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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.

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The tracer concentration (a) and the logarithm of the recovery rate (b) of sodium fluorescein under loaded and non-loaded conditions. A transport enhancement of 1.24 was found for 3 N loading, which is comparable with previous experimental measurements. As anticipated, higher loads (5 N and 7 N) result in greater transport enhancements.
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fig5: The tracer concentration (a) and the logarithm of the recovery rate (b) of sodium fluorescein under loaded and non-loaded conditions. A transport enhancement of 1.24 was found for 3 N loading, which is comparable with previous experimental measurements. As anticipated, higher loads (5 N and 7 N) result in greater transport enhancements.

Mentions: This tissue diffusivity of 31.8 μm2·s−1 was then used to simulate the loaded condition (Figure 5). From the time courses of solute concentration (Figure 5a) and the logarithm of the recovery at the FRAP site under loaded and non-loaded conditions (Figure 5b), the transport enhancement (Kload/Kdiff) was 1.24 for the 3N loading 3N, which fell within 1 s.d. above or below from the previously obtained experimental mean value (Kload/Kdiff=1.31±0.24).27 In addition, we ran FRAP simulations with higher loads (5 N and 7 N). As anticipated, we observed faster fluorescence recovery and greater transport enhancement as load magnitude increased (Figure 5). Taken together, these results provide strong evidence that supports the use of FEBio segment transport model to predict the pore pressure and fluid flux in mechanically loaded bone.


A multiscale 3D finite element analysis of fluid/solute transport in mechanically loaded bone
The tracer concentration (a) and the logarithm of the recovery rate (b) of sodium fluorescein under loaded and non-loaded conditions. A transport enhancement of 1.24 was found for 3 N loading, which is comparable with previous experimental measurements. As anticipated, higher loads (5 N and 7 N) result in greater transport enhancements.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig5: The tracer concentration (a) and the logarithm of the recovery rate (b) of sodium fluorescein under loaded and non-loaded conditions. A transport enhancement of 1.24 was found for 3 N loading, which is comparable with previous experimental measurements. As anticipated, higher loads (5 N and 7 N) result in greater transport enhancements.
Mentions: This tissue diffusivity of 31.8 μm2·s−1 was then used to simulate the loaded condition (Figure 5). From the time courses of solute concentration (Figure 5a) and the logarithm of the recovery at the FRAP site under loaded and non-loaded conditions (Figure 5b), the transport enhancement (Kload/Kdiff) was 1.24 for the 3N loading 3N, which fell within 1 s.d. above or below from the previously obtained experimental mean value (Kload/Kdiff=1.31±0.24).27 In addition, we ran FRAP simulations with higher loads (5 N and 7 N). As anticipated, we observed faster fluorescence recovery and greater transport enhancement as load magnitude increased (Figure 5). Taken together, these results provide strong evidence that supports the use of FEBio segment transport model to predict the pore pressure and fluid flux 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.


Related in: MedlinePlus