Reduction in the initial wear of ultrahigh molecular weight polyethylene after compressive creep deformation

Although the wear of ultrahigh molecular weight polyethylene (UHMWPE) total joint implant components has received much attention, the creep of this polymer has been inadequately studied. The objectives of this study were to determine whether creep affects the wear of UHMWPE and, if so, to measure the magnitude of this effect. Cylindrical specimens were machined from GUR 4150HP extruded unirradiated UHMWPE rod stock, compressed at three different pressures (0, 4 and 8 MPa) for 10 000 min to simulate creep, and then unloaded for 10 000 min. Wear tests were conducted by unidirectionally sliding the ends of these UHMWPE cylinders at a speed of 125 mm s^-1 on a highly polished stainless steel disc with a contact pressure of 4 MPa in bovine serum. Wear of the compressed specimens was only 38% as great as that of the noncompressed specimens (p < 0.01). There was no significant difference in the amount of wear of specimens compressed at pressures of 4 MPa vs. 8 MPa. It is presently unclear whether this reduction in wear is due to a creep-induced reduction in asperity height, or to a creep-induced increase in UHMWPE's wear resistance.