Effects of silicon on osteoclast cell mediated degradation, in vivo osteogenesis and vasculogenesis of brushite cement

Calcium phosphate cements (CPCs) are being widely used for treating small scale bone defects. Among the various CPCs, brushite (dicalcium phosphate dihydrate, DCPD) cement is widely used due to its superior solubility and ability to form a new bone. In the present study, we have studied the physical, mechanical, osteoclast-like-cell differentiation and in vivo osteogenic and vasculogenic properties of silicon (Si) doped brushite cements. The addition of Si did not alter the phase composition of the final product and regardless of the Si level, all samples included beta-tricalcium phosphate (beta-TCP) and DCPD. 1.1 wt% Si addition increased the compressive strength of undoped brushite cement from 4.78 +/- 0.21 MPa to 5.53 +/- 0.53 MPa, significantly. Cellular activity was studied using a receptor activator of nuclear factor kappa beta ligand (RANKL) supplemented osteoclast-like-cell precursor RAW 264.7 cells. Phenotypic expressions of the cells confirmed successful differentiation of RAW 264.7 monocytes to osteoclast-like-cells on undoped and doped brushite cements. An increased activity of osteoclast-like cells was noticed due to Si doping in the brushite cement. An excellent new bone formation was found in all cement compositions, with significant increase in Si doped brushite samples as early as 4 weeks post implantation in a rat femoral model. After 4 weeks of implantation, no significant difference was found in blood vessel formation between the undoped and doped cements, however, a significant increase in vasculogenesis was found in 0.8 and 1.1 wt% Si doped brushite cements after 8 weeks. These results show the influence of the Si dopant on the physical, mechanical, in vitro osteoclastogenesis and in vivo osteogenic and vasculogenic properties of brushite cements.