Bone is a natural composite of mineralized collagen fibrils and hydroxyapatite mineral crystals with a complex hierarchical organization at multiple length scales. In the hierarchy, lamella is the basic structural unit for both cortical and trabecular bones, bridging between the nano and mesoscales of bone. From the perspective of composite mechanics, the mechanical behavior of lamella depends on the material property and spatial arrangement of the collagen fibrils, mineral crystals, non-collagenous proteins, and matrix water. Such ultrastructural property directly affects the bulk mechanical behavior of bone. In fact, previous evidence shows that bone toughness is rooted at its ultrastructure level.

Age or disease related bone brittleness is a major health concern and has been extensively investigated. However, the relationship between the ultrastructure and brittleness of bone is still poorly implicit. It was recently reported that the degree of intrafibrillar mineralization may play a significant role in the fragility of bone in osteogenesis imperfecta (OI), a genetic bone disorder that leads to severe brittleness of bone tissues. To elucidate the underlying mechanism, a 2-D plane strain multiscale cohesive finite element model was built to mimic the structure of bone lamella and simulated under both compressive and tensile load to capture effect of intrafibrillar mineralization on the fragility fracture of OI bones. The simulation result was verified with experimental result. Results shows that, diminishing intrafibrillar mineralization may be a major reason of the significant decrease in the strength and toughness of OI bone.