Synthesis and characterization of a phytic acid/mesoporous 45S5 bioglass composite coating on a magnesium alloy and degradation behavior

In order to decrease the degradation rate and improve the bioactivity of a magnesium alloy, a phytic acid and mesoporous 45S5 bioglass composite coating (PMBC) has been synthesized on the AZ31 magnesium alloy by a two-step method. The phase, surface morphology and structure of the composite coatings were characterized by X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy. The composite coating consisting of an interior layer of mesoporous 45S5 bioglass and an outer layer of phytic acid/magnesium phytic acid was dense, crack-free and had no remarkable interface between the inner and outer coating. The bonding strength of the composite coating to the magnesium alloy substrate was 15.2 ± 1.5 MPa. The immersion test in simulated body fluid (SBF) showed that the composite coating could provide obvious protection for the substrate and greatly decreased the degradation rate to 0.62 mg per cm2 per day from the uncoated sample of 2.93 mg per cm2 per day on the sixteenth day. And the outer coating of phytic acid could induce the formation of apatite, suggesting good bioactivity of the coated magnesium alloy.