Effect of type of contact, counterface surface roughness, and contact area on the wear and friction of extensively cross-linked, vitamin E stabilized UHMWPE.

Abstract

Novel extensively cross-linked, vitamin E stabilized polyethylene (VEXLPE) materials are expected to provide improved wear and oxidation resistance in orthopedic implants. Noncyclic, multidirectional pin-on-disk (POD) wear tests were performed for VEXLPE with flat-on-flat (FoF) and ball-on-flat (BoF) specimen configurations against CoCr counterfaces of varying surface roughness (S_a = 0.02-0.74 μm). In addition, wear tests (FoF) were performed for VEXLPE pins of varying nominal contact area (7.07-113 mm² ) with consistent load regimen against polished CoCr disks. All specimen couples were also friction tested with a multidirectional, circularly translating POD device. In all tests, calf serum was used as the lubricant. In comparison with earlier, similar tests for conventional, gamma-sterilized ultra-high molecular weight polyethylene (UHMWPE) and for extensively cross-linked, heat treated UHMWPE (XLPE), the tribological findings for the present VEXLPE appeared promising with respect to its possible clinical use in prosthetic joints, particularly as an acetabular liner against large-diameter femoral heads, and in nonconforming contacts. Contrary to the well-known, paradoxical behavior of conventional UHMWPE, the VEXLPE wear factor decreased with increasing contact area.