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- Local measurements of viscoelastic moduli of entangled actin...Local measurements of viscoelastic moduli of entangled actin networks using an oscillating magnetic bead micro-rheometer
Biophysical Journal, Volume 66, Issue 6, 1 June 1994, Pages 2210-2216
F. Ziemann, J. Rädler and E. Sackmann
AbstractA magnetically driven bead micro-rheometer for local quantitative measurements of the viscoelastic moduli in soft macromolecular networks such as an entangled F-actin solution is described. The viscoelastic response of paramagnetic latex beads to external magnetic forces is analyzed by optical particle tracking and fast image processing. Several modes of operation are possible, including analysis of bead motion after pulse-like or oscillatory excitations, or after application of a constant force. The frequency dependencies of the storage modulus, G'(omega), and the loss modulus, G''(omega), were measured for frequencies from 10(-1) Hz to 5 Hz. For low actin concentrations (mesh sizes epsilon > 0.1 micron) we found that both G'(omega) and G''(omega) scale with omega 1/2. This scaling law and the absolute values of G' and G'' agree with conventional rheological measurements, demonstrating that the magnetic bead micro-rheometer allows quantitative measurements of the viscoelastic moduli. Local variations of the viscoelastic moduli (and thus of the network density and mesh size) can be probed in several ways: 1) by measurement of G' and G'' at different sites within the network; 2) by the simultaneous analysis of several embedded beads; and 3) by evaluation of the bead trajectories over macroscopic distances. The latter mode yields absolute values and local fluctuations of the apparent viscosity eta(x) of the network.
Abstract | PDF (774 kb) - Cell poking: quantitative analysis of indentation of thick v...Cell poking: quantitative analysis of indentation of thick viscoelastic layers
Biophysical Journal, Volume 55, Issue 4, 1 April 1989, Pages 683-690
M. Duszyk, B. Schwab, G.I. Zahalak, H. Qian and E.L. Elson
AbstractA recently introduced device, the cell poker, measures the force required to indent the exposed surface of a cell adherent to a rigid substratum. The cell poker has provided phenomenological information about the viscoelastic properties of several different types of cells, about mechanical changes triggered by external stimuli, and about the role of the cytoskeleton in these mechanical functions. Except in special cases, however, it has not been possible to extract quantitative estimates of viscosity and elasticity moduli from cell poker measurements. This paper presents cell poker measurements of well characterized viscoelastic polymeric materials, polydimethylsiloxanes of different degrees of polymerization, in a simple shape, a flat, thick layer, which for our purposes can be treated as a half space. Analysis of the measurements in terms of a linear viscoelasticity theory yields viscosity values for three polymer samples in agreement with those determined by measurements on a macroscopic scale. Theoretical analysis further indicates that the measured limiting static elasticity of the layers may result from the tension generated at the interface between the polymer and water. This work demonstrates the possibility of obtaining quantitative viscoelastic material properties from cell poker measurements and represents the first step in extending these quantitative studies to more complicated structures including cells.
Abstract | PDF (836 kb) - Red cell extensional recovery and the determination of membr...Red cell extensional recovery and the determination of membrane viscosity
Biophysical Journal, Volume 26, Issue 1, 1 April 1979, Pages 101-114
R.M. Hochmuth, P.R. Worthy and E.A. Evans
AbstractA theory of membrane viscoelasticity developed by Evans and Hochmuth in 1976 is used to analyze the time-dependent recovery of an elongated cell. Before release, the elongated cell is the static equilibrium where external forces are balanced by membrane elastic force resultants. Upon release, the cell recovers its initial shape with a time-dependent exponential behavior characteristic of the viscoelastic solid model. It is shown that the model describes the time-dependent recovery process very well for a time constant in the range of 0.1–0.13 s. The time constant is the ratio membrane surface viscosity eta:membrane surface elasticity mu. Measurements for the shear modulus mu of 0.006 dyne/cm give a value for the surface viscosity of red cell membrane as a viscoelastic solid material of eta = mu tc = (6–8) X 10(-4) poise .cm.
Abstract | PDF (993 kb) - …more
Copyright © 1975 The Biophysical Society. All rights reserved.
Biophysical Journal, Volume 15, Issue 3, 233-237, 1 March 1975
doi:10.1016/S0006-3495(75)85814-0
Research Article
Viscoelastic analysis of high molecular weight, alkali-denatured DNA from mouse 3T3 cells
E.L. Uhlenhopp
Abstract
Alkaline lysates of mouse 3T3 cells showed viscoelastic properties characteristic of very large molecules of single-stranded DNA. The viscoelastic retardation time and the sensitivity to low doses of nitrogen mustard and of X-irradiation suggest a molecular weight in excess of 10–10 daltons. Contact-inhibited cells yielded larger single strands than actively growing cells.
