Carbon fibre reinforced polyetheretherketone (CFR-PEEK) has been introduced recently as an alternative material to be used in joint prostheses. During injection moulding of the CFR-PEEK the carbon fibres tend to become orientated in the direction of the plastic flow. The direction of these fibres may affect the wear produced by these materials. Reciprocation only and reciprocation plus rotation (multi-directional) pin-on-plate wear tests were performed on PAN-based CFR-PEEK against itself. The plates were manufactured with the carbon fibres mainly orientated either longitudinally (in the direction of reciprocation motion) or mainly transversally (perpendicular to the direction of motion) to determine the effect of carbon fibre orientation on the wear of these materials. For each test, four pin and plate samples were tested (two reciprocation only and two reciprocation plus rotation) for three and a half million cycles at a cycle frequency of 1 Hz under a 40 N load (which resulted in a contact stress of about 2 MPa). The lubricant used was bovine serum diluted with de-ionised water to a protein content of 17 gl-1. This was maintained at 37 °C. The wear was determined gravimetrically. Soak control specimens were used to account for any weight changes due to lubricant absorption. The average steady-state wear for the CFR-PEEK samples that underwent reciprocation motion only was found to be 5.41 and 18.7 × 10-8 mm3N-1m-1 for the longitudinal carbon fibres and the transverse fibres respectively. For the multi-directional tests, the average steady-state wear was 5.88 and 19.9 × 10-7 mm3N-1m-1 for the longitudinal and transverse fibres respectively. It is clear from these results that for both reciprocation motion only and reciprocation plus rotation the wear was considerably lower with the fibres orientated in the longitudinal direction than the transverse direction. Also, these tests show that reciprocation only gives approximately an order of magnitude lower wear than multi-directional motion. It can be concluded that the wear rate of CFR-PEEK is lower when the sliding motion occurs in the same direction as the carbon fibre orientation. Also, in these pin-on-plate tests, the wear produced using reciprocation motion only was an order of magnitude lower than that for the tests using multi-directional motion. The authors wish to thank INVIBIO Ltd for funding this research.
