Entanglement Density Tunes Microscale Nonlinear Response of Entangled Actin

Abstract

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 $c^{\ast }\simeq 0.4$ mg/ml for nonlinear features to emerge. For $c>c^{\ast }$, entangled actin stiffens at short times with the degree of stiffening $S$ and corresponding timescale $t_{stiff}$ scaling with the entanglement tube density, i.e. $S\sim t_{stiff}\sim d_t^{-1}\sim c^{3/5}$. The network subsequently yields to a viscous regime with the yield distance $d_y$ scaling linearly with yield force $f_y$ and inversely with the entanglement length ($f_y\sim d_y\sim l_e^{-1}\sim c^{2/5}$). Stiffening and yielding dynamics are consistent with recent theoretical predictions for nonlinear cohesive breakdown of entanglements. We further show that above $c^{\ast }$ force relaxation proceeds via slow filament disengagement from dilated tubes coupled with $\sim$10x faster lateral hopping, with the corresponding concentration dependences in agreement with recent theoretical predictions for entangled rigid rods.

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Cited by in corpus (3)

• Unexpected entanglement dynamics in semidilute blends of supercoiled and ring DNA
• Synergistic interactions between DNA and actin trigger emergent viscoelastic behavior
• Active Disassembly and Reassembly of Actin Networks Induces Distinct Biphasic Mechanics