B-doped hardystonite bioceramics from preceramic polymers and fillers: Synthesis and application to foams and 3D-printed scaffolds

Highly porous hardystonite-based bioceramics, in the form of foams and 3D scaffolds, were obtained by the thermal treatment, in air, of silicone resins and engineered micro-sized oxide fillers. Besides CaO and ZnO precursors (CaCO3 and ZnO powders), calcium borate, in both hydrated and anhydrous form (Ca2B6O11·5H2O and Ca2B6O11, respectively), was added to commercial silicone resins, with a significant impact on the microstructural evolution. In hydrated form, calcium borate led to a substantial foaming of silicone-based mixtures, at low temperature (420 °C); after dehydration, upon firing, the salt provided a liquid phase, favouring ionic interdiffusion, with the development of novel B-contaning hardystonite-based solid solutions (Ca2Zn1-xB2xSi2-xO7). Although fired at lower temperature than previously developed silicone-derived hardystonite cellular ceramics (950 °C, instead of 1200 °C), the newly obtained foams and scaffold exhibit substantial improvements in the mechanical properties.