Plasma spray deposition of hydroxyapatite coatings from sol precursors

Plasma spray deposition of hydroxyapatite (HA) coatings is a well established commercial process. When deposited on metallic substrates, these coatings have been shown to promote bone fixation and osteconductivity. A concern with current coatings is the formation of relatively large debris particles during resorption. The size of the debris is related to the particle size of the powder injected into the plasma during the deposition process. The use of solution precursors or dispersions of fine particle size powders as the feedstock for plasma spraying has been shown to produce submicron/nanocrystalline structured coatings from relatively inexpensive precursors. Nanocrystalline HA coatings may improve the resorption of the coating in the body, avoiding the irritant effect of large particles which may be seen in current thermal sprayed HA coatings. We have explored the use of sols prepared from several different precursors as the feedstock for the plasma spray deposition of HA coatings on Ti6A14V substrates, employing statistical design of experiments to establish optimal deposition conditions. We report on the formation and the characteristics of the coatings as a function of the deposition parameters. The presence of different Ca-P crystalline and amorphous phases was assessed by X-ray diffraction analysis. The coating microstructure was characterized by scanning/transmission electron microscopy. The suitability of the technique to coat biomedical implants is discussed.