Silicon excretion from bioactive glass implanted in rabbit bone.

Bioactive glass granules were implanted in the tibiae of rabbits in order to determine the pathway of the silicon released from bioactive glass in vivo. We traced and quantified the silicon released by obtaining 24-h urine samples and blood samples for up to 7 months after implantation. Bone tissue as well as the following organs were resected for chemical and histopathological analyses: kidney, liver, lung, lymph nodes, and spleen. The urinary silicon of the implanted group was significantly higher than in the control group. From the data, the calculated average excretion rate was approximately 1.8 mg/day, and as such, the amount of implanted silicon was excreted within statistical bounds in 24 weeks. At this point, only elevated concentrations of silicon were found at the implant site and not in the other organs. The concentrations of silicon measured in the urine were well below saturation. Since no significant increase in silicon was found in any of the organs including the kidney, the increased silicon excretion rate was within the physiological capacity of rabbits. Therefore, it can be concluded that the resorbed silica gel is harmlessly excreted in soluble form through the urine.