In the production of aerogel from the liquid silk gel in silk gland of fully grown larvae of domestic Bombyx mori silkworm, when the unfolding time of liquid silk gel in water at room temperature did not exceed 10 min, obtained aerogel showed hydration and could be dissolved into water by the water annealing at 50°C. On the other hand, when the unfolding time of liquid silk gel reached 4 hours, the water solubility of obtained aerogel was limited although the hydration behavior could be observed. Sericin and only limited fibroin fractions could be dissolved by the water annealing at 50°C. The difference in water solubility between the two type aerogels could be explained considering the molecular interactions between fibroin and sericin fractions. The interactions seems to be dissociated if the unfolding time of liquid silk gel in water at room temperature exceed a certain period.

Wide angle X-ray diffraction (WAXD) curves were measured on the divided portions of freeze-dried silk gland of fully grown larvae of domestic Bombyx mori silkworm, and the influence of sericin fractions on the crystal modification of fibroin was investigated. It was found that fibroin molecules could be modified to crystal precursor of Silk II when sericin P was secreted, and then, turned to crystal precursor of Silk I when sericin M was secreted.

We have previously reported the incorporation of an azide-bearing unnatural amino acid, 4-azidophenylalanine (AzPhe), into silk fibroin, and showed that the azide group of AzPhe can be used as a selective handle for chemical modification by click chemistry. In this study, we investigated the intermolecular crosslinking between AzPhe-incorporated silk fibroin molecules by click chemistry, because crosslinking could be an effective way to alter the mechanical properties of silk fibroin materials. A bifunctional crosslinking agent, DBCO-PEG4-DBCO, which bears azide-reactive DBCO groups on both ends of the PEG chain, was used for crosslinking, and molecular-weight changes after the crosslinking reaction were investigated by electrophoresis. The results showed that the crosslinking reaction with DBCO-PEG4-DBCO proceeded with just a small fraction of silk fibroin. It was assumed that the steric constraint between silk fibroin molecules inhibited the reaction. In order to create some distance between the reactive sites for crosslinking and the main chain of silk fibroin, we first reacted DBCO-PEG4-DBCO with AzPhe-incorporated silk fibroin to introduce a DBCO-functionalized PEG linker and then reacted the resulting DBCO-PEG4-modified silk fibroin with another bifunctional crosslinking agent, PEG7-bis-azide, which bears DBCO-reactive azide groups on both ends of the PEG chain. As a result, increased amounts of crosslinked silk fibroin were observed by electrophoresis, indicating that the distance between reactive sites and silk fibroin main chain is important for efficient intermolecular crosslinking.

Eri silkworm, Samia cynthia ricini, which belongs to Satuirniidae, lives in subtropical area and Okinawa islands are suited for its sericulture because of availability of tropical plants to feed on. A porous structure has been observed from a cross section of cocoon filament produced by eri silkworm which does not exist in cocoon of domesticated silkworm. In this study, functionality of two kinds of silk powder (cocoon shell powder and fibroin powder) from eri silkworm was investigated, and the result was compared with that of silk powder (fibroin powder) from domesticated silkworm. We found that silk powder from eri silkworm has hygroscopicity, moisture desorption, and deodorization, similar to that from domesticated silkworm. These results indicate that silk powder from eri silkworm is suited for high performance silk products and suggest that it has an attractive potential for skin care and as an anti-odor agent.

The highly efficient genome-editing tool transcription activator-like effector nuclease (TALEN) was used to modify a Bombyx endogenous gene, Ser1, to create silkworm strains that secrete sericins of different sizes and properties. Double-stranded breaks were introduced by two pairs of TALENs that targeted the 5th and 7th exons of Ser1 to eliminate the intervening exon 6. Two mutant strains were selected, and it was confirmed that they carried truncated Ser1 genes that lacked exon 6. The cocoon sericin components of the truncated Ser1 strains were characterized using sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The approximately 300-kDa sericin components, sericins M, were not detected in the homozygous Ser1 mutant cocoons, whereas they were the most abundant sericin components in the wild-type cocoons. Instead, two or three novel sericin components with lower molecular masses were observed. The truncated Ser1 cocoon shells were found to have lower sericin contents than the wild-type cocoon shells, probably because the efficiency of Ser1 production decreased in the truncated Ser1 mutants with the decrease in molecular size. The cocoon sericins were extracted more efficiently in water at 60°C and 80°C from the truncated Ser1 cocoons than from the wild-type cocoons. This is consistent with the prediction that the mutant Ser1 proteins would show higher solubility in water because of less amount of the β-sheet structure. The truncated Ser1 mutant silkworms tended to fail in spinning and often made coarse cocoons. However, they excreted silk proteins by reduced feeding in the last larval instar stage.

Three-dimensional (3D) silk fibroin (SF) nanofiber non-woven fabric was fabricated by wet electrospinning (WES) using SF aqueous spinning solution and a liquid bath as a collector. Citric acid buffered solution at pH 3.8 supplemented with t-butyl alcohol (t-BuOH) was used as the liquid bath. The t-BuOH concentration influenced the apparent pore size and porosity of the WES non-woven fabric. The maximum pore size was formed at 30% of t-BuOH. The as-spun WES non-woven fabric structure had a crystallized form. Cell adhesion on the WES non-woven fabric was lower than that produced on the non-woven fabric by traditional dry electrospinning (DES), but no difference was observed in cell proliferation rates between WES and DES non-woven fabrics. Cells adhered and proliferated on both the surface and the inner spaces of WES non-woven fabric, although cells adhered only on the surface of DES non-woven fabric consisting of high fiber density. The WES non-woven fabric is anticipated for use as a cell scaffold mimicking an extracellular matrix in tissue.

We report a facile and environmentally friendly approach to prepare hierarchical structured graphene oxide (GO)-Fe₃O₄ nanoparticles (NPs) hybrid nanosheets and Ag nanoparticles bimetallic composite coated silk fiber nanocomposites through hyperbranched poly(amide-amine) (HBPAA)-directed self-assembly technology. In such structure, HBPAA served as a molecular “double-sided tape” not only gluing AgNPs to the fiber surfaces but also adhering GO- Fe₃O₄NPs to the surfaces of HBPAA/AgNPs to form the protective layer of HBPAA/AgNPs and then improve the biosecurity and durability. The prepared silk fiber nanocomposites can be served as a small household magnet and have efficient, safe and durable antibacterial activities. These nanocomposites could be easily recycled without a decrease in their antibacterial activities due to the synergistic effects between the AgNPs and GO-Fe₃O₄NPs hybrid nanosheets with large amounts of active sites.

We arranged functions such as the water supply in each development stage of a silk reeling pan seen in our country, drainage, a shape, the size and performed the comparison with “the Suwa type silk reeling pan” based on the result. In the second period of the development stage of a silk reeling pan seen in our country, a modification was performed with the collective pipe physics and chemistry of materials (worker, water, heat source) with the construction of the large-scale factory production system. In addition, a modification was performed to support a dish simmered in cocoon called the Suwa-style silk reeling method, silk reeling technology, and it was confirmed that “a Suwa type silk reeling pan” was established.

This study assessed the characters of transgenic silkworm (C515-SpA1x2, F1-hybrid of C515-SpA1 and C515-SpA2) producing cocoons and silk thread with a spider dragline silk protein component. Comparison to the original race (C515) used for generating the transgenic silkworm and the generated transgenic silkworm strains (C515-SpA1 and C515-SpA2) revealed greater cocoon and cocoon shell weights for C515-SpA1x2. The C515-SpA1x2 cocoon showed a linear filament size decrease from the outer to the inner layer, with slight difference between maximum and minimum filament size. Results show that the C515-SpA1x2 cocoon maintained the character of C515. Compared to C515, the C515-SpA1x2 cocoons exhibited slightly greater average cocoon filament length. Reeling testing revealed no significant difference between C515-SpA1x2 and C515 cocoons, but the former showed better reelability.