Heart-valve poppets

Lipids have proven to be quite active in polymer environments (13-15). Investigations in the 1960 s performed on silicone rubber heart valve poppets (16) demonstrated that polydimethylsiloxanes with low cross-link densities and low silica filler underwent significant lipid uptake in vivo. 

Thermal analyses have been used for over 20 years to characterise heart-valve poppets (silicone elastomer) implanted into humans [29] and to evaluate the in vivo absorption of lipids and related compounds fix)m the body. Important deleterious effects on the implants, observed under in vivo conditions include changes in the hardness and mechanical properties, which appear to be associated with colour changes from white to yellow then brown. Because the thermal curves of the samples extracted from new and unused implants were almost identical, the differences were attributed to materials absorbed into the polymer matrix. Thermal analyses may therefore be useful in understanding the behaviour of these poppets in vivo. Table 1 shows the thermoanalytical data for new and used poppets, with those used poppets differing in terms of the extent extracted materials in vivo. 

The silicone-rubber heart-valve poppets contain unreacted polymer which appears to be absent after the poppet has been exposed to body fluids. When the question was raised as to whether the new poppets contain a material subject to oxidation at a lower temperature than for the bulk of the poppet, nitrogen studies showed decomposition at the same temperature but to a lesser extent. For the new poppets in air a mass loss of about 9% was observed, while for those samples showing an apex at 390 °C, the percent of absorbed material was... 

This study [30] provides important information on silicone heart valve poppets including what is absorbed and what may be lost on implantation. 

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