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TECHNICAL PAPERS: Bone/Orthopedic

Microstructural Mechanics of Collagen Gels in Confined Compression: Poroelasticity, Viscoelasticity, and Collapse

[+] Author and Article Information
Preethi L. Chandran, Victor H. Barocas

Department of Biomedical Engineering, University of Minnesota, 312 Church St SE, Minneapolis, MN 55455

J Biomech Eng 126(2), 152-166 (May 04, 2004) (15 pages) doi:10.1115/1.1688774 History: Received June 13, 2003; Revised November 03, 2003; Online May 04, 2004
Copyright © 2004 by ASME
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Figures

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Confined compression chamber
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15 mm Collagen gel before for compression testing. (a) Intensity map. The piston region appears black at the right of the image, and the bar in the lower right is 1 mm. (b) Birefringence map. The magnitude of each vector is scaled to represent the retardation along the extinction angle, averaged over pixels. The piston region shows no optical activity. (c) Retardation profile vs. position along length of the sample. Retardation is averaged over a width of three 3 pixels at y=64 (see 2a).
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Response to 10% Step Compression (0.02 sec) in 5 mm gel. (a) Stress response to step compression. (b) Retardation, (c) orientation and (d) concentration profiles along the length of the chamber, before and immediately (3 s) after compression. The arrows in 3b show the translation of profile features. Bulk (intact) and near-piston (collapsed) regions are marked A and B, respectively.
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Stress Relaxation after 10% Step Compression in 5 mm gel. (a) Stress response during relaxation. (b) Retardation, (c) orientation and (d) concentration profiles along the length of the chamber, at different stages of stress relaxation. The time points of the profiles in (b)–(d) are marked on the stress response plot (a). The birefringence profiles (b and c) in the bulk relax to original state. The near-piston region gets compressed against the piston (b, c and d)
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Piston retraction after Relaxation of 10% Step Compression of 5 mm gel. Retardation is shown along the length of the chamber, before and after compression (as in 3b) and after piston retraction. The retardation profile after retraction (gray open diamonds) shows near complete recovery of the original state (black solid diamonds) in the bulk but not in the near-piston region.
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Response to 10% Step Compression in 15 mm gel. (a) Stress response during compression and relaxation. (b) Retardation profiles along the length of the chamber, at different stages of stress relaxation. The corresponding time points are marked on the stress response plot (a).
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Response to Ramp (0.1%/s) Compression in 5 mm gel. (a) Stress response during compression and relaxation. (b) Retardation, (c) orientation, and (d) concentration profiles along the length of the chamber, before and during compression. The compression is initially greater towards the piston but soon gets transmitted throughout. The retardation and orientation change everywhere in proportion to the gel strain (shown by the translation of profile features). The corresponding time points are marked on the stress response plot (a).
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Stress Relaxation after Ramp (0.1%/s) Compression in 5 mm gel. (a) Stress response during compression and relaxation. (b) Retardation, (c) orientation, and (d) concentration profiles along the length of the chamber, at different stages of stress relaxation. The gel moves away from the piston. The corresponding time points are marked on the stress response plot (a).
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Ramp (0.1%/s) Compression in 15 mm gel. (a) Stress response during compression and relaxation. (b) Retardation profiles along the length of the chamber, during ramp and at different stages of stress relaxation. The corresponding time points are marked on the stress response plot (a).
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Stress Evolution in Step vs. Ramp Compression of 5 mm gel. A logarithmic time scale is used to resolve the short-time data for step compression. The peak stress was higher in the step case, but the long-time stress was higher in the ramp case.
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Center-of-Mass (COM) Motion of 5 mm Gel in Step vs. Ramp Compression. In both cases, the COM was displaced toward the closed end of the cup during compression. During relaxation, the COM moved toward the piston in the step case but away from the piston in the ramp case.

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