The use of calcium phosphate cements (CPC) for bone tissue engineering (BTE) is quite popular as bone grafts, due to their composition being similar to the mineral phase of the bones, and their ability to induce regeneration of natural surrounding bone tissues. Their low mechanical resistance, however, prevents these materials to be used in load-bearing applications. The reinforcement with a carbon nanophase is promising due to its very high mechanical strength, in a way to improve mechanical resistance of CPCs while open up the possibility for these materials to be applied as structured bone substitutes, that also favor bone regeneration.
The focus of this study is to build graphene reinforced CPC structures by Direct Ink Writing (DIW), an extrusion-based 3D printing process with the potential to produce complex geometries, and to orient graphene in the direction of the extrusion flow, increasing mechanical properties of filaments. However, the great challenge of this work is to adjust process parameters with rheology of the ink, since it changes over time due to the setting reaction of cements.
The methodology consisted, first, of producing the CPC powder, and characterizing it in terms of composition, powder morphology, setting kinetics and formation of apatite crystals by using different aqueous solutions. An extensive study of the rheological and setting behavior of pure and graphene-doped cementitious pastes was then conducted. Individual filaments and porous cubic structures were printed with the optimized ink, enabling a mechanical characterization of the structures at different scales. A precise characterization of the distribution and orientation of the graphene platelets was also conducted and related to the mechanical properties.