Surface Characteristics and Biocompatibility of Anodic Calcium and Phosphate Coatings on Mg-Ca-Mn Alloy

Objectives: Anodizing is one of surface modification methods for increasing the corrosion resistance of biomaterial surfaces. The aim of this study was to evaluate the effect of anodic calcium phosphate coating on surface characteristics and biocompatibility of Mg-Ca-Mn alloy.
Methods: Mg-1.5 wt% Ca-0.6 wt% Mn specimens (15 mm diameter, 2 mm thickness) were prepared and anodized in electrolyte solution containing 1M NaOH,0.1M Ca(NO₃)₂, and 0.06M NH₄H₂PO₄ for 5 minutes at room temperature with a platinum plate as the cathode at constant anodizing current of 500 mA and various anodizing voltage of 5, 10 and 15V. The surface morphology and composition were analyzed by scanning electron microscopy (SEM) and energy disperive spectroscopy (EDS). Immersion test was performed and cytotoxicity was assessed on day 3 by MTT assay using MC3T3-E1 cells.
Results: As a result of anodization, an oxide layer containing calcium and phosphorus was formed on the surface of the magnesium alloy. As the anodizing voltage increased from 5 V to 10 V, the oxide layer became thicker. However, when the anodizing voltage was 15 V, the oxide layer became thinner and porous.
After immersion test, weight loss and pH variation were smaller in anodized groups than in control group. Cells spread polygonally on the surface of magnesium alloy anodized at voltage of 10 V and cell projections connecting the cells were visible, while cell projections were less developed in the other
groups. Cell proliferation on day 3 was significantly higher in anodized groups than in control group (p<0.05). In addition, the rate increased with the anodizing voltage (p<0.05).
Conclusions: This result suggests that anodic calcium phosphate coating could enhance surface properties and bioactivity of Mg-Ca-Mn alloy.