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TECHNICAL PAPERS

An in Vitro Model of Neural Trauma: Device Characterization and Calcium Response to Mechanical Stretch

[+] Author and Article Information
Donna M. Geddes

School of Biomedical Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0405

Robert S. Cargill

School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0405e-mail: robert.cargill@me.gatech.edu

J Biomech Eng 123(3), 247-255 (Jan 11, 2001) (9 pages) doi:10.1115/1.1374201 History: Received December 27, 1999; Revised January 11, 2001
Copyright © 2001 by ASME
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References

Figures

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(A)Photograph and (B)schematic of the CSA deformation mechanism, the epifluorescence microscope, and the membrane/washer assembly. Cells grown on a silicone membrane are imaged with the inverted epifluorescence microscope. Upon displacement of the translating arm, the membrane is stretched over the fixed, flat circular surface of the Delrin form, resulting in a transfer of strain onto the attached cells. The cells remain in the same focal plane throughout the membrane stretch, as shown by the dotted line. The microscope objective is positioned just below the membrane and images the cells throughout the deformation period.
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Diagram illustrating a triad of microspheres in the unstrained (left) and strained (right) configuration. The parameters necessary for the calculation of the two-dimensional Green’s strain imposed on the silicone membrane are labeled.
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Schematic diagram illustrating the use of the seeding circle and the location of cells on the silicone membrane. The seeding circle forms a dam around the cell inoculation area and contains the media needed to nourish the cells while in culture.
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Axial strain in the two-direction (E22, squares) and shear strain (E12, triangles) versus axial strain in the one-direction (E11) illustrating the equibiaxial nature of the strain. The two axial strains are virtually equal (lying on a line with slope of 1) whereas the shear strain is zero for the range of axial strains tested, indicating equibiaxial strain.
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The average axial components of Green’s strain are plotted versus translating arm displacement. These data were pooled together to develop a power law relationship between the two variables.
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Three representative strain histories as recorded with the motion control software and the corresponding prescribed waveforms for each are shown. The actual strain values are the E11 component of the strain tensor calculated using the calibration curve from the displacement data from the LVDT.
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Representative calcium transients for three different strain magnitudes when strained at 10 second−1 . Upon mechanical strain, there is an immediate rise in [Ca2+]i followed by a gradual recovery period. The peak change in [Ca2+]i and the end [Ca2+]i are dependent on the degree of strain magnitude.
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Representative calcium transients for three different strain rates when strained at 0.30. As in Fig. 7, upon mechanical strain there is an immediate rise in [Ca2+]i followed by a gradual recovery period. At low strain rates, only very small changes in [Ca2+]i are seen. However, as the rate is increased, both the peak and end [Ca2+]i increase as well.
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Relative peak increases in [Ca2+]i (the difference between peak and baseline emission ratios) are shown for all tested strains and strain rates. The response of 24 to 40 cells was averaged for each strain regime. Relative peak [Ca2+]i is shown to be dependent on both strain and strain rate as well as the interactions between the two (p<0.002). Standard error bars are also shown.
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Relative peak increases in [Ca2+]i presented as a contour plot to illustrate the synergistic dependence on strain rate and magnitude. These data can be employed in the development of tolerance criteria to mechanical stretch for individual neurons.
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Relative amount of recovery (the difference between end and baseline emission ratios) are shown for all strain rates and magnitudes tested. As with peak increase in [Ca2+]i, there exists a synergistic dependence on strain magnitude and rate (p<0.04). Note the three distinct levels of recovery seen in the data. Standard error bars are also shown.
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The percent of cells responding, defined as those with peak changes in [Ca2+]i greater than twice their baseline [Ca2+]i, are presented in this graph. The percent of cells responding is seen to vary as a function of both strain magnitude and strain rate (p<0.001).

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