Mechanical properties, microstructure, and bioactivity of β-Si3N4/HA composite ceramics for bone reconstruction

Pure hydroxyapatite (HA) as bone graft substitute has excellent osteogenic activity, but it has lower fracture toughness and its biological activity is harmed by the addition of toughening phases, which limits its clinical application. To alleviate the contradiction, columnar beta-Si3N4 as the toughening phase and La3+/Y3+ sintering aid as active ions are used in this study to prepare beta-Si3N4/HA composite biomaterials. According to the results, hardness and toughness of 10 wt% beta-Si3N4/HA composite prepared by cold press sintering at 1300 degrees C were 6.44 GPa and 1.69 MPa m1/2, respectively, being 110% and 140% higher than those of pure HA. Moreover, 10 wt% beta-Si3N4/HA composite exhibited better protein adsorption capacity and obviously stimulated adhesion, proliferation, and osteogenic differentiation of osteoblast. In addition, it was found that sintering aid not only facilitated the improvement of mechanical properties, but also promoted the formation of 100-200 nm nanostripe structure, which was beneficial to cell adhesion. Determination of La3+ concentration combined with biological experiments also proved that its concentration range from 4x10(-8) M to 6 x 10(-8)M was beneficial to cell proliferation and osteogenic differentiation. In summary, beta-Si3N4 and sintering aids were shown to improve mechanical properties of HA at maintaining the biological activity of the latter.