WEAR ANALYSIS OF BJORK-SHILEY DELRIN TILTING DISC HEART-VALVES

Prosthetic heart valves must open and close 40 million cycles annually , year in and year out, in a biochemically active and corrosive medium and without benefit of periodic maintenance. Examination of explanted Bjork-Shiley Delrin Heart Valves revealed that some valves developed wear grooves in the Delrin occluder disc from contact with the inlet s trut. With Delrin Heart Valve implant durations reaching 20 or more ye ars, studies were initiated to fully analyze the wear of explanted val ves. Delrin discs from 15 explanted valves with implant durations of u p to 20 years (800 million cycles of operation) were dimensionally ins pected; the wear features and profiles measured by stylus profilometer and optical comparator; wear surfaces mapped by Moire shadow interfer ometry; and the surfaces examined by scanning electron microscope. Pul satile flow heart valve simulator studies were conducted to determine valve disc impact velocity and impulsive force-time characteristics. M aterial tests were conducted on circa 1970 Delrin coupons to determine the wear-related physical properties of the Delrin disc. These invest igations cast light upon the wear behavior of Delrin occluder discs, a nd hence their effects upon valve performance and valve life could be evaluated. The wear phenomenon as seen on clinically explanted valves can be attributed to percussive impact wear concepts. The wear depth f rom this mechanism is shown to be a logarithmic function with respect to cycles and time. The amount of wear observed on the periphery of th e explanted Delrin discs returned to date suggests that clinically sig nificant increases in valve regurgitation in implanted valves has not likely occurred. Disc retention safety margin appears not to be substa ntially affected. In conclusion, wear of the disc in the 15 Bjork-Shil ey Delrin Heart Valves in this study does not appear to be a factor af fecting valve life.