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A multiscale 3D finite element analysis of fluid/solute transport in mechanically loaded bone

View Article: PubMed Central - PubMed

ABSTRACT

The transport of fluid, nutrients, and signaling molecules in the bone lacunar–canalicular system (LCS) is critical for osteocyte survival and function. We have applied the fluorescence recovery after photobleaching (FRAP) approach to quantify load-induced fluid and solute transport in the LCS in situ, but the measurements were limited to cortical regions 30–50 μm underneath the periosteum due to the constrains of laser penetration. With this work, we aimed to expand our understanding of load-induced fluid and solute transport in both trabecular and cortical bone using a multiscaled image-based finite element analysis (FEA) approach. An intact murine tibia was first re-constructed from microCT images into a three-dimensional (3D) linear elastic FEA model, and the matrix deformations at various locations were calculated under axial loading. A segment of the above 3D model was then imported to the biphasic poroelasticity analysis platform (FEBio) to predict load-induced fluid pressure fields, and interstitial solute/fluid flows through LCS in both cortical and trabecular regions. Further, secondary flow effects such as the shear stress and/or drag force acting on osteocytes, the presumed mechano-sensors in bone, were derived using the previously developed ultrastructural model of Brinkman flow in the canaliculi. The material properties assumed in the FEA models were validated against previously obtained strain and FRAP transport data measured on the cortical cortex. Our results demonstrated the feasibility of this computational approach in estimating the fluid flux in the LCS and the cellular stimulation forces (shear and drag forces) for osteocytes in any cortical and trabecular bone locations, allowing further studies of how the activation of osteocytes correlates with in vivo functional bone formation. The study provides a promising platform to reveal potential cellular mechanisms underlying the anabolic power of exercises and physical activities in treating patients with skeletal deficiencies.

No MeSH data available.


Load-induced fluid flux at tissue level. (a) The distribution of the fluid flux magnitude and the flow direction at t=2.6 second during the loading phase. (b) The temporal changes of the fluid flux at several selected locations in both cortical (locations A–F) and trabecular sites (locations G–H).
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fig7: Load-induced fluid flux at tissue level. (a) The distribution of the fluid flux magnitude and the flow direction at t=2.6 second during the loading phase. (b) The temporal changes of the fluid flux at several selected locations in both cortical (locations A–F) and trabecular sites (locations G–H).

Mentions: The local distribution of load-induced fluid flux could be obtained from the segment model. The local fluid flow varied cyclically as a function of time and a snapshot of the fluid flow field at t=2.6 s is shown in Figure 7a. The flows for the surface elements are shown with the vectors, with the length indicating flow magnitude and arrow indicating the flow direction; and the flow magnitude for other elements are indicated with pseudo-colors (Figure 7a). Overall, higher flow rates were found near the endosteal surfaces. The temporal profiles of flow magnitude at the selected locations are shown in Figure 7b. Comparing with fluid pressure that dropped to zero after t=4 s in most locations (Figure 6b), fluid flow at location B and C persisted till t=5 s (Figure 7b). Among all those selected locations, location C near the endosteal surface experienced the largest flux. Fluid flow was also found in the trabecular site (as shown in locations G and H), although the flux was relatively smaller than that in the adjacent endosteal cortical bone (Figure 7).


A multiscale 3D finite element analysis of fluid/solute transport in mechanically loaded bone
Load-induced fluid flux at tissue level. (a) The distribution of the fluid flux magnitude and the flow direction at t=2.6 second during the loading phase. (b) The temporal changes of the fluid flux at several selected locations in both cortical (locations A–F) and trabecular sites (locations G–H).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5037578&req=5

fig7: Load-induced fluid flux at tissue level. (a) The distribution of the fluid flux magnitude and the flow direction at t=2.6 second during the loading phase. (b) The temporal changes of the fluid flux at several selected locations in both cortical (locations A–F) and trabecular sites (locations G–H).
Mentions: The local distribution of load-induced fluid flux could be obtained from the segment model. The local fluid flow varied cyclically as a function of time and a snapshot of the fluid flow field at t=2.6 s is shown in Figure 7a. The flows for the surface elements are shown with the vectors, with the length indicating flow magnitude and arrow indicating the flow direction; and the flow magnitude for other elements are indicated with pseudo-colors (Figure 7a). Overall, higher flow rates were found near the endosteal surfaces. The temporal profiles of flow magnitude at the selected locations are shown in Figure 7b. Comparing with fluid pressure that dropped to zero after t=4 s in most locations (Figure 6b), fluid flow at location B and C persisted till t=5 s (Figure 7b). Among all those selected locations, location C near the endosteal surface experienced the largest flux. Fluid flow was also found in the trabecular site (as shown in locations G and H), although the flux was relatively smaller than that in the adjacent endosteal cortical bone (Figure 7).

View Article: PubMed Central - PubMed

ABSTRACT

The transport of fluid, nutrients, and signaling molecules in the bone lacunar–canalicular system (LCS) is critical for osteocyte survival and function. We have applied the fluorescence recovery after photobleaching (FRAP) approach to quantify load-induced fluid and solute transport in the LCS in situ, but the measurements were limited to cortical regions 30–50 μm underneath the periosteum due to the constrains of laser penetration. With this work, we aimed to expand our understanding of load-induced fluid and solute transport in both trabecular and cortical bone using a multiscaled image-based finite element analysis (FEA) approach. An intact murine tibia was first re-constructed from microCT images into a three-dimensional (3D) linear elastic FEA model, and the matrix deformations at various locations were calculated under axial loading. A segment of the above 3D model was then imported to the biphasic poroelasticity analysis platform (FEBio) to predict load-induced fluid pressure fields, and interstitial solute/fluid flows through LCS in both cortical and trabecular regions. Further, secondary flow effects such as the shear stress and/or drag force acting on osteocytes, the presumed mechano-sensors in bone, were derived using the previously developed ultrastructural model of Brinkman flow in the canaliculi. The material properties assumed in the FEA models were validated against previously obtained strain and FRAP transport data measured on the cortical cortex. Our results demonstrated the feasibility of this computational approach in estimating the fluid flux in the LCS and the cellular stimulation forces (shear and drag forces) for osteocytes in any cortical and trabecular bone locations, allowing further studies of how the activation of osteocytes correlates with in vivo functional bone formation. The study provides a promising platform to reveal potential cellular mechanisms underlying the anabolic power of exercises and physical activities in treating patients with skeletal deficiencies.

No MeSH data available.