Volume 22, Issue 5 (September 1994)
Wear Analysis of Björk 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 Björk-Shiley Delrin Heart Valves revealed that some valves developed wear grooves in the Delrin occluder disc from contact with the inlet strut. With Delrin Heart Valve implant durations reaching 20 or more years, studies were initiated to fully analyze the wear of explanted valves.
Delrin discs from 15 explanted valves with implant durations of up to 20 years (800 million cycles of operation) were dimensionally inspected; the wear features and profiles measured by stylus profilometer and optical comparator; wear surfaces mapped by Moiré shadow interferometry; and the surfaces examined by scanning electron microscope. Pulsatile flow heart valve simulator studies were conducted to determine valve disc impact velocity and impulsive force-time characteristics. Material tests were conducted on circa 1970 Delrin coupons to determine the wear-related physical properties of the Delrin disc. These investigations cast light upon the wear behavior of Delrin occluder discs, and 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 from this mechanism is shown to be a logarithmic function with respect to cycles and time. The amount of wear observed on the periphery of the explanted Delrin discs returned to date suggests that clinically significant increases in valve regurgitation in implanted valves has not likely occurred. Disc retention safety margin appears not to be substantially affected. In conclusion, wear of the disc in the 15 Björk-Shiley Delrin Heart Valves in this study does not appear to be a factor affecting valve life.