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Spider dragline silk is a remarkably strong fiber that makes it attractive for numerous applications. Much has thus been done to make similar fibers by biomimic spinning of recombinant dragline silk proteins. However, success is limited in part due to the inability to successfully express native-sized recombinant silk proteins (250–320 kDa). Here we show that a 284.9 kDa recombinant protein of the spider Nephila clavipes is produced and spun into a fiber displaying mechanical properties comparable to those of the native silk. The native-sized protein, predominantly rich in glycine (44.9%), was favorably expressed in metabolically engineered Escherichia coli within which the glycyl-tRNA pool was elevated. We also found that the recombinant proteins of lower molecular weight versions yielded inferior fiber properties. The results provide insight into evolution of silk protein size related to mechanical performance, and also clarify why spinning lower molecular weight proteins does not recapitulate the properties of native fibers. Furthermore, the silk expression, purification, and spinning platform established here should be useful for sustainable production of natural quality dragline silk, potentially enabling broader applications.

Structure design provides an effective solution to develop advanced soft materials with desirable mechanical properties. However, creating multiscale structures in ionogels to obtain strong mechanical properties is challenging. Here, an in situ integration strategy for producing a multiscale‐structured ionogel (M‐gel) via ionothermal‐stimulated silk fiber splitting and moderate molecularization in the cellulose‐ions matrix is reported. The produced M‐gel shows a multiscale structural superiority comprised of microfibers, nanofibrils, and supramolecular networks. When this strategy is used to construct a hexactinellid inspired M‐gel, the resultant biomimetic M‐gel shows excellent mechanical properties including elastic modulus of 31.5 MPa, fracture strength of 6.52 MPa, toughness reaching 1540 kJ m−3, and instantaneous impact resistance of 3.07 kJ m−1, which are comparable to those of most previously reported polymeric gels and even hardwood. This strategy is generalizable to other biopolymers, offering a promising in situ design method for biological ionogels that can be expanded to more demanding load‐bearing materials requiring greater impact resistance. A high‐performance biomimetic ionogel is developed by in situ multiscale design of silk fiber in a cellulose‐ions matrix. The biomimetic ionogel shows high ionic conductivity of 49.6 mS cm−1 and ultra‐strong mechanical properties with a fracture strength of 6.5 MPa and impact resistance as high as 3.07 kJ m−1, holding great application potential in flexible bioelectronics and smart protective devices.

The utilization of harmful chemicals, such as ions of heavy metals, organic and inorganic dyes, and oils, has expanded dramatically due to rapid industrialization and urbanization. The haphazard discharge of these chemicals has menaced the terrain and aquatic bodies, causing transfiguration for aquatic and non-aquatic life. Frequently used techniques like membrane filtration and reverse osmosis for effluent removal have impediments such as toxic sludge generation, erratic pollutant removal, and an expensive process that is annihilated using the most efficient technique of effluent treatment, ‘Adsorption’. Conventional adsorbents, like activated carbon, generate secondary sludge and are challenging to reactivate post-treatment. Hence, an abundantly accessible natural material like silk fibroin is used as an adsorbent with superior mechanical properties, biodegradability, and regenerability. The silk fibers obtained post-degumming are then functionalized and used with several engineered biomaterials forming composites, exhibiting excellent adsorption efficiencies for removing metal ions and dyes and separating oil from water. With adsorption efficiencies of greater than 90% for copper ions, 93.75% for lead ions, and adsorption capacities of 88.5 mg/g for acid-yellow 11, and 74.63 mg/g for naphthol orange, functionalized silk composites can be employed to discard pollutants. This review emphasizes the characteristics of functionalized silk fibroins for the removal of various heavy metal ions. Furthermore, it discusses the optimal parameters required for adsorption and kinetics and isotherms, followed by the thermodynamic evaluation, which gives insights into the reaction's spontaneity.

The creation of protein‐based magnetic fibers is a strategic issue in the field of advanced biocompatible materials, particularly relevant for technological sectors such as soft robotics and smart medicine. Here, we endow artificial spider silk fibers, which outperform many man‐made fibers in terms of mechanical properties, with magnetic functionality through the incorporation of magnetic nanoparticles. We present two novel composite fibers, containing magnetite nanoparticles coated with aminopropylsilane and dextran, and compare them with a third fiber type, which was made, following an approach previously developed by us, using magnetite nanoparticles coated with dimercaptosuccinic acid. The nanoparticles also differ in their mean size, varying between 9 and 32 nm. The fibers are produced by wet spinning, with a nominal magnetite concentration in the 0.2–20 wt.% range. However, the coating rules the colloidal stability of the nanoparticles in the spinning dope and their tendency to agglomerate. Therefore, the actual magnetite concentration and the degree of dispersion of the nanoparticles in the fibers are different in the different composites, as revealed by magnetic analyses. All fibers, even those with the highest magnetite content, remain ductile, whereas the mechanical strength is only slightly reduced compared to the fiber without nanoparticles, hence without magnetic functionality. Artificial spider silk fibers are endowed with magnetic functionality by incorporating magnetite nanoparticles, with different coating and size, at nominal magnetite concentrations between 0.2 and 20 wt.%. The fibers are robust and ductile. The characteristics of the nanoparticles determine their degree of dispersion in the fibers and are crucial to achieve a high magnetite content, thus ruling the magnetic performance.

Metal ions are involved in the conformational transition of silk fibroin and influence the structure and mechanical properties of silk fibers. However, the dynamic characteristics of metal ions during the formation of silk fibers remain unclear. In this study, we found that the silk glands of silkworms contain various metal elements, with varying levels of the metal elements in different zones of the glands and higher levels in the anterior silk glands. Additionally, the content of various metallic elements in the silk glands varied greatly before and after spinning, similar to their content in different cocoon layers, thus, indicating that the anterior silk glands maintain a certain metal ion environment for the transport and conformational transformation of the silk proteins. Most of the metallic elements located in fibroin were confirmed using degumming experiments. For the first time, a scanning electron microscope energy spectrometry system was used to characterize the metal elements in the cross-section of silk and cocoons. These findings have deepened our understanding of the relationship between the overall metal ion environment and silk fiber formation and help us further conceptualize the utilization of metal ions as targets to improve the mechanical properties of the silk fibers.

Ultrafine fibers are widely employed because of their lightness, softness, and warmth retention. Although silkworm silk is one of the most applied natural silks, it is coarse and difficult to transform into ultrafine fibers. Thus, to obtain ultrafine high-performance silk fibers, we employed anti-juvenile hormones in this study to induce bimolter silkworms. We found that the bimolter cocoons were composed of densely packed thin fibers and small apertures, wherein the silk diameter was 54.9% less than that of trimolter silk. Further analysis revealed that the bimolter silk was cleaner and lighter than the control silk. In addition, it was stronger (739 MPa versus 497 MPa) and more stiffness (i.e., a higher Young’s modulus) than the trimolter silk. FTIR and X-ray diffraction results revealed that the excellent mechanical properties of bimolter silk can be attributed to the higher β-sheet content and crystallinity. Chitin staining of the anterior silk gland suggested that the lumen is narrower in bimolters, which may lead to the formation of greater numbers of β-sheet structures in the silk. Therefore, this study reveals the relationship between the structures and mechanical properties of bimolter silk and provides a valuable reference for producing high-strength and ultrafine silk fibers.

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.

With growing environmental awareness, natural fibers have recently received significant interest as reinforcement in polymer composites. Among natural fibers, silk can potentially be a natural alternative to glass fibers, as it possesses comparable specific mechanical properties. In order to investigate the processability and properties of silk reinforced composites, vacuum assisted resin transfer molding (VARTM) was used to manufacture composite laminates reinforced with woven silk preforms. Specific mechanical properties of silk/epoxy laminates were found to be anisotropic and comparable to those of glass/epoxy. Silk composites even exhibited a 23% improvement of specific flexural strength along the principal weave direction over the glass/epoxy laminate. Applying 300 kPa external pressure after resin infusion was found to improve the silk/epoxy interface, leading to a discernible increase in breaking energy and interlaminar shear strength. Moreover, the effect of fabric moisture on the laminate properties was investigated. Unlike glass mats, silk fabric was found to be prone to moisture absorption from the environment. Moisture presence in silk fabric prior to laminate fabrication yielded slower fill times and reduced mechanical properties. On average, 10% fabric moisture induced a 25% and 20% reduction in specific flexural strength and modulus, respectively.

Fiber microactuators are interesting in wide variety of emerging fields, including artificial muscles, biosensors, and wearable devices. In the present study, a robust, fast‐responsive, and humidity‐induced silk fiber microactuator is developed by integrating force‐reeling and yarn‐spinning techniques. The shape gradient, together with hierarchical rough surface, allows these silk fiber microactuators to respond rapidly to humidity. The silk fiber microactuator can reach maximum rotation speed of 6179.3° s−1 in 4.8 s. Such a response speed (1030 rotations per minute) is comparable with the most advanced microactuators. Moreover, this microactuator generates 2.1 W kg−1 of average actuation power, which is twice higher than fiber actuators constructed by cocoon silks. The actuating powers of silk fiber microactuators can be precisely programmed by controlling the number of fibers used. Lastly, theory predicts the observed performance merits of silk fiber microactuators toward inspiring the rational design of water‐induced microactuators. A new kind of robust and fast‐responsive silk microactuators, by integrating experimental and theoretical designs, are presented. These microactuators feature an ultrafast response speed for humidity change with performance that can compare with the most advanced microactuator systems.

The growing demand for sustainable, high-performance composite materials has increased the interest in natural fibers as reinforcements for brake friction materials (BFMs). Silk and Grewia optiva fibers, in particular, have emerged as promising candidates for BFMs due to their good mechanical properties, biodegradability, and availability. To evaluate their potential, friction materials were formulated with 6% Grewia (GF), 6% silk (SF), and a hybrid formulation containing 3% of both fibers (SGF), alongside a reference material reinforced with 6% aramid fiber (AF). These composites were then tested on a braking tribometer using an extended SAE J2522 procedure to assess their performance. The AF formulation showed slightly better wear resistance and the GF formulation showed inferior performance during high-temperature cycles, whereas SF and SGF performed close to the reference formulation (AF) in these sections. In terms of friction stability, SF matched the AF formulation, while GF demonstrated significantly poorer stability. The first high-temperature exposure of the BFMs (Fade 1) served as a critical thermal settlement phase, after which they demonstrated both improved friction stability and repeatable performance characteristics. Finally, this study demonstrates that silk fiber represents a viable, sustainable alternative to aramid in BFMs, exhibiting comparable performance in terms of friction stability and thermal resistance.