Class: BE-210
Group: W7
Members: Lytal Kaufman, Jenny Li, Alisa Plesco, Jonathan Rogers
Date: April 30, 1998
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Abstract:
The purpose of this experiment was to evaluate the effects of gamma radiation sterilization on the material properties of ultra high molecular weight polyethylene (UHMWPE) and the extent to which these effects influence the choice of sterilization method. Four tests were performed on the polyethylene component of a Zimmer-brand knee implant and a pre-sterilized polyethylene block. From the differential scanning calorimeter, the onset temperature increased 1.37% from the interior to the surface of the knee sample and 3.85% from the surface sample to the block sample. The average value of heat of fusion increased 15.3% comparing the surface knee sample to the block sample. Using the density gradient column, an increase in density of 0.91% was observed between the control sample and the interior of the irradiated sample, and an increase of 2.04% was observed between the control and the surface of the irradiated sample. From the hardness testing, an increase in hardness of 17.3% was found for the irradiated knee sample. For the wear test, the maximum coefficient of friction between the metal and the polyethylene surfaces was found to be 51.7% higher for the irradiated sample than the control when the equal amount of normal force of 300 lbs was applied. The results of the wear test were plotted as depth versus distance across the specimen. The wear measurements showed a 39% decrease in maximum penetration for the irradiated sample compared to the block sample. The results indicated the irradiated sample was harder and more resistant to creep deformation. However, the irradiated sample exhibited a higher coefficient of friction and reduced abrasive wear resistance. All factors must be considered when choosing the best method of sterilization.