The effect of phospholipids on the biodegradation of polyurethanes by lysosomal enzymes

Although biodegradation of model poly(ester-urethane)s and poly(ether-urethane)s has been demonstrated using a single enzyme system (cholesterol esterase (CE)) in vitro, in vivo biodegradation most likely involves many processes acting together. In this study, the physical (film vs textured surface) and chemical (poly(urethane)s containing polycaprolactone (PCL) vs poly(tetramethylene oxide) (PTMO)) nature of the materials as well as the products of enzymatic reactions known to occur during the inflammatory response (CE and phospholipase A(2) (PLA)) were assessed for their effects on poly(urethane) (PU) biodegradation in vitro. A mixed micelle (phosphatidylcholine (PC):lysoPC (LPC):oleic acid (OA); 2: 1 : 1) significantly increased the release of radiolabelled products from a C-14-labelled poly(ester-urethane) (TDI/PCL/ED) caused by CE. This effect was further enhanced when this material was cast as a textured surface. A model poly(ether-urethane) showed no significant enhancement of CE-mediated hydrolysis in the presence of phospholipids and their breakdown products whether cast as a film or a textured surface. PLA caused a small but significant release of radiolabel from 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 during the inflammatory response when PLA is activated, enhancement of the biodegradation of a PU could occur by direct action of PLA on the poly(ester-urethane) and by stimulation of CE due to the formation of LPC and OA occuring when PLA hydrolyses PC, its natural substrate.