Antibacterial, immunomodulatory, and osteogenic activities of ZnO/Zn3(PO4)2 composite micro/nano-structured coatings on titanium surfaces

Infections and loosening remain two significant challenges in the clinical application of titanium (Ti) implants. Zinc oxide (ZnO) nanostructured coatings possess remarkable antibacterial properties and osteogenesis potential, but their instability-induced physiological toxicity needs to be improved. In this work, ZnO/zinc phosphate (Zn 3 (PO 4 ) 2 ) composite micro/nano-scaled flower-like structural coatings were constructed on Ti implant surfaces by magnetron sputtering combined with two-step hydrothermal treatments to address these concerns. The results showed that the composite micro/nano-structures became larger with the increase of the concentration of the second hydrothermal precursor (dipotassium hydrogen phosphate), while the coatings became more hydrophilic. In addition, the composite coatings exhibited excellent antibacterial properties, mediated macrophage polarization towards anti-inflammatory and pro-healing M2 phenotype, and promoted osteogenic differentiation of bone marrow mesenchymal stem cells. This surface modification strategy, which utilizes the partial conversion of ZnO to Zn 3 (PO 4 ) 2 to balance the antibacterial and cell-modulating properties of Ti implants, holds great promise for clinical applications.