Excretion of resorption products from bioactive glass implanted in rabbit muscle

Bioactive glass granules were implanted in the paraspinal muscle of rabbits 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 and blood samples for up to 6 months after implantation. Furthermore, local muscle tissue as well as the following organs were resected for chemical and histopathological analyses: brain, heart, kidney, liver, lung, lymph nodes, spleen, and thymus. The urinary silicon of the group with implanted granules was significantly higher than in the sham-operated, control group. The average excretion rate was 2.4 mg/day, and as such, 100% of the implanted silicon was excreted in 19 weeks. No elevated concentrations of silicon were found at the implant sites or in the other organs at sacrifice, that is, 24 weeks. The histological appearance of all organs was normal throughout. The concentrations of silicon measured in the urine were well below saturation and because no significant increase in silicon was found in any organ, including 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.