Direct growth of structurally controllable hydroxyapatite coating on Ti-6Al-4V through a rapid hydrothermal synthesis

[Display omitted] •A facile hydrothermal growth of hydroxyapatite directly on Ti-6Al-4V is developed.•The nanostructure of hydroxyapatite deposited on Ti-6Al-4V can be easily controlled.•A nanowire-induced porous hydroxyapatite structure exhibits the better bioactivity. Titanium alloys have been used as an implant material for many years due to their high ductility, high strength, excellent corrosion resistance and better biocompatibility. However, this biomaterial as an implant still requires the functionally bioactive surface coating to improve the osseointegration between the implant and bone tissue. Herein, we develop a facile hydrothermal synthesis of using the mixture of calcium hydroxide and sodium tripolyphosphate to directly form a structurally tunable hydroxyapatite coating on the Ti-6Al-4V surface. The result shows that the structure of hydroxyapatite can be readily controlled by modifying the Ti-6Al-4V surface with TiO2 via a short heat treatment. The treated Ti-6Al-4V can provide the rapid growth of hydroxyapatite fibers to form a porous structure interwoven with wire-like shapes in comparison with untreated Ti-6Al-4V presenting needle-like shapes. This structural difference results from the formation of TiO2 assisting in initial nucleation of hydrothermal hydroxyapatite growth. The bioactivity result reveals a better proliferation rate on the wire-like sample is enabled to correlate with the porous structure, crystallinity, and wettability of hydroxyapatite. Our results here not only indicate the feasibility of a structurally controllable hydroxyapatite through a rapid hydrothermal synthesis but also provide insights into optimizing preferred structures on implant surfaces.