Comparative wear and wear debris under three different counterface conditions of crosslinked and non-crosslinked ultra high molecular weight polyethylene.

The wear debris generated from ultra high molecular weight polyethylene (UHMWPE) have been recognised as one of the major causes of failure in total hip replacements (THR). It is essential to reduce the wear debris generated from UHMWPE acetabular cups in order to minimise this problem. Debris in the submicron size range is believed to have greater osteolytic potential. It is now known that crosslinked UHMWPE acetabular cups have reduced volumetric wear rates but little is known about the influence of crosslinking on the size and morphology of the wear debris. In this study, the wear of grade GUR 1020 crosslinked (vacuum gamma irradiated), GUR 1120 crosslinked (acetylene enhanced irradiated) and non cross linked (ethylene oxide sterilised) GUR 1020 UHMWPE was compared in multidirectional pin-on-plate wear tests under three different counterface conditions (smooth, isotropically rough and scratched counterfaces). Multidirectional motion was chosen because this motion was closer to the relative motion in the natural hip. From this study, better wear resistance of crosslinked UHMWPE compared with non-crosslinked UHMWPE was demonstrated for the smooth counterface conditions. However, in the rough and scratched counterface conditions, the vacuum gamma irradiated crosslinked material produced significantly higher wear rates than the non-crosslinked material. The analysis of the wear debris showed that the majority of the volume of the acetylene enhanced crosslinked UHMWPE wear debris was in the most biologically active size range (0.1 to 0.5 microm). In contrast, the non-crosslinked material and the vacuum gamma irradiated crosslinked material had a greater proportion of the volume of the debris in the larger size ranges which are less biologically active. This has important implications for its osteolytic potential.

A comparison of the wear and debris generation of GUR 1120 (compression moulded) and GUR 4150HP (ram extruded) ultra high molecular weight polyethylene.

The wear debris generated from UHMWPE (ultra high molecular weight polyethylene) has been recognised as one of the major causes of failure in THR (total hip replacement). GUR 1120 (compression moulded) and GUR 4150HP (ram extruded) which are currently the most frequently used materials in THR were studied in pin-on-plate wear test. The wear particles generated from this test were observed by scanning electron micrograph and analysed by image analysis. The results from this study showed that GUR 4150HP had superior wear resistance than GUR 1120 under relatively high wear factor conditions. These results also highlighted the importance of multidirectional motion and its effect on the wear rates of UHMWPE. The multidirectional motion tended to show a higher wear factor than previous studies using unidirectional motion conducted under otherwise similar conditions. The wear debris analysis conducted with the wear particles collected from unidirectional (relatively rough) pin-on-plate wear tests (GUR 1120 and GUR 4150HP) showed that the greatest number of particles had a size range of 0.1-0.5 micron followed by 0.5-1.0 micron, 1.0-5.0 microns and 5.0-10.0 microns, in both GUR 1120 and GUR 4150HP. However, comparing the masses of the wear particles, the bigger size range of greater than 10 microns, had the highest percent mass followed by 1.0-5.0 microns, 0.5-1.0 micron, 0.1-0.5 micron and 5.0-10.0 microns.