Soft glassy rheology and structural damping

Remarkably, in the limit that the frequency is small (compared to 0) and the imposed deformations are small (such that the rate for hopping out of wells is dominated by x), Sollich's theory leads directly to the structural damping equation (Eq. 3.2). The data reported above establish firmly that the mechanical behavior of cells conforms well to Eq. 3.2. If Sollich's theory and underlying ideas are assumed to apply to the data reported here, then the parameters in Eq. 3.2 (x, G0, 0) can be...

Principles of continuum models

A continuum cell model provides the displacement, strain, and stress fields induced in the cell, given its initial geometry and material properties, and the boundary conditions it is subjected to (such as displacements or forces applied on the cell surface). Laws of continuum mechanics are used to solve for the distribution of mechanical stress and deformation in the cell. Continuum cell models of interest lead to equations that are generally not tractable analytically. In practice, the...

O

Oosawa and colleagues found that actin polymerizes in two phases (a) an unfavorable nucleation phase involving an actin trimer and (b) a rapid assembly phase in which actin monomers add to both barbed and pointed ends. In the presence of excess ATP, actin does not polymerize to equilibrium but to a 'treadmilling' steady-state in which monomers continuously add to the barbed end and fall off of the pointed end. reactions. Oozawa also assumed that spontaneous...

N J Z u2

Where Z is the frequency variable to integrate over and P denotes a principal value integral, one can then calculate the real part of the compliance. Knowing both real and imaginary parts of the compliance, one then finds the complex shear modulus via where R is the probe bead radius. This procedure is explained in detail in Schnurr etal. (1997). The shear modulus can also be derived from position fluctuation data in a different way. After first calculating the mean square displacement as a...

Measurements of cell mechanics

The mechanical torque of the bead is proportional to the external magnetic field (which was generated using an electromagnet), the bead's magnetic moment (which was calibrated by measuring the speed of bead rotation in a viscous medium), and the cosine between the bead's magnetization direction with the direction of the twisting field. Consider the specific torque of a bead, T, which is the mechanical torque per bead volume, and has dimensions of stress (Pa). The ratio of the complex-specific...

Introduction

A new model of cell structure to explain how the internal cytoskeleton of adherent cells mediates alterations in cell functions caused by changes in cell shape was proposed in the early 1980s by Donald Ingber and colleagues (Ingber et al., 1981 Ingber and Jamieson, 1985). This model is based on a building system known as tensegrity architecture (Fuller, 1961). The essential premise of what is known as the cellular tensegrity model is that the cytoskeletal lattice carries preexisting tensile...

Info

G' vs. frequency in HASM cells under control conditions ( , n 256), and after 10 min. treatment with the contractile agonist histamine 10-4 M ( , n 195), the relaxing agonist DBcAMP 10-3 M ( , n 239) and the actin-disrupting drug cytochalasin D 2 x 10-6 M ( , n 171). At all frequencies, treatment with histamine caused G' to increase, while treatment with DBcAMP and cytoD caused G' to decrease. Under all treatment conditions, G increased with increasing frequency, f, according to a...

Biphasic solidfluid models of cell mechanics

Viscoelastic behavior in cells can arise from both flow-dependent (fluid-solid interactions and fluid viscosity) and flow-independent mechanisms (for example, intrinsic viscoelasticity of the cytoskeleton). Previous studies have described the cytoplasm of solid-like cells as a gel or as a porous-permeable, fluid-saturated meshwork (Oster, 1984 Oster, 1989 Pollack, 2001) such that the forces within the cell exhibit a balance of stresses arising from hydrostatic and osmotic pressures and the...

FC Mac Kintosh

ABSTRACT Most plant and animal cells possess a complex structure of filamentous proteins and associated proteins and enzymes for bundling, cross-linking, and active force generation. This cytoskeleton is largely responsible for cell elasticity and mechanical stability. It can also play a key role in cell locomotion. Over the last few years, the single-molecule micromechanics of many of the important constituents of the cytoskeleton have been studied in great detail by biophysical techniques...

Experimental measurements of intracellular mechanics

ABSTRACT Novel methods to measure the viscoelasticity of soft materials and new theories relating these measurements to the underlying molecular structures have the potential to revolutionize our understanding of complex viscoelastic materials like cytoplasm. Much of the progress in this field has been in methods to apply piconewton forces and to detect motions over distances of nanometers, thus performing mechanical manipulations on the scale of single macromolecules and measuring the...

Do microtubules carry compression

Microscopic visualization of green fluorescent protein-labeled microtubules of living cells see Fig. 6-2 shows that microtubules buckle as they oppose contraction of the actin network Waterman-Storer and Salmon, 1997 Wang et al., 2001 . It was not known, however, whether the compression that causes this buckling could balance a substantial fraction of the contractile prestress. To investigate this possibility, an energetic analysis of buckling of microtubules was carried out Stamenovic et al.,...