We report on the structural transformations of Bioglass ® during thermal treatments. Just after the glassy transition, at 550 °C, a glassy phase separation occurs at 580 °C, with the appearance of one silicate-and one phosphate-rich phase. It is followed by the crystallization of the major phase Na 2 CaSi 2 O 6 , from 610 to 700 °C and of the secondary phase, silicorhenanite, at 800 °C. The latter evolves from the phosphate-rich glassy phase, which is still present after the first crystallization. In order to control the processing of glass-ceramic products from Bioglass ® , crystallization kinetics were studied via differential scanning calorimetry measurements in the range of 620-700 °C and temperature-timetransformation curves were established.

Sintering and crystallisation phenomena in powders of a typical bioactive glass composition (45S5 Bioglass) have been investigated in order to gain further understanding of the processes involved in the fabrication of Bioglass, based glass-ceramic scaffolds for tissue engineering applications. In situ experiments in an environmental scanning electron microscope with a heating stage were carried out to follow the morphology of Bioglass particles during sintering and crystallisation. Optimal processing parameters for the manufacture of Bioglass based glass-ceramic scaffolds by the foam-replica technique were determined. To assess the in vitro performance and bioreactivity of Bioglass -derived glass-ceramic scaffolds, the biodegradation of samples in simulated body fluid (SBF) was investigated using various techniques, including SEM, TEM, XRD and EDX. The mechanism of interaction of the glass-ceramic surface with SBF was determined, which involves (i) preferential dissolution at glass/crystal interfaces, (ii) break-down of crystalline particles into very fine grains through preferential dissolution at crystal structural defects, and (iii) amorphisation of the crystalline structure by introduction of point defects produced during ion exchange. The present report thus offers for the first time a complete assessment of the processing parameters, microstructure, and in vitro performance of Bioglass derived glass-ceramic scaffolds intended for bone tissue engineering.

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