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.

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.

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.

Alanine transaminase (ALT) is an important amino acid-metabolizing enzyme in silkworm Bombyx mori L., and is mainly involved in transferring glutamate to alanine (serving as an essential precursor in silk protein synthesis) through transamination. Therefore, it is generally believed that silk protein synthesis in the silk gland and the cocoon quantity increase with the increase in ALT activity to a certain extent. Here, a novel analytical method was developed to determine the ALT activity in several key tissues of Bombyx mori L. including the posterior silk gland, midgut, fat body, middle silk gland, trachea and hemolymph, by combining the direct-analysis-in-real-time (DART) ion source with a triple-quadrupole mass spectrometer. In addition, a traditional ALT activity assay, the Reitman–Frankel method, was also used to measure ALT activity for comparison. The ALT activity results obtained via the DART-MS method are in good agreement with those obtained via the Reitman–Frankel method. However, the present DART-MS method provides a more convenient, rapid and environmentally friendly quantitative method for ALT measurement. Especially, this method can also monitor ALT activity in different tissues of Bombyx mori L. in real time.