Wear and friction properties of prosthetic joint materials evaluated on a reciprocating pin-on-flat apparatus

Abstract

A three-station reciprocating pin-on-flat apparatus was constructed for tribological studies of materials for total replacement joints. Flat-ended cylindrical ultra-high molecular weight polyethylene (UHMWPE) pins were worn against Co-Cr-Mo, Al 2O 3, ZrO 2 and Si 3N 4 counterfaces in distilled, de-ionized water. The temperature of the test environment was 37 ± 1 °C. The nominal contact pressure was 4.8 MPa, sliding distance per cycle 50 mm, frequency 1 Hz and test length 7 × 10 6 cycles with ZrO 2 and 5 × 10 6 cycles with all other counterfaces. The wear of the pins was measured gravimetrically at intervals of 5 × 10 5 cycles. The frictional forces were recorded continuously. The average wear factors of UHMWPE against Co-Cr-Mo, Al 2O 3, ZrO 2 and Si 3N 4 were of the order of 10 −7, 10 −9, 10 −9 and 10 −8 mm 3 N −1 m −1 and the average coefficients of static friction were 0.10, 0.11, 0.13 and 0.13, respectively. The results indicate that Al 2O 3 and ZrO 2 are distinctly superior to Co-Cr-Mo as counterfaces for UHMWPE in prosthetic joints. The difference between the wear of UHMWPE against Co-Cr-Mo and that against Al 2O 3 is consistent with clinical observations. The apparatus will be a useful tool in the screening of new materials, surface treatments and coatings for prosthetic joints.