Novel bioactive and biodegradable glass ceramics with high mechanical strength in the CaO--SiO2--B2O3 system

Novel bioactive and biodegradable glass ceramics with high mechanical strength in the (50-x/2)CaO. SiO(2)--xB(2)O(3) (4.2 < or = x < or = 17.2) system were investigated. The systems consisted of three phases: monoclinic wollastonite, calcium metaborate, and amorphous borosilicate matrix. The glass ceramics containing 4.2 mol% and 8.4 mol% B(2)O(3) showed high bulk density and a dense microstructure. Mechanical strengths of the glass ceramics were higher than those of other bioactive ceramics: high compressive strength (2813 MPa), bending strength of 212 MPa, and fracture toughness of 3.12 MPa. m(1/2). The glass-ceramic formed apatite layer on their surface in the simulated body fluid and showed significant biodegradation. The degree of apatite formation in the glass ceramics depended on the calcium metaborate content and borosilicate glassy matrix. Additional calcium metaborate and borosilicate glassy matrix increased the apatite formation rate on the surface. It might be likely that calcium metaborate causes supersaturation of Ca ions, for its high solubility in SBF and the water-reactive borosilicate glassy matrix formed Sibond;OH groups on the surface to provide nucleation sites for apatite formation. Also, through in vitro test for the biocompatibility of the CaO--SiO(2)--B(2)O(3) glass ceramics, no cytotoxicity of the glass ceramics were found. The results on bioactivity and noncytotoxicity indicated that glass ceramics in the (50-x/2)CaO. SiO(2)--xB(2)O(3) (4.2 < or = x < or = 17.2) system could be useful as a biodegradable bone replacement material.