Effects of changes of osteocyte shape on fluid flow and fluid shear stress of loaded bone

Abstract

Background: Load-induced pressure gradients (PG) result in interstitial fluid flow in bone tissue, which is not only provides sufficient nutrient supply and metabolic pathway for the bone cells, but also enables bone cells to accept external mechanical signals. Methods: We calculate the number and distribution of bone canaliculus around the osteocyte based on the varying shape of osteocyte, and then use these calculated parameters and other microstructure data of bone tissue to estimate the anisotropy permeability of the lacunar–canalicular. Finally, according to the calculated parameters, the poroelastic finite element models of the osteon are established, and the influence of the osteocyte shape on the fluid flow properties of osteon under the axial displacement load is analyzed. Two kinds of boundary conditions are considered on the cement line of osteon, elastic restrained (BC1) and displacement confined (BC2). Results: In the range of parameters we studied, the changes of osteocyte shape (Case1-Case6) make the maximum value of PG, pore pressure (PP), fluid velocity (FV) and fluid shear stress (FSS) 33.36%, 67.67%, 8.6% and 26.6% larger than the Reference model in BC1, respectively. And the maximum value of PG, PP, FV and FSS are 65.39%, 67.67%, 8.4% and 29% larger than reference model in BC2. The maximum PG, PP, FV and FSS in BC2 are 96.72%, 95.51%, 97.87% and 97.13% larger than that in BC1, respectively. The permeability of elongated osteocyte model (Case 3, Case 4 and Case 6) have a difference of one magnitude order in X and Y direction. Conclusion: The changes of osteocyte shape has a significant impact on the degrees of anisotropy for fluid flow and porous media of osteon. This model can facilitate better accurately quantifying the fluid flow in lacuna-canalicular system.