Cytotoxic evaluation of silicon nitride-based ceramics

Silicon nitride-based ceramics are potential candidates as materials for orthopedic implants due to their chemical stability associated with suitable fracture toughness and propitious tribologic characteristics. Therefore, in this work, dense silicon nitride components are investigated considering their suitability as biomaterials. Initially, two different compositions of silicon nitride were considered, using ytterbium, yttrium and aluminum oxides as sintering aids. The materials were sintered in a carbon resistance furnace under nitrogen atmosphere and were analyzed by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM) in order to characterize the microstructure. Indentation method was applied in order to obtain hardness and fracture toughness measurements, and in vitro test of cytotoxicity was performed for a preliminary biological evaluation. A microstructure composed of grains of beta-silicon nitride distributed in a secondary phase was observed. The samples achieved fracture toughness values of 5 MPa m^1/2 and Vickers hardness values of 13 GPa. Since a nontoxic behavior has been observed during the cytotoxicity tests with the samples, this finding suggests that silicon nitride-based ceramic can be used as a material for clinical applications.