CaO-P<sub>2</sub>O<sub>5</sub> Glass-Hydroxyapatite Thin Films Obtained by Laser Ablation: Characterisation and In Vitro Bioactivity Evaluation

Abstract

Hydroxyapatite (HA) coatings have been applied to improve adhesion of non -cemented implants to host bone. Plasma spraying is the most common technique leading to thick calcium phosphate films (>120μm). Pulse laser deposition (PLD), is a possible alternative method to obtain thin (<10 μm), well adherent hydroxyapatite (HA) films. Similarly to synthetic HA, biological apatites contain Ca 2+ , PO4 3- and OH - , but also several trace ions, like Na + , Mg 2+ , K + and F - , which may be introduced by CaO-P2O5 glasses. In this study, calcium phosphate coatings based on HA and glass modified HA were applied by PLD onto Ti-6Al-4V, using deposition times of 3 hours. SBF immersion up to 1 week was used to test the films bioactivity. PLD thin films before and after SBF immersion were observed by SEM/EDS and analysed by XPS and XRD. PLD thin films presented columnar cross section structures, independently of the coatings' chemical composition. After SBF immersion, apatite films formed on PLD coatings, both of HA and HA+1.5% glass, did not present the usual morphology of immersion films, but appeared to replicate the previous films. The main difference between HA and modified HA coatings could be seen in the XPS analyses at short immersion periods. Natural apatite was calcium deficient with a Ca/P of ±1.2-1.3. The results seem to indicate that modified HA coatings with lower Ca/P ratio induced earlier formation of natural apatite.