Effect of materials' processing methods on the 'in vitro' bioactivity of wollastonite glass-ceramic materials

The work examines the influence of the microstructure on the in vitro bioactivity of two glass-ceramics with the same chemical composition in the SiO2-CaO system. Ceramizing a glass, via powder technology route (W1), and by sol-gel method (W2), formed two glass-ceramics composed of the same crystalline phases, but differed in microstructure. Both glass-ceramics were soaked in simulated body fluid up to 4 weeks using the same conditions. An hydroxyapatite (HA)-like layer formed on the surfaces of both samples but a different formation rates yielded differences in the microstructure. The W2 glass-ceramic showed faster HA-like formation because its smaller crystalline grains dissolved more readily. In addition, the thicker glassy phase at the grain boundaries facilitated a faster formation of silanol groups on the surface of the amorphous SiO2 interlayer, a reaction that is considered to be a prerequisite for HA-like formation. Comparison of glass-ceramics synthesized by the two preparation methods was carried out. The interfacial reaction product was examined by scanning and transmission electron microscopy. Both instruments were fitted with energy-dispersive X-ray analyzers. Additional changes in ionic concentration, using inductively couple plasma atomic emission spectroscopy, were determined.