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

Abstract

In this work, a conversion coating of phytic acid (PA)/calcium ion (Ca2+) 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 Ca2+ 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/Ca2+ 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)&Ca2+ was decreased by about three orders (2.726 × 10−4 A/cm2 to 4.304 × 10−7 A/cm2). In vitro tests showed that a Ca2+ 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.