Modeling and simulation of osteocyte process–fluid interaction in a canaliculus

Abstract

An osteocyte is a bone cell situated inside a hard bone matrix in an interstice (lacuna). It has many dendritic structures called cellular processes that radiate outward from the cell through the bone matrix via cylindrical openings (canaliculi). Osteocytes can sense stress and strain applied by the interstitial fluid flow and respond by releasing biochemical signals that regulate bone remodeling. In vitro experiments have suggested that the stress and strain typically experienced at the macroscale tissue level have to be amplified 10× in order for osteocytes to have a significant response in vivo. This stress and strain amplification mechanism is not yet well understood. Previous studies suggest that the processes are the primary sites for mechanosensation thanks to the tethering elements that attach the process membrane to the canalicular wall. However, there are other potential factors which may also contribute to stress and strain amplification, such as canalicular wall geometry and osteocyte-associated proteins in the interstitial space called pericellular matrix. In this work, we perform computational studies to study how canalicular wall roughness affects stress and strain amplification. Our major finding is that the wall roughness induces significantly greater wall shear stress (WSS) on the process when the wall roughness increases flow resistance; and the roughness has relatively smaller influence on the WSS when the resistance remains the same.