[Crystalline structure of endoprosthetic UHMWPE in relation to sterilization and mechanical processing]

We analysed the changes in crystallinity in sterilized and machined UHMWPE products used in the manufacture of total joint components. For this purpose, so-called DC measurements of absolute crystallinity and infrared spectroscopy for determining the relevant crystallinity were carried out. The DSC measurements are based on a further development of differential thermo-analysis (DTA), and a comparison of the melting enthalpy of an unknown material in comparison with known material. The results show particularly high values for gamma sterilized products, and the lowest values, i.e. the least brittleness, after sterilization with ETO. The crystallinity of the original material was 55%, that after gamma sterilized 56.5%, and after steam autoclaving 57.9%; after gamma sterilized in argon 56%, and after ETO sterilized 57.7%. During the period prior to the manufacture of the end product, a wide range of values is determinable. The average crystallinity of the end products varies between 55.4% and 61.6%. Among other things, changes in crystallinity during storage and after implantation must be taken into account. To summarize, we recommended ethylene oxide sterilization, after which the best values of crystallinity were seen in both semi-finished and finished products (prostheses).