Strontium-substituted hydroxyapatite thin films grown by pulsed laser deposition

Strontium substitution for calcium in the hydroxyapatite structure has lately attracted growing interest due to its beneficial effects on both bone formation and prevention of bone resorption. Coating Ti implants with Sr2+ substituted hydroxyapatite is expected to enhance the bioactivity of the surface and stimulate bone apposition. To this end, we deposited thin films of hydroxyapatite with different substitutions of Sr2+ for Ca2+ on Ti substrates by Pulsed Laser Deposition (PLD). Solid solutions of Sr-Ca hydroxyapatites [Ca10-xSrxHA(x = 0-1)] were prepared by direct synthesis in aqueous medium at 90°C. Sr2+ insertion led to a decrease of crystallinity degree, which accounted for the simultaneous reduction of the crystal dimensions. For PLD experiments, we used an UV excimer (KrF*) laser source (248 nm, ~7.4 ns) operating at a repetition rate of 2 Hz. The fluence during target irradiation was set at 2.4 J/cm2, and substrate temperature kept at 400°C. The depositions were performed from HA at different degrees of Sr2+ substitution for Ca2+ (x = 0; 0.1; 0.5; 1). All structures were post-treated in a H2O enriched atmosphere for 6 h. The results of structural and morphological characterizations carried out on the obtained structures indicated that the coatings, which adhered well to the substrates, were made of crystalline HA and contained strontium with a (Ca + Sr)/P molar ratio close to the stoichiometric value of HA.