Oxidation level changes in radiation sterilized ultra high molecular weight polyethylene [medical implant material application]

Summary form only received as follows: The objective of this study was to monitor the change in oxidation levels of radiation sterilized ultra high molecular weight polyethylene (UHMWPE) with time. Specimens of UHMWPE were packaged in air and sterilized at 2.5 megarads or 3.7 megarads using a commercial cycle. Control specimens from the same lot of material which were not sterilized were monitored over the same time period. Each sample was sectioned upon receipt to produce three 100 μm thick specimens which were characterized using Fourier transform infrared (FTIR) microscopy. Spectra were collected at 100 μm increments using a vernier stage and adjustable slit aperture. The initial surface oxidation levels were 300% greater than control samples for both radiation levels. After 12 months of storage, additional samples were prepared and examined. Samples irradiated at 3.7 megarads in air showed an additional 500% increase in surface oxidation which extended 200 μm into the material. For the sample irradiated at 2.5 megarads a 300% additional increase in oxidation level was found on the surface but the oxidation level was only 170% greater at 200 μm. These results suggest that radiation sterilized UHMWPE undergoes significant increases during storage. Oxidation of radiation sterilized UHMWPE implants may have a significant impact on the bearing properties of these materials