In situ fabricated Zn-ZnO@HA coating on magnesium alloy with robust adhesion, superior anticorrosion, and osteogenic activity

Hydroxyapatite (HA) is widely used in bone implants due to its inherent biocompatibility, however, conventional single-layer HA coating still faces limitations when applied to biodegradable magnesium alloys. In this study, a Zn-ZnO@HA nanocomposite coating was fabricated on AZ31B magnesium alloy through in situ ZnO doping assisted by ion plating combined with hydrothermal treatment. The results demonstrated that in situ generated ZnO on the ion-plated Zn layer effectively promoted HA nucleation and growth, resulting in a stable and well-adhered nanostructured coating. The composite coating exhibited superior mechanical performance, with a bonding strength (12.88 N) and plasticity index (0.76), significantly higher than those of the single-layer HA. Electrochemical analyses revealed that the Zn-ZnO@HA coating increased the polarization resistance by approximately seven orders of magnitude, while decreasing the corrosion rate and carrier concentration by approximately two and three orders of magnitude, respectively. Compared with the bare AZ31B substrate, and exhibited long-term degradation stability in simulated body fluid (SBF), attributed to the synergistic effects of barrier protection, cathodic protection, and self-healing behavior of the Zn/ZnO/HA interface. Moreover, owing to the broad-spectrum antibacterial properties of Zn and ZnO, the composite coating effectively inhibits bacterial adhesion and proliferation, thereby offering potential protection for maintaining an aseptic implant interface. In vitro studies further confirm that the Zn-ZnO@HA coating creates a favorable microenvironment for osteogenic differentiation, significantly enhancing early alkaline phosphatase activity and promoting late-stage mineralized nodule formation. Overall, the Zn-ZnO@HA nanocomposite coating integrates outstanding corrosion resistance with high bioactivity, offering an effective strategy for surface functionalization of biodegradable magnesium alloy bone implants.