In vitro evaluation of coatings for joint implants: A case study of ZrBN-Cu

The investigation of friction response behavior and underlying mechanisms of modified implants in a simulated human tissue fluid environment is critical for assessing their in vivo service life. This study presents an in vitro evaluation of implant coatings through integrated experimental and simulation approaches. A series of ZrBN-Cu composite films were fabricated using non-equilibrium magnetron sputtering, and the composition, microstructure, mechanical properties, chemical stability, and tribological behavior in bovine serum albumin (BSA) solution were systematically characterized. The results reveal that the ZrBN-Cu films comprise fcc-ZrN, hcp-ZrB 2 , and fcc-Cu. With increasing Cu content, the hardness and elastic modulus initially increase and subsequently decrease, reaching peak values of 25.45 GPa and 274.99 GPa, respectively, at a Cu concentration of 1.1 at.%. Moreover, the ZrBN-Cu film with 1.1 at.% Cu demonstrates optimal electrochemical stability, exhibiting a corrosion current density of 1.6×10 -6 A/cm 2 and a corrosion potential of -0.04 V, indicative of superior chemical resistance. In BSA solution, the coefficient of friction gradually decreases and stabilizes at 0.11. The wear rate initially declines and then slightly increases with Cu content, reaching a minimum value of 2.1×10 -8 mm 3 N -1 m -1 at 1.1 at.% Cu. The lubrication and wear mechanisms of the ZrBN-Cu/BSA system were analyzed from lubrication state, adsorption behavior, and tribochemical reactions. The findings suggest that: (1)The ZrBN-Cu/BSA system operates under boundary lubrication conditions. (2)Cu incorporation facilitates the formation of a stable physical and chemical adsorption layer on the surface, while B enhances the structural integrity of this layer. (3)Cu exerts a catalytic effect, promoting the degradation of BSA molecules during friction and resulting in the formation of high-molecular-weight carbon-based compounds with lubricating properties.