Effects of silica on the bioactivity of calcium phosphate composites <Emphasis Type="Italic">in vitro</Emphasis>

In the present study, silica-calcium phosphate composites (SiO₂-CaP composites) were developed by mixing the starting materials (SiO₂ and CaHPO₄) in different ratios with the addition of 0.1% w/v NaOH solution. The phase composition of the SiO₂-CaP composites was determined by XRD and FTIR. After thermal treatment at 350 ^C/1 h and at 1000 ^C/3.5 h; all SiO₂-CaP composites composed of -quartz, -cristobalite and -Ca2P2O7. The presence of calcium phosphate enhanced the transformation of -quartz into -cristobalite at 1000 ^C. SEM observation indicated favorable attachment and spreading of neonatal rat calvaria osteoblasts onto the surface of silica-rich SiO₂-CaP composites. After attachment, these cells produced significantly higher amount of protein and expressed higher AP activity than cells attached to silica-poor samples. Results of the study suggested that the silica-based composites are more bioactive than calcium phosphate-based composites. Silica promoted the expression of osteoblast phenotype by both solution-mediated effect and direct interaction with the surface of the substrate.