Pulsed laser deposition and processing of biocompatible hydroxylapatite thin films

Abstract

Calcium phosphate-based ceramics were deposited on Ti-6Al-4V and Si substrates by pulsed laser deposition. The calcium phosphate phase (amorphous, α- or β-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°C, films were amorphous. Above 400°C, the gaseous environment during deposition determined the crystalline phase of the films. In Ar or in vacuum at 500–600°C, films were amorphous. In O 2, deposition of α-tricalcium phosphate was favored between 400 and 700°C and β-tricalcium phosphate was favored above 700°C. Films deposited in low pressures of O 2 (<0.05 Torr) were P-deficient. The correct stoichiometry was approached as the pressure of O 2 in the chamber during deposition increased. In water vapor-enriched inert gas environments, deposition of hydroxylapatite was observed at temperatures between 400 and 700°C and tetracalcium phosphate was observed at temperatures above 700°C. Adhesion of crystalline HA films deposited at 600°C in Ar/H 2O 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.