Local measurements of viscoelastic moduli of entangled actin networks using an oscillating magnetic bead micro-rheometer

Ziemann, Florian; Rädler, Joachim O.; Sackmann, E.

doi:10.1016/s0006-3495(94)81017-3

Cited by 293 publications

(255 citation statements)

References 17 publications

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confidence: 68%

“…Mutual particle interactions are induced by an external magnetic field. As we demonstrate, theory and experiment are in good agreement, and also allow for microrheological measurements [16].For simplicity, we assume a homogeneous, isotropic, infinitely extended elastic matrix, and low-amplitude deformations. Applying a bulk force density f b (r) to the matrix, its equilibrated state satisfies the linear elastostatic Navier-Cauchy equations [17],…”

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confidence: 63%

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Forces on Rigid Inclusions in Elastic Media and Resulting Matrix-Mediated Interactions

et al. 2016

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To describe many-particle systems suspended in incompressible low-Reynolds-number fluids, effective hydrodynamic interactions can be introduced. Here, we consider particles embedded in elastic media. The effective elastic interactions between spherical particles are calculated analytically, inspired by the approach in the fluid case. Our experiments on interacting magnetic particles confirm the theory. In view of the huge success of the method in hydrodynamics, we similarly expect many future applications in the elastic case, e.g. for elastic composite materials. planes, vehicles, ships, and propellers [4]. All these processes are described by the Navier-Stokes equations [5] or variants thereof. This set of equations typically poses significant challenges during solution due to a convective nonlinearity reflecting inertial effects. Basically, turbulence is driven by the inertial term. It often renders analytical solutions impossible.The situation changes for small dimensions and velocities or high viscosity. Then, the relative strength of inertial effects, measured by the Reynolds number, is low. The nonlinearity can be neglected. A Green's function in terms of the so-called Oseen matrix is then available, which formally solves the problem analytically [6,7]. In this way, semi-dilute colloidal suspensions, i.e. the dispersion of nano-to micrometer-sized particles in a fluid [7,8], or microswimmer suspensions [9] are described effectively. The explicit role of the fluid is eliminated and replaced by effective hydrodynamic interactions between the suspended particles [6,7].Despite the success of this theoretical approach for colloidal suspensions, hardly any investigations consider a surrounding elastic solid instead of a suspending fluid. This is surprising, since, as we show below, the formalism can be adapted straightforwardly to linearly elastic matrices and is confirmed by our experiments. Our approach will, for instance, facilitate describing the response of elastic composite materials to external stimuli. Such materials consist of more or less rigid inclusions embedded in an elastic matrix. They are of growing technological interest and may serve, e.g., as soft actuators or sound attenuation devices [10].In previous theoretical studies, the physics of one single rigid or deformable inclusion was addressed [11,12], also under acoustic irradiation [13]. For more than a single inclusion, mainly the so-called load problem was analyzed theoretically for a pair of rigid inclusions: one prescribes displacements of two rigid inclusions in an elastic matrix, and then determines the forces necessary to achieve these given displacements [14].Here, we take the converse point of view, based on the cause-and-effect chain in our experiments: external forces are imposed onto the inclusions, or mutual forces between the inclusions are induced, for example to actuate the material or to tune its properties. In response to the forces, the inclusions are displaced. Since they cannot penetrate through the surrounding elastic ma...

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confidence: 68%

supporting

confidence: 63%

Forces on Rigid Inclusions in Elastic Media and Resulting Matrix-Mediated Interactions

et al. 2016

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“…Scattering techniques are then sometimes more convenient than direct methods developed recently to investigate the dynamics of individual polymers, such as flicker analysis [38] and microrheology [39], which are still plagued by some technical complications [40]. They allow to probe in a quick and reliable experiment the internal dynamics of single polymers with the necessary statistical averaging inherently included.…”

Section: Discussionmentioning

confidence: 99%

Dynamic scattering from solutions of semiflexible polymers

Kroy¹,

Frey²

1997

Phys. Rev. E

120

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The dynamic structure factor of semiflexible polymers in solution is derived from the wormlike chain model. Special attention is paid to the rigid constraint of an inextensible contour and to the hydrodynamic interactions. For the cases of dilute and semidilute solutions exact expressions for the initial slope are obtained. When the hydrodynamic interaction is treated on the level of a renormalized friction coefficient, the decay of the structure factor due to the structural relaxation obeys a stretched exponential law in agreement with experiments on actin. We show how the characteristic parameters of the system (the persistence length ℓp, the lateral diameter a of the molecules, and the mesh size ξm of the network) are readily determined by a single scattering experiment with scattering wavelength λ obeying a ≪ λ ≪ ℓp and λ < ξm. We also find an exact explicit expression for the effective (wave-vector-dependent) dynamic exponent z(k) < 3 for semiflexible polymers and thus an enlightening explanation for a longstanding puzzle in polymer physics.

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“…The experimental setup was described previously [25,32]. The inhomogeneous field is generated with a soft iron core exhibiting a sharp wedge-shaped edge.…”

Section: The Magnetic Bead Microrheometermentioning

confidence: 99%

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

Heinrich

Sackmann²

2006

Acta Biomaterialia

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The micro-viscoelasticity of the intracellular space of Dictyostelium discoideum cells is studied by evaluating the intracellular transport of magnetic force probes and their viscoelastic responses to force pulses of 20-700 pN. The role of the actin cortex, the microtubule (MT) aster and their crosstalk is explored by comparing the behaviour of wild-type cells, myosin II null mutants, latrunculin A and benomyl treated cells. The MT coupled beads perform irregular local and long range directed motions which are characterized by measuring their velocity distributions (P(v)). The correlated motion of the MT and the centrosome are evaluated by microfluorescence of GFP-labelled MTs. P(v) can be represented by log-normal distributions with long tails and it is determined by random sweeping motions (v $ 0.5 lm/s) of the MTs (caused by tangential forces on the filament ends coupled to the actin cortex) and by intermittent bead transports parallel to the MTs (v max $ 1.5 lm/s). The tails are due to spontaneous filament deflections (with speeds up to 10 lm/s) attributed to pre-stressing of the MT by local cortical tensions, generated by dynactin motors generating plus-end directed forces in the MTs. The viscoelastic responses are strongly non-linear and are mostly directed opposite or perpendicular to the force, showing that the cytoplasm behaves as an active viscoplastic body with time and force dependent drag coefficients. Nano-Newton loads exerted on the soft MT are balanced by traction forces arising at the MT ends coupled to the actin cortex and the centrosome, respectively. The mechanical coupling between the soft microtubules and the viscoelastic actin cortex provides cells with high mechanical stability despite the softness of the cytoplasm.

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Local measurements of viscoelastic moduli of entangled actin networks using an oscillating magnetic bead micro-rheometer

Cited by 293 publications

References 17 publications

Forces on Rigid Inclusions in Elastic Media and Resulting Matrix-Mediated Interactions

Forces on Rigid Inclusions in Elastic Media and Resulting Matrix-Mediated Interactions

Dynamic scattering from solutions of semiflexible polymers

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

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