Mechanical behaviour of cancellous bone tissues used for the manufacturing of heterologous bone grafts

In this work, the mechanical behaviour of cancellous bone tissues used for the manufacturing of commercial heterologous bone grafts was investigated both at small and at large strains. Three different tissues were examined. They were obtained from equine bones after a specific proprietary enzymatic-based treatment aimed at achieving perfect biocompatibility while preserving the collagenous part. Two tissues had the mineral content of the bones of origin (femur, humerus), whereas the third was markedly demineralized (femur). The response at small strains and at failure was studied by means of monotonic compression tests in quasi-static conditions. Stiffness and strength turned out to be governed by the apparent density of the tissue, with specimen size and geometry, and tissue macro-structural characteristics, only playing a secondary role. A ductile- and a brittle-like failure was exhibited by the demineralized tissue and the non-demineralized ones, respectively. The large deformation behaviour was studied by means of cyclic compression tests, which clearly highlighted the occurrence of plasticity (for strains higher than ≈1.9%), and allowed to study the strain accumulation processes, at the macromechanical level. More in-depth microstructural analyses were carried out on the demineralized tissue. Flexural tests were also performed.