In-situ synthesis of hydroxyapatite-SiO₂ reinforced MgO bioceramic via Dual Plasma Electrolytic Oxidation: Structural and biodegradable properties

In the present work, hydroxyapatite (HA) and silicon dioxide (SiO₂) was in-situ synthesized in a MgO bioceramic on AZ31 via sequential dual plasma electrolytic oxidation (PEO). This process integrates bioactive compounds into the coating, which results in a dense and functional surface with significantly enhanced corrosion resistance and biological response. The structural response of resulting films indicated that the first PEO in silicate electrolyte yielded MgO-SiO₂ hierarchical porous coating with relatively big pores, while using the second PEO in calcium glycerol phosphate (CaGP) can be resulted in synthesized HA in the pancake-like areas and inner pores of MgO-SiO₂ film and diminished porosity to 8.63% and an average pore size of 3.5 µm². In vitro bioactivity assessment clarified that the simultaneous presence of SiO ₂ and HA in the modified PEO coating with an optimum morphology and an average thickness of 37 µm leads to the significant the biological sustainability of magnesium due to development of non-stoichiometric hydroxyapatite-rich regions over 3 to 10 days of exposure in simulated body fluid (SBF). Moreover, the biodegradation results revealed that HA-SiO₂ reinforced PEO coating as a result of the second PEO had retained a remarkable 16-fold increase in its protective performance after a 10-day cycle.