Bioactive glass granules of a narrow size range (300-355 μm) implanted in bone tissue fully react in situ to form internal silica-gel cores with a calcium-phosphate rich surface. In a unique process, the internal silica-gel core degrades and what remains is an external calcium-phosphate shell. Inside the excavated granules, osteoprogenitor cells differentiate and form new bone tissue that has not originated from the external surface of the granule or from pre-existing bone. This thesis addresses the fate of the resorbed silica-gel and also its possible effect on bone tissue.

With a series of bioactive glass implantation studies in rabbit muscle and bone, we demonstrated that the excretion of bioactive glass resorption products can be quantified by tracing the silicon content of the tissues and body fluids. The silicon-containing resorption product dissolved into the local tissue and then diffused into the bloodstream. Filtered by the kidney, the resorption product was excreted through the urine. During the resorption process, there was no permanent accumulation of silicon in the tissues and the excretion rate was within physiologically tolerable ranges.

To test the possible cellular effects of bioactive glass’ dissolution products, we treated two bone-like cell lines with different solution extracts and quantified alkaline phosphatase activity. Cell cultures treated with the dissolved species from bioactive glass did not exhibit a higher alkaline phosphatase activity. We also observed no increase in alkaline phosphatase activity for bone-like cells treated with only dissolved silicon. Therefore, if there is a solution-mediated effect then it likely results from cellular products secreted by cells in contact with the bioactive glass and not ions leaching from the material.