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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.


Related in: MedlinePlus

Axial strains from the whole-bone FE model. Only the portion corresponding to the segment model is shown. Due to the combination of compression and bending, the anterior–medial surface (FRAP site) was under tension.
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fig2: Axial strains from the whole-bone FE model. Only the portion corresponding to the segment model is shown. Due to the combination of compression and bending, the anterior–medial surface (FRAP site) was under tension.

Mentions: The intact tibia bone was deformed by a combined mode of compression and bending under the 3 N compressive load applied at the ends. A tensile strain of ~450 μƐ was predicted on the relatively flat anteromedial tibial surface around the FRAP site (30% distal from the proximal end), and compressive strains were mostly found on the posterior cortex (Figure 2). In this linear FEA model, the strain values were proportional to the assumed Young’s modulus. Our predicted tensile strain of 450 μƐ at the region of interest (FRAP site) matched well with the experimentally measured data of ~400 μƐ.27 Thus, we concluded that the assumed material properties of 20 GPa Young’s modulus and 0.33 Poisson’s ratio were justified for the subsequent transport modeling.


A multiscale 3D finite element analysis of fluid/solute transport in mechanically loaded bone
Axial strains from the whole-bone FE model. Only the portion corresponding to the segment model is shown. Due to the combination of compression and bending, the anterior–medial surface (FRAP site) was under tension.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig2: Axial strains from the whole-bone FE model. Only the portion corresponding to the segment model is shown. Due to the combination of compression and bending, the anterior–medial surface (FRAP site) was under tension.
Mentions: The intact tibia bone was deformed by a combined mode of compression and bending under the 3 N compressive load applied at the ends. A tensile strain of ~450 μƐ was predicted on the relatively flat anteromedial tibial surface around the FRAP site (30% distal from the proximal end), and compressive strains were mostly found on the posterior cortex (Figure 2). In this linear FEA model, the strain values were proportional to the assumed Young’s modulus. Our predicted tensile strain of 450 μƐ at the region of interest (FRAP site) matched well with the experimentally measured data of ~400 μƐ.27 Thus, we concluded that the assumed material properties of 20 GPa Young’s modulus and 0.33 Poisson’s ratio were justified for the subsequent transport modeling.

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