Delrin as an occluder material

Delrin (DR) has been used in biomedical applications for more than 25 years. Because of durability concerns, it was replaced by the expensive Pyrolytic Carbon (PC) in numerous cardiac valves. However, the durability problem could be related to design rather than poor materials selection. Recent reports on brittle fracture of PC, leading to sudden deaths, have prompted a critical comparison between DR and PC in the St. Vincents Mechanical (SVM) heart valves. Three SVM-DR and SVM-PC valves were subjected to accelerated life cycle tests, and examined for wear at 400 million cycles. These results were compared to those of Björk-Shiley Delrin (BS-DR) valves. Wear in BS-DR valves in vivo for more than 17 years were also analyzed and compared. Using a linear (wear depth)-log (cycles) plot, wear rates in mm/log (million cycles) were obtained. The results showed that the wear rates for DR and PC in SVM valves are close. The double reduction in wear rate of the SVM-DR, compared to BS-DR, is probably due to the lower contact stresses of the SVM valves. SVM-DR in vivo should, therefore, have lower wear. The PC discs also showed edge chipping and hairline cracks. The authors conclude that the durability of DR can be improved by design and, since it is more impact resistant than PC, it is a safer, more inexpensive occluder material for cardiac valves.