Hydrothermal deposition of high strength biocompatible magnesium phosphate coating through in situ conversion of AZ91D-3Ca magnesium substrate

Magnesium and its alloys are biodegradable and biocompatible with elastic modulus close to the natural bone which makes them suitable as an orthopedic implant. Poor corrosion resistance and high hydrogen evolution rate are two factors hindering their use as commercial implants. To overcome these challenges, a biocompatible magnesium phosphate coating was deposited using a single step hydrothermal method. Scanning Electron Microscopy (SEM/EDX) and X-Ray Diffraction (XRD) methods were used to analyze the structural and chemical compositions of these coatings. In addition, investigation on their adhesion, degradation, cellular proliferation, and gene expression were studied extensively. SEM analysis confirmed a uniform and defect-free deposition occurs in hydrothermal conditions. XRD validated the presence of Periclase (MgO), magnesium phosphate (Mg3(PO4)2) and Brucite (Mg(OH)2) phases. Degradation studies revealed the hydrogen evolution rate is remarkably decreased and corrosion properties were considerably improved as compared to the bare magnesium alloy. In-Vitro biocompatibility testing with pre-osteoblast (MC3T3-E1) via cell viability assay (Alamar blue reduction test) portrayed almost 100 % host cell proliferation both in coated and positive control samples after 8 days. Comparing coated and untreated magnesium alloy in SEM images, greater cell adhesion was seen to the coated surface. It is concluded that magnesium phosphate coatings can be used commercially as they are compact, highly crystalline, defect-free, bioresorbable, cytocompatibility, well-adhered, and protective in nature. Hence, phosphate-coated magnesium alloy is qualified to be used to protect biodegradable metallic implants.