Osmotic Force-Controlled Microrheometry of Entangled Actin Networks

Abstract

In studying a magnetic bead's creep response to force pulses in an entangled actin network we have found a novel regime where the bead motion obeys a power law x(t) approximately t(1/2) over two decades in time. It is flanked by a short-time regime with x(t) approximately t(3/4) and a viscous with x(t)approximately t. In the intermediate regime the creep compliance depends on the actin concentration c as c(-beta) with beta approximately 1.1 +/- 0.3. We explain this behavior in terms of osmotic restoring force generated by the piling up of filaments in front of the moving bead. A model based on this concept predicts intermediate x(t) approximately t(1/2) and long-time regimes x(t) approximately t in which the compliance varies as c(-4/3), in agreement with experiment.

Active mechanical stabilization of the viscoplastic intracellular space of Dictyostelia cells by microtubule–actin crosstalk

“…This gives rise to a local osmotic pressure counteracting the driving force. Such behaviour has indeed been observed for entangled actin networks and it has been shown theoretically that this effect leads to a square root law of the bead motion [37]. The active forces driving the fast initial motions (such as the fast deflections shown in Fig.…”

Entanglement Density Tunes Microscale Nonlinear Response of Entangled Actin

“…[12][13][14] For example, we previously showed that for flexible polymers, active microrheology reported macroscopic properties for probe sizes > 3x the tube diameter of the network. [15][16][17] Nonetheless, flows induced by microrheology are in fact non-uniform, and can lead to polymer buildup at the leading edge and depletion at the trailing edge of a moving probe leading to unique microscale visoelastic regimes not present at the macroscale, 18,19 leading to unique microscale viscoelastic regimes not present at the macroscale. 19,20 However, it is these discrepancies between the two techniques that can actually shed light on the microscale structures of biopolymer networks and varying lengthscale-dependent mechanical regimes.…”

“…[15][16][17] Nonetheless, flows induced by microrheology are in fact non-uniform, and can lead to polymer buildup at the leading edge and depletion at the trailing edge of a moving probe leading to unique microscale visoelastic regimes not present at the macroscale, 18,19 leading to unique microscale viscoelastic regimes not present at the macroscale. 19,20 However, it is these discrepancies between the two techniques that can actually shed light on the microscale structures of biopolymer networks and varying lengthscale-dependent mechanical regimes. 18,21 Despite these technological advances, most of the previous rheological studies on actin networks have focused on the near-equilibrium linear regime (accessible to passive microrheology techniques) and mechanics of cross-linked networks.…”

Rheology at the micro-scale: new tools for bio-analysis

“…This method has advantages over both complicated active microrheology techniques, where complex experimental set-ups are necessary to exert an external force for performing stress-controlled measurements; and invasive passive video particle tracking of submicronprobes embedded (either via endocytosis or micropipette injection) within the cell's cytoskeleton [13][14][15][16][17][18][19][20] .…”

“…those monitoring cell pharmacological response. Indeed, when compared to single cell viscoelasticity assays using techniques such as magnetic tweezers, atomic force microscopy and an optical stretcher, as employed in [13][14][15][16][17][18][19][20] , our method has the advantage of revealing the changes of the cell's viscoelastic properties over a wide range of frequencies (here from ∼1 Hz up to ∼1 kHz), to a high level of accuracy.…”