Entanglement Density Tunes Microscale Nonlinear Response of Entangled Actin

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• 作者：Bekele Gurmessa ; Robert Fitzpatrick ; Tobias T. Falzone ; Rae M. Robertson-Anderson
• 刊名：Macromolecules
• 出版年：2016
• 出版时间：May 24, 2016
• 年：2016
• 卷：49
• 期：10
• 页码：3948-3955
• 全文大小：461K
• 年卷期：0
• ISSN：1520-5835

文摘

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 nonlinear response. By measuring the resistive force exerted on the microsphere during and following strain, we reveal a critical concentration c_c ≃ 0.4 mg/mL for nonlinear features to emerge. For c > c_c , entangled actin stiffens at short times with the degree of stiffening S and corresponding time scale t_stiff scaling with the entanglement tube density, i.e., S ∼ t_stiff ∼ d_t^–1 ∼ 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 ∼ d_y ∼ l_e^–1 ∼ 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_c force relaxation proceeds via slow filament disengagement from dilated tubes coupled with ∼10× faster lateral hopping, with the corresponding concentration dependences in agreement with recent theoretical predictions for entangled rigid rods.