CHARACTERIZATION OF HIGH-VELOCITY OXY-FUEL COMBUSTION SPRAYED HYDROXYAPATITE

Bioceramic coatings, created by the high velocity oxy-fuel combustion spraying of hydroxyapatite (HA) powders onto commercially pure titaniu m, were characterized in order to determine whether this relatively ne w coating process can be successfully applied to bioceramic coatings o f orthopaedic and dental implants. Fourier transform infrared spectros copy, X-ray diffraction and scanning electron microscopy were used to characterize both the HA starting powders and coatings. A 12wk immersi on test was conducted and the resulting changes in the coatings were a lso characterized. Calcium ion release during dissolution was measured with flame atomic absorption during the first 6 weeks of the immersio n study. A comparison of powder and coating X-ray diffraction patterns and lattice parameters revealed an HA-type coating with some loss in crystallinity. Fourier transform infrared results showed a partial los s of the OH- group during spraying, however the phosphate groups were still present. Scanning electron microscopy analysis showed a lamellar structure with very close coating-to-substrate apposition. The coatin gs experienced a loss of calcium during the immersion study, with the greatest release in calcium occurring during the first 6 days of the s tudy. No significant structural or chemical changes were observed duri ng the 12wk immersion study. These results indicate that the high velo city oxy-fuel process can produce an HA-type coating; however, the pro cess needs further optimization, specifically in the areas of coating- to-substrate bond strength and minimization of phases present other th an HA, before it would be recommended for commercial use.