The biomechanical effects of fatigue on the porcine bioprosthetic heart valve.

Characterization of the mechanisms of degeneration of porcine bioprosthetic heart valves (BHV) during long-term cyclic loading is required for predicting and ultimately preventing their failure. Isolation of purely mechanical effects from host biological ones is a necessary first step in understanding the fatigue process as a whole. Thus, in this review we focus on mechanical factors alone as a means of isolating their role in altering biomechanical properties and ultimately their contribution to the fatigue damage process. Mechanical evaluations included tension controlled biaxial, 3-point flexural, and uniaxial failure tests performed on cuspal tissue following 0, 50, 100, 200, and 300 x 10(6) in vitro accelerated test cycles. Overall, biaxial mechanical results indicate a decreasing radial extensibility that can be explained by stiffening of the effective collagen fiber network as well as a small decrease in the splay of the collagen fibers. Moreover, these results suggest that the loss in flexural rigidity with fatigue that we have previously measured (ASAIO 1999; 45:59-63) may not be because of loss of collagen stiffness alone, but also to fiber debonding and degradation of the amorphous extracellular matrix. We discuss the implications of these results that point toward the development of chemical-treatment methods that seek to maintain the integrity of the amorphous extracellular matrix to ultimately extend BHV long-term durability.