Modeling and simulation of an osteocyte cellular process interacting with fluid flow in three dimensions*

An osteocyte is a bone cell located inside hard bone matrix in an interstice called a lacuna. It has many dendritic structures called processes that extend outward through the bone matrix through openings called canaliculi. Osteocytes are believed to play an important role in bone development as they can sense stress applied by the interstitial fluid flow and respond by releasing signals that regulate bone remodeling. Experiments have suggested that the stress and strain typically experienced at the macroscale tissue level have to be amplified at least 10X in order for osteocytes to have a significant response in vivo.  The mechanisms by which stress/strain is amplified and localized is not yet well understood.

 

The osteocyte has many seemingly randomly oriented processes.  Each resembles a tapered porous cylindric structure submerged in fluid that is encased by a rough canalicular wall.  To better understand force generation along these structures, we use a 3D model of a cellular process, represented by a gradually tapered cylinder, interacting with a fluid flow in a canaliculus. The roughness of the canalicular wall is modelled by randomly generated protrusions on the wall. The fluid is modelled as a viscous incompressible Newtonian fluid. The flow is modeled by the lattice Boltzmann equations (D3Q19 model). The fluid-structure-interaction is handled by the immersed boundary method.

Our preliminary results show a significant increase in deformation (therefore force as well) of the cellular process when the canalicular wall is rough, compared to the smooth wall case. This suggests roughness may play a significant role in stress/strain amplification.