Tribocorrosion investigation on biomaterials for total hip replacements

Introduction: The combined action of mechanical wear and corrosion, known as tribocorrosion, is a degradation mechanism occurring in biological environments. A clear example is the total hip replacements where the chemical aggressivity of synovial fluid, coupled with the coupling between liner and cup or head affects the long-term survival of the medical devices. At the moment hard coatings are commonly adopted for improving the tribological properties. This study aimed thus to compare the tribocorrosion performance of TiNbN-coated AISI 316L stainless steel, uncoated AISI 316L stainless steel, and CoCrMo alloy under testing conditions representative of the range of motion and applied loads occurring in total hip replacements.
Methods: Dry and lubricated tribological tests were carried out by a linear reciprocating tribometer and a potentiostat supplied with an electrochemical cell. The counterpart was Titanium Grade V whereas the solution was composed of sodium chloride (0.9% NaCl per 500 ml of distilled water, pH 5.8). For the corrosive part, open-circuit potential, galvanic, potentiodynamic and potentiostatic tests were conducted. Finally, surface analysis was achieved via optical confocal/interferometric profilometry and scanning electron microscopy.
Results: TiNbN-coated stainless steel showed the least favorable corrosion response when tested under purely electrochemical conditions, while maintaining good performance during combined tribocorrosion testing. CoCrMo exhibited the best overall behavior under tribocorrosion conditions. However, this alloy was associated with the greatest wear of the titanium counterbody and the highest friction-related response under dry sliding conditions. These findings indicate that the ranking of the materials varied according to whether corrosion, wear, or their synergistic interaction was the dominant mechanism.
Conclusions: The results demonstrate that corrosion resistance alone is not sufficient to predict the performance of metallic biomaterials under tribocorrosion conditions. The response of the complete tribosystem, including the wear of the counterbody, must be considered when selecting materials and coatings for biomedical applications.