Performance and failure process of green recycling solutions for preparing high degradation resistance coating on biomedical magnesium alloys

Abstract

We used phytic acid sodium salt hydrate (Na₁₂Phy) as a micro-arc oxidation (MAO) electrolyte and systemically investigated its influences on AZ31B coating characteristics and the MAO solution failure process. Na₁₂Phy increased both phosphorus (P) and calcium (Ca) amounts as well as thickness, and adhesion strength of MAO coatings. MAO treatment, especially in a base solution with 4 g L⁻¹ Na₁₂Phy (Na₁₂Phy-4C), significantly improved degradation resistance and in vitro cytocompatibility of AZ31B alloys. LC-MS/MS analysis showed that during MAO treatment, Na₁₂Phy molecules were hydrolyzed from an anti-nutrient into absorbed inorganic phosphates by fish and a series of lower inositol phosphates with physiological activity. With increasing cycles of MAO treatment, the MAO sample achieved gradually decreased degradation resistance, but even after 50 cycles, it still had good cytocompatibility. Furthermore, 50% MAO waste solution was not toxic to Pengze crucian carp (Carassius auratus var. Pengze) during a 96 h acute toxicity test, suggesting that Na₁₂Phy-containing MAO solution has potential for use in future applications.