A wettability-transformable superhydrophobic composite coating of hydroxyapatite/bismuth sulfide/lauric acid on AZ31B Mg alloy with dual-function of antibacterial and osteogenic properties

Recently, superhydrophobic magnesium (Mg)-based implants are attracting extensive interest due to their superior corrosion resistance and specific anti-bacterial adhesion characteristics. Nevertheless, the superhydrophobic surface is not conducive to cell adhesion and proliferation, which limits the application of superhydrophobic medical Mg alloys . Herein, the superhydrophobic composite coating of hydroxyapatite (HA)/bismuth sulfide (Bi 2 S 3 )/lauric acid (LA) was prepared on AZ31B Mg alloys via hydrothermal and impregnation methods, and the water contact angle of the composite coating was up to 156°, endowing Mg alloys with excellent corrosion resistance and antibacterial properties. Furthermore, the surface of the superhydrophobic coating can be transformed to hydrophilicity upon 808 nm near-infrared (NIR) light irradiation, due to the photothermal effect of Bi 2 S 3 that led to the phase transition of the lauric acid on the surface of the composite coating. After 5 min NIR light irradiation, the contact angle decreased from 156° to 60.6°, and the electrochemical tests showed that the superhydrophobic composite coating with wettability-transformable could provide effective protection for Mg alloy substrate. The antibacterial efficiency of the coated Mg alloy reached 99.9% against Staphylococcus aureus and 95.8% against Escherichia coli , respectively. Meanwhile, the superhydrophobic composite coating with wettability-transformable had good biocompatibility with over 81.2% cell viability on MC3T3-E1 cells and good early cell growth and adhesion. This work provides a strategy for preparing wettability-transformable superhydrophobic hydroxyapatite coatings on Mg-based implants with dual-function of antibacterial ability and osteogenic activity.