Silica Gel Template for Calcium Phosphates Crystallization.

Synthetic calcium phosphates exhibit good properties as biomaterials, such as biocompatibility, bioactivity, and osteoconductivity, and they have important applications in the fields of bone tissue engineering and orthopedic therapies. In this work, we performed an extensive characterization of the composite calcium phosphates/silica synthesized in gel by varying the pH and density of the silica solution. As a function of the pH values, brushite, octacalcium phosphate, hydroxyapatite, and monetite crystallization have been obtained, while changing the silica solution density the crystals are covered by different amounts of silica which results differently structured as a function of the pH. These materials have been analyzed using several experimental techniques (X-ray diffraction, differential scanning calorimetry, Fourier transform infrared spectroscopy, transmission electron microscopy, scanning electron microscopy, and field emission scanning electron microscopy). Large brushite crystals present amorphous silica both embedded within them and deposited on the crystal surfaces. The resulting calcium phosphate-silica composite is deposited as a powder, but it can be also easily molded into monolithic forms. The results of this study could be of significance in the field of biomaterials for considerable improvements of performance of bone implants in terms of osteointegration and in possible association to set up calcium phosphates-silica biocomposites.