Abstract
Osteocytes play a significant role in the regulation of bone mass.Osteocyte processes are thought to sense the flow of interstitial fluid that is driven through the osteocyte canaliculi by mechanical stimuli forced on the bone,but how this flow elicits a cellular response is unknown.Recent theoretical models assume that osteocyte canaliculi contain ultrastructural features that amplify the fluid flow-derived mechanical signal.However,the calcified bone matrix has considerably hampered studies on the osteocyte process within its canaliculus.Therefore,we applied UHVEM tomography at 2 MeV to reconstruct unique three-dimensional images of osteocyte canaliculi in 1 μm sections of human bone.A realistic 3-dimensional image-based model of a single canaliculus was constructed,and the fluid dynamics of a Newtonian fluid flow within the canaliculus was analyzed.We created virtual 2.2 nm-thickness sections through a osteocyte canaliculus.The canalicular wall had a highly irregular surface,and contained protruding structures similar in size and shape to collagen fibrils.We also found that the microscopic surface roughness of the canalicular wall strongly influenced the fluid flow profiles,whereby highly inhomogeneous flow patterns emerged.Based on these observations,new and realistic models can be developed that will significantly enhance our understanding of the process of mechanotransduction in bone.
