One of the most important objectives in the field of biomaterials science and engineering is development of new materials as bone substitutes. Silica ( SiO 2) has an important role in the biomineralization and biological responses. The aim of this research was to prepare and characterize hydroxyapatite-silica ( HA - SiO 2) composite nanopowder with different content of silica. Hydroxyapatite-silica composite nanopowders with 20 and 40 wt% silica were prepared using a sol–gel method at 600°C with phosphoric pentoxide and calcium nitrate tetrahydrate as a source of hydroxyapatite; also, tetraethylorthosilicate and methyltriethoxisilane as a source of silica. Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) techniques were used for characterization and evaluation of the products. The results indicated the presence of nanocrystalline hydroxyapatite phase beside amorphous silica phase in prepared composite nanopowders. Moreover, by increasing the content of silica in composite nanopowders, the crystallinity will be decreased,and the ability of the product as a bone substitute material might be controlled by changing the content of the ingredients and subsequently its structure.

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Synthetic biomimetic carbonated hydroxyapatite (CHA) has shown significant promise in bone tissue engineering for its mechanical and chemical biocompatibility and osteogenic potential. Variations in the size of hydroxyapatite particles have also been shown to contribute to the hydroxyapatite's osteogenic success. However, synthesizing biomimetic CHA with optimal osteogenic properties using a simple synthesis methodology to make highly reproducible, biomimetic, and osteogenic CHA has not been evaluated fully. The objective of this study was to synthesize submicron CHA particles using a nanoemulsion method. We hypothesized that by varying the synthesis technique we could control particle size while still creating highly biomimetic CHA typically produced during nanoemulsion synthesis. Furthermore, we hypothesized that 500 nm CHA particles would induce greater osteoblastic differentiation compared to larger or smaller CHA particles. X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and dynamic light scattering were used to characterize the chemical composition, shape, and size of CHA synthesized through variations in pH, temperature and stirring speed during synthesis. Manipulation of pH showed the ability to selectively tailor CHA particle size from 200-900 nm in a reproducible manner while maintaining the chemical composition.In addition, 500 nm particles elicited the most rapid increase in osteoblastic differentiation and did not decrease cell viability compared to 200 and 900 nm particles.

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