Analyses of a silicone elastomer heart ball valve

This work represents a preliminary study of one case history of a silicone heart valve. The laboratory techniques employed have proven useful in characterizing the polymer before and after implantation. Before any model explaining ball variance can be proposed it must be determined whether the polymer loses its integrity because specific constituents in the body fluids interact with primary valence bonds in the polymer chains, or if the fluids simply cause swelling and plasticization of the crosslinked system and the damage is the result of mechanical work on the weaker polymer system. Detailed kinetic and thermodynamic studies are underway to answer these questions. The work summarized in this paper refers to the evaluation of only one specimen and should not be taken to mean that every silicone ball from a heart valve prosthesis will show this variance. The incidence of functionally variant silicone balls as reported to one manufacturer represents approximately 1.5% of the aortic and less than 0.05% of the mitral prostheses which have been supplied by this manufacturer. A small percent of valves of this type have the potential of becoming functionally variant and this is one failure mode which should be considered in the implantation of silicone ball valves.