Effect of graphene on setting and mechanical behaviour of tricalcium phosphate bioactive cements

The potential reinforcing effect of graphene on calcium phosphate cements (CPCs) for injectable bone substitutes and scaffolds is presented. The influence of graphene (0-3.84 vol%) on the microstructural development during setting and the resultant mechanical properties of CPCs constituted by α + β-tricalcium phosphate is analysed. Optimum setting conditions were established using uniaxial compression strength of CPC and composites with pristine and functionalized graphene and liquid/solid ratios (L/S = 0.5-0.6 mL/g) that allowed the mixing and spatulation of the powders. Tensile strength of optimised materials has been determined using the Diametric Compression of Discs Test (DCDT). X-ray diffraction, Raman spectroscopy and FE-SEM-EDS on fracture surfaces were used to investigate phase composition and morphological changes in set specimens. Strengthening occurs for functionalized graphene additions up to 1.96 vol% due to different toughening mechanisms. Crack deflection, bridging and branching by graphene and, finally, the pull-out of the unbroken graphene sheets have been identified. Interlayer sliding between the graphene before pulling-out is an additional toughening process. Main effect of graphene on strength is the increase of reliability.