Hexagonal hydroxyapatite formation on TiO2nanotubes under urea modulation

Abstract

Hexagonal prism-like hydroxyapatite (HA) crystals were synthesized under hydrothermal conditions utilizing the combination modulation of TiO₂ nanotubes and urea. TiO₂ nanotubes were used as templates to induce HA crystal nucleation under hydrothermal conditions. Comparison of HA formation on nanotubular surfaces and flat surfaces demonstrated that nanotubular surfaces favored prism-like hexagonal HA crystallization. Urea was selected as the precipitation agent to control the HA growth and mediate its morphology. The hydrothermal temperature should be high enough to lead the decomposition of urea in order to ensure HA formation. Density functional theory (DFT) calculation showed that the urea had higher binding energy with (100) surfaces than with (001) surfaces, and therefore could inhibit the growth of (100) surfaces of HA, which possibly influenced the morphological development of HA crystals. This study demonstrated that HA crystal growth could be modulated in its nucleation and growth stage. It also implied that computer simulation might play an important role to select the suitable precipitation agent in order to obtain crystals with specially designed morphology.