Dissolution behaviour of calcium phosphate coatings obtained by laser ablation.

Pulsed laser deposited calcium phosphate coatings on titanium alloy have been tested under simulated physiological conditions in order to evaluate the changes in morphology, composition and structure. The coatings were deposited under different conditions to obtain different crystalline structures, ranging from amorphous and mixed crystalline phases to pure crystalline hydroxyapatite (HA). The coated samples were immersed in a Ca-free Hank's balanced salt solution for up to 5 days. Characterization of the coatings was performed by X-ray diffraction, scanning electron microscopy and Fourier-transform Raman spectroscopy before and after immersion. Their dissolution behaviour was also monitored through their mass loss and calcium release. Coatings of pure HA preserve their morphology and structure during the exposure time in solution. In multiphasic coatings, consisting of HA with tetracalcium phosphate (TetraCP) or beta-tricalcium phosphate (beta-TCP) with a-tricalcium phosphate (alpha-TCP), microporosity is induced by the complete dissolution of TetraCP or gamma-TCP. Amorphous calcium phosphate coatings totally dissolve.