Flow and forces on a rigid osteocyte immersed in bone: Effects of the flow network and pericellular matrix*

Osteocytes are cells that play an important role in bone remodeling.  When exposed to forces, they emit signals that can cause other bone cells to produce or degrade the extracellular matrix that provides the bone with structure.  The amount of force necessary to generate such signals in vitro has been observed to be at least tenfold more than the typical macroscale forces experienced by bones in everyday life.  In vivo studies, however, can be difficult as cells are encased in a complex lacuna-canalicular network.  In such networks, osteocytes are surrounded by fluid and small canals that link osteocytes together.  How the geometry of such networks contribute to magnification of macroscale forces is not yet fully known.  In addition, the presence of pericellular matrix, cell-associated proteins that occupy the fluid surrounding the cell, has also been theorized to have a potential role.  In this study we use a two-dimensional model of a rigid osteocyte in a canalicular network to consider the questions of how the number of canaliculi and pericellular matrix may affect force generation on the osteocyte.  The lattice Boltzmann equations (the D2Q9 model) are used to model the viscous incompressible flow.  Differentiation of interpolated velocity and pressure fields is used to estimate the forces on the surface of the osteocyte.  By developing the model using an idealized ellipsoidal geometry, the numerical and physiological capabilities are assessed.  Initial results suggest that while a pericellular matrix tends to impede flow, it may enhance the fluid forces felt on the surface of the osteocyte.  We will share these and more results, especially the effects of the number of canaliculi on force generation on the osteocyte.  Such results carry implications for how to recover normal bone remodeling function in pathological scenarios such as osteoporosis.