Spark plasma sintered CaO-rich bioglass-derived glass-ceramics with different crystallinity ratios: A detailed investigation of their behaviour during biological tests in SBF

The in-vitro behaviour of three series of dense materials with different crystallization degree and phases produced by Spark Plasma Sintering (SPS) from CaO-rich bioglass powders is investigated by soaking them up to 14 days in Simulated Body Fluid (SBF). The completely amorphous materials produced after 2 min at 730 °C display the more pronounced substrate-solution interaction. This is highly beneficial for the rapid generation (<3 days) of an apatite layer on the substrate surface. Larger amounts of such phase are also produced during the entire immersion period. These characteristics are moderately mitigated when 80 wt.% of the glass is crystallized at 850 °C with the main formation of α-CaSiO3. Nonetheless, more severe SPS conditions (1000 °C, 20 min) lead to specimens rich of β-CaSiO3 that still retain 12 wt.% of the amorphous nature while scarcely interact with SBF. The apatite formation is correspondingly delayed (7 days) and its amount significantly decreased.