CHEMICAL-STABILITY OF POLYETHER URETHANES VERSUS POLYCARBONATE URETHANES

The relative chemical stability of two commercially available polyuret hanes-Pellethane, currently used in biomedical devices, and Corethane, considered as a potential biomaterial-was investigated following agin g protocols in hydrolytic and oxidative conditions (HOC, water, hydrog en peroxide, and nitric acid) and in physiological media (PHM, phospha te buffer, lipid dispersion, and bile from human donors). The chemical modifications induced on these polymers were characterized using diff erential scanning calorimetry (DSC), gel permeation chromatography (GP C), and Fourier transform infrared spectroscopy (FTIR). With the excep tion of nitric acid, all of the aging media promoted a mild hydrolytic reaction leading to a slight molecular weight loss in both polymers. When aged in water and hydrogen peroxide, Pellethane experienced struc tural modifications through microdomain phase separation along with an increase of the order within the soft-hard segment domains. The incub ation of Pellethane in nitric acid also resulted in an important decre ase of the melting temperature of its hard segments with chain scissio n mechanisms. Moreover, incubation in PHM led to an increase of the or der within shorter hard-segment domains. FTIR data revealed the presen ce of aliphatic amide molecules used as additives on the Pellethane's surface. The incubation of Corethane under the same conditions promote d an almost uniform molecular reorganization through a phase separatio n between the hard and soft segments as well as an increase of the sho rt-range order within the hard-segment domains. Incubation of this pol ymer in nitric acid also resulted in a chain scission process that was less pronounced than that measured for the Pellethane samples. Finall y, lipid adsorption occurred on the Corethane sample incubated in bile for 120 days. Overall data indicate that polycarbonate urethane prese nts a greater chemical stability than does polyetherurethane. (C) 1997 John Wiley & Sons, Inc.