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Recently, Bombyx mori silk fibroin (SF) has been shown to be a suitable material for vascular prostheses for small arteries. In this study, we developed a softer SF graft by coating water-dispersed biodegradable polyurethane (PU) based on polycaprolactone and an SF composite sponge on the knitted SF vascular graft. Three kinds of 13C solid-state nuclear magnetic resonance (NMR), namely carbon-13 (13C) cross-polarization/magic angle spinning (MAS), 13C dipolar decoupled MAS, and 13C refocused insensitive nuclei enhanced by polarization transfer (r-INEPT) NMR, were used to characterize the PU-SF coating sponge. Especially the 13C r-INEPT NMR spectrum of water-dispersed biodegradable PU showed that both main components of the non-crystalline domain of PU and amorphous domain of SF were highly mobile in the hydrated state. Then, the small-diameter SF artificial vascular grafts coated with this sponge were evaluated through implantation experiments with rats. The implanted PU-SF-coated SF grafts showed a high patency rate. It was confirmed that the inside of the SF grafts was covered with vascular endothelial cells 4 weeks after implantation. These results showed that the water-dispersed biodegradable PU-SF-coated SF graft created in this study could be a strong candidate for small-diameter artificial vascular graft.

Bombyx mori silk fibroin (SF) fibers possess excellent mechanical properties together with biocompatibility and have attracted great attention in applications including biomaterials. The SF-polyurethane (PU) composite materials are expected to improve the mechanical properties and expand the application of SF. In this article, PU consisting of isophorone diisocyanate (IPDI) and poly (butylene adipate) is synthesized and characterized using 13 C solid-state NMR spectroscopy. Then, the regenerated SF-PU (95: 5 wt%) fiber is prepared, which results in a 11.7% increase in tensile strength and 81% increase in elongationat-break compared with those of SF fiber. The reason for the increase is due to the increase of random coil conformation in SF observed by 13 C solid-state NMR and the presence of IPDI in the PU. Thus, it can be emphasized that this PU is very effective in changing the conformation of SF fiber by increasing random coil fraction and improve the mechanical properties.

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