Stress corrosion cracking in Björk-Shiley convexo-concave prosthetic heart valves due to random in vivo electrochemical pulsing.
Welded downstream struts of Björk-Shiley Convexo-Concave heart valves show failure in vivo, but not in in vitro testing. A pyrolytic carbon pivoting disk occluder closes against a Haynes 25 alloy ring, which is electrochemically machined from solid with the upstream retaining struts. The weld area is de-alloyed, with residual porosity and carbide inclusions. The valve becomes a short-circuited electrochemical cell when fully open or closed. It is an aggressive chloride electrolyte, whose high pulsed flow (2 m/s) ensures that supply of oxygen-rich cathode reactant is not mass-transport-limited. During the flight of the occluder, the cell is randomly at open circuit. A random current pulse is applied to the metal parts on circuit closure. Failure is not from simple mechanical fatigue, but from stress-corrosion-cracking and erosion of the less noble weld area caused by these pulses. All welded valves of this type may be susceptible to ultimate in vivo failure.
Xiao
K
K
Center for Electrochemical Systems and Hydrogen Research, Texas Engineering Experiment Station/Texas A & M University, College Station, USA.
Appleby
A J
AJ
D001672:Biocompatible Materials; D002986:Clinical Trials as Topic; D003343:Corrosion; D004563:Electrochemistry; D005260:Female; D006350:Heart Valve Prosthesis / Q000592:standards*; D006801:Humans; D008297:Male; D008670:Metals; D011475:Prosthesis Failure; D013314:Stress, Mechanical
D001672:Biocompatible Materials; D008670:Metals