Calcium phosphate formation on TiO2 nanomaterials of different dimensionality

摘要

Calcium phosphates (CaPs) composites with different TiO2 nanomaterials (TiNMs) have recently attracted attention due to their potential application as implant materials for hard tissue regeneration. Among different synthetic routes for such composites, biomimetic synthesis attracts special attention as a green synthesis route. To rationalize biomimetic synthesis, the influence of surface structure and surface charge density of different TiNMs on CaPs precipitation should be determined. In this paper, for the first time, the influence of TiO2 nanoparticles (TiNPs) and titanate nanotubes (TiNTs) on CaPs spontaneous precipitation was investigated. In addition, the ability of TiNMs to induce CaPs formation in corrected simulated body fluid (c-SBF) was tested. The advancement of the CaPs precipitation was followed by potentiometric measurements, while the obtained materials were characterized by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy (RS), powder X-ray diffraction (PXRD), scanning (SEM) and transmission (TEM) electron microscopy, electron paramagnetic resonance spectroscopy (EPR), Brunauer-Emmett-Teller surface area analysis (BET), dynamic (DLS) and electrophoretic light scattering (ELS), atomic force microscopy (AFM) and thermogravimetric (TGA) analysis. Both TiNMs showed poor ability to promote CaPs formation in c-SBF which can be attributed to their low absolute zeta-potential value. However, during spontaneous precipitation, they exhibited uncommon dual influence on precipitation kinetics, i.e. inhibition of initially formed amorphous calcium phosphate (ACP) transformation at lower and promotion at higher concentrations. After one hour of reaction time, in the presence of both TiNMs, calcium deficient hydroxyapatite was formed (CaDHA). Morphology of the CaDHA depended on the type and concentration of TiNMs. However, PXRD, EPR and TGA characterization confirmed that there is no significant difference between CaDHA formed in the presence of different TiNMs, which indicates that CaDHA composites with different TiNMs could be prepared at similar conditions. In addition, they can be prepared in a much shorter time compared to the usual procedure with SBF. Obtained results confirm the importance of surface structure and charge in CaPs - TiNMs interactions. They as well contribute to a deeper insight into precipitation processes on the nanosurfaces, which enables a rational approach not only in the biomimetic synthesis of novel biocomposites for hard tissue regeneration but also of composites for other applications.