Characterization of a Water-Dispersed Biodegradable Polyurethane-Silk Composite Sponge Using 13C Solid-State Nuclear Magnetic Resonance as Coating Material for Silk Vascular Grafts with Small Diameters

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.

Novel Biodegradable Polyurethanes Reinforced With Green Nanofibers for Applications in Tissue Engineering

New class of green biocomposites were designed and synthesized for tissue engineering applications. These newly introduced non-cytotoxic, biodegradable polyurethane composites had different compositions (i.e., ratio of hard to soft segments) of the linear, aliphatic hexamethylene diisocyanate and polycaprolactone diol. The porosity was introduced in the polyurethane matrix using a combination of salt leaching and thermally induced phase separation (TIPS). The resulting interconnected pore size was characterized using Scanning Electron Microscope (SEM) to be between 125-355 μm. Porosity was determined using liquid displacement and found to be between 70-75% for non-reinforced matrices, 64-70% for reinforcement with 5 wt% biocellulose nanofiber (BCNF), 59-69% for 10 wt% BCNF, and 57-69% for 15 wt% BCNF biocomposite samples. Dependent on the composition, compressive strength showed up to a little less than two-fold increase (85%) for green BCNF reinforcement of 5 wt% and more than two-fold increase (120%) for 10 wt%. The tensile strength also increased up to almost two-fold (114%) for reinforcement with 5 wt% BCNF and to more than two-fold (140%) for 10 wt% reinforcement. Higher degrees of reinforcement showed a detrimental effect on both properties. Properties demonstrate that this novel class of nanostructured biocomposite holds potential to be utilized as scaffolds for tissue regeneration.