In vitro dissolution of various calcium-phosphate coatings on Ti6Al4V

The biomimetic route allows the formation of various Calcium-Phosphate (Ca-P) coatings that cannot be produced by the most usual technique: plasma-spraying. Amorphous carbonated Ca-P (ACCP), Octacalcium Phosphate (OCP) and Carbonated Apatite (CAp) coatings could be prepared by the biomimetic route on Titanium alloy (Ti6Al4V) plates. The in vitro dissolution of these biomimetic Ca-P coatings were compared with a commercially available Hydroxyapatite (HAp) plasma-sprayed coating. The overall coatings of similar thickness (similar to 30 mum) were soaked into various media: Simulated Physiological Solution at pH=7.3 (physiological conditions), pH=5.0 (inflammatory conditions) and pH=3.0 (total dissolution) and in a cell-culture medium (alpha-MEM). The dissolution rate of these various Ca-P coatings was determined by measuring Calcium release by Atomic Absorption Spectroscopy. Our results showed that more acidic the medium was, faster the coating dissolved. Furthermore, depending on the pH, the dissolution sequence of decreasing dissolution rate differs: at pH=7.3, ACCP > HAp > CAp > OCP; at pH=5.0 ACCP < OCP < HAp < CAp and at pH=3.0 ACCP < OCP < CAp < HAp. These different dissolution rates can be explained by specific solubilities, crystal size and microstructure of the coatings. Besides, all the Ca-P coatings soaked into alpha-MEM evolved to a carbonated apatite structure resulting from ionic exchanges between the coating and the surrounding medium.