Mechanical properties and hydration of nanosized silica/calcium phosphate composite bone cements

Nano SiO₂/calcium phosphate cement (nSiO₂/CPC) composite bone cements were prepared by adding nSiO₂into calcium phosphate cement (CPC). The setting times, compressive strengths and exothermal behavior of nSiO₂/CPC composite bone cements with the different nSiO₂ contents were investigated by the Vicat needle, mechanical testing machine and isothermal conduction calorimetry. The phase composition and fracture morphologies of the nSiO₂/CPC pastes were examined by X-ray diffraction and scanning electron microscopy. The results indicate that the setting time of nSiO₂/CPC composite bone cements containing 5% nSiO₂ decreases from 16 min to 10 min and its compressive strength increases from (24±2) MPa to (33±4) MPa, but when the nSiO₂content exceeds 5% (in mass), growth of hydroxyapatite is retarded and the compressive strength of the composite bone cements decreases. In the process of hydration, on the one hand, nSiO₂ acts as filler, and adsorbs free water from liquid solution, which results in increasing of the real P/L of CPC, and retarding the hydration of CPC. The diameter and number of the pores in nSiO₂/CPC pastes decrease because of the increase of the real solid liquid ratio. On the other hand, the reaction of nSiO₂ and Ca(OH)₂ produced by hydration of CPC leads to form CSH gel, which improves the interface between nSiO₂ filler and CPC matrix. Hence the nSiO₂/CPC composite bone cements with short setting time and high compressive strength could be achieved by adding the appropriate nSiO₂amount.