PULSED-LASER DEPOSITION AND PROCESSING OF BIOCOMPATIBLE HYDROXYLAPATITE THIN-FILMS

Calcium phosphate-based ceramics were deposited on Ti-6Al-4V and Si substrates by pulsed laser deposition. The calcium phosphate phase (amorphous, alpha- or beta-tricalcium phosphate, tetracalcium phosphate, or hydroxylapatite), Ca/P ratio and surface morphology of the films were related to deposition conditions. Deposition of crystalline films required both elevated substrate temperature and a reactive gas environment. At substrate temperatures < 400-degrees-C, films were amorphous. Above 400-degrees-C, the gaseous environment during deposition determined the crystalline phase of the films. In Ar or in vacuum at 500-600-degrees-C, films were amorphous. In O2, deposition of alpha-tricalcium phosphate was favored between 400 and 700-degrees-C and beta-tricalcium phosphate was favored above 700-degrees-C. Films deposited in low pressures Of O2 (< 0.05 Torr) were P-deficient. The correct stoichiometry was approached as the pressure of O2 in the chamber during deposition increased. In water vapor-enriched inert gas environments, deposition of hydroxylapatite was observed at temperatures between 400 and 700-degrees-C and tetracalcium phosphate was observed at temperatures above 700-degrees-C. Adhesion of crystalline HA films deposited at 600-degrees-C in Ar/H2O was excellent, but films that were amorphous (deposited either at room temperature or in a non-reactive gas environment) and tricalcium phosphate films did not adhere well to the substrates.