Study on strontium doped bioactive coatings on titanium alloys surfaces by micro-arc oxidation

In order to improve the bioactivity of titanium alloy, hydroxyapatite coatings with different amounts of Sr doping were prepared on the Ti6Al4V surface by micro-arc oxidation (MAO) using electrolytes containing Ca(CH3COO)2, NaH2PO4, and different concentrations of Sr(CH3COO)2, and EDTA-2Na was used as a complexing agent to complex Ca and Sr ions. The coatings' thickness, phase composition, microstructure morphology, and elemental distribution were examined, and the hydrophilicity and bioactivity were evaluated by contact angle and MC3T3-E1 preosteoblasts proliferation experiments. The results show that the concentration of Sr(CH3COO)2 in the electrolyte has little effect on the anodic oxide film breakdown voltage. However, the higher the concentration, the smaller the stable value of the MAO voltage is. The thickness of the MAO coating decreases with the increase of Sr concentration in the electrolyte, and the coatings mainly consist of strontium-containing hydroxyapatite, rutile, and anatase phases. The rise in Sr content leads to a decrease in Ca content, and both Ca and Sr content on the surfaces of the coatings are higher than that on the interior. (Ca + Sr)/P in all coatings is close to 1.67, which is similar to human bone. Moreover, all coating surfaces have good hydrophilicity, the Sr-doped MAO coatings promote the proliferation of MC3T3-E1 preosteoblasts, and the cell proliferation is higher on the coatings with higher Sr content.