Laser deposition of hydroxyapatite coatings

We have demonstrated low temperature (500 - 600°C) laser deposition of dense hydroxyapatite (HA) coatings. Under optimum processing conditions, the HA coatings possess a nominal calcium/phosphorus ratio of 1.66 and exhibit a fully crystalline single phase structure. This deposition technique is based on the application of a pulsed excimer laser (wavelength λ = 248 nm, pulse duration t = 25 × 10^-9 sec) to ablate a dense stoichiometric HA target. The HA target was prepared by cold pressing HA powders synthesized by addition of phosphoric acid to a suspension of calcium hydroxide in a closed system with constant nitrogen bubbling. High substrate temperatures (≥ 600°C) during film deposition led to phosphorus deficient coatings because of re-evaporation of phosphorus during the deposition process. The stabilization of various calcium and phosphorus phases in the film was controlled by a number of process parameters such as substrate temperature, chamber pressure and presence of water vapor in the chamber. Rutherford backscattering spectrometry, energy dispersive x-ray analysis, transmission electron microscopy, scanning electron microscopy and x-ray diffraction techniques were employed to determine the structure-processing relationships.