| Researching Intervertebral Disc Mechanobiology and Tissue Engineering.
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| Spine
Bioengineering
workgroup, Summer 2008: front row: Mark Freedman, James, Kristin Funabashi back row: Karrie Godburn, Ben Walter, Art Michalek, Ana Barbir, Devina Purmessur |
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| James C.
Iatridis (Head) Karrie Godburn, BS (Lab Manager) Devina Purmessur, PhD Art Michalek, MS Ana Barbir, MS Benjamin A Walter, BS Mark Freedman Kristin Funabashi |
On
campus collaborators: Ian A.F. Stokes: Ortho/Rehab Robert Monsey: Ortho/Rehab David Aronsson: Ortho/Rehab Jeffrey Laible: Civil & Environmental Eng Martin Krag: Ortho/Rehab Junru Wu: Physics Helene Langevin: Neurology |
Off
campus collaborators: Mauro Alini: AO Research Institute, Davos, Switzerland Keita Ito: AO Research Institute, Davos, Switzerland John Antoniou: McGill University, Montreal, Canada Tapas Goswami: McGill University, Montreal, Canada Peter Roughley: McGill University, Montreal, Canada Rocky Tuan: Cartilage Biology & Orthopaedics Branch, NIAMS, NIH |
| Alumni
Time in the
Lab Current Position Cynthia Lee, PhD 2002-2005 Senior Scientist - Cartilage Technologies , DePuy Biologics Diana Hidalgo, MS, 2004-2005 Delphine Perie-Curnier, PhD 2003-2004 Research Scientist, Laboratoire de Biomecanique, Toulouse cedex, France Lisa Hovey, B.S. 2004 Julia Owen, B.S. 2003-2004 PhD Student, Bioengineering, UC Berkeley Heather Boepple, B.S. 2005 Tissue Regeneration, Inc. David Ryan, B.S. 2003-2004 Research Technician (Lab Manager), Orthopaedic Mechanobiology Lab, University of Maryland, College Park Brennan Schaeffer, B.S. 2003 Suzanne Kavy, B.S., 2003 M Eng student, Transportation, Cornell University Laura Albert, B.A. 2003 David Korda, B.S. 2003-2006 MS Student, Mechanical Engineering, Cornell University Anna Snarski, B.A. 2004-2006 DVM Student, Purdue University Kazunori Masuoka, M.D. 2005 Dept. of Ortho Surg, National Defense Medical College, Saitama, Japan J Stinnett-Donnelly, M.S. 2004-2006 MD Student, University of Vermont Jeffrey J. MacLean, M.S. 1999-2006 MD Student, University of Vermont John Jack Costi, Ph.D. 2005-2006 Research Faculty, Repatriation General Hospital & Flinders University, Adelaide, Australia Karin Wuertz, Ph.D. 2006-2007 Research faculty, University of Zurich, Switzerland Jake Lubinsky, M.S. 2006-2007 Alon Lai, Ph.D. 2008 Post-doctoral Fellow, Hong Kong Polytechnic University Casey Korecki, Ph.D. 2003-2008 Post-doctoral Fellow, NIAMS, NIH, Bethesda, MD |
| Diagram of human lumbar intervertebral disc and dissection of cylindrical-shaped specimens of anulus fibrosus. Axial and radial correspond to orientations parallel and perpendicular to the vertebral body line of the spine, respectively. Annulus layers are roughly 0.1-0.3 mm thick with approximately 40 fiber bundles per layer alternating at roughly +/- 30 degrees. | Photograph of normal (left) and degenerative human L2-3 intervertebral discs. |
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| Material
properties range from the predominantly viscous vitreous humor of the
eye to the predominantly elastic spinal motion segment. You can also
compare the range of viscoelastic properties from the nucleus pulposus
to the anulus fibrosus.
See reference:
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| This was the
first comprehensive study to investigate shear
material
properties of the anulus fibrosus and tested the hypotheses
that these shear mechanical properties of the anulus are affected by
amplitude and frequency of shearing, applied compressive stress, and
degenerative state of the tissue. The figure on the right exhibits the
effect of increasing compressive stress on the dynamic shear material
properties of the anulus.
See reference:
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| The goal of this
study was to investigate the influence of the changes in tissue
structure and
composition on the electrokinetic behavior of intervertebral disc
tissues.
It was found that the streaming potential of the anulus fibrosus
depended
on the degenerative grade of the discs and on the specimen orientation
in
which the fluid flows. The dynamic streaming potential responses of
anulus
fibrosus (shown on right) were sensitive to the degeneration of the
disc. The alteration of streaming potential reflects
the changes in tissue composition and structure with degeneration.
See reference:
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The PEACE finite element model was written using MATLAB software based on the models of Gu et al 1993, and Simon et al 1996. Geometry was taken as a thin horizontal slice of disc (5 mm thick) with idealized horizontal plane dimensions characteristic of a human lumbar disc. Boundary conditions included impermeable, insulated, frictionless, and rigid top and bottom surfaces so that there was no vertical flow. This could represent the conditions at the mid-elevation of a disc. The mechano-electrochemical material coefficients were taken from the literature. Values for healthy and degenerated fixed charge density distributions were taken from experimentally determined values for 26 year old and 74 year old discs from Urban & Holm 1986. The healthy distribution had values for FCD approximately 0.15M at the edge of the disc and approximately 0.3 M at the center of the disc. The u-w solution was obtained for: 1) a swelling & compression test where the disc was equilibrated in 0.2M NaCl followed by a step compressive stress of 0.2 MPa; and 2) an applied electrical potential on the boundaries where point A was set to 0 mV and point B was set to twice the natural potential (i.e., -10.75 and –6.3 mV for healthy and degenerated discs, respectively).
The Figure below demonstrates the model prediction of the hydraulic pressurization of the healthy intervertebral disc slice at equilibrum. Significant alterations in the load carrying mechanism from healthy to degenerated discs were determined with the healthy disc carries most of the loading through fluid stress (pressurization). The degenerated disc, on the other hand, carries significantly more stresses in the solid matrix which could predispose the increased matrix damage. Alterations in the disc fixed charge density from healthy to degenerated will affect load carrying mechanisms, fluid content, and electrical potential response. These differences have implications for disc failure, disc nutrition, modulation of cellular activities, and tissue remodeling.
See reference:
Iatridis
JC, Laible JP, Krag MH: Influence of fixed charge density magnitude and
distribution
on the intervertebral disc: Applications of a poroelastic and chemical
electric
model, J Biomechanical Engineering, 125:12-24, 2003
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