Bioactivity and electrochemical behavior of bovine-derived hydroxyapatite coatings deposited by oxy-acetylene flame spraying

Metallic implants used for bone fracture treatment have been widely investigated because of their mechanical properties and their ability to provide structural support. However, their performance may be limited by the interaction with physiological environments. Thermally sprayed hydroxyapatite (HAp) coatings have therefore been explored as bioactive surface modifications to improve the performance of metallic implants. Among the available deposition techniques, oxy-acetylene flame spraying (OAFS) offers advantages in terms of cost-effectiveness and industrial scalability. Nevertheless, the use of bovine-derived HAp (BHAp) as feedstock for thermal-sprayed BHAp coatings remains scarcely explored. In this study, the bioactivity and electrochemical behavior of BHAp coatings deposited by OAFS were evaluated. Increasing the flame stoichiometry parameter (ϕ) increased the coating thickness from 106 to 485 µm and promoted the formation of secondary phases, including tricalcium phosphate (TCP) and tetracalcium phosphate (TTCP), as a result of BHAp thermal decomposition. After immersion in Kokubo’s simulated body fluid (SBF), the bioactive and electrochemical responses of the coatings were influenced by their phase composition and microstructure. In particular, the presence of TTCP in the samples promoted a heterogeneous bone-like apatite formation, whereas the coating without TTCP showed accelerated and more homogeneous apatite formation, accompanied by an increase in thickness from 106 to 275 µm. Furthermore, all coatings exhibited lower corrosion current densities than the Ti substrate, with values varying from 239 to 75 nA/cm 2 . These results show that OAFS conditions influence the phase composition, bioactivity, and electrochemical behavior of bovine-derived HAp coatings, supporting their potential use as bioactive implant coatings.