THE EFFECT OF PHOSPHOLIPIDS ON THE BIODEGRADATION OF POLYURETHANES BYLYSOSOMAL-ENZYMES

Although biodegradation of model poly(ester-urethane)s and poly(ether- urethane)s has been demonstrated using a single enzyme system (cholest erol esterase (CE)) in vitro, in vivo biodegradation most likely invol ves many processes acting together. In this study, the physical (film vs textured surface) and chemical (poly(urethane)s containing polycapr olactone (PCL) vs poly(tetramethylene oxide) (PTMO)) nature of the mat erials as well as the products of enzymatic reactions known to occur d uring the inflammatory response (CE and phospholipase A(2) (PLA)) were assessed for their effects on poly(urethane) (PU) biodegradation in v itro. A mixed micelle (phosphatidylcholine (PC):lysoPC (LPC):oleic aci d (OA); 2: 1 : 1) significantly increased the release of radiolabelled products from a C-14-labelled poly(ester-urethane) (TDI/PCL/ED) cause d by CE. This effect was further enhanced when this material was cast as a textured surface. A model poly(ether-urethane) showed no signific ant enhancement of CE-mediated hydrolysis in the presence of phospholi pids and their breakdown products whether cast as a film or a textured surface. PLA caused a small but significant release of radiolabel fro m TDI/PCL/ED which was enhanced in the presence of its substrate, PC, and a mixture of PC with its breakdown products, LPC and OA. Based on the results of this study, it may be possible to hypothesize that duri ng the inflammatory response when PLA is activated, enhancement of the biodegradation of a PU could occur by direct action of PLA on the pol y(ester-urethane) and by stimulation of CE due to the formation of LPC and OA occuring when PLA hydrolyses PC, its natural substrate.