Hierarchical coating design for AZ31 Mg alloys with corrosion resistance and bioactivity optimization

Magnesium (Mg) alloys are ideal candidates for biodegradable orthopedic implants, whereas the clinical utility is hindered due to excessive corrosion behavior. In this study, the novel hierarchical coating was designed for AZ31 Mg alloy to control corrosion and improve bioactivity. The process involved laser texturing treatment of the Mg substrate, followed by hierarchical coating where the bioactive glass coating (BC) as sublayer and BG-polyvinyl alcohol hydrogel composite (HC) as upper layer. The morphology, structure, interfacial properties and corrosion behavior of Mg specimens with coating treatment were investigated via SEM, EDS, XRD, XPS and electrochemical test. The cytocompatibility and osteoinductivity of MC3T3-E1 cells seeded on Mg specimens was investigated in vitro cell proliferation assay. The results of study demonstrated the mechanically interlocked interface could be created by laser texturing, thus significantly improving coating adhesion. With further coating treatment, the BC layer within crystalline phase could act as stable corrosion barrier, to reduce mass loss of Mg alloy immersed in simulated body fluid (SBF). Based on this, the HC coating was observed to effectively seal pores of BC layer as dense upper layer for hierarchical design (MgL-HC@BC), thus resulting in exceptional corrosion resistance and ability to maintain the pH in the physiological range, and consequently promoting cell adhesion with osteogenic differentiation. As such, this work presented a feasible and highly effective strategy for fabricating advanced bio-functional surfaces on biodegradable magnesium implants.