The Regulation Of Silicate On Hydroxyapatite Nucleation In Simulated Body Fluids

The mechanism and regulation strategies of hydroxyapatite (HAP) crystallization were im-portant for physiological, pathological mineralization and the synthesis of biomimetic materials. The presence of silicon (Si) inmammalian systems was considered to be induction factor for HAP nucleation. But its mechanism was still unclear. In this work, we quantitatively evaluated the ef-fect of silicate on kinetics of HAP nucleation in simulated body fluids (SBF) with various amount of silicate. The crystallization of HAP in calcium phosphate solutions was monitored by a pH meter, and the change of crystallization stages was characterized by Transmission Electron Micro-scope (TEM), Fourier Transform Infrared Spectrum (FTIR), X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), etc. Dual roles for silicate in ACP-mediated HAP nucleation were revealed. Charged silicate monomers and oligomers existed in undersaturated silicate solutions (0.05-0.5 mM), which acted as nucleation centers for the ACP. As a result, smaller ACP particles with larger surface areas were formed, which nucleated HAP faster. In contrast, for high concen-trations of silicate (3-8 mM), the silicates were polymerized and precipitated on the ACP surface, which led to the merging of nearby ACP and produced larger ACP (with smaller surface area) with a shell of polysilicate. In this condition, the nucleation of HAP was retarded. This dose depen-dent effect of silicate on HAP nucleation enriched our understanding of the chemical functions of silicate during bone formation.