TiO2 nanotube arrays induced deposition of hydroxyapatite coating by hydrothermal treatment

► TiO2 nanotube array layer can induce the hydrothermal deposited hydroxyapatite. ► At suitable condition, hydroxyapatite coating is in a special two-layer structure. ► CaTiO3 is formed on the tube orifice of TiO2 nanotube after hydrothermal.