In vitro self-densification and photo-responsive antibacterial activity of quercetin loaded polyelectrolyte complex on AZ31 magnesium alloy

Biodegradable magnesium (Mg) alloys have received widespread attention as bone fixation implants due to their excellent biocompatibility and mechanical compatibility. However, their rapid corrosion rate in solutions containing Cl − ions and the risk of postoperative bacterial infections limit their application. Herein, a quercetin (Qu) loaded polyelectrolyte complex was fabricated on the micro-arc oxidation coated AZ31 alloy (referred to as the PVP/PEI-ICG/Qu coating) to regulate the degradation of the Mg matrix and avoid bacterial infections. The results displayed that the PVP/PEI-ICG/Qu coated substrate significantly reduced the corrosion current density to (2.86 ± 1.89) × 10 −7 A·cm −2 , which was an order of magnitude lower than that of the AZ31 alloy [(8.86 ± 1.35) × 10 −6 A·cm −2 ], due to the combined physical barriers provided by the PVP/PEI complex, the underlying MAO layer and the self-densification effect. Qu was loaded in a single step and protected by polyelectrolyte network, allowing for its release in response to near-infrared light (NIR) irradiation. Additionally, the antibacterial rate of the PVP/PEI-ICG/Qu coating reached 99.8 % ( S. aureus ) and 99.9 % ( E. coli ), thanks to the synergistic effects of Qu and its photothermal and photodynamic properties stimulated by 808 nm NIR irradiation, with a photothermal conversion efficiency of 45.2 %. Moreover, the coating demonstrated excellent biocompatibility, enhancing cell viability by up to 120.8 %. This antibacterial composite coating with good corrosion resistance and antibacterial activity provides a promising strategy for developing antibacterial Mg-based orthopedic implants.