Near-infrared responsive superhydrophobic coating with wettability transition on magnesium alloy for enhanced...

Magnesium alloy superhydrophobic coatings for orthopedic implants face challenges such as weak interfacial bonding, limited antibacterial effect due to passive physical repulsion, and superhydrophobicity that hinders osteogenic performance. In this study, an integrated composite coating consisting of polydopamine (PDA), hydroxyapatite (HA), and lauric acid (LA) was developed to enhance the interfacial bonding with the magnesium alloy substrate by mechanical interlocking and chemical bonding. Inspired by the multiscale structure of sea urchin spines, a stable Cassie-Baxter superhydrophobic surface was achieved by constructing a micro/nano structure, followed by modification with low-surface-energy LA. Furthermore, near-infrared (NIR) irradiation was employed to activate the PDA photothermal effect, inducing a wettability transition. The composite coating exhibited a 63.1 % increase in interfacial bonding strength compared to the HA/LA coating. The superhydrophobic surface effectively reduced bacterial adhesion by more than 88 % through physical repulsion against Escherichia coli and Staphylococcus aureus, and killed over 90 % of Escherichia coli via a mechanical bactericidal effect induced by the sea urchin-like structure. Upon NIR irradiation, the photothermal effect achieved 99 % antibacterial efficiency and induced a wettability transition, which promoted osteoblast adhesion area by 112-fold. This integrated strategy provides new insights for the future development of magnesium alloy implants.