Preparation of Calcium Phosphate Coatings on Titanium Using the Thermal Substrate Method and Their in vitro Evaluation

Hydroxyapatite (Ca10(PO4)6(OH)2, HAp) and dicalcium phosphate anhydrous (Ca(H2PO4)2, DCPA) were coated onto titanium substrates using the thermal substrate method in an aqueous solution containing calcium and phosphate ions at 150◦C with pH values in the range 4–8. Specimens with the HAp and DCPA layer were immersed in a simulated body fluid (SBF) to examine the dissolution and induced HAp growth behaviour of the coated layers in the SBF. No precipitation occurred on the coated DCPA layer after 7 days immersion in the SBF, and also the DCPA did not dissolve in the SBF. On the other hand, a new precipitate, which was identified as HAp, nucleated after 1 day and grew in a spherical manner on soaking the HAp substrate specimens in the SBF. The influence of small quantities of DCPA in the HAp layer on the coating’s bioactive property in the SBF was negligible as the DCPA was not on the surface of the coated layer.