[Changes in crystallinity by sterilization and processing of ultrahigh molecular polyethylene used in endoprosthetics]

We wanted to analyze crystallinity changes during sterilization in raw and in UHMWPE components for total joint arthroplasty manufactured.

To analyze the crystallinity DSC measurements and to determine the relative crystallinity infrared spectroscopy was performed. The DSC measurements were based on a comparison between the melting enthalpy of one known material to the unknown material.

The raw manufactured non-sterilized sample showed a value for the DSC-measured crystallinity of 55.5%; the sample after gamma-sterilization without air was 56.0%, and with air 56.5%. The crystallinity after ethylene-oxide sterilization was 57.7% and after autoclavation 57.9%. The manufacturing time from the raw to the arthroplasty part showed some what different results. The average crystallinity of the samples differed between 55.4% and 61.6%. The best results were achieved in ETO-sterilized samples and one gamma-sterilized sample without air. The highest values were seen for the Hylamer.

In summary, the best values for crystallinity were seen in both raw and completed arthroplasty products with ETO sterilization. For medical use cancerogenous factors must be excluded. Gamma-sterilization without air can be accepted as well. Increasing the crystallinity too much can lead to more wear debris.