In vitro bioactivity of silicon nitride–hydroxyapatite composites

Silicon nitride-based ceramics are characterised especially by high chemical resistance, superior combination of fracture toughness, hardness and bioinertness. However, the biological applications often require additional properties, e.g. bioactivity enabling stronger bonding to the host tissue. Hydroxyapatite coating prepared by sol–gel route, which provides pure, stable and nano-crystalline product is one of the ways to achieve bioactivity of bioinert ceramics. Therefore silicon nitride–hydroxyapatite composites were prepared by infiltration of hydroxyapatite precursor sol into the silicon nitride based porous ceramics. The conditions of sol preparation were optimised to be appropriate for pure HA synthesis: ageing at elevated temperature (85 °C) and calcinations at 500 °C for 1 h. Cytotoxicity and in vitro bioactivity of Si 3 N 4 –HA composites were tested in order to verify the effect of hydroxyapatite addition on the biological properties of composite. After immersion of porous composite into simulated body fluid (SBF) for 21 days, calcium phosphate layer was formed on the surface of silicon nitride–hydroxyapatite composites, indicating their bioactivity.