WEAR STUDIES IN ARTIFICIAL HEART VALVES

Abstract

An occluder-wear simulator has been developed to study the progress of wear on disk occluders in mechanical heart valves under the simulated body condition. This, together with a simple pin-on-disk wear rig, has been used to investigate the wear of several polymeric candidate materials under different conditions. The abrasive-wear behaviour of these polymers was found to relate well to two room-temperature parameters as suggested by Lancaster (1968-69). The measured wear rates were sensitive to surface roughness and to the amount of back transfer during wear when smoother steel counterfaces were used. Delrin was found to have good wear resistance here, especially when the wear debris were not removed quickly. With smooth titanium counterfaces, the wear of Delrin was found to be nearly independent of the molecular weight. All, except PES 4800G which also worn badly, exhibited an incubation period with very little wear. Abrasion was the dominant wear-mechanism for all except medical grade UHMWPE where a delamination mechanism was observed. The long-term test data obtained from the simulator compared well with data from commercially available life-testers and measurements on explanted occluders. The short-term tests showed that Delrin (with smooth titanium counterfaces) offered the best compromise between wear resistance and wear-debris size amongst all the disk-occluder candidate materials tested under this simulated body condition.