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

Abstract

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 (Bi2S3)/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 Bi2S3 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.