In vivo calcium phosphate formation induced by sol-gel-prepared silica.

Implantation with plugs made of a porous sol-gel-prepared silica into the femurs of goats demonstrated that a calcium phosphate was formed both on the silica plugs and within the pores inside the silica plugs 12 weeks postoperatively. This observation indicates that a highly hydrated silica surface is effectively catalytic for calcium phosphate nucleation. Calcification can be triggered in physiologic solution under stimulation of the silica gel. A high level of silicon in the uncalcified osteoid region of young bone is thus thought to provide a number of SiOH groups for initiating calcium phosphate formation. Our results provide some information about the mechanism of calcium phosphate mineralization in higher animals. We believe that heterogeneous nucleation of apatite can be induced from metastable calcium phosphate solutions including physiologic fluids on those specific surfaces of materials, where there are abundant acidic OH groups.