In vitro degradation and dual responsively antibacterial zeolitic imidazolate frameworks-8@Rhein composite coating on magnesium alloy

Magnesium alloys attract wide attention as bone implant materials due to their outstanding biodegradable and biocompatible properties. However, its rapid degradation rate and bacterial infections after implanting limit its applications. Herein, a self-sacrificing Mg(OH)2 coating was formed on the MAO coated samples to avoid the dissolution of the MAO coating, promoting the in-situ growth of zeolitic imidazolate frameworks-8@Rhein coating on the MAO coated AZ31 alloys (defined as MAO/ZIF-8@Rhein coating). Results displayed that the MAO/ZIF-8@Rhein coating provides favorable corrosion resistance due to the physical barriers of ZIF-8@Rhein NPs and inner MAO coating. Rhein is one-step loaded by ZIF-8 NPs and released in response to both pH changes and near-infrared light (NIR) irradiation to kill bacteria. Additionally, the antibacterial rate of MAO/ZIF-8@Rhein coating reaches to 99.95 % (E. coli) and 99.90 % (S. aureus) under the synergy of contact-killing of Rhein and its photothermal effect by irradiation of 808 nm NIR light, and the photothermal conversion efficiency comes up to 53.4 %. Therefore, this dual responsively antibacterial composite coating with good corrosion resistance will promote the applications of Mg alloys in the biomedical field.