The osteocyte lacuno-canalicular network in bone investigated by synchrotron radiation-based techniques

Abstract

Bone has a complex hierarchical structure, which is essential for its performance. Bone is typically replete with cells called osteocytes that are embedded in the mineralized bone matrix in osteocyte lacunae, which are interconnected by canaliculi only a few hundred nanometer wide to form a vast cellular network. Our understanding of the osteocyte lacuno-canalicular network has been limited because of difficulties to image the cellular network within the opaque bone matrix in 3D. Synchrotron X-ray computed tomography is ideally suited to study the lacuno-canalicular network in bone because it combines the high penetration power of X rays with sub-micron resolution while retaining a fast acquisition time and thus high throughput. We discuss how synchrotron radiation-based tomography techniques have given insights into the osteocyte network in bone both in the form of regular tomography and, for higher resolution studies, in the form of nanotomography such as holotomography. These studies have provided quantitative measures of osteocyte lacunar properties and their relation to location within bones and bone challenges such as immobilization or lactation. Nanotomography revealed new features of the canalicular network that we term canalicular junctions, which are likely to play an important but hitherto hidden role in fluid flow dynamics within the bone cellular network. The examples illustrate how tomography provides information on complex biological materials like bone and we foresee that these capabilities will continue to improve with future/upgraded synchrotron X-ray sources.