Effect of the HA/β-TCP Ratio on the Biological Performance of Calcium Phosphate Ceramic Coatings Fabricated by a Room-Temperature Powder Spray in Vacuum

Four calcium phosphate ceramic coatings, the less soluble hydroxyapatite (HA) coating, the more soluble β-tricalcium phosphate (β-TCP) coating, and two biphasic calcium phosphate (BCP) coatings with HA/β-TCP ratios of 70/30 and 30/70 were fabricated by spraying each corresponding powder onto a titanium substrate at room temperature (RT) in a vacuum, in order to investigate the effect of the HA/β-TCP ratio on the dissolution behavior and the cellular responses of the coating. No secondary phases, except for HA and β-TCP, were observed for the coatings in the X-ray diffraction results. The coating compositions were almost the same as those of the starting powders because the coating was conducted at RT. Microscopic examination of the coatings revealed crack-free and dense microstructures. The BCP coatings exhibited dissolution rates intermediate between those of the pure HA and β-TCP coatings. The dissolution rate of the coatings was largely dependent on their HA/β-TCP ratio. The cell proliferation and differentiation results indicated that the cellular responses of the coatings were not proportional to their dissolution rates. The 3HA–7TCP (HA/β-TCP ratio of 30/70) coating exhibited an optimal dissolution rate for excellent biological performance.