Mechanical properties of segmented polyether polyurethanes for blood pump applications

Summary

The effects of test environment (cholesterol-lipid solution, saline solution, and room air), temperature (24°, 37°, and 50°C), and cyclic rate (0.8, 2, and 5 Hz) on the fatigue properties of Biomer and Toyobo TM5 polyurethanes were studied to obtain basic data for the design of artificial heart pumps and for the development of accelerated endurance test methods.

The mechanical properties of these materials deteriorated more significantly following immersion in plasma-analogous cholesterol-lipid solution than by exposure to saline solution or room atmosphere; this environmental effect was enhanced by cyclic deformation. Static and dynamic stress relaxation were greater at the higher ambient temperature. Although there was no significant difference in the stress relaxation behavior between the fatigue tests at 2 and 5 Hz at the same number of cycles, the stress reduction was much greater in the case of 0.8-Hz testing. These property changes were significantly less in Biomer than in Toyobo TM5 polyurethane. The material elasticity or flexibility did not significantly depend upon the ambient temperature or cyclic rate of fatigue testing.

The changes in the tensile properties of Toyobo TM5 polyurethane caused by the in vitro fatigue testing at the cyclic rate of 2 Hz in the cholesterol-lipid solution kept at 37°C were similar to the in vivo changes observed in the diaphragms of blood pumps implanted into animals.