We have extended the usefulness of the 24.5CaO -^s(27.5-x)Na_2O - 6P_2O_5 -^s(42+x)SiO_2 (wt percent) (with x=0-10) bioactive glass series by introducing engineered porosity in bulk samples. The glasses are prepared by the melt-quench method with an amorphous phase separated microstructure that varies with SiO_2 fraction. For 42-43 and 50-52 wt percent SiO_2, the phase separation occurs by nucleation and growth, giving two disconnected phases. The glasses containing 44-49 wt percent, SiO_2 show interconnected structure typical of spinodal decomposition. The degree of interconnectivity of the amorphous phases depends on the thermal history. Heat treatment produces two main crystalline phases of sodium calcium silicates, viz. Na_2Ca_2Si_3O_9 and Na_2CaSi_3O_8. Additional calcium silicate (CaSiO_3) and calcium phosphate (Ca_4P_6O_(19)) phases are also present. Immersion of samples in a simulated body fluid (SBF) shows that the formation of hydroxyapatite on the surface is significantly higher in the heat treated samples. Controlled leaching in 1N HCl introduces multi-modal nano-macro porosity, which is expected to improve their usefulness as bone scaffolds.
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