Zn/Mg/Cu co-doped Ti-6Al-4V alloy simultaneously modulates immune responses and stimulates osteogenesis

To improve the osseointegration of Ti-6Al-4V implants, a Zn-, Mg-, and Cu-doped composite coating was fabricated via soft sparking micro-arc oxidation (S-MAO). The resulting S-MAO coating retained a porous microstructure and was successfully doped with the intended elements (Zn, Mg, Cu). The Zn/Mg/Cu components in the composite coating potentiated macrophage polarization towards the reparative M2 phenotype, as evidenced by an approximately 1.4-fold upregulation of CD206⁺ and a 31 % downregulation of CD86⁺. This immunomodulatory effect subsequently upregulated the expression of osteogenic genes BMP2, COL1A1, Runx2, and OCN by approximately 2.2-, 2.1-, 2.6-, and 1.7-fold, respectively. Furthermore, MC3T3-E1 cells cultured on the composite coating exhibited a characteristic spread morphology with significantly increased pseudopodia number and length, indicating enhanced cell adhesion and early osteogenic commitment. Additionally, the coating significantly enhanced ALP activity and mineralized nodule formation, which are associated with the direct osteogenic effects of Zn, Mg, and Cu. In summary, the composite coating promotes osteoblast differentiation and mineralization by modulating the immunomodulatory microenvironment and directly inducing the release of osteogenic factors. Therefore, this multi-element co-doping strategy offers a promising approach for developing bioactive titanium implants with enhanced osseointegration.