Bioactivity and mechanical properties of SiO2–CaO–P2O5 glass-ceramics

Glass-ceramics in the system SiO2–CaO–P2O5, with 55 mol% of silicon content, with and without phosphorus, were obtained by thermal treatment of sol–gel glasses as the precursors. The influence of the composition of the precursor glass on the crystallisation, bioactive behaviour and mechanical properties of these glass-ceramics was investigated. An interesting result is that when phosphorus was not present in the precursor glass, the biaxial flexural strength of the glass-ceramics increased by one order of magnitude. The crystalline phases obtained were similar in both glass-ceramics, although when phosphorus was present the crystallisation of tricalcium phosphate and the stabilisation of the Wollastonite phase at high temperature in the glass-ceramic took place Both glass-ceramics, without and with phosphorus, showed a fast in vitro bioactive response; a new apatite-like layer fully covered the surface of both materials after soaking in simulated body fluid for a short time. The rate of the apatite layer formation mainly depended on the sintering process, which took place at lower temperatures in the glass-ceramics without phosphorus. The glass-ceramics containing phosphorus showed a decrease in the values of the Weibull coefficient, an increase of porosity and pore size, and a heterogeneous microstructure, worsening their mechanical properties.