Incorporate biosafe additives into self-healing coating on Mg for enhanced interfacial biocompatibility recovery

Local defects in coatings allow aggressive electrolytes penetrate to the coating/substrate interface, accelerating the corrosion of the exposed Mg substrate and compromising its biocompatibility. In this work, self-healing calcium hydrogen phosphate dihydrate (DCPD) coating incorporated with 3,5-dinitrosalicylic acid (3,5-D) or 5-amino salicylic acid (5-A) is designed on Mg. The results reveal that the self-healing and corrosion resistance performance of DCPD improves after adding 3,5-D/5-A. Namely, incorporating 3,5-D/5-A into DCPD accelerates the self-healing process and repair the coating at the initial stage. The released 3,5-D/5-A additives could adsorb on the exposed Mg surface and combine with the Ca 2+ ions to precipitate. The interfacial adsorption mechanism of 3,5-D/5-A additives is disclosed by quantum chemical calculation. The simultaneously responsive adsorption and deposition of additives during coating degradation increase the thickness and compactness of the deposition layer at the coating defects, further inhibiting corrosion and stabilizing pH. These findings suggest taking biocompatibility recovery into consideration of preparing self-healing coating for biomedical applications.