PHYSICAL AND MECHANICAL-BEHAVIOR OF STERILIZED BIOMEDICAL SEGMENTED POLYURETHANES

Changes in the physical and mechanical behavior induced by two sterili zation methods, gamma irradiation and ethylene oxide, were determined on two commercial medical-grade segmented polyurethanes. The two mater ials have different chemical composition: one is an aromatic poly(ethe r urethane urea), Biospan(TM), and the other an aliphatic ether-free p olyurethane, Chronoflex(TM). Properties before and after sterilization procedures were compared resulting in specific structural changes for each formulation. The thermal and mechanical properties were examined using differential scanning calorimetry (DSC), dynamic mechanical ana lysis (DMA), stress-strain measurements, and its hysteresis cycle. Mol ecular weight measurements were performed by gel permeation chromatogr aphy (GPC). Sterilized Biospan samples showed a decrease in the soft-s egment glass transition temperature (T-g,T-s) and an increase in the s oft. segment crystallization heat along the quenching process. Sterili zed Chronoflex materials showed the opposite behavior. The hysteresis percent and residual strain percent increased after sterilization. The same effect was observed when irradiation dose and strain level incre ased. Surface analysis performed by scanning electron microscopy showe d magnification of original surface defects after sterilization. (C) 1 997 John Wiley & Sons, Inc.