Home > Events > PhD Candidate Thomas Metzger - "Experimental and Computational Investigation of Bone Marrow Mechanobiology"

PhD Candidate Thomas Metzger - "Experimental and Computational Investigation of Bone Marrow Mechanobiology"

Start: 3/29/2016 at 9:00AM
End: 3/29/2016 at 12:00PM
Location: 103 Multidisciplinary Research Building
Event Type:
  • Ph.D. Defense
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Bone is a metabolically active adaptive tissue, constantly repairing and remodeling depending on its biochemical and biomechanical environment. Activities of daily living, such as running and weight lifting, play a critical role in maintaining bone health. While the osteocyte is considered the primary mechanosensory cell in bone, the bone marrow provides a niche for a multitude of mechanosensitive cell types that may also play a role in maintaining bone health. The characterization of trabecular bone marrow during whole bone loading has been difficult due to its location, surrounded by cortical bone or within the complex geometry of trabecular bone. However, utilizing high-resolution computational simulations of real trabecular architecture provides essential micromechanical insights into the mechanics of bone marrow during whole bone loading.

This dissertation investigated the micromechanical environment of trabecular bone marrow during whole bone loading using combined numerical and experimental techniques. First, fresh bone marrow was experimentally tested to identify an appropriate constitutive model. The properties were highly non-Newtonian, viscous and deteriorated with storage. A power-law fluid constitutive model was adopted for later simulations. The fluid constitutive model was compared to several alternative elastic and viscoelastic formulations in computational models. The solid models could not capture the fluid behavior despite the high viscosity and low velocities.

Bone marrow pressure was measured experimentally. Six porcine femora were loaded cyclically while pressure and load were monitored. The marrow pressure reached 5 kPa, and the pressure gradients reached 0.46 kPa/mm. These experimental pressure gradients induced shear stress within the marrow pore space in the range of 2 Pa.  A novel high-resolution fluid-structure interaction finite element simulation was developed to further understand the coupled relationship between the trabecular bone and bone marrow during compression. Simulations illustrated that increased strain rate, bone marrow viscosity, and BV/TV increase the pressure and shear stress within the bone marrow.  In order to investigate how the calculated marrow shear stress is translated to the cell level, multi-scale models were applied.  At the cell-level, the marrow shear stress was amplified by 4 times due to localized cell adhesion. However, this effect was attenuated as the adipocyte content in the marrow increased.  Finally, in the conclusion of this work, experimental and computational studies seek to further elucidate the role of marrow mechanobiology on de novo bone formation in vivo

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