Enhancing mechanical and biological properties of biphasic calcium phosphate ceramics by adding calcium oxide

There is a big challenge to achieve a balance between mechanical characteristics and biological properties in biphasic calcium phosphate (BCP) ceramics. The present study investigated the effects of calcium oxide (CaO) addition on the sintering behaviors and biological performances of BCP ceramics. The characterizations of surface structure, phase composition and crystal structure demonstrated that the addition of CaO could stabilize calcium-deficient hydroxyapatite (CDHA) phase and reduce grain size in BCP ceramics, so as to better mimic chemical composition and crystal structure of the natural bony minerals. Mechanical tests indicated that the addition of CaO could increase the compressive strength, flexural strength and fracture toughness of BCP ceramics, because of the enhanced crack deflection associated with a transgranular to intergranular cracking. Due to high content of CDHA phase, small grain size and slightly alkali environment, BCP ceramics with appropriate amount of CaO addition (2%) could promote the spreading and osteogenic differentiation of BMSCs. The strong bone-like apatite formation ability predicted a good osteoinductive potential of BCP ceramics with CaO addition. In summary, these findings suggest that the addition of CaO offers a promising strategy for design and fabrication of BCP ceramics with superior mechanical and biological properties.