Dr. Greenlee. Animal Testing Scientists in Amsterdam, The Netherlands, took cubes of bioactive glass and implanted them into the tibias of guinea pigs in 1986. After 8, 12, and 16 weeks of implantation, the guinea pigs were euthanized and their tibias were harvested. The implants and tibias were then subjected to a shear strength test to determine the mechanical properties of the implant to bone boundary, where it was found to have a shear strength of 5 N/mm2. Electron microscopy showed the ceramic implants had bone remnants firmly adhered to them. Further optical microscopy revealed bone cell and blood vessel growth within the area of the implant which was proof of biocompatibility between the bone and implant. Bioactive glass was the first material found to create a strong bond with living bone tissue. Structure Solid state NMR spectroscopy has been very useful in determining the structure of amorphous solids. Bioactive glasses have been studied by 29Si and 31P solid state MAS NMR spectroscopy. The chemical shift from MAS NMR is indicative of the type of chemical species present in the glass. The 29Si MAS NMR spectroscopy showed that Bioglass 45S5 was a Q2 type-structure with a small amount of Q3 ; i.e., silicate chains with a few crosslinks. The 31P MAS NMR revealed predominately Q0 species; i.e., PO43−; subsequent MAS NMR spectroscopy measurements have shown that Si-O-P bonds are below detectable levels Compositions There have been many variations on the original composition which was Food and Drug Administration (FDA) approved and termed Bioglass. This composition is known as Bioglass 45S5. Other compositions include: 45S5: 45 wt% SiO2, 24.5 wt% CaO, 24.5 wt% Na2O and 6.0 wt% P2O5. Bioglass® S53P4: 53 wt% SiO2, 23 wt% Na2O, 20 wt% CaO and 4 wt% P2O5. (S53P4 is the only bacterial growth inhibiting bioactive glass). 58S: 58 wt% SiO2, 33 wt% CaO and 9 wt% P2O5. 70S30C: 70 wt% SiO2, 30 wt% CaO. 13-93: 53 wt% SiO2, 6 wt% Na2O, 12 wt% K2O, 5 wt% MgO, 20 wt% CaO, 4 wt% P2O5. Bioglass 45S5 The composition was originally selected because of being roughly eutectic. The 45S5 name signifies glass with 45 wt.% of SiO2 and 5:1 molar ratio of Calcium to Phosphorus. Lower Ca/P ratios do not bond to bone. The key composition features of Bioglass is that it contains less than 60 mol% SiO2, high Na2O and CaO contents, high CaO/P2O5 ratio, which