3D-printed bone-inspired composites

Nature is an unlimited source of knowledge and advice for scientists and engineers. In particular, the optimized natural hierarchical materials are a good source of inspiration for the design of new smart materials. Among these, an intriguing material is bone, with a lightweight structure, providing support for animal bodies. The optimal combination of mechanical properties, in particular the significant toughness, makes it very attractive for research studies. The fracture behavior of bone is an interesting field of research from both medical and engineering viewpoints. In particular, engineers are interested in studying bone to get inspiration for the design of new materials. The design of new materials inspired by nature is an innovative and interdisciplinary research area, particularly attractive and known as biomimetics. By using a biomimetic approach, we design and realize a new composite material with an internal structure inspired to the microstructure of cortical bone. The new material, which is a 3D-printed synthetic polymer composite, is characterized by a repeating structural unit with a circular-cylindrical shape, designed to mimic the osteons. We characterize the material under static loading conditions (i.e. tensile) and we investigate the fracture behavior by performing tests in presence of a crack. We carried out tests in two directions, accounting for the anisotropy the bone-like composites. To investigate the effect of the osteon geometry, we designed two materials: i) characterized by perfectly circular osteons and, ii) characterized by elliptical osteons. In both cases, we paid attention to keep the osteon volume ratio constant and equal to that measured in mid-age human bone. The results of the tests prove how the osteon geometry and their arrangement affect the crack path and the overall behavior of the composite. By observing the failure mode, we also noticed several similarities with the toughening mechanisms occurring in cortical bone, such as crack deflection and branching, constrained microcracking and fibril bridging. This confirms the validity of the bone-inspired design to mimic the fracture behavior of cortical bone at microstructural level.