Masters Theses

Date of Award

5-2002

Degree Type

Thesis

Degree Name

Master of Science

Major

Materials Science and Engineering

Major Professor

Raymond A. Buchanan

Committee Members

Roberto S. Benson, Carl J. McHargue

Abstract

One of the primary life-limiting factors for modern total joint arthroplasty components is ultrahigh-molecular-weight polyethylene (UHMWPE) wear-debris-induced periprosthetic osteolysis, which leads to aseptic implant loosening and, ultimately, the need for revision surgery. Therefore, substantially reducing the wear rate of UHMWPE orthopaedic implant components is critical to extending the in vivo lifetime of these implants. This work is an effort to compare the wear performance of a novel radiation treatment, ultraviolet (UV) radiation, to that of other UHMWPE materials. The UHMWPE materials tested include conventional, unmodified, ram extruded (C-RE); gamma-irradiated (7.5 Mrads), ram extruded (G-RE); UV irradiated (100 J/cm2), ram extruded (UV100-RE); UV irradiated (150 J/cm2), ram extruded (UV150-RE); conventional, unmodified, compression molded (C-CM); and UV irradiated (150 J/cm2), compression molded (UV150-RE). The UV irradiated material sets were exposed to UV radiation (λ=248 nm) at various doses to induce crosslinking within the polymer. Pin-on-disk wear tests were performed for a simulated 6 years of in vivo use and the amount of wear was quantified via profilometry. Wear tests were performed with UHMWPE disks against a Co-Cr-Mo (ASTM F799) pin at a contact stress of 3.45 MPa. Diluted bovine blood serum with additions of sodium azide (NaN3) and EDTA was utilized as the lubricant to simulate synovial fluid. Fourier Transform Infrared Spectroscopy (FTIR) spectra in attenuated total reflectance (ATR) mode were also collected, when possible, before irradiation, after irradiation, and after shelf storage. A total of 18 pin-on-disk wear tests were performed. Examination of the average wear rates and factors revealed that the unmodified, compression-molded (C-CM) polyethylene demonstrated the best wear resistance under the current test conditions. The UV-irradiated material (150 J/cm2) also demonstrated increased average wear resistances. However, an analysis of variation revealed that the standard deviation in the majority of the material sets was large enough to result in statistically insignificant differences in average wear rates and factors. The only statistically significant differences in wear resistance were between the C-CM material and the UV150-CM material, the G-RE material, and the UV100-RE material. The average oxidation indices decreased slightly after irradiation. In addition, an analysis of variance showed that all oxidation indices increased by statistically significant amounts after storage in air. Finally, it is important to note that the range of wear factors calculated for the variety of materials tested on the UT pin-on-disk machine are within the range of wear factors reported in the literature.

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