Enhanced osteoblast differentiation and osseointegration of a bio-inspired HA nanorod patterned pore-sealed MgO bilayer coating on magnesium

Endosseous magnesium (Mg) and its alloy implants are meeting obstacles due to their fast degradation and the resultant poor cytocompatibility and osseointegration. Herein, a bio-inspired coating (named HT24h), comprising an outer layer of narrow interrod spaced hydroxyapatite (HA) nanorods mimicking the osteoclast-created nanotopography of the bone matrix at remodeling sites and an inner layer of pore-sealed MgO was fabricated on Mg using microarc oxidation (MAO) and hydrothermal treatment (HT). Its effects on in vitro hFOB1.19 cell functions such as proliferation, differentiation and extracellular matrix mineralization as well as in vivo osteogenesis, bone-implant contact, push-out force and pushed-out failure mode assessed osseointegration were investigated, together with porous MgO (MAO₀)- and MgO containing Mg(OH)₂-sealing-pores (HT2h)-coated Mg. Compared to MAO₀- and HT2h-coated Mg, HT24h-coated Mg greatly enhanced osteoblast functions, which is ascribed to the HA nanorod derived up-regulated intracellular Ca²⁺ and down-regulated intracellular Mg²⁺ concentrations as well as the lightened H₂ evolution and alkalization of the surrounding medium. Owing to the enhanced osteoblast functions, HT24h-coated Mg greatly enhanced osseointegration and its pushed-out failure occurred predominantly within the peri-implant bone rather than within the coating for HT2h-coated Mg and at the coating/Mg interface for MAO₀-coated Mg, giving rise to an advanced Mg-based implant with improved clinical performance.