Hierarchical Imaging and Mechanical Characterization of Cortical Bone

The hierarchical structure of cortical bone plays a key role in its mechanical performance and in the development of fragility fractures such as those occurring in the femoral neck. While bone structure has been extensively studied at the macro- and microscale, increasing evidence suggests that nanostructural features also contribute to mechanical performance and may be relevant for understanding age- and disease-related changes such as osteoporosis. This thesis aims to improve the multiscale structural characterization of cortical bone, with a particular focus on the human femoral neck, and to relate nanostructural variations to local mechanical properties. For this, advanced imaging methods, in particular X-ray scattering imaging in 2D and 3D are employed in combination with state-of-the-art micromechanical testing. Two complementary studies were conducted. The first investigates tissue-level nanostructural variations across clinical fracture-relevant anatomical sites in the human femoral neck using a combination of high-throughput 2D and 3D X-ray scattering imaging. A statistically large dataset covering 78 femoral necks revealed systematic differences in nanostructural parameters between superior and inferior regions, including variations in mineral size and organization, collagenâ mineral alignment, and out-of-plane fibrillar orientation. These structural differences were complemented by nanoindentation and microradiography, enabling a combined assessment of nanostructure, local mechanics, and bone mineral density, although isolating the relative contribution of each factor remained challenging due to tissue heterogeneity. The second study focuses on the lamellar structure of cortical bone using three-dimensional X-ray scattering tensor tomography, enabling the measurement of fibrillar orientations within individual lamellae. This approach consistently revealed alternating lamellar orientations of opposing chiralities with respect to the Haversian canals across 17 samples, while also highlighting the heterogeneity of lamellar patterns. These findings extend earlier observations of lamellar and sublamellar architectures to the osteonal length scale, further emphasizing the strongly hierarchical nature of bone. Mechanical testing and compositional analysis provided additional insight into the mechanical implications of the revealed patterns, however, no robust structureâ property correlations were identified, possibly due to microstructural variability and the limited sample size. Finally, methodological developments in the combined use of 2D and 3D imaging and reconstruction were introduced and applied throughout this work. These advances improve the ability to characterize complex hierarchical materials but also reveal remaining limitations in robust 3D structural characterization over extended fields of view. To highlight the challenges of strong biological variability and complex hierarchy in human cortical bone, a comparative study on f