Fast formation of a novel bilayer coating with enhanced corrosion resistance and cytocompatibility on magnesium

Abstract

A novel bilayer coating (HT5h) composed of hydroxyapatite (HA) and MgO without any other phase components was fabricated on Mg by hydrothermal treatment (HT) of micro-arc oxidation (MAO) derived MgO in an aqueous solution containing Ca-EDTA and KH₂PO₄ for 5 h. The coating comprised an outer layer of HA nanorods with a narrow interrod spacing of less than 70 nm and an inner layer of MgO containing HA-sealing-pores. The adhesion strength, corrosion resistance and cytocompatibility of the HT5h coating were investigated, together with the MAO-derived coating (named as MAO₀, consisting of porous MgO) and bare Mg. The adhesion strength was identified by adhesion–tension tests; corrosion resistance was determined by static immersion and electrochemical tests in a phosphate buffer saline (PBS), while cytocompatibility was characterized by MTT assays and actin-nucleus staining assays of hFOB1.19 cells. The obtained results showed that both MAO₀ and HT5h coatings possessed relatively high cohesive strengths, and the HT5h coating appeared more effective than the MAO₀ coating in the protection of Mg from corrosion. Moreover, the mitochondrial activity, adhesion, and proliferation of osteoblasts were significantly enhanced on HT5h coated Mg compared to bare and MAO₀ coated Mg. The improved corrosion resistance and cytocompatibility may bring the HA and pore-sealed MgO bilayer coated Mg as Mg-based biomaterials closer to clinical reality.