The effects of hydroxyl groups on Ca adsorption on rutile surfaces: a first-principles study

Abstract

Hydroxyl groups on titanium surfaces have been believed to play an important role in absorbing Ca in solution, which is crucial in the formation of bioactive calcium phosphates both in vitro and in vivo. CASTEP, a first-principles density functional theory (DFT) code, was employed to investigate Ca adsorption on various rutile (110) surfaces in order to clarify how hydroxyl groups effect Ca adsorption. The surfaces modeled in the present study include a bare rutile (110) surface, a hydroxylated rutile (110) surface, an oxidized rutile (110) surface, and a rutile (110) surface bonded with mixed OH groups and water. The results reveal that not all OH groups favors to attract Ca adsorption and loosely bonded OH and water on a rutile surface actually combine with Ca during adsorption. An oxidized rutile surface has the highest ability to attract Ca atoms, which partially explains that alkali-treated Ti surfaces could induce hydroxyapatite formation in alkaline environments.

Characterization of Nano-Scale Hydroxyapatite Coating Synthesized from Eggshells Through Hydrothermal Reaction on Commercially Pure Titanium

“…Ti surface seemed to be more abundant, which might be attributed to the formation of the anatase phase after heat treatment at 500 • C. Previous studies have shown that only weakly absorbed OH − disappears at lower heat-treatment temperatures, while OH − that is strongly bounded with Ti remains on the surface at temperatures up to 600 • C and more [30,31]. Moreover, it has been observed that only strongly bounded OH − groups are responsible for the bioactivity of Ti surfaces [32,33].…”

Oxidative power of aqueous non-irradiated TiO 2 -H 2 O 2 suspensions: Methylene blue degradation and the role of reactive oxygen species

“…The deprotonation of Ti-OH to Ti-Osurface groups due to the lower isoelectric point (iep) of TiO2 compared to the pH of body fluids (iepTiO2 = 5-6, physiological pH = 7.4) favours the electrostatic attraction of calcium ions. 8,9 This has been shown to lead to the formation of metastable calcium phosphate which can be transformed to bone-like hydroxyapatite during bone remodelling. 10,11 Further, Ti-OH surface groups play an important role in the interaction with biomolecules, particularly for the adsorption of serum proteins such as albumin and fibronectin.…”

Surface modification of Ti–6Al–4V alloy for biomineralization and specific biological response: Part I, inorganic modification

“…Moreover it has been observed that only strongly bound hydroxyls groups are effectively responsible of titanium bioactivity [40,43].…”