Papers by Author: Masuhiro Tsukada

Abstract: Larval silk/cement proteins from a caddisfly, Stenopsyche marmorata, were isolated as a protein mixture of Smsp-1, 2, 3 and 4. Smsp-1 is a giant phosphorylated protein, which occupies ca. 45%-mass of the silk gland content, and composed of a long-range periodic amino acid sequences, involving 8 kinds of characteristic segments. The silk protein film was prepared and drawn in water up to 9-folds of the initial axis length, then the drawn film was subjected to polarized FT-IR and WAXD. The results implied that the Smsp-1 backbone adopts two different conformations, one of which was the β-turn-like conformers. The molecular mechanic studies were separately performed to evaluate the solid-state chain structures of the hydrophobic/Pro-rich segments 3 and 4, which are enriched in the primary sequence of Smsp-1, and the results were coincident with those from the vibration spectra and WAXD. The molecular dynamic (MD) studies were also carried out in order to estimate their preferred chain conformations in a solution state. The MD trajectory suggests that the segments 3 and 4 tend to adopt a turn-like conformation, which is a potential precursor of the β-turn-like conformers. In conclusion, the underwater silk proteins have a fiber-forming mechanism, which is substantially different from a silkworm, Bombyx mori.

Abstract: Electrospinning is a scientifically attractive spinning technique, since it can produce fibers with the diameters ranging from the sub-micron to nano dimensional scale. The fiber diameters and their standard deviation primarily depend on the polymer solution properties and electrospinning process variables. Silk sericin powder was obtained from the raw silk fiber of Bombyx mori silkworm. The solution was prepared by dissolving silk sericin powder in water at 85 °C for 30 minutes. In the electrospinning process, voltage 20 kV was applied and the inner diameter of the syringe needle was 0.3 mm. The distance from the syringe tip to the target was 15 cm. The sericin nanofibers with smooth surfaces can not be produced at 40 wt%. However, fine nanofibers were produced at the concentrations of 50 wt% and 60 wt%. It was suggested that the average diameters of the nanofibers increased with increasing solution concentration and the optimum concentration was 50 wt% for best nanofibers. Then solution 50 wt% was electrospun with different voltages from 13 kV to 25 kV, the working distance is 10 cm, the as-spun silk nanofibers were produced and exhibited fine nanofibers with smooth surfaces. The average diameters and diameter distributions of the nanofibers decreased with increasing voltage.