Ag/ZIF-8/Mg-Al LDH composite coating on MAO pretreated Mg alloy as a multi-ion-release platform to improve corrosion resistance, osteogenic activity, and photothermal antibacterial properties

In this study, an Ag/zeolitic-imidazolate framework (ZIF-8)/Mg-Al layered double hydroxide (LDH) (Ag/ZIF-8/LDH) composite coating was prepared on the surface of a micro-arc oxidation (MAO)-pretreated magnesium alloy through a hydrothermal reaction with the addition of ZIF-8 nanoparticles in a hydrothermal solution. The influence of the ZIF-8 nanoparticles on the corrosion resistance, biocompatibility, antimicrobial properties, and osteogenicity of the composite coatings was systemically investigated. The results indicated that the formed Ag/ZIF-8/LDH composite nanosheets sealed the micropores and cracks in the MAO coating well, resulting in a more integrated and denser morphology. The ZIF-8-comprising composite coating exhibited better corrosion resistance in vitro. In addition, the Zn2+ in ZIF-8 and Ag+ release of the Ag nanoparticles in the coating, together with the good photothermal conversion performance of the Ag/ZIF-8/LDH coating, could quickly generate photothermal temperature under near-infrared light, to achieve a synergistic antibacterial effect. The effective antibacterial coefficients against Staphylococcus aureus and Escherichia coli were 99.8 % and 99.89 %, respectively. Additionally, the cells on the composite coating exhibited good osteogenic activity with higher alkaline phosphatase (ALP) activity because of the Zn2+ and Mg2+ from the LDH. This strategy may be a promising approach for post-treatment of MAO coatings to enhance protection and provide multiple functionalities for biomedical Mg alloys.