Large deformation compression induced crystallinity degradation of conventional and highly crosslinked UHMWPEs

The effect of a large compressive plastic deformation on the melt temperature (Tm), lamellar thickness, crystallinity, and density of four UHMWPEs (two conventional and two highly crosslinked) was examined. The materials were prepared from a single batch of medical grade GUR 1050 resin (Ticona, Bayport, TX, USA). The two conventional UHMWPEs were as-received (virgin) and gamma radiation sterilized at 30 kGy in a nitrogen atmosphere (radiation sterilized). The two highly crosslinked UHMWPEs were each irradiated at 100 kGy and then post-processed with one of either two thermal treatments: annealing, which was done below the melt transition temperature (Tm), at 110 °C for 2 h (110 °C-annealed); and, remelting, which was done above Tm, at 150 °C (150 °C-remelted). Differences in changes upon compression between the materials were examined using ANCOVA analyses. The 150 °C-remelted material showed a significant change in Tm and lamellar thickness upon compressive plastic deformation whereas the other three UHMWPE materials did not. However, all of the materials showed significantly decreased crystallinity and density upon compressive deformation. The findings of this study support that microstructural evolution during compressive deformation is a function of UHMWPE formulation, as affected by irradiation and post-irradiation heat treatment.