Objectives: Due to its process feasibility as well as reasonably high coating bond strength, plasma spray is perhaps the most popularly used deposition technique for implant applications of hard tissues. Hydroxyapatite (HA) and hydroxyapatite-bioactive glass (HA-BG) coatings have been plasma-sprayed on Ti-6Al-4V substrate using sinter-granulated HA and HA-BG powders. Methods: The phase, structure and bond strength of plasma-sprayed coatings prior to and after immersion in Hanks' physiological solution were investigated. One-way ANOVA statistical analysis was used to evaluate the statistical significance of bond strength data. Results: The sinter-granulated HA powder was irregularly-shaped and appeared quite dense. When 5 wt% or more BG was added in HA, the powder became rough and porous. X-ray diffraction patterns showed that the presence of BG enhanced the decomposition of HA structure during fabrication of the powder. The plasma spray process itself also enhanced the decomposition of apatite. Surface morphology of the present HA-BG coatings was not much different from that of HA coating, which consisting of patches of smooth and shiny glassy film and irregularly-shaped particles. Reasonably high bond strengths were obtained from all as-plasma-sprayed coatings. When immersed in Hanks' solution, however, all coatings largely lost their bond strengths. The statistical analysis showed that the bond strength of HA coating significantly declined from 53.6 MPa, the as-coated bond strength, down to 21.8 MPa after immersion for 7 days (p < 0.001). 95HA/5BG and 92.5HA/7.5BG coatings lost 62% and 55% in bond strength, respectively, after 7-day immersion. Conclusion: These bond strengths of the present coatings largely declined when immersed in Hanks' solution.

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