Characterization of Bilayered Brushite/hydroxyapatite Coatings on Titanium Substrate

The two-stage process of the calcium phosphate layer deposition – the plate-like brushite particles electrochemically deposited in the first stage and electrophoretically coated by the hydroxyapatite layer in the second stage – on titanium substrate was studied in this paper. The results showed that compact calcium phosphate layers of different thickness, roughness and morphology can be prepared by this method. Because of large shrinkage of the second hydroxyapatite layer during annealing, only a thin coating of hydroxyapatite on brushite forms the final calcium phosphate layer without any cracks. The main phases after thermal treatment of depositions in argon at given temperatures (from 800 to 960°C) were βTCP, β-Ca2P2O7 and TiO2. The phosphorus enriched regions (probably TixPy phases) are formed up to 3μm far from the titanium substrate surface in the annealing process which causes a reduction in the content of phosphorus in calcium phosphate coatings. Calcium phosphates in annealed depositions can be transformed to hydroxyapatite by hydrolysis at pH=10.8. The results showed good bioactivities of coatings in SBF.