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TECHNICAL PAPERS

An Axisymmetric Boundary Integral Model for Assessing Elastic Cell Properties in the Micropipette Aspiration Contact Problem

[+] Author and Article Information
Mansoor A. Haider

Department of Mathematics, North Carolina State University, Box 8205, Raleigh, NC 27695-8205  

Farshid Guilak

Orthopaedic Research Laboratories, 375 MSRB, Box 3093, Duke University Medical Center, Durham, NC 27710

J Biomech Eng 124(5), 586-595 (Sep 30, 2002) (10 pages) doi:10.1115/1.1504444 History: Received July 01, 1999; Revised May 01, 2002; Online September 30, 2002
Copyright © 2002 by ASME
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References

Figures

Grahic Jump Location
Computational mesh for the micropipette aspiration contact problem with M=40 quadratic boundary elements for the case a/R=0.4,ε/a=0.05: (a) Cell geometry and distribution of elements. The length L0 is used to compute a characteristic strain (L0−2R)/(2R) for the cell. (b) Micropipette geometry and illustration of cell-micropipette contact. The aspiration length L(p) is measured relative to the point with coordinates (0,0,R).
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Simulations of the equilibrated elastic cell response using scaled pressure increments Δp/E=0.01 for the case ε/a=0.05,M=40. The deformed cell profiles are shown at equally spaced intervals of total applied pressure until the the characteristic strain exceeded a value of 0.2: (a) A small aspect ratio a/R=0.4. (b) A large aspect ratio a/R=0.7.
Grahic Jump Location
The cell response as measured by the aspiration length L/a with increasing micropipette-to-cell aspect ratio a/R. The aspiration length is shown as a function of the scaled pressure Δp/E for increments of 0.01 until the characteristic strain exceeded a value of 0.2: (a) ε=0.02,M=50. (b) ε=0.05,M=40. (c) ε=0.08,M=40.
Grahic Jump Location
Sensitivity of the aspiration length L/a to the curvature ε/a of the micropipette edge for the case a/R=0.5. The aspiration length is shown as a function of the scaled pressure Δp/E for increments of 0.01 until the characteristic strain exceeded a value of 0.2.
Grahic Jump Location
The cell response as measured by characteristic strain (L0−2R)/(2R) with increasing micropipette-to-cell aspect ratio a/R. The characteristic strain is shown as a function of the scaled pressure Δp/E for increments of 0.01 until the the value of the strain exceeded 0.2: (a) ε=0.02,M=50. (b) ε=0.05,M=40. (c) ε=0.08,M=40.
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Adjustment factor for the Young’s modulus E, as predicted by the halfspace solution of Theret et al. 19, required to obtain agreement with predictions of the spherical cell model. The ratio of the wall function Φp≈2.1 and response function Ψ in equation (21) is plotted as a function of the aspiration length L/a for L/a>0.3 with scaled pressure increments of 0.01 until the characteristic strain exceeded a value of 0.2: (a) ε=0.02,M=50. (b) ε=0.05,M=40. (c) ε=0.08,M=40.
Grahic Jump Location
Video images of micropipette aspiration of a primary human chondrocyte: (a) Resting state of the cell with a tare pressure applied to form a seal between the cell and the micropipette. (b) As step pressures are applied, a portion of the cell enters the micropipette and the contact area between the cell and micropipette is gradually increased. (c) With larger pressures, the length of cell within the pipette may exceed the inner radius of the micropipette, and significant contact occurs between the cell and the inside wall of the micropipette (arrow). Scale bar equals 5 microns.

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