Cu ions-regulated interfacial evolution and promoted Vroman effect on Cu-ZTA ceramics in mixed protein solutions

Inadequate interfacial lubrication frequently limits the clinical efficacy of ceramic orthopedic implants. This study investigated the tribological behavior of Cu doped zirconia-toughened alumina (Cu-ZTA) in single (bovine serum albumin, BSA; human gamma globulin, HGG) and mixed (BSA+HGG) protein solutions. Low-level Cu doping (3 and 5 wt%) significantly improved lubrication performance, with the mixed protein solution providing the most effective lubrication and HGG demonstrating superior anti-wear capacity compared to BSA. Mechanistically, released Cu ions acted as an interfacial regulator that promoted the Vroman effect by neutralizing the surface charge of HGG and promoting its conformational unfolding and aggregation, which facilitated the displacement of pre-adsorbed proteins and the formation of a robust HGG-dominated lubricating film. In the protein mixture, BSA further enhanced the composite film's thickness and stability, achieving synergistic lubrication. This ion-mediated interfacial evolution endowed the lubricating film on the ceramic surface with superior load-bearing capacity and shear resistance.