum measurement. Through this, it was found that the citric acid due to its maximum number of carboxyl groups than acetic acid and tannic acid promoted the disaggregation of dyes and enhanced the dye diffusion to fiber surface. As a result, the dye fixation and color strength of silk and polyamide fibers were all significantly improved when using citric acid at pH 6 with the steaming for 5 min. From the SEM analysis, it was seen that the surface morphology of silk/polyamide fibers was not so much affected. Compared with the traditional dyeing method, this method exhibited enhanced color performance with a shorter dyeing process, lower chemical consumption and nice fastness property. This work presented a potential and practical application of natural additives in the dyeing of multi-component fabrics to achieve eco-friendly and high-quality textile products.

Composite GO@Silk membrane for capillary-driven energy conversion

Capillary-driven energy conversion based on saline electrolytes has attracted significant interest in recent years. The use of two-dimensional (2D) layer-by-layer membranes on this purpose have been widely reported, due to the sub-nanometer channels in such membranes provide a good capillary effect. The present study provides novel insights into the capillary-driven energy conversion performance of a 2D composite membrane consisting of a graphene oxide (GO) matrix and natural silk fibers. Notably, the composite structure of the GO@silk membrane results in a greater physical robustness, while the silk fibers increase the charge density of the 2D layers and hence improve their ion selectivity. Under the combined effects of capillary-driven flow in the layer channel and an overlapped electrical double layer (EDL) at the interface between the electrolyte and the negatively charged GO@silk structure, counter-ions (i.e., Na+) are readily attracted and transferred to the layer spacing of the membrane, resulting in the formation of an electrical voltage and current. We numerically and experimentally investigate the contribution of the silk mass ratio on the performance of the composite membrane. The electrolyte and tilt angle are found to show significant effect on output voltage and current. The experimental results show that the voltage and current have high values of 0.22 V and 12 μA, respectively. Overall, the present results suggest the feasibility of utilizing a stack of composite membrane structures to perform environmental energy conversion on a larger scale.

Restructuring the Interface of Silk-Polycaprolactone Biocomposites Using Rigid-Flexible Agents.

Natural fiber-reinforced biocomposites with excellent mechanical and biological properties have attractive prospects for internal medical devices. However, poor interfacial adhesion between natural silk fiber and the polymer matrix has been a disturbing issue for such applications. Herein, rigid-flexible agents, such as polydopamine (PDA) and epoxy soybean oil (ESO), were introduced to enhance the interfacial adhesion between Antheraea pernyi (Ap) silk and a common medical polymer, polycaprolactone (PCL). We compared two strategies of depositing PDA first (Ap-PDA-ESO) and grafting ESO first (Ap-ESO-PDA). The rigid-flexible interfacial agents introduced multiple molecular interactions at the silk-PCL interface. The "Ap-PDA-ESO" strategy exhibited a greater enhancement in interfacial adhesion, and interfacial toughening mechanisms were proposed. This work sheds light on engineering strong and tough silk fiber-based biocomposites for biomedical applications.

Peculiar Tensile and Fracture Behaviors of Natural Silk Fiber in the Presence of an Artificial Notch

Natural silk fibers achieve remarkable toughness by exploiting hierarchical structure organizations over many length scales. These hierarchical architectures are often decorated with defects that usually lead to catastrophic failure of artificial polymer materials. Silk fibers are self-tolerant of intrinsic/artificial defects to give surprising fracture toughness, but how they fulfill this function and the underlying mechanism remain elusive. Here, we unveil this puzzle by experimentally and theoretically investigating the tensile and facture behaviors of Antheraea pernyi (A. pernyi) silk monofilaments containing an artificial notch of controlled depth. The introduced transverse notch can be blunted effectively by ahead developed longitudinal crack through fibrillar separation. The notched silk fibers show ductile failure with tensile behavior dominated by the magnitude of longitudinal crack, which depends not only on the notch size but also on the interface interaction between nanofibrils. We propose that the highly oriented, disentangled nanofibrillar structure of A. pernyi silk offers it distinct tensile properties, path of crack propagation, and fracture mode in comparison with highly oriented synthetic fibers.

The mechanical behavior of silk-fibroin reinforced alginate hydrogel biocomposites - Toward functional tissue biomimetics

Soft tissues are constructed as fiber-reinforced composites consisting of structural mechanisms and unique mechanical behavior. Biomimetics of their mechanical behavior is currently a significant bioengineering challenge, emphasizing the need to replicate structural and mechanical mechanisms into novel biocomposite designs. Here we present a novel silk-based biocomposite laminate constructed from long natural silk and fibroin fibers embedded in an alginate hydrogel matrix. Controlling the mechanical features of these laminates were studied for different fiber volume fractions (VF) and orientations using unidirectional tensile tests. Three material systems were investigated having different fiber orientations: longitudinal (0°), transverse (90°), and cross-plied (0/90°). The general behavior of the biocomposite laminates was anisotropic hyperelastic with large deformations. Longitudinal fibroin laminates have shown a tensile modulus of 178.55 ± 14.46 MPa and tensile strength of 18.47 ± 2.01 MPa for 0.48 VF. With similar VF, cross-plied fibroin laminates demonstrated structural shielding ability, having a tensile modulus and tensile strength of 101.73 ± 8.04 MPa and 8.29 ± 1.63 MPa for only a third of the VF directed in the stretching direction. The stress-strain behavior was in a similar range to highly stiff native human soft tissues such as ligament and meniscus. These findings demonstrate the potential of the fibroin fiber-reinforced biocomposites to mimic the mechanics of tissues with a quantitatively controlled amount of fibers and designed spatial arrangement. This can lead to new solutions for the repair and replacement of damaged functional and highly stiff soft tissues.