Sintering and concomitant crystallization of bioactive glasses

The sintering of bioactive glasses allows for the preparation of complex structures, such as three-dimensional porous scaffolds. Such 3D constructs are particularly interesting for clinical applications of bioactive glasses in bone regeneration, as the scaffolds can act as a guide for in-growing bone cells, allowing for good integration with existing and newly formed tissue while the scaffold slowly degrades. Owing to the pronounced tendency of many bioactive glasses to crystallize upon heat treatment, 3D scaffolds have not been much exploited commercially. Here, we investigate the influence of crystallization on the sintering behavior of several bioactive glasses. In a series of mixed-alkali glasses an increased CaO/alkali metal oxide ratio improved sintering compared to Bioglass 45S5, where dense sintering was inhibited. Addition of small amounts of calcium fluoride helped to keep melting and sintering temperatures low. Unlike glass 13-93, these new glasses crystallized during sintering but this did not prevent densification. Variation in bioactive glass particle size allowed for fine-tuning the microporosity resulting from the sintering process.