(Bio)degradable Urethane-Elastomers for Electrospun Vascular Grafts

Abstract

Electrospinning is a very powerful method to create cellular scaffolds for regenerative medicine – especially for artificial vascular grafts. Commercially available thermoplastic polyurethane elastomers (TPUs), like Pellethane™ are FDA approved and have already shown excellent biomechanical properties as electrospun vascular grafts. In order to induce the growth of a neo artery and hence increase the long-term patency of the graft, the use of biodegradable TPUs is beneficial. Therefore we aim for the development of degradable TPUs. In preliminary studies the mechanical properties of segmented TPUs were examined. The tendencies of the properties of the compression-molded bulk materials were also found for the electrospun materials. It could also be shown that the substitution of the aromatic 4,4′-methylene diphenyl diisocyanate building blocks in Pellethane™ with the aliphatic hexamethylene diisocyanate – to avoid toxic aromatic amines as degradation products - only causes minor loss of strength. To obtain degradable TPUs, our concept is to incorporate cleavable ester bonds into the polymer chain. For this purpose, lactic- and terephthalic ester-based cleavable chain extenders were used. The expected degradation products showed no cytotoxicity in-vitro. Degradation tests of polymer samples in phosphate buffered saline at elevated temperatures confirmed the degradability of the new polymers.