Dissolution behavior of plasma-sprayed hydroxyapatite coatings

The long-term stability of plasma-sprayed hydroxyapatite coatings is influe nced by the dissolution behavior of the coating in in vivo conditions. Plas ma-spraying generates a mixture of phases and this study has focused on how the balance of phases affects the in vitro dissolution behavior of the coa tings in double distilled-deionized water and in tris-buffer solutions. The pH changes in double distilled-deionized water were monitored, whilst the pH value was maintained at 7.25 for the tris-buffer solution at 37 degreesC with 5% CO2 atmosphere. The phosphate and calcium ions released were measu red using UV-Visible Spectrophotometer and Atomic Absorption Spectroscopy r espectively. Changes in crystal and surface topology were also studied. The results indicate that the dissolution behavior of the coatings depends on several factors. The rate of release of phosphate ions was found to increas e significantly for the tris-buffer solution compared to the deionized wate r, indicating that the presence of electrolyte constituents affects the dis solution behavior of the coatings. The Ca/P ratio in the tris-buffer soluti on is approximately three. Increases in the level of crystallinity of the c oatings significantly decreased the dissolution rate and hence, the amount of phosphate ions released. The higher the percentage of crystallinity, the higher the stability of the coating under in vitro conditions. (C) 2000 Kl uwer Academic Publishers.