Tough protein-carbon nanotube hybrid fibers comparable to natural spider silks

Heat-Insulated Regenerated Fibers with UV Resistance: Silk Fibroin/Al2O3 Nanoparticles

The various wastes generated by silkworm silk textiles that are no longer in use are increasing, which is causing considerable waste and contamination. This issue has attracted widespread attention in countries that use a lot of silk. Therefore, enhancing the mechanical properties of regenerated silk fibroin (RSF) and enriching the function of silk are important directions to expand the comprehensive utilization of silk products. In this paper, the preparation of RSF/Al2O3 nanoparticles (NPs) hybrid fiber with different Al2O3 NPs contents by wet spinning and its novel performance are reported. It was found that the RSF/Al2O3 NPs hybrid fiber was a multifunctional fiber material with thermal insulation and UV resistance. Natural light tests showed that the temperature rise rate of RSF/Al2O3 NPs hybrid fibers was slower than that of RSF fibers, and the average temperature rose from 29.1 °C to about 35.4 °C in 15 min, while RSF fibers could rise to about 40.1 °C. UV absorption tests showed that the hybrid fiber was resistant to UV radiation. Furthermore, the addition of Al2O3 NPs may improve the mechanical properties of the hybrid fibers. This was because the blending of Al2O3 NPs promoted the self-assembly of β-sheets in the RSF reaction mixture in a dose-dependent manner, which was manifested as the RSF/Al2O3 NPs hybrid fibers had more β-sheets, crystallinity, and a smaller crystal size. In addition, RSF/Al2O3 NPs hybrid fibers had good biocompatibility and durability in micro-alkaline sweat environments. The above performance makes the RSF/Al2O3 NPs hybrid fibers promising candidates for application in heat-insulating and UV-resistant fabrics as well as military clothing.

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.

Polysaccharide-protein microparticles based-scaffolds to recover soft tissue loss in mild periodontitis

Periodontal regeneration is extremely limited and unpredictable due to structural complications, as it requires the simultaneous restoration of different tissues, including cementum, gingiva, bone, and periodontal ligament. In this work, spray-dried microparticles based on green materials (polysaccharides - gums - and a protein - silk fibroin) are proposed to be implanted in the periodontal pocket as 3D scaffolds during non-surgical treatments, to prevent the progression of periodontal disease and to promote the healing in mild periodontitis. Arabic or xanthan gum have been associated to silk fibroin, extracted from Bombyx mori cocoons, and loaded with lysozyme due to its antibacterial properties. The microparticles were prepared by spray-drying and cross-linked by water vapor annealing, inducing the amorphous to semi-crystalline transition of the protein component. The microparticles were characterized in terms of their chemico-physical features (SEM, size distribution, structural characterization - FTIR and SAXS, hydration and degradation properties) and preclinical properties (lysozyme release, antibacterial properties, mucoadhesion, in vitro cells adhesion and proliferation and in vivo safety on a murine incisional wound model). The encouraging preclinical results highlighted that these three-dimensional (3D) microparticles could provide a biocompatible platform able to prevent periodontitis progression and to promote the healing of soft tissues in mild periodontitis.

Two-in-One Spider Silk Protein with Combined Mechanical Features in All-Aqueous Spun Fibers

Major ampullate (MA) spider silk reveals outstanding mechanical properties in terms of a unique combination of high tensile strength and extensibility, unmatched by most other known native or synthetic fiber materials. MA silk contains at least two spider silk proteins (spidroins), and here, a novel two-in-one (TIO) spidroin was engineered, resembling amino acid sequences of such two of the European garden spider. The combination of mechanical and chemical features of both underlying proteins facilitated the hierarchical self-assembly into β-sheet-rich superstructures. Due to the presence of native terminal dimerization domains, highly concentrated aqueous spinning dopes could be prepared from recombinant TIO spidroins. Subsequently, fibers were spun in a biomimetic, aqueous wet-spinning process, yielding mechanical properties at least twice as high as fibers spun from individual spidroins or blends. The presented processing route holds great potential for future applications using ecological green high-performance fibers.

The Size Effect of Silver Nanoparticles on Reinforcing the Mechanical Properties of Regenerated Fibers

Regenerated silk fibroin (RSF), made from discarded silk cocoons, can be processed into regenerated silk fibers by a simple, inexpensive, and environmentally friendly wet-spinning process. However, the breaking strength and toughness of most RSF fibers are lower than those of natural silk. In this study, Ag nanoparticles (NPs) of different sizes were introduced into RSF to form RSF/AgNPs hybrid fibers by wet spinning. The effects of AgNPs of different sizes on the mechanical properties and structure of the hybrid fibers were investigated. The results demonstrated that the mechanical properties of hybrid fibers were significantly improved, especially the breaking strain, after the addition of four different sizes of AgNPs. With the reduction in AgNPs size (2-60 nm), the breaking strength and breaking strain of hybrid fibers tended to increase. The results showed that the hybrid fibers containing 2 nm AgNPs were remarkable, with excellent mechanical properties and toughness, and the breaking strain reached 138.27%, which was far greater than blank RSF fibers (15.02%) and even natural silk (about 21%). The S-FTIR and WAXD showed that, compared with the larger AgNPs, the smaller AgNPs contributed more to the formation of silk fibroin β-sheet and crystallinity, and reduced the β-crystallite size. This study is helpful to understand the relationship between the size of nanoparticles and the mechanical properties of hybrid fibers.

Electrospun Silk Fibroin-CNT Composite Fibers: Characterization and Application in Mediating Fibroblast Stimulation

Electrospinning is a simple, low-cost, and highly efficient technique to generate desirable nano/microfibers from polymer solutions. Silk fibroin (SF), a biopolymer found in Bombyx mori cocoons, has attracted attention for various biomedical applications. In this study, functionalized CNT was incorporated in SF to generate biocomposite fibers by electrospinning. The electrospun (E-spun) fibers were well aligned with morphology mimicking the locally oriented ECM proteins in connective tissues. While as-spun fibers dissolved in water in just two minutes, ethanol vapor post-treatment promoted β-sheet formation leading to improved fiber stability in an aqueous environment (>14 days). The addition of a minute amount of CNT effectively improved the E-spun fiber alignment and mechanical strength while retained high biocompatibility and biodegradability. The fibers’ electrical conductivity increased by 13.7 folds and 21.8 folds, respectively, in the presence of 0.1 w% and 0.2 w% CNT in SF fibers. With aligned SF-CNT 0.1 % fibers as a cell culture matrix, we found electrical stimulation effectively activated fibroblasts from patients of pelvic organ prolapse (POP), a connective tissue disorder. The stimulation boosted the fibroblasts’ productivity of collagen III (COLIII) and collagen I (COLI) by 74 folds and 58 folds, respectively, and reduced the COLI to COLIII ratio favorable for tissue repair. The developed material and method offer a simple, direct, and effective way to remedy the dysfunctional fibroblasts of patients for personalized cell therapeutic treatment of diseases and health conditions associated with collagen disorder.

From Mesoscopic Functionalization of Silk Fibroin to Smart Fiber Devices for Textile Electronics and Photonics

Bombyx mori silk fibers exhibit significant potential for applications in smart textiles, such as fiber sensors, fiber actuators, optical fibers, and energy harvester. Silk fibroin (SF) from B. mori silkworm fibers can be reconstructed/functionalized at the mesoscopic scale during refolding from the solution state into fibers. This facilitates the mesoscopic functionalization by engaging functional seeds in the refolding of unfolded SF molecules. In particular, SF solutions can be self-assembled into regenerated fiber devices by artificial spinning technologies, such as wet spinning, dry spinning, microfluidic spinning, electrospinning, and direct writing. Meso-functionalization manipulates the SF property from the mesoscopic scale, transforming the original silk fibers into smart fiber devices with smart functionalities, such as sensors, actuators, optical fibers, luminous fibers, and energy harvesters. In this review, the progress of mesoscopic structural construction from SF materials to fiber electronics/photonics is comprehensively summarized, along with the spinning technologies and fiber structure characterization methods. The applications, prospects, and challenges of smart silk fibers in textile devices for wearable personalized healthcare, self-propelled exoskeletons, optical and luminous fibers, and sustainable energy harvesters are also discussed.

Toughening Wet-Spun Silk Fibers by Silk Nanofiber Templating

Regenerated silk fibers typically fall short of silkworm cocoon fibers in mechanical properties due to reduced fiber crystal structure and alignment. One approach to address this has been to employ inorganic materials as reinforcing agents. The present study avoids the need for synthetic additives, demonstrating the first use of exfoliated silk nanofibers to control silk solution crystallization, resulting in all-silk pseudocomposite fibers with remarkable mechanical properties. Incorporating only 0.06 wt. % silk nanofibers led to a ∼44% increase in tensile strength (over 600 MPa) and ∼33% increase in toughness (over 200 kJ/kg) compared with fibers without silk nanofibers. These remarkable properties can be attributed to nanofiber crystal seeding in conjunction with fiber draw. The crystallinity nearly doubled from ∼17% for fiber spun from pure silk solution to ∼30% for the silk nanofiber reinforced sample. The latter fiber also shows a high degree of crystal orientation with a Herman's orientation factor of 0.93, a value which approaches that of natural degummed B. mori silk cocoon fiber (0.96). This study provides a strong foundation to guide the development of simple, eco-friendly methods to spin regenerated silk with excellent properties and a hierarchical structure that mimics natural silk. This article is protected by copyright. All rights reserved.

Photothermal Regenerated Fibers with Enhanced Toughness: Silk Fibroin/MoS2 Nanoparticles

The distinctive mechanical and photothermal properties of Molybdenum sulfide (MoS2) have the potential for improving the functionality and utilization of silk products in various sectors. This paper reports on the preparation of regenerated silk fibroin/molybdenum disulfide (RSF/MoS2) nanoparticles hybrid fiber with different MoS2 nanoparticles contents by wet spinning. The simulated sunlight test indicated that the temperature of 2 wt% RSF/MoS2 nanoparticles hybrid fibers could rise from 20.0 °C to 81.0 °C in 1 min and 98.6 °C in 10 min, exhibiting good thermal stability. It was also demonstrated that fabrics made by manual blending portrayed excellent photothermal properties. The addition of MoS2 nanoparticles could improve the toughness of hybrid fibers, which may be since the mixing of MoS2 nanoparticles hindered the self-assembly of β-sheets in RSF solution in a concentration-dependent manner because RSF/MoS2 nanoparticles hybrid fibers showed a lower β-sheet content, crystallinity, and smaller crystallite size. This study describes a new way of producing high toughness and photothermal properties fibers for multifunctional fibers' applications.

Thermochromic Silks for Temperature Management and Dynamic Textile Displays

HIGHLIGHTS

Wearable and smart textiles are constructed by integrating embroidery technology and 5G cloud communication, showing promising applications in temperature management and real-time dynamic textile displays. Thermochromism is introduced into the natural silk to produce high-performance thermochromic silks (TCSs) through a low cost, sustainable, efficient, and scalable strategy. The interfacial bonding of the continuously produced TCSs is in situ analyzed and improved through pre-solvent treatment and is confirmed using synchrotron Fourier transform infrared microspectroscopy.

ABSTRACT

Silks have various advantages compared with synthetic polymer fibers, such as sustainability, mechanical properties, luster, as well as air and humidity permeability. However, the functionalization of silks has not yet been fully developed. Functionalization techniques that retain or even improve the sustainability of silk production are required. To this end, a low-cost, effective, and scalable strategy to produce TCSs by integrating yarn-spinning and continuous dip coating technique is developed herein. TCSs with extremely long length (> 10 km), high mechanical performance (strength of 443.1 MPa, toughness of 56.0 MJ m⁻³, comparable with natural cocoon silk), and good interfacial bonding were developed. TCSs can be automatically woven into arbitrary fabrics, which feature super-hydrophobicity as well as rapid and programmable thermochromic responses with good cyclic performance: the response speed reached to one second and remained stable after hundreds of tests. Finally, applications of TCS fabrics in temperature management and dynamic textile displays are demonstrated, confirming their application potential in smart textiles, wearable devices, flexible displays, and human–machine interfaces. Moreover, combination of the fabrication and the demonstrated applications is expected to bridge the gap between lab research and industry and accelerate the commercialization of TCSs. [Image: see text]

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s40820-021-00591-w.

Analysis of the Contribution of Conformation and Fibrils on Tensile Toughness and Fracture Resistance of Camel Hairs

Animal hairs, like other natural fibers, display excellent mechanical properties, especially, the tensile toughness and fracture resistance. Several structure-mechanics models have attributed mechanical superiority of hair to its unique nanocomposite structure which consists of intermediate filaments and matrix. However, the contribution of fibrils and their associated interfaces on the mechanical properties of animal hairs remains unclear. Herein, using the small- and wide-angle X-ray scattering, and an ultrahigh-speed microcamera system, it is confirmed that the conformation and fibrils (which represent both nanofibrils and microfibrils) of the keratin channel endow tensile toughness and fracture resistance to camel hairs. During the stretching process, an α-β transition occurred at the secondary structure level, leading to the formation of a tensile plateau, which improves the toughness compared with the structure without a conformation transition. Meanwhile, fibrils further toughened the camel hairs and resisted their crack propagation through confined fibrillar slippage, splitting, and pulling. These structure-property relations in natural hairs can inspire damage-tolerant polymer fiber design.

Ultrafine and High-Strength Silk Fibers Secreted by Bimolter Silkworms

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.

Artificial ligament made from silk protein/Laponite hybrid fibers

With developments in tissue engineering, artificial ligaments are expected to be future materials for anterior cruciate ligament (ACL) reconstruction. However, poor healing of the intraosseous part after ACL reconstruction significantly hinders their applications in this field. In this study, a bioactive clay Laponite (LAP) was introduced into the regenerated silk fibroin (RSF) spinning dope to produce functional RSF/LAP hybrid fibers by wet-spinning. These RSF/LAP hybrid fibers were then woven into artificial ligament for ACL reconstruction. The structure and mechanical properties of RSF/LAP hybrid fibers were extensively studied by different means. Results confirmed the presence of LAP in RSF fibers and revealed that the addition of LAP slightly deteriorated the comprehensive mechanical properties of RSF fibers. However, they were still much tougher (with higher breaking energy) than those of degummed natural silkworm silk that was earlier used for making artificial ligament. The artificial ligament woven from RSF/LAP hybrid fibers showed better cytocompatibility and osteogenic differentiation with mouse pre-osteoblasts in vitro than those made from degummed natural silkworm silks and pure RSF fibers. Furthermore, in vivo study in a rat ACL reconstruction model demonstrated that the presence of LAP in the artificial ligament could significantly enhance the graft osseointegration process and also improve the corresponding biomechanical properties of the artificial ligament. Based upon these results, the RSF/LAP hybrid fibers, which can be mass produced by wet-spinning process, are believed to have a great potential for use as artificial ligament materials for ACL reconstruction. STATEMENT OF SIGNIFICANCE: In this study, we successfully introduced Laponite (LAP), a kind of clay that has the function of osteogenic induction, into regenerated silk fibroin (RSF) fibers, which was prepared by a mature wet-spinning method developed in our lab. We believe that through artificial spinning, additional functional components can be added into RSF fibers, which one can hardly achieve with natural silks. We showed that the artificial ligament woven from RSF/LAP hybrid fibers had better cytocompatibility and osteogenic differentiation for mouse pre-osteoblasts in vitro, and significantly enhanced the graft osseointegration process and improved the corresponding biomechanical properties in a rat ACL reconstruction model in vivo, compared to those artificial ligaments made from degummed natural silkworm silks and pure RSF fibers.

Colorless Silk/Copper Sulfide Hybrid Fiber and Fabric with Spontaneous Heating Property under Sunlight

With the increasing demand for comfort, thinness, and warmth of fabrics, various functional fibers have emerged. However, natural silkworm silk, as one of the most widely used natural fibers in textile, faces the issue that it cannot be modified during the spinning process like synthetic fibers. Herein, copper sulfide nanoparticles (CuS NPs) with a near-infrared (NIR) absorption property were first prepared by using regenerated silk fibroin (RSF) as the biological template. Then, trace CuS NPs prepared in RSF solution (no more than 100 ppm) were added into the RSF spinning dope to prepare colorless RSF/CuS hybrid fibers via wet-spinning process. The tensile test of the RSF/CuS hybrid fibers showed that the toughness was improved with the addition of CuS NPs, which completely met the requirements of textile development. The temperature of RSF/CuS hybrid fiber bundles could increase 18.5 °C within 3 min under 1064 nm laser irradiation with power density of 1.0 W/cm². Finally, these RSF/CuS hybrid fiber bundles were woven into silk fabric or embroidered on a cotton fabric. Under the simulated sunlight, the temperature of RSF/CuS fabric could increase to more than 40 °C from room temperature. Also, as per the infrared images, the pattern of embroidery displayed a significant difference in temperature increase as compared to cotton matrix. Based on these results, an almost colorless RSF/CuS hybrid fiber that can be mass produced by wet spinning may have great potential in the fabrication of dyeable, light, and comfortable silk functional fabric with spontaneous heating characteristics under sunlight.

A supertough electro-tendon based on spider silk composites

Compared to transmission systems based on shafts and gears, tendon-driven systems offer a simpler and more dexterous way to transmit actuation force in robotic hands. However, current tendon fibers have low toughness and suffer from large friction, limiting the further development of tendon-driven robotic hands. Here, we report a super tough electro-tendon based on spider silk which has a toughness of 420 MJ/m3 and conductivity of 1,077 S/cm. The electro-tendon, mechanically toughened by single-wall carbon nanotubes (SWCNTs) and electrically enhanced by PEDOT:PSS, can withstand more than 40,000 bending-stretching cycles without changes in conductivity. Because the electro-tendon can simultaneously transmit signals and force from the sensing and actuating systems, we use it to replace the single functional tendon in humanoid robotic hand to perform grasping functions without additional wiring and circuit components. This material is expected to pave the way for the development of robots and various applications in advanced manufacturing and engineering.

Direct Observation of Native Silk Fibroin Conformation in Silk Gland of Bombyx mori Silkworm

To understand the natural silk spinning mechanism, synchrotron Fourier transform infrared (S-FTIR) microspectroscopy was employed in this study to monitor the conformation changes of silk protein in the silk gland of Bombyx mori silkworm. The ultrahigh brightness of S-FTIR microspectroscopy allowed the imaging of the silk gland with micrometer-scale spatial resolution. Herein, tissue sections of a silk gland, including cross-section slices and longitudinal-section slices, were characterized. The results obtained clearly confirm that the conformation of the silk fibroin changes gradually along the silk gland from the tail to the spinneret. In the middle silk gland, silk fibroin mainly contains random coil/helix conformation. When it comes to the spinneret through the anterior silk gland, the content of β-sheet increases, but the content of random coil/helix instead reduces gradually. Further, the β-sheet distribution in the cross-section of the anterior silk gland was imaged using S-FTIR mapping technique. The results show that the structural distribution of the silk fibroin in cross-section is uniform without significant shell-core structure, which implies that the primary driving force to induce the conformation transition of silk fibroin from random coil/helix to β-sheet during the spinning process is elongational flow of silk fibroin in the silk gland and not the shear force between the silk fibroin and the lumen wall of silk gland. These direct pieces of evidence of silk fibroin structure in the silk gland would definitely promote a deeper understanding of the natural spinning process.

Effect of stress on the molecular structure and mechanical properties of supercontracted spider dragline silks

Supercontraction is one of the most interesting properties of spider dragline silks. In this study, changes in the secondary structures of the Nephila edulis spider dragline silk after it was subjected to different supercontraction processes were investigated by integrating synchrotron Fourier transform infrared (S-FTIR) microspectroscopy and mechanical characterization. The results showed that after free supercontraction, the β-sheet lost most of its orientation, while the helix and random coils were almost totally disordered. Interestingly, by conducting different types of supercontractions (i.e., stretching of the free supercontracted spider dragline silk to its original length or performing constrained supercontraction), it was found that although the molecular structures all changed after supercontraction, the mechanical properties almost remained unchanged when the length of the spider dragline silk did not change significantly. The other interesting conclusion obtained is that the manual stretching of a poorly oriented spider dragline silk cannot selectively improve the orientation degree of the β-sheet in the spider silk, but increase the orientation degree of all conformations (β-sheet, helix, and random). These experimental findings not only help to unveil the structure-property-function relationship of natural spider silks, but also provide a useful guideline for the design of biomimetic spider fiber materials.

Super-strong and Intrinsically Fluorescent Silkworm Silk from Carbon Nanodots Feeding

Fluorescent silk is fundamentally important for the development of future tissue engineering scaffolds. Despite great progress in the preparation of a variety of colored silks, fluorescent silk with enhanced mechanical properties has yet to be explored. In this study, we report on the fabrication of intrinsically super-strong fluorescent silk by feeding Bombyx mori silkworm carbon nanodots (CNDs). The CNDs were incorporated into silk fibroin, hindering the conformation transformation, confining crystallization, and inducing orientation of mesophase. The resultant silk exhibited super-strong mechanical properties with breaking strength of 521.9 ± 82.7 MPa and breaking elongation of 19.2 ± 4.3%, improvements of 55.1% and 53.6%, respectively, in comparison with regular silk. The CNDs-reinforced silk displayed intrinsic blue fluorescence when exposed to 405 nm laser and exhibited no cytotoxic effect on cells, suggesting that multi-functional silks would be potentially useful in bioimaging and other applications.

Structural and Mechanical Properties of Silk from Different Instars of Bombyx mori

Silkworm silk has excellent mechanical properties, biocompatibility, and promising applications in the biomedical sector. Silkworms spin silk at the beginning and end of each of their five instar stages, as well as spinning mature silk after the fifth instar. We evaluated the mechanical properties and structure of 10 kinds of silk fibers from different stages. A tensile test showed that instar beginning silk, instar end silk, and mature silk possess distinct properties. Attenuated total reflectance Fourier-transform infrared spectroscopy and X-ray diffraction results showed that the excellent mechanical properties of instar end silk are attributed to higher β-sheet content and suitable crystallinity. Liquid chromatography-tandem mass spectrometry showed that P25 protein content in IV-E silk is 2.9× higher than that of cocoon silk. This study can offer guidelines for further biomimetic investigations into the design and manufacture of artificial silk protein fibers with novel function.

Obtaining high mechanical performance silk fibers by feeding purified carbon nanotube/lignosulfonate composite to silkworms

Silkworm fibers have attracted widespread attention for their superb glossy texture and promising mechanical performance. The mechanical properties can be reinforced with carbon nanofillers, particularly carbon nanotubes (CNTs), depending on the CNT content in the silk fibers. In order to increase the CNT content, lignosulfonate (LGS) was used as a surfactant to ameliorate the CNT solubility, dispersibility, and biocompatibility. The resulting CNT/LGS nano-composite was further processed through an additional purification method to remove excess surfactant and enhance the CNT/LGS ratio. Then the purified biocompatible single and multiple-walled CNTs were fed to silkworms, leading to a large CNT content in the resulting silk fibers. Reinforced silk fibers were produced with a mechanical strength as high as 1.07 GPa and a strain of 16.8%. The toughness modulus is 1.69 times than that of the unpurified group. The CNT-embedded silk fibers were characterized via Raman spectrometry and thermogravimetric analysis (TGA), demonstrating that the CNT content in the silk fibers increased 1.5-fold in comparison to the unpurified group. The increased CNT content not only contributed to the self-assembly into buffering knots of silk fibers, but it also enhanced the conductivity of graphitized silk. Our coating and purification strategies provide a potential facile way to obtain natural silk fibers with high mechanical performance.

Silkworm fibers have attracted widespread attention for their superb glossy texture and promising mechanical performance.

Conductive regenerated silk-fibroin-based hydrogels with integrated high mechanical performances

Strong and tough RSF-based hydrogels that could be used as a strain sensor, a touch screen pen and an electronic skin were developed.

Electrospun protein-CNT composite fibers and the application in fibroblast stimulation

Functional biopolymer scaffolds are in high demand for tissue regeneration. In this study, we incorporated functionalized CNT in collagen or silk protein solution to generate biocomposite fibers by electrospinning. The addition of CNT reinforced the strength of the scaffolds and rendered the fibers electrical conductivity to not only facilitate the E-spun fiber formation but also grant the fibers an additional functionality that can be utilized for cell stimulation. Considering fiber dimension, alignment, mechanical strength, electrical conductivity and biocompatibility, silk-CNT fibers containing a minute amount of CNT (0.05%) outperformed other fiber types. The modulation effect of these fibers was examined by their application in inducing polarization and activation of fibroblasts with cellular deficit. While the fibroblasts on both collagen-CNT and silk-CNT fibers synthesized a substantially higher level of collagen type III (COLIII) than cells on pure protein fibers to reduce the abnormally high COLI/COLIII ratio, electrical stimulation boosted the collagen productivity by 20 folds in cells on silk-CNT than on collagen-CNT due to silk-CNT's high electrical conductivity. The developed approach can be potentially utilized to remedy the dysfunctional fibroblasts for therapeutic treatment of diseases and health conditions associated with collagen disorder.

Tensan Silk-Inspired Hierarchical Fibers for Smart Textile Applications

Tensan silk, a natural fiber produced by the Japanese oak silk moth ( Antherea yamamai, abbreviated to A. yamamai), features superior characteristics, such as compressive elasticity and chemical resistance, when compared to the more common silk produced from the domesticated silkworm, Bombyx mori ( B. mori). In this study, the "structure-property" relationships within A. yamamai silk are disclosed from the different structural hierarchies, confirming the outstanding toughness as dominated by the distinct mesoscale fibrillar architectures. Inspired by this hierarchical construction, we fabricated A. yamamai silk-like regenerated B. mori silk fibers (RBSFs) with mechanical properties (extensibility and modulus) comparable to natural A. yamamai silk. These RBSFs were further functionalized to form conductive RBSFs that were sensitive to force and temperature stimuli for applications in smart textiles. This study provides a blueprint in exploiting rational designs from A. yamanmai, which is rare and expensive in comparison to the common and cost-effective B. mori silk to empower enhanced material properties.

Fluorinated graphene as an anticancer nanocarrier: an experimental and DFT study

Both experimental and theoretical research was conducted to explore the performance of fluorinated graphene as a novel anticancer nanocarrier, and we also reported its first application in cancer chemo-photothermal therapy.

Enhancing Mechanical Properties of Silk Fibroin Hydrogel through Restricting the Growth of β-Sheet Domains

Usually, regenerated silk fibroin (RSF) hydrogels cross-linked by chemical agents such as horseradish peroxide (HRP)/H₂O₂ perform elastic properties, while display unsatisfactory strength for practical applications especially as load-bearing materials, and inadequate stability when incubated in a simulated in vivo environment. Here, the RSF hydrogel with both excellent strength and elasticity was prepared by inducing the conformation transition from random coil to β-sheet in a restricted RSF network precross-linked by HRP/H₂O₂. Such "dual-networked" hydrogels, regarding the one with 10 wt % RSF (Mw: 220 kDa) as a representative, show around 100% elongation, as well as the compressive modulus and tensile modulus up to 3.0 and 2.5 MPa respectively, which are much higher than those of physically cross-linked natural polymer hydrogels (commonly within 0.01-0.1 MPa at the similar solid content). It has been shown that the enhanced comprehensive mechanical properties of RSF hydrogels derive from the formation of small-sized and uniformly distributed β-sheet domains in the hydrogel during the conformation transition of RSF whose size is limited by the first network formed by cross-linkers with HRP/H₂O₂. Importantly, the tough RSF hydrogel changes the normally weak recognition of various RSF hydrogels and holds a great potential to be the material in biomedical field because it seems to be very promising regarding its biocompatibility, biodegradability, etc.

Precise correlation of macroscopic mechanical properties and microscopic structures of animal silks—using Antheraea pernyi silkworm silk as an example

The structure of wild silkworm silk can be controlled by reeling rate, thus regulating its mechanical performance from close to spider dragline silk to domestic silkworm silk.

Microstructural evolution of regenerated silk fibroin/graphene oxide hybrid fibers under tensile deformation

The stress–strain curve and proposed model of microstructural change of silk fibroin/GO hybrid fibers during the stretching deformation.

Feeding Single-Walled Carbon Nanotubes or Graphene to Silkworms for Reinforced Silk Fibers

Silkworm silk is gaining significant attention from both the textile industry and research society because of its outstanding mechanical properties and lustrous appearance. The possibility of creating tougher silks attracts particular research interest. Carbon nanotubes and graphene are widely studied for their use as reinforcement. In this work, we report mechanically enhanced silk directly collected by feeding Bombyx mori larval silkworms with single-walled carbon nanotubes (SWNTs) and graphene. We found that parts of the fed carbon nanomaterials were incorporated into the as-spun silk fibers, whereas the others went into the excrement of silkworms. Spectroscopy study indicated that nanocarbon additions hindered the conformation transition of silk fibroin from random coil and α-helix to β-sheet, which may contribute to increased elongation at break and toughness modules. We further investigated the pyrolysis of modified silk, and a highly developed graphitic structure with obviously enhanced electrical conductivity was obtained through the introduction of SWNTs and graphene. The successful generation of these SWNT- or graphene-embedded silks by in vivo feeding is expected to open up possibilities for the large-scale production of high-strength silk fibers.

Dramatic Enhancement of Graphene Oxide/Silk Nanocomposite Membranes: Increasing Toughness, Strength, and Young's modulus via Annealing of Interfacial Structures

We demonstrate that stronger and more robust nacre-like laminated GO (graphene oxide)/SF (silk fibroin) nanocomposite membranes can be obtained by selectively tailoring the interfacial interactions between "bricks"-GO sheets and "mortar"-silk interlayers via controlled water vapor annealing. This facial annealing process relaxes the secondary structure of silk backbones confined between flexible GO sheets. The increased mobility leads to a significant increase in ultimate strength (by up to 41%), Young's modulus (up to 75%) and toughness (up to 45%). We suggest that local silk recrystallization is initiated in the proximity to GO surface by the hydrophobic surface regions serving as nucleation sites for β-sheet domains formation and followed by SF assembly into nanofibrils. Strong hydrophobic-hydrophobic interactions between GO layers with SF nanofibrils result in enhanced shear strength of layered packing. This work presented here not only gives a better understanding of SF and GO interfacial interactions, but also provides insight on how to enhance the mechanical properties for the nacre-mimic nanocomposites by focusing on adjusting the delicate interactions between heterogeneous "brick" and adaptive "mortar" components with water/temperature annealing routines.

Exploration of the tight structural-mechanical relationship in mulberry and non-mulberry silkworm silks

The Bombyx mori silkworm is well known as it has been bred by our ancestors with mulberry tree leaves for thousands of years. However, Bombyx mori is not the only silkworm that can produce silk, many other kinds of silkworms can also make silks for commercial use. In this research, we compare the mechanical properties of five different commercial silk fibres including domesticated mulberry Bombyx mori, non-mulberry semi-domesticated eri Samia ricini, and wild tropical tasar Antheraea mylitta and muga Antheraea assamensis. The results demonstrate that the non-mulberry silk fibres have a relatively high extensibility as compared to the mulberry silk fibres. In the meantime, the non-mulberry silk fibres show comparatively unique toughness to the mulberry silk fibres. Synchrotron radiation FTIR microspectroscopy, synchrotron radiation wide angle X-ray diffraction, and Raman dichroism spectroscopy are used to analyze the structural differences among the five species of silk fibres comprehensively. The results clearly show that the mechanical properties of both mulberry and non-mulberry silk fibres are closely related to their structures, such as β-sheet content, crystallinity, and the molecular orientation along the fibre axis. This study aims to understand the differences in the structural and mechanical properties of different mulberry and non-mulberry silk fibres, which are of importance to the related research on understanding and utilizing the non-mulberry silk as a biomaterial. We believe these investigations not only provide insight into the biology of silk fibroins from the non-mulberry silkworms but also offer guidelines for further biomimetic investigations into the design and manufacture of artificial silk protein fibres with novel morphologies and associated material properties for future use in different fields like bioelectronics, biomaterials and biomedical devices.

Hybrid Silk Fibers Dry-Spun from Regenerated Silk Fibroin/Graphene Oxide Aqueous Solutions

Regenerated silk fibroin (RSF)/graphene oxide (GO) hybrid silk fibers were dry-spun from a mixed dope of GO suspension and RSF aqueous solution. It was observed that the presence of GO greatly affect the viscosity of RSF solution. The RSF/GO hybrid fibers showed from FTIR result lower β-sheet content compared to that of pure RSF fibers. The result of synchrotron radiation wide-angle X-ray diffraction showed that the addition of GO confined the crystallization of silk fibroin (SF) leading to the decrease of crystallinity, smaller crystallite size, and new formation of interphase zones in the artificial silks. Synchrotron radiation small-angle X-ray scattering also proved that GO sheets in the hybrid silks and blended solutions were coated with a certain thickness of interphase zones due to the complex interaction between the two components. A low addition of GO, together with the mesophase zones formed between GO and RSF, enhanced the mechanical properties of hybrid fibers. The highest breaking stress of the hybrid fibers reached 435.5 ± 71.6 MPa, 23% improvement in comparison to that of degummed silk and 72% larger than that of pure RSF silk fiber. The hybrid RSF/GO materials with good biocompatibility and enhanced mechanical properties may have potential applications in tissue engineering, bioelectronic devices, or energy storage.