Accelerated in vitrotesting, especially high temperature aging, is commonly used to identify degradation mechanisms and predict clinical performance of biostable polymers.In this analysis, we compare the impact of hydrolytic high temperature aging on the bulk polymer properties of multiphase polyurethane elastomers to their in vivoperformance.Samples of polyurethane (PU) and polydimethylsiloxane-based polyurethane (SPU) were incubated for timed intervals in aqueous buffer (pH ~ 7) at different temperatures (37, 55, 72, 85�C). The time-dependent changes in the specimen's total weight, molecular weight and mechanical properties were examined. Morphology of the polymers were studied with optical (SEM), thermal (DSC) and mechanical (DMA) techniques. Chemistry of the polymers in bulk or surface were studied by FTIR-ATR and GPC. Specimens taken from human explants, through 5 years, were analyzed in the same fashion and compared to those from the accelerated in vitrostudy.The in vitro samples water absorption increased significantly with temperature (T), resulting in a not linear relationship between the logarithm of effective diffusivity and (1/T). For the in vivosamples, high magnification SEM data showed shallow surface cracking of PU and no cracking on SPU samples.FTIR-ATR analysis revealed weak loss of H-carbonyls responsible for hydrogen bonding between hard segments of PU samples and weak oxidation of the polyether soft segments of both polymers. The molecular weight and tensile property losses in the accelerated testing did not correlate with those from the human implanted samples. The DSC analysis displayed an endothermic transition near 60�C, suggesting morphology changes or phase separation during the aging. Dynamic mechanical thermal analysis presented non-linear relationships of storage versus loss modulus, suggesting molecular rearrangements occurring at high temperatures.These results suggest that the applicability of time temperature superposition theory in predicting long-term biostability of implanted multiphase polyurethane materials is limited.

Impact of in vitro accelerated degradation testing on the chemistry of multiphase polyurethane elastomers

247th National Meeting (2014)

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