Dependence of calcium phosphate formation on nanostructure of rutile TiO₂(110) surfaces

Abstract

To demonstrate the effect of the surface nanostructures on the osteoconductivity of titanium dioxide (TiO2), formation of calcium phosphate on the rutile TiO2(110) surfaces in Hanks’ balanced salt solution (HBSS) was examined using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) techniques. When the TiO2(110) surfaces annealed in air were immersed in HBSS, calcium phosphate particles were formed on the surface. The calcium phosphate formation was suppressed by further annealing of the surfaces in O2 before the immersion in HBSS. The suppression of calcium phosphate formation is attributed to the transformation of the topmost layer of the air-annealed TiO2(110) surface from amorphous to rutile. The arrangement of the phosphate ions adsorbed on the rutile (1 × 1) surface does not match the hydrogen phosphate ion lattice of the CaHPO4 sheet of brushite.

Surface Oxygen Vacancies of Rutile Nanorods Accelerate Biomineralization

“…In this study, it was reasonable to further speculate that the surface oxygen vacancy defects of rutile nanorods were beneficial for the adsorption of Ca 2+ , facilitating the heterogeneous nucleation of HA onto rutile nanorods. For example, Sasahara et al reported that CaP particles were able to precipitate on the air-annealed TiO 2 (110) surface but were suppressed once the substrate was preannealed in O 2 before immersion in Hanks’ balanced salt solution (HBSS) because of the transformation of the amorphous phase in the topmost layer to the rutile phase, which resulted in the failing lattice mismatch for epitaxial growth of brushite . Transformation of the amorphous phase in the topmost layer to the rutile phase after annealing in O 2 suggested the elimination of surface oxygen vacancies.…”

“…For example, Sasahara et al reported that CaP particles were able to precipitate on the air-annealed TiO 2 (110) surface but were suppressed once the substrate was preannealed in O 2 before immersion in Hanks’ balanced salt solution (HBSS) because of the transformation of the amorphous phase in the topmost layer to the rutile phase, which resulted in the failing lattice mismatch for epitaxial growth of brushite. 25 Transformation of the amorphous phase in the topmost layer to the rutile phase after annealing in O 2 suggested the elimination of surface oxygen vacancies. Previous studies also indicated that hydrothermally grown rutile TiO 2 nanowires were intrinsically full of oxygen vacancy defects, which were significantly reduced after annealing at 500 °C in air, as vacancy condensation into internal voids occurred during the heat treatment.…”

Functionalization of Titanium Dioxide by In Situ Surface Crystallization of Bisphosphonate-Based Coordination Complexes

“…In this case, the reactive hydroxy groups from the metal oxide could be available to react with one of the components of the BPCCs [divalent metal (M 2+ ) or BP] to induce surface nucleation and promote crystallization. Based on the high affinity of TiO 2 to bind to calcium ions, − it is expected that these atoms could form monolayers in the surface of the metal oxide and serve as a template to promote the crystallization of BPCCs. In this manner, the coordination complexes will be anchored into the TiO 2 via an interlayer of calcium ions during their hydrothermal synthesis.…”