In vivo degradation of silicone rubber poppets in prosthetic heart valves.

Dynamic shear modulus G' was measured throughout the volume of three nonvariant silicone rubber poppets which were recovered from aortic prosthetic heart valves that had been implanted for 4 days, 52 days, and 8 years. Similar measurements were obtained for two unused silicone rubber poppets. Although the recovered poppets exhibited no obvious physical evidence of damage, the silicone rubber had undergone in vivo degradation throughout the poppet volume as indicated by decreases in modulus. The measurements also indicate that the poppet surface degrades at a rate faster than the core. Further, comparison with data reported in the literature suggests that the surfaces of variant poppets degrade at a rate faster than the surfaces of nonvariant poppets.