Nano-hydroxyapatite crystal formation based on calcified TiO2 nanotube arrays

The lack of biological activity of pure titanium as a dental implant has attracted increasing attention. This condition can be improved by preparing a layer of nano-hydroxyapatite (nano-HA) coating that is stable and does not easily fall off, which however, remains a challenge. Here, we report the preparation of nano-HA crystals on calcified titanium oxide (TiO 2 ) nanotube arrays by means of anodization, heat treatment, calcification in vacuum and hydrothermal phosphorylation, achieving the chemical bonding between the nano-HA coating and TiO 2 substrate. The mechanism of coating formation was also investigated. The results confirmed that annealing at 450 °C could convert the amorphous nanotubes to the anatase structure. Calcium titanate (CaTiO 3 ) was formed on the surface of nanotubes by heat treatment after calcification, which could provide nucleation sites for the formation of nano-HA. Needle-like nano-HA crystals were subsequently formed on the surface of the TiO 2 nanotube arrays. The scratch test showed that the adhesion strength between the formed nano-HA coating and the TiO 2 nanotube arrays was higher than 29.17 ± 1.07 N. In vitro cell proliferation and adhesion experiments showed that the nano-HA coating had good biocompatibility. Alkaline phosphatase (ALP) activity and osteocalcin (OCN) expressions highlighted the higher osteoconductivity of the nano-HA coating on the surface of TiO 2 nanotube arrays compared to the pure Ti.