Pressure and shear stress in trabecular bone marrow during whole bone loading.
Skeletal adaptation to mechanical loading is controlled by mechanobiological signaling. Osteocytes are highly responsive to applied strains, and are the key mechanosensory cells in bone. However, many cells residing in the marrow also respond to mechanical cues such as hydrostatic pressure and shear stress, and hence could play a role in skeletal adaptation. Trabecular bone encapsulates marrow, forming a poroelastic solid. According to the mechanical theory, deformation of the pores induces motion in the fluid-like marrow, resulting in pressure and velocity gradients. The latter results in shear stress acting between the components of the marrow. To characterize the mechanical environment of trabecular bone marrow in situ, pore pressure within the trabecular compartment of whole porcine femurs was measured with miniature pressure transducers during stress-relaxation and cyclic loading. Pressure gradients ranging from 0.013 to 0.46 kPa/mm were measured during loading. This range was consistent with calculated pressure gradients from continuum scale poroelastic models with the same permeability. Micro-scale computational fluid dynamics models created from computed tomography images were used to calculate the micromechanical stress in the marrow using the measured pressure differentials as boundary conditions. The volume averaged shear stress in the marrow ranged from 1.67 to 24.55 Pa during cyclic loading, which exceeds the mechanostimulatory threshold for mesenchymal lineage cells. Thus, the loading of bone through activities of daily living may be an essential component of bone marrow health and mechanobiology. Additional studies of cell-level interactions during loading in healthy and disease conditions will provide further incite into marrow mechanobiology.
Tissue Mechanics Laboratory, Bioengineering Graduate Program, University of Notre Dame, United States.
Thomas A
TA
Metzger
Department of Aerospace and Mechanical Engineering, University of Notre Dame, United States.
Stephen A
SA
Schwaner
Department of Aerospace and Mechanical Engineering, University of Notre Dame, United States.
Anthony J
AJ
LaNeve
Tissue Mechanics Laboratory, Bioengineering Graduate Program, University of Notre Dame, United States.
Tyler C
TC
Kreipke
Tissue Mechanics Laboratory, Bioengineering Graduate Program, University of Notre Dame, United States. Electronic address: gniebur@nd.edu.
Glen L
GL
Niebur
D000203:Activities of Daily Living; D000818:Animals; D001853:Bone Marrow / Q000502:physiology*; D005269:Femur / Q000166:cytology / Q000502:physiology*; D057446:Hydrodynamics; D006874:Hydrostatic Pressure; D059630:Mesenchymal Stem Cells / Q000166:cytology; D008954:Models, Biological; D010011:Osteocytes / Q000166:cytology; D011312:Pressure; D033081:Shear Strength; D013314:Stress, Mechanical; D013552:Swine; D016474:Weight-Bearing
Bone marrow; Computational modeling; Experimental measurements; Trabecular bone; Whole bone loading