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Simulation of damage in a porcine prosthetic heart valve.

A model of a bioprosthetic porcine valve has been produced which simulates the non-linear elastic behaviour of the fixed tissue and the re-inforcement of the leaflets by collagen fibre bundles. The loading on the model is a spatially uniform but temporally varying distribution of pressure. Bending is allowed in the tissue of the leaflets and is shown to be significant in determining the behaviour and failure modes of the leaflets. The simulation of the undamaged valve is validated against in vitro pulse duplicator studies and a simple fluid--solid interaction simulation. Progressive damage is introduced into three models of the valve at a location where tears have been commonly found in vivo. It was found that during the opening and closing of the valve the tip of the tears were subject to mode III or tearing displacements, but that in the fully closed or diastolic state the tear tip was subject to mode I or opening displacements such that it would be expected to propagate parallel to the line of attachment to the stent. The tear tip stresses increased with the length of the tear so that the rate of tearing would be expected to increase with length.