P44 THE WEAR OF PEEK-COCRMO AND CFR-PEEK-COCRMO ASSESSED ON A PIN-ON-PLATE MACHINE

Abstract

Introduction: In an attempt to prolong the lives of implantable devices, several ‘new’ materials are undergoing examination to determine their suitability as joint couplings. As part of a series of tests, polyetherether-ketone (PEEK) against cobalt chrome molybdenum (CoCrMo) and carbon fibre reinforced-PEEK against CoCrMo were tested on a multidirectional pin-on-plate machine.

Materials and methods: The two four station pin-on-plate machines used in this study applied both reciprocation and rotational motion. Each material combination was tested individually on separate machines. Four samples of PEEK pins against CoCrMo plates were tested and eight samples (two tests) of CFR-PEEK pins against CoCrMo plates were tested. The pins were supplied by Invibio Ltd. A 40 N load was provided to each station. The lubricant used was 24.5 % bovine serum (protein content: 15 g/l) and this was heated to 37 degrees C. The wear was assessed gravimetrically and the tests each completed 2 million cycles.

Results: On average, the pin and plate wear factors were 7.37 and 0.010 x 10 -6 mm3/Nm for PEEK-CoCrMo and 0.144 and 0.011 x 10 -6 mm3/Nm for the CFR-PEEK against CoCrMo specimens respectively. These results show the wear of the components corrected relative to the control specimens that therefore took into account the weight gain due to lubricant absorption.

Discussion: The CFR-PEEK pins gave considerably lower wear against CoCrMo than the PEEK pins. It is interesting to note that the total wear factor provided by high carbon CoCrMo pins articulating against high carbon CoCrMo plates (which is known as a low wearing material combination in hip implants) was found to be 0.84 x 10 -6 mm3/Nm (1) which is actually higher than that found in these studies for CFR-PEEK against CoCrMo tested under the same conditions.

Conclusions: CFR-PEEK articulating against CoCrMo provided much lower wear than the PEEK-CoCrMo samples. This material combination also gave lower wear than metal-on-metal samples. This, therefore, indicates that this material combination may perform well in joint applications.