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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.


FEBio simulation of fluid pore pressure in the segment model. (a) The pore fluid pressure field at t=3 s at the cross-section containing the FRAP site (location A). (b) The temporal fluid pressure changes at the cortical (A–F) and trabecular sites (G, H) during one loading cycle (Figure 1b).
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fig6: FEBio simulation of fluid pore pressure in the segment model. (a) The pore fluid pressure field at t=3 s at the cross-section containing the FRAP site (location A). (b) The temporal fluid pressure changes at the cortical (A–F) and trabecular sites (G, H) during one loading cycle (Figure 1b).

Mentions: The pore fluid pressure distribution (Figure 6) was obtained at t=3 s when the loading peaked at 3 N (Figure 1b). In general, negative pressures were found in the regions under tension and positive pressures in the compressed regions, and the pressure magnitude in the cortex increases with the distance to the neutral plane (Figure 6a). Negative pressures were found in the trabecular area adjacent the cortex under compression (location G shown in blue shades), suggesting a more complex local loading pattern there. The temporal changes of the fluid pressure were shown during one loading cycle in Figure 6b, where location A (corresponding to the FRAP site) experienced a peak pressure of −8 MPa, and a high 17 MPa pressure was found in location D. Pressures in the trabecular locations (G and H) were relatively smaller in magnitude. Reducing permeability by one or two orders of magnitude (2.8×10−21 and 2.8×10−22 m2), peak pressure was found to vary slightly (<10%) or modestly (<25%) at locations A (+7% and +15%), B (+6% and +15%), C (−9% and −17%), D (+7% and +18%), E (+4% and +14%), F (−6% and −17%), G (+8% and +24%), and H (−6% and −18%), respectively.


A multiscale 3D finite element analysis of fluid/solute transport in mechanically loaded bone
FEBio simulation of fluid pore pressure in the segment model. (a) The pore fluid pressure field at t=3 s at the cross-section containing the FRAP site (location A). (b) The temporal fluid pressure changes at the cortical (A–F) and trabecular sites (G, H) during one loading cycle (Figure 1b).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig6: FEBio simulation of fluid pore pressure in the segment model. (a) The pore fluid pressure field at t=3 s at the cross-section containing the FRAP site (location A). (b) The temporal fluid pressure changes at the cortical (A–F) and trabecular sites (G, H) during one loading cycle (Figure 1b).
Mentions: The pore fluid pressure distribution (Figure 6) was obtained at t=3 s when the loading peaked at 3 N (Figure 1b). In general, negative pressures were found in the regions under tension and positive pressures in the compressed regions, and the pressure magnitude in the cortex increases with the distance to the neutral plane (Figure 6a). Negative pressures were found in the trabecular area adjacent the cortex under compression (location G shown in blue shades), suggesting a more complex local loading pattern there. The temporal changes of the fluid pressure were shown during one loading cycle in Figure 6b, where location A (corresponding to the FRAP site) experienced a peak pressure of −8 MPa, and a high 17 MPa pressure was found in location D. Pressures in the trabecular locations (G and H) were relatively smaller in magnitude. Reducing permeability by one or two orders of magnitude (2.8×10−21 and 2.8×10−22 m2), peak pressure was found to vary slightly (<10%) or modestly (<25%) at locations A (+7% and +15%), B (+6% and +15%), C (−9% and −17%), D (+7% and +18%), E (+4% and +14%), F (−6% and −17%), G (+8% and +24%), and H (−6% and −18%), respectively.

View Article: PubMed Central - PubMed

ABSTRACT

The transport of fluid, nutrients, and signaling molecules in the bone lacunar&ndash;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&ndash;50&thinsp;&mu;m 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.