A novel method to synthesize hydroxyapatite coating with hierarchical structure

A novel process has been developed for the preparation of a hydroxyapatite (HA) coating with a hierarchical structure on a Ti substrate. The Ti substrate was first subjected to electrolytic deposition at −1.6 V (versus Ag/AgCl/KCl) in a solution of 0.042 M Ca(NO3)2·4H2O and 0.025 M NH4H2PO4 at 85 °C for 3 min, and then post-treated in a 0.25 M NaOH solution, with the addition of 0.05 M Na3Cit at 85 °C for 5 h. The experimental results showed that the coating experienced a phase conversion from octacalcium phosphate to HA after the post-treatment step. The HA coating had well-distributed, micro-sized pores comprising three-dimensional interconnected mesoporous HA belts, which would greatly increase the porosity and surface area of the coating.