Biotribological study of multilayer coated metal-on-metal hip prostheses in a hip joint simulator

Metal-on-metal (MOM) hip joint bearings have demonstrated low wear rates and nowadays this contact pair has being considered as an alternative to metal-on-polymer (MOP) joint replacements. However, wear of MOM joints is a concern due to the toxicity and biological reaction of wear debris and metallic corrosion. This has motivated to investigate the possibility to apply thin hard coatings on metallic heads to reduce the wear and metallic ion release. The aim of the present study was to investigate the wear properties of metal-on-metal hip prostheses with surface engineered femoral heads using a multilayer coating (TiN/CrN)×3, in comparison with metal-on-metal pairs in a hip joint simulator. Different surface PVD coatings were applied on surgical grade wrought cobalt–chromium alloy femoral heads: multilayer (TiN/CrN)×3, CrN single layer and diamond-like carbon (DLC). These femoral heads were tested against high carbon content cast cobalt–chromium alloy acetabular cups using a three-axial multi-station hip joint simulator (FIME II). During the wear tests three directions of motion were applied with the following amplitudes: flexion–extension (FE) ±23°, abduction–adduction (AA) ±23° and internal–external (IER) ±8°. All components were tested at 1.2 Hz under a Paul-type loading curve and bovine calf serum solution as lubricant. Results showed that both; the PVD coatings protects the femoral heads reducing wear up to 5 times in the case of the DLC coating and 28 and 55 times in the case of (TiN/CrN)×3 and CrN respectively compared with the MOM femoral heads.