Electrodeposition of Ca–P coatings on biodegradable Mg alloy: In vitro biomineralization behavior

Preparing stabilized apatite on biodegradable Mg alloy may improve biocompatibility and promote osteointegration. In the present work, three kinds of Ca–P coatings, brushite (DCPD, CaHPO4·2H2O), hydroxyapatite (HA, Ca10(PO4)6(OH)2) and fluoridated hydroxyapatite (FHA, Ca5(PO4)3(OH)1−xFx) are fabricated by electrodeposition on a biodegradable Mg–Zn alloy. The crystalline structures, morphologies and compositions of these Ca–P coatings have been characterized by X-ray diffrection, scanning electron microscopy and energy-dispersive spectoscopy. The effects of these coatings on the degradation behavior and mineralization activity of the Mg–Zn alloy have also been investigated. The experimental results showed that these coatings decreased the degradation rate of Mg–Zn alloy, while the precipitates on the uncoated and DCPD-coated Mg–Zn alloy in modified simulated biological fluid had low Ca/P molar ratios, which delayed bone-like apatite formation. Both the HA and FHA coating could promote the nucleation of osteoconductive minerals (bone-like apatite or β-TCP) for 1 month. However, the HA coating transformed from DCPD through alkali heat treatment was fragile and less stable, and therefore its long-term corrosion resistance was not satisfactory. Instead, the FHA was more stable and had better corrosion resistance, and thus it should be better suited as a coating of Mg implants for orthopedic applications.