Class: BE-210
Group: R6
Members: Amie Borgstrom, Louis Kolman, Robert Ledger, Maryam Malik
Date: April 29, 1998
Full Text

Abstract:
Changes in density, percent crystallinity, and elastic modulus caused by fabrication processes were measured in ultra high molecular weight polyethylene to determine if surface oxidation occurred during fabrication. The samples of polyethylene used for testing included a non-sterilized compression molded block, inner and surface regions of a gamma irradiated knee implant, and a resin in powder form. Densities of the irradiated samples fell within the accepted ASTM density standard of 0.930-0.944 g/cm3. Compression molding caused a decrease in percent crystallinity between the resin and block form (86.51% to 52.40%). Gamma irradiation and further machining caused the crystallinity of the material to increase to 59.58%. All calculated elastic moduli agreed within 7.5% of the 703 MPa elastic modulus experimentally determined by Deng et al. No statistical difference was found between the densities, percent crystallinities, or elastic moduli of the interior and surface of the irradiated material. No discoloration due to oxidation was observed under the light microscope (20x).

Results implied insignificant oxidation in these samples. Furthermore, no conclusion could be made solely on the effects of gamma sterilization, as there was no control sample against which to compare the irradiated sample.