Mechanical properties of medical grade expanded polytetrafluoroethylene: The effects of internodal distance, density, and displacement rate

Expanded polytetrafluoroethylene (e-PTFE) is used successfully in a multitu de of biomedical and clinical applications, The success of this biomaterial is due to its microporous structure that allows biointegration for fixatio n, as well as overall mechanical integrity. The mechanical properties and d egree of tissue ingrowth depend on the microstructure of the expanded polym er foam, yet little is known about the correlation of the internodal distan ce and other microstructural features with the monotonic tensile properties . Complete structure-property correlation can be used to provide invaluable knowledge for the design of biomedical devices, The purpose of this study was to investigate the monotonic tensile properties of e-PTFE over a range of medically relevant microstructural features and manufacturing parameters . The microstructural and manufacturing parameters considered were internod al distance, linear density, volumetric density, and reduction ratio. Addit ionally, the effect of displacement rate on mechanical properties was studi ed. We found that the ultimate stress and strain increased linearly with li near density (R-2 = 0.88 and 0.67, respectively). Surprisingly, elastic mod ulus did not correlate with any parameter measured and only weak correlatio ns were found between all properties and internodal distance. The yield and ultimate stresses increased with increasing displacement rate (R-2 = 0.88 and 0.57, respectively), The findings from this study indicate that linear density is a better predictor of mechanical properties than internodal dist ance and may be the preferred parameter to control when specifying a materi al for implantation in load bearing situations. (C) 1999 John Wiley & Sons, Inc.