New insights into the bioactivity of SiO2–CaO and SiO2–CaO–P2O5 sol–gel glasses by molecular dynamics simulations

The structures of binary xCaO . (100 - x)SiO2glasses with x = 10, 20 and 30 mol-% and ternary(20 - x)CaO . xP2O5 . 80SiO2 glasses with x = 3, 10, 15,17 and 20 mol-% have been studied by means of classicalmolecular dynamics simulations using both the melt-quenchedand the sol–gel protocols. The structural picturederived correlates the bioactive behaviour to the combinedeffects of the connectivity of the extended silicate networkand to the tendency to form (or not to form) non-homogeneousdomains. In this context, a mathematical relationshipthat relates the Ca/P ratio in the Ca phosphatemicro-segregation zones to the P2O5 content in ternaryglasses has been developed and this has been used to finetuningthe optimum amount of P in a glass for its highest invitro bioactivity. The composition with optimal Ca/P ratio,80SiO2 . 14.8CaO . 5.2P2O5 has been synthesized and the results of bioactivity tests have confirmed the prediction.