A fluid flow model in the lacunar-canalicular system under the pressure gradient and electrical field driven loads

The lacunar-canalicular system(LCS)is acknowledged to directly participate in bone tissue remodeling.The fluid flow in the LCS is synergic driven by the pressure gradient and electric field loads due to the electro-mechanical properties of bone.In this paper,an idealized annulus Maxwell fluid flow model in bone canaliculus is established,and the analytical solutions of the fluid velocity,the fluid shear stress,and the fluid flow rate are obtained.The results of the fluid flow under pressure gradient driven(PGD),electric field driven(EFD),and pressure-electricity synergic driven(P-ESD)patterns are compared and discussed.The effects of the diameter of canaliculi and osteocyte processes are evaluated.The results show that the P-ESD pattern can combine the regulatory advantages of single PGD and EFD patterns,and the osteocyte process surface can feel a relatively uniform shear stress distribution.As the bone canalicular inner radius increases,the produced shear stress under the PGD or P-ESD pattern increases slightly but changes little under the EFD pattern.The increase in the viscosity makes the flow slow down but does not affect the fluid shear stress(FSS)on the canalicular inner wall and osteocyte process surface.The increase in the high-valent ions does not affect the flow velocity and the flow rate,but the FSS on the canalicular inner wall and osteocyte process surface increases linearly.In this study,the results show that the shear stress sensed by the osteocyte process under the P-ESD pattern can be regulated by changing the pressure gradient and the intensity of electric field,as well as the parameters of the annulus fluid and the canaliculus size,which is helpful for the osteocyte mechanical responses.The established model provides a basis for the study of the mechanisms of electro-mechanical signals stimulating bone tissue(cells)growth.

Multi-scale mechanotransduction of the poroelastic signals from osteon to osteocyte in bone tissue

In order to quantify the poroelastic mechanical signals conduction and evaluate the biomechanical effectiveness of functional units(osteocyte processes,canaliculi and lacuna)in lacunar-canalicular system(LCS),a multiscale poroelastic finite element model was established by using the Comsol Multiphysics software.The poroelastic mechanical signals(pore pressure,fluid velocity,von-Mises stress,strain)were analyzed inside the osteon-osteocyte system.The effects of osteocyte(OCY)’s shape(ellipse and circle),long axis directions(horizontal and vertical)and mechanical properties(Elastic modulus and permeability)on its poroelastic responses were examined.It is found that the OCY processes is the best mechanosensor compared with the OCY body,lacunae and canaliculi.The mechanotransduction ability of the elliptic shaped OCY is stronger than that of circular shaped.The pore pressure and flow velocity around OCYs increase as the elastic modulus and permeability of OCY increase.The established model can be used for studying the mechanism of bone mechanotransduction at the multiscale level.

压力与电场协同作用下具有初级纤毛和胶原小丘的骨细胞的力学响应研究

骨细胞内的力学传感器是骨细胞感知周围力学环境变化的最重要的细胞器.为了评估骨陷窝骨小管系统(LCS)内胶原小丘、细胞突触和初级纤毛作为力学传感器的生物力学效应,我们利用COMSOL Multiphysics软件开发了一种压力-电场-结构相互作用的骨细胞模型,以描述在流体流动和电场刺激下LCS中胶原小丘,初级纤毛以及细胞突触作为骨细胞中力学传感器的力学感应效果.分析了LCS中的力学信号(孔隙压力、流体速度、应力、变形)并且研究了胶原小丘弹性模量的变化、细胞突触的数量和.位置、初级纤毛的长度和位置对骨细胞内力学传感器的力学敏感性以及骨细胞总体多孔弹性响应的影响.结果表明,初级纤毛和.胶原小丘的存在将会导致骨细胞部分位置产生明显的应力集中(比骨细胞体其他位置的应力大1-2个数量级).相比于细胞突触沿骨细胞短轴方向生长,沿长轴方向生长可以刺激骨细胞产生更大的应力.当初级纤毛位于骨细胞顶部时,初级纤毛基底的应力比初级纤毛位于骨细胞底部时大8 Pa.然而,胶原小丘和初级纤毛的存在并不影骨细胞整体的力学信号分布.所建立的模型可用于在多尺度水平上研究骨力学信号的传导机制.