Abstract
Cortical bone has a hierarchical structure. In microstructure, cortical bone is a composite structure of the osteonal and non-osteonal regions and it is regarded as "osteon composites". In nanostructure, cortical bone is a multi-phase nanocomposite material consisting of collagen and hydroxyapatite (HAp). The relationship between the mechanical properties and the hierarchical structure of cortical bone has not been fully investigated and elucidated. This study used strip specimens aligned with the bone axis taken from the cortical bone of a bovine femur. In the experiments, elastic modulus and strength of the specimens were measured by tensile tests. The degree of c-axis orientation of HAp crystals in the specimens was measured by X-ray diffraction method. The area ratio of osteonal region at the cross sections of the specimens was determined. Indentation tests using an AFM probe were conducted at the osteonal and non-osteonal regions in the cross-section. As a result, the elastic modulus and strength were higher in specimens with lower area ratio of the osteonal region. Indentation tests show that the contact stiffness of the osteonal region was lower than that of the non-osteonal region; however, the difference was not so large. The degree of HAp orientation was higher in specimens with lower area ratio of the osteonal region. Furtehr, the elastic modulus in the bone axial direction depended on the degree of c-axis orientation of HAp crystals.
