Bone mineral properties and 3D orientation of human lamellar bone around cement lines and the Haversian system

Bone is a complex, biological tissue made up primarily of collagen fibrils and biomineral nanoparticles. The importance of hierarchical organization in bone was realized early on, but the actual interplay between structural features and the properties on the nanostructural and crystallographic level is still a matter of intense discussion. Bone is the only mineralized tissue that can be remodeled and, at the start of the formation of new bone during this process, a structure called a cement line is formed on which regular bone grows. Here, the orientational relationship of nanostructural and crystallographic constituents as well as the structural properties of both nanostructural and crystallographic constituents around cement lines and the Haversian system in human lamellar bone are investigated. A combination of small- and wide-angle X-ray scattering tensor tomography is employed together with diffraction tomography and synchrotron computed tomography to generate a multi-modal image of the sample. This work shows that the mineral properties vary as a function of the distance to the Haversian canal and, importantly, shows that the cement line has differing mineral properties from the surrounding lamellar bone, in particular with respect to crystallite size and degree of orientation. Cement lines make up a significant portion of the bone matrix despite their small size, hence the reported findings on an altered mineral structure, together with the spatial modulation around the Haversian canal, have implications for the formation and mechanics of bone.