Comparative physical tests on segmented polyurethanes for cardiovascular applications.

In order to select a candidate segmented polyurethane (SPU) elastomer for cardiovascular prostheses, a series of physical tests was carried out on five commercially available biomedical polyurethanes. The tests were performed on uniformly thick sheets (0.2-0.3 mm), obtained by solvent casting from THF (Cardiothane 51, Pellethane 2363 80A, Estane 5714 F1, and Estane 58810) or DMAC (Biomer). Tensile mechanical tests at 23 and 37 degrees C showed for all the copolymers typical stress/strain behaviour of elastomeric materials, with small individual differences. Hydrolytic stability was investigated at 85, 60, and 37 degrees C, at increasing times of exposure (96-168 h), in water or alkaline buffer (pH = 10). As indicated by gel permeation chromatography, in almost all cases a degradation of the molecular weight (particularly the M w) was noticed after the hydrolytic tests, but tensile, thermal (by DSC) and dynamic mechanical properties were substantially not affected. SEM was also performed on the materials, before and after the hydrolytic tests. Changes in the morphology of the materials (related to degradation effects) was observed only in the case of Biomer, as shown also by the thermomechanical analyses. After this first series of physical tests, a clear choice of a particular SPU among the five investigated was not found.