This study investigated the influences of decreased mulberry leaf feeding to Bombyx mori silkworms after the fourth day during the fifth instar. Specifically, we examined effects on cocoon yield, cocoon thread fineness and morphology, and fibroin crystallinity. When feed amounts were decreased by 50% from normal amounts, the silkworm bodies became smaller and the cocoon thread yield and length decreased, suggesting that such feeding conditions exceed the limits of the inherent silkworm homeostatic system. Furthermore, because of insufficient synthesized amounts of sericin A, the twin fibroin filaments constructing the cocoon thread were not fully covered with the sericin layer. Nevertheless, the amounts of sericin P and sericin M were sufficient for fiber-structural formation of fibroin. By contrast, a shortage of mulberry leaf feeding by 25% compared to normal feeding amounts slightly decreased the cocoon yield because the silkworms’ homeostatic protection system balanced the cocoon yield with silkworm growth.

Cocoon shells in some white-cocoon races of silkworms are known to emit yellowish-white, yellowish-green, or purple fluorescence under black light. Three-dimensional fluorescence analysis has revealed that a fluorescent flavonoid in white cocoon shells is probably responsible for yellow fluorescence, and on average, the intensity of this fluorescence is higher in the Chinese races than in the Japanese races. Recently, a recombinant protein production method using a transgenic silkworm has been developed; this was found to be useful for producing different types of recombinant proteins. Genetically modified silks have also been produced from transgenic silkworms. The fibroin H chain gene vector and ordinary breeding methods have been used for producing transgenic silkworm races that are adapted for the mass production of recombinant silks with fluorescent colors. However, strains containing fluorescent substances in the sericin layer are undesirable for breeding fluorescent silk. Therefore, we investigated the presence or absence of yellow fluorescence in commercial white-cocoon races and found that differences in fluorescence intensity among individuals in some strains. The Chinese silkworm races MCS3, MCS181, and MCS107, which lacked yellow fluorescence, were bred by selecting cocoons lacking yellow-fluorescent substances.

Silk is attracting interested not only as a material for clothing but also as a medical and industrial material. Development of higher strength silk is anticipated for all applications. A high-strength silk thread producing silkworm strain “MC502” has been developed through selective breeding, whereas improving the raw silk yield is necessary to support its practical use. Earlier studies have demonstrated that “MC502 × J137” can improve the raw silk yield while maintaining high strength characteristics of MC502, although the effects of reverse crossbreeding “J137 × MC502” on cocoon thread character are not clear. Therefore, we investigated differences in rearing duration, cocoon thread character, and raw silk yield, if any, between forward and reverse crossbreeding of MC502 and J137. No significant difference was found in the rearing duration or reeling test score, between forward and reverse crossbreeding. Moreover, the raw silk yields were similar. Depending on the rearing year, some differences in cocoon shell weight and strength of the raw silks were found between forward and reverse crossbreeding. These differences were few and slight: both raw silks retained their high-strength character. Therefore, no marked difference in cocoon thread character was found between the forward and reverse crossbreeding of MC502 and J137.

For this study, we specifically examined water temperatures used for cooking cocoons and reeling raw silk. To assess technology changes, we examined 68 academic documents and technical books about raw silk production, published from the Meiji era (1869–1912), Taisho era (1912–1926), and Showa era (1926–1989). The findings confirmed a dispersion of water temperatures used for cooking cocoons and reeling raw silk from the early to mid-Meiji era. Water temperatures for cooking cocoons and reeling raw silk converged at a high temperature after the late Meiji era.

Factors causing the dispersion of water temperatures for cooking cocoons and reeling in the first half of the Meiji era were low-quality cocoon raw materials, underdeveloped cocoon drying technologies, and production processes specialized for efficiency. We also surmised that cocoon cooking water temperature convergence to higher temperatures from around 1900 was attributable to the continuation of efficiency-oriented production objectives and the subsequent shift to quality-oriented production objectives because of improved cocoon raw material quality.

Sericin gel film (sericin GF), prepared from a cocoon layer made exclusively of sericin produced by Sericin Hope strain, has potential application as a wound dressing material because of its excellent hydrophilicity, ease of handling, and low cell adhesion property. For this study, to clarify the sericin GF wound-dressing properties further, its drug release profile and moisture permeability were analyzed. The results demonstrated that sericin GF can function as a drug releasing material. The loading of low and medium molecular sized model drugs in sericin GF caused their rapid elution from it. The moisture permeability of sericin GF in the dry condition was less than that of filter paper and greater than that of a commercially available medical film material. In the wet condition, by contrast, sericin GF did not inhibit water permeation at all. These results suggest that sericin GF can regulate the moisture content of wound sites. Findings obtained from this study further clarified the properties of sericin GF as a wound dressing.

We investigated the feasibility of immobilized enzymes on silk fibers in which functional enzymes are fixed through tagging the silk-binding peptide (YN42), a fibroin-binding peptide discovered in 2011 by phage display. Fluorescent protein-fused enzymes (cellulase and β-glucosidase, derived from termites) containing YN42 peptide at the N-terminus were expressed in the silk glands of transgenic silkworm using the GAL4/UAS gene expression system. The resultant cocoons showed fluorescence, indicating successful expression of the introduced recombinant enzymes on the silk fibers. When the cocoons were immersed in assay solution containing substrate, their enzyme activities were confirmed by detecting the enzymatically degraded products. The enzyme activity in the cocoon was maintained after repeating 5 min reactions. Ten-round reaction assay was done by replacing the substrate after each cycle. Moreover, the activity was observed even after the cocoons had been incubated at 37°C for four days, demonstrating excellent immobilization performance of the enzymes onto silk. Considering their use in a bioreactor, we tested whether our material is tolerant of continuous flow reactions. Enzyme activity was maintained even after 10 repetitions of 24-h continuous flow reaction, demonstrating excellent immobilization ability on silk. These results demonstrated that silk fibers immobilized with enzymes through YN42 binding peptide can be useful as matrix for enzyme-based bioreactors.

Antibacterial and antiviral activities of silk fibers grafted with acrylic acid (AA) and methacrylic acid (MA) as anionic monomers were investigated. The weight gain on graft polymerization was found to be proportional to the monomer concentration. The weight gain reached 24.6% using MA, whereas AA reached only 6.8%. The grafted silk fibers inhibited bacterial growth of Gram-negative bacteria: Staphylococcus aureus. The inhibition efficacy increased linearly with the weight gain. However, AA-grafted silk fibers exhibited significantly greater inhibition than MA-grafted silk fibers, although both grafted samples were comparable in terms of weight gain. The anionic grafted silk fibers also revealed antiviral activity against influenza A virus H1N1. This report is the first describing that silks modified solely by graft polymerization exhibit viral inactivation.

This report describes a cocoon shell protein dissolution method using lithium bromide aqueous solution under vigorous mixing conditions. Using a crushing and mixing machine called the “Multi-bead Shocker,” silkworm cocoon shells were dissolved completely in 7–9 M LiBr solution buffered with Tris-HCl at pH 9 to a 20 mg/ml concentration. Additionally, cocoon shell proteins were dissolved in over 120 mg/ml when using 7 M – 8 M LiBr solution.

Animal welfare in the fashion industry has been discussed actively in recent years. In fact, because of doubts about the necessity and propriety of the killing of animals during production processes, a movement to avoid animal materials such as fur has emerged, especially in Western countries. Simultaneously, consciousness about animal ethics, including animal rights and animal liberation movements, has activated discussions worldwide to reconsider the human–animal relationship.

This paper presents a review of the history of animal welfare and animal ethics development. Then issues involved in these discussions are considered. Specifically, the anthropocentric mode of thought which accompanies the view of animals with clear separation between humans and animals is pointed out, along with the fact that discussion of the human–animal relationship itself does not include practical activities.

Additionally, to develop these discussions comprehensively in the future, this discussion specifically examines the Kuyō spirit of producers who witness the killing of animals. Finally, based on the discussion presented above, the future of animal welfare and animal ethics in the silk industry are explored.