Photothermal-controlled sustainable degradation of protective coating modified Mg alloy using near-infrared light

Abstract Controlling the corrosion rate is critical for practical applications of Mg-based alloys. In this work, we constructed a protective coating of hybrid polycaprolactone (H-PCL)/indocyanine green (ICG) on AZ31 Mg alloy, whose degradation rate was controlled by 808-nm near-infrared (NIR) light irradiation. The corrosion behaviors of H-PCL/ICG coated Mg alloys were systematically investigated by potentiodynamic polarization tests, electrochemical impedance spectroscopy (EIS) and hydrogen evolution experiments. The results disclosed that the H-PCL/ICG composite coating could effectively protect Mg alloy from corroding without NIR light irradiation. In contrast, under 808-nm NIR light irradiation, the corrosion resistance of this composite coating was decreased significantly, i.e., the corrosion current density ( i corr ) increased from (8.81 ± 1.068) × 10 −8 to (1.22 ± 0.545) × 10 −6 A·cm −2 . This is because the component of ICG in the coating was excited to produce heat locally, which triggered the glass transition temperature ( T g ) of H-PCL in the coating, resulting in the motion of the molecular chain segment. Consequently, the electrolytes penetrated the coating and corroded the Mg substrate. In vitro biological experiment indicated that the synthesized coating exhibited good cytocompatibility. Hence, these findings will provide a new strategy for designing novel photoresponsive coatings to remotely adjust the degradation rate of biodegradable metals for biomedical applications. Graphic abstract