Biodegradable PTMC-MAO composite coatings on AZ31 Mg-alloys for enhanced Corrosion-resistance

Abstract

Bio-absorbable magnesium (Mg) alloys exhibit significant promise for implantable medical devices, particularly in orthopedic applications. However, their limited corrosion resistance and rapid degradation rates have hindered their clinical translation. To address this long-standing challenge, here we developed a composite coating system (PTMC-MAO) for Mg-alloys, seamlessly integrating Microarc oxidation (MAO) and Poly-(Trimethylene Carbonate) (PTMC) layers. Leveraging the synergistic effects between MAO coatings, generated through micro-arc oxidation, and PTMC coatings, synthesized via gradual dropwise addition, our approach effectively controls corrosion and degradation rates of a widely applied Mg-alloy (AZ31) both in terms of kinetics and thermodynamics. Compared with the uncoated AZ31, the PTMC-MAO coatings exhibited greater positive Ecorr of -1290 mV and lower icorr of 5.3nA· cm-2 with a significant 851-fold reduction. The coatings reached up to a distinguished protection efficiency (η) of 99.9%, accompanying with the higher impedance |Z| of 4×105 Ω·cm2. The ΔpH change and the released Mg2+ concentration were 0.25 and 42μg/ml, respectively, after 21 days of immersion. Both values were superior to those observed for the AZ31 substrate. These results highlight the transformational potential of PTMC-MAO composite coatings, indicating their feasibility as a new class of materials for engineering the surfaces of Mg-based degradable implants.