Comparative investigation of the adhesion and osteoconductivity properties of different silicon nitride qualities in vitro

Abstract

The remarkable stoichiometric flexibility of hydroxyapatite (HAp) enables the formation of a variety of charged structural sites at the material's surface which facilitates bone remodeling due to binding of biomolecule moieties in zwitterionic fashion. This thesis aimed to evaluate for the first time that an optimized biomedical grade silicon nitride (Si3N4) demonstrated cell adhesion, proliferation and improved osteoconductivity comparable to highly defective, non-stoichiometric natural hydroxyapatite. Human osteoblast-like SaOS-2 cells were cultured onto silicon nitride ceramic disks with different surface treatments. Four qualities of Si3N4 ceramics were chosen for in vitro testing: as sintered, chemically etched, nitrongen annealed and thermally oxidized samples. For comparison were investigated alumina and titanium alloy, which, nowadays, represent the most relevant biomaterials used in the orthopaedic field. Si3N4's zwitterionic-like behavior is a function of the dualism between positive and negative charged off-stoichiometric sites, we can hypothesize that the N2 thermally treated Si3N4 surface becomes increasingly zwitterionic-like and thus capable to bind charged functional groups in biomolecules in zwitterionic forms. Off-stoichiometry sites thus greatly promote the interaction with positively and negatively charged functional groups in biomolecules, as it occurs with calcium and phosphate sites in Hap and result in the biologically effective characteristics of silicon nitride.