A novel polydopamine/hydroxyapatite composite coating on Mg alloy with excellent corrosion resistance and biocompatibility

A novel composite coating with excellent corrosion resistance and biocompatibility on Mg–3Al–2Sn alloy was prepared by combining the advantages of polydopamine (PDA) and hydroxyapatite (HAP), and was investigated by scanning electron microscopy, electrochemical test, and in vitro cellular tests. The results showed that the PDA/HAP composite coating with a thickness of 19.7 μm covers the underlying PDA cracks and Mg matrix and effectively reduces the corrosion current density of the alloy from 266 to 1.53 μA cm −2 . The PDA/HAP coating exhibits excellent corrosion resistance with a 99.42 % corrosion inhibition efficiency, superior to the majority of developed HAP composite coatings to date. Meanwhile, it maintains stable pH and the lowest hydrogen evolution (4.7 ± 0.05 mL/cm 2 ) after 7 days of immersion in SBF, and retains a dense intact structure without damage. Additionally, the PDA/HAP coating exhibits excellent biocompatibility, as MC3T3-E1 cells cultured in its extract show numbers and morphologies close to those of the control group, maintain stable viability over 5 days, and indicate no significant cytotoxicity. Finally, the bonding and corrosion protection mechanisms of the PDA/HAP composite coating were discussed.