Confined Compression of a Tissue-Equivalent: Collagen Fibril and Cell Alignment in Response to Anisotropic Strain

[+] Author and Article Information
T. S. Girton, V. H. Barocas, R. T. Tranquillo

Departments of Chemical Engineering & Materials Science and Biomedical Engineering, University of Minnesota, Minneapolis, MN

J Biomech Eng 124(5), 568-575 (Sep 30, 2002) (8 pages) doi:10.1115/1.1504099 History: Received September 01, 1999; Revised May 01, 2002; Online September 30, 2002
Copyright © 2002 by ASME
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Schematic of the compression chamber showing the U-shaped polycarbonate gasket, porous piston allowing fluid to escape into an adjacent cavity, and a depiction of cells and beads in a field.
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Calculation of strain from a triad of beads in a field of the compression chamber.
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(a) Relationship between strain-based fibril density and relative fluorescence versus distance from piston. Error bars represent the standard deviation from 3 samples compressed to the same extent. (b) Normalized fluorescence as a function of distance from the piston and position relative to the compression axis. Note the uniformity of the compression evident in the lack of variation of normalized fluorescence away from the compression axis.
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Displacement of large and small polystyrene microbeads as a function of distance from the piston. Note the equivalence of the displacement for both size beads. Error bars represent 1 standard deviation (n=3).
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Retardation and angle of extinction as a function of distance from piston. Retardation is a measure of the strength of fibril alignment whereas angle of extinction is a measure of the mean direction of fibril alignment. Note that the retardation and thus fibril alignment decrease as the distance from the piston increases. Error bars represent 1 standard deviation.
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Retardation as a function of network strain. Three separate experiments are indicated with the symbols. The data show a strong correlation between network strain and retardation. (No account was made for network density variation due to compression in this plot, such as normalizing retardation with respect to network density, since the scaling of retardation with network density may not simply be linear.)
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Time dependence of cell alignment. Cell alignment within 1 hr after compression as compared to cell alignment 24 hr after compression shows no significant difference for 3 different experiments having different strains.
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Micrographs of HFF in a field of the compression chamber before compression (a) and 1 hr after compression (b, c) or 24 hr after compression (d). A comparison of (a) and (b) reveals alignment of each cell changed immediately as if by a passive deformation/convection associated with the compression (i.e., the morphology of each cell is mostly unchanged), whereas a comparison of (c) and (d) reveals cells have exhibited significant motility during the 23 hr after the initial observation following compression (i.e. cell morphologies, positions and/or alignments are mostly different).
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Cell alignment as a function of network strain for HFF and SMC. Cell alignment (normal to the direction of compressive strain) increases with the magnitude of strain. Also plotted are the cell alignment values for the successive step strain experiment, where each point represents the cell alignment vs. total strain after 3 consecutive step compressions separated by 12 hr. The error bars represent the standard deviation of the cell alignment for 3 samples compressed to the same strain.




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