In vitro stability of a novel compliant poly(carbonate-urea) urethane to oxidative and hydrolytic stress

Poly(ester) urethane and poly(ether)urethane vascular grafts fail in vivo b ecause of hydrolytic and oxidative degradative mechanisms. Studies have sho wn that poly(carbonate)urethanes have enhanced resistance. There is still a need for a viable, nonrigid, small-diameter, synthetic vascular graft. In this study, we sought to confirm this by exposing a novel formulation of co mpliant poly(carbonate)urethane (CPU) manufactured by an innovative process , resulting in a stress-free. Small-diameter prosthesis, and a conventional poly(ether) urethane Pulse-Tec graft known to readily undergo oxidation in a variety of degradative solutions, and we assessed them for the developme nt of oxidative and hydrolytic degradation, changes in elastic properties, and chemical stability. To simulate the in vivo environment, we used buffer ed solutions of phospholipase A(2) and cholesterol esterase; solutions of H 2O2/CoCl2, t-butyl peroxide/CoCl2 (t-but/CoCl2), and glutathione/t-butyl pe roxide/CoCl2 (Glut/t-but/CoCl2); and plasma fractions I-IV, which were deri ved from fresh human plasma centrifuged in poly(ethylene glycol). To act as a negative control, both graft types were incubated in distilled water. Sa mples of both graft types (100 mm with a 5.0-mm inner diameter) were incuba ted in these solutions at 37 degreesC for 70 days before environmental scan ning electron microscopy, radial tensile strength and quality control, gel permeation chromatography, and in vitro compliance assessments were perform ed. Oxidative degradation was ascertained from significant changes in molec ular weight with respect to a control on all Pulse-Tec grafts treated with t-but/CoCl2, Glut/ t-but/CoCl2, and plasma fractions I-III. Pulse-Tec graft s exposed to the H2O2/CoCl2 mixture had significantly greater compliance th an controls incubated in distilled water (p < 0.001 at 50 mmHg). No changes in molecular weight with respect to the control were observed for the CPU samples; only those immersed in t-but/CoCl2 and Glut/t-but,/CoCl2 showed an 11% increase in molecular weight to 108,000. Only CPU grafts treated with the Glut/t-but/CoCl2 mixture exhibited significantly greater compliance (p < 0.05 at 50 mmHg). Overall, results from this study indicate that CPU pres ents a far greater chemical stability than poly(ether)urethane grafts do. 2 001 John Wiley & Sons, Inc.