Trials on an extension of the iso standard of accelerated fatigue test for prosthetic heart valves: application for polymer valves

A methodol ogy for an accelerated fatigue test for polymer valves has not yet been established by ISO. First, durability testers were employed to ascertain the durability of Jellyfish valves under physiologic temperature as well as pressure difference at valve closure. Then, the validity of ISO requirements was checked. The results indicated that neither fracture location nor lifetime was coincident between accelerated fatigue tests (1200 BPM) and an animal experiment (105 BPM). For the next step, finite element analysis was performed to clarify the reason for different fracture locations. The results revealed that a brittle fracture occurred at a stress-concentrated area in the fatigue tests, whereas a ductile fracture occurred at a strain-concentrated area in the animal experiment. These findings emphasized that the fracture mechanism was different between practical in vitro fatigue tests and the animal experiment. As a result, it was found that the current accelerated fatigue test recommended by ISO has limitations for predicting the durability of polymer valves.