The effects of a phytic acid/calcium ion conversion coating on the corrosion behavior and osteoinductivity of a magnesium-strontium alloy

In this work, a conversion coating of phytic acid (PA)/calcium ion (Ca 2+ ) was prepared on a magnesium-strontium (Mg-Sr) alloy surface through a layer-by-layer self-assembly method. The effect of the pH value on the corrosion resistance of coatings was studied systematically. The addition of a Ca 2+ could enhance the intermolecular chelation of PA and repair the defects of the coating itself. The results of electrochemical and immersion testing confirmed that a PA/Ca 2+ conversion coating could adjust the corrosion rate of Mg-Sr alloys. Compared to a bare Mg-Sr alloy, the corrosion current density of Mg&OH&PA(5.5)&Ca 2+ was decreased by about three orders (2.726 × 10 −4  A/cm 2 to 4.304 × 10 −7  A/cm 2 ). In vitro tests showed that a Ca 2+ in the coatings could not only promote the formation of apatite , but also favored osteoblast proliferation. In addition, this conversion coating could significantly enhance the expression of alkaline phosphatase activity by 50–60% compared to a bare Mg-Sr alloy.