Effect of sterilisation and aging on ultra high molecular weight polyethylene used in medical implants

The aging behaviour of ultra high molecular weight polyethylene has been st udied following gamma irradiation (25 or 40 kGy) in air or in inert atmosph ere (vacuum packed). Accelerated aging procedures used elevated temperature (70 degrees C) and/or pressurised oxygen (5 bar). The variation in polymer properties with depth into the polymer were determined using density measu rements, infrared spectroscopy, and differential scanning calorimetry. Comp arison of these results indicates a good correlation between the measuremen t techniques. Tensile and impact properties of the irradiated polymer after accelerated aging were also determined. Results were compared with shelf o r in vivo aged total joint replacement components. It appears that days in pressured oxygen at 70 degrees C is approximately equivalent to weeks in ai r at 70 degrees C, which is approximately equivalent to years 'on the shelf ' or in vivo. Differences were observed for in vivo aging depending on the length of time on the shelf prior to implantation. PRCPA/1473. (C) 1998 The Institute of Materials.