Active Entanglement-Tracking Microrheology Directly Couples Macromolecular Deformations to Nonlinear Microscale Force Response of Entangled Actin

Falzone, Tobias T.; Robertson‐Anderson, Rae M.

doi:10.1021/acsmacrolett.5b00673

Cited by 34 publications

(44 citation statements)

References 39 publications

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“…The latter is being pursued by Robertson-Anderson and coworkers using F-actin [68,69] and DNA [70]. Even more definitive tests of our theory may be performed via simulations of entangled needles under various nonlinear deformations.…”

Section: Discussionmentioning

confidence: 97%

A force-level theory of the rheology of entangled rod and chain polymer liquids. I. Tube deformation, microscopic yielding, and the nonlinear elastic limit

Schweizer

Sussman

2016

The Journal of Chemical Physics

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We employ a first principles, force-level approach to self-consistently construct the anharmonic tube confinement field for entangled fluids of rigid needles and for primitive-path (PP) level chains in two limiting situations where chain stretching is assumed to either completely relax or remain unrelaxed. The influence of shear and extensional deformation and polymer orientation is determined in a nonlinear elastic limit where dissipative relaxation processes are intentionally neglected. For needles and PP-level chains, a Gaussian analysis of transverse polymer dynamical fluctuations predicts that deformation-induced orientation leads to tube dilation. In contrast, for deformed polymers in which chain stretch does not relax we find tube compression. For all three systems, a finite maximum transverse entanglement force localizing the polymers in effective tubes is predicted. The conditions when this entanglement force can be overcome (a force imbalance) by an externally applied force associated with macroscopic deformation can be crisply defined in the nonlinear elastic limit, and the possibility of a "microscopic absolute yielding" event destroying the tube confinement can be analyzed. For needles and contour-relaxed PP chains, this force imbalance is found to occur at a stress of order the equilibrium shear modulus and thus a strain of order unity, corresponding to a mechanically fragile entanglement tube field. However, for unrelaxed stretched chains, tube compression stabilizes transverse polymer confinement, and there appears to be no force imbalance. These results collectively suggest that the crossover from elastic to irreversible viscous response requires chain retraction to initiate disentanglement. We qualitatively discuss comparisons with existing phenomenological models for nonlinear startup shear, step strain, and creep rheology experiments.

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Section: Discussionmentioning

confidence: 97%

A force-level theory of the rheology of entangled rod and chain polymer liquids. I. Tube deformation, microscopic yielding, and the nonlinear elastic limit

Schweizer

Sussman

2016

The Journal of Chemical Physics

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“…To determine the macromolecular mechanisms underlying the observed relaxation behavior, we evaluate fits of the force curves to a range of exponential and power-law functions that have been previously used to fit relaxation data for entangled and crosslinked biopolymer networks 27,[36][37][38]48 . We find that the force relaxations for all composites can be well fit to a sum of three exponential decays with well-separated time constants (Fig.…”

Section: As Shown Inmentioning

confidence: 99%

“…Despite the relevance of actin-microtubule composites to biology, physics, and engineering, most in vitro studies to date have focused on single-component networks of either actin or microtubules 4,[34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] . In response to strain, entangled actin networks have been reported to exhibit varying degrees of stiffening, softening, and yielding depending on the actin concentration and the scale of the strain 36,38,39 .…”

Section: Introductionmentioning

confidence: 99%

Varying crosslinking motifs drive the mesoscale mechanics of actin-microtubule composites

Ricketts

Francis

Farhadi

et al. 2019

Preprint

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The cytoskeleton dynamically tunes its mechanical properties by altering the interactions between semiflexible actin filaments, rigid microtubules, and crosslinking proteins. Here, we use optical tweezers microrheology and confocal microscopy to characterize how varying crosslinking motifs impact the microscopic and mesoscale mechanics and mobility of actin-microtubule composites. We show that, upon subtle changes in the crosslinking pattern, composites separate into two distinct classes of force responseprimarily elastic versus more viscous behavior. For example, a composite in which actin and microtubules are crosslinked to each other is markedly more elastic than one in which both filaments are crosslinked but cannot link together. Notably, this distinction only emerges at mesoscopic scales in response to nonlinear forcing, whereas varying crosslinking motifs have little impact on the microscale mechanics and steadystate mobility of composites. Our unexpected scale-dependent results not only inform the physics underlying key cytoskeleton processes and structures, but, more generally, provide valuable perspective to materials engineering endeavors focused on polymer composites.

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“…Further, our recent microrheology measurements show that nonaffine filament displacements and stress-softening due to bending modes are suppressed in the nonlinear regime. 25 In fact, classical DE theory predictions for nonlinear mechanics are largely the same for flexible and rigid polymers due to the fast equilibration of chain stretch via Rouse modes. 27,39,40 We finally note that tube models and extensions there of have all been developed for monodisperse entangled polymer systems, whereas networks of actin as well as most synthetic polymers have a distribution of lengths around the mean.…”

Section: Introductionmentioning

confidence: 99%

Entanglement Density Tunes Microscale Nonlinear Response of Entangled Actin

et al. 2016

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We optically drive a microsphere at constant speed through entangled actin networks of 0.2 -1.4 mg/ml at rates faster than the critical rate controlling the onset of a nonlinear response. By measuring the resistive force exerted on the microsphere during and following strain we reveal a critical concentration c * 0.4 mg/ml for nonlinear features to emerge. For c > c * , entangled actin stiffens at short times with the degree of stiffening S and corresponding timescale t sti f f scaling with the entanglement tube density, i.e. S ∼ t sti f f ∼ d

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Active Entanglement-Tracking Microrheology Directly Couples Macromolecular Deformations to Nonlinear Microscale Force Response of Entangled Actin

Cited by 34 publications

References 39 publications

A force-level theory of the rheology of entangled rod and chain polymer liquids. I. Tube deformation, microscopic yielding, and the nonlinear elastic limit

A force-level theory of the rheology of entangled rod and chain polymer liquids. I. Tube deformation, microscopic yielding, and the nonlinear elastic limit

Varying crosslinking motifs drive the mesoscale mechanics of actin-microtubule composites

Entanglement Density Tunes Microscale Nonlinear Response of Entangled Actin

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