Understanding the response of complex materials to external force is central to fields ranging from materials science to biology. Here, we describe a novel type of mechanical adaptation in cross-linked networks of F-actin, a ubiquitous protein found in eukaryotic cells. We show that shear stress changes the network's nonlinear mechanical response even long after that stress is removed. The duration, magnitude and direction of forcing history all change this mechanical response. While the mechanical hysteresis is long-lived, it can be simply erased by force application in the opposite direction. We further show that the observed mechanical adaptation is consistent with stress-dependent changes in the nematic order of the constituent filaments. Thus, this mechanical hysteresis arises from the changes in non-linear response that originates from stress-induced changes to filament orientation. This demonstrates that F-actin networks can exhibit analog read–write mechanical hysteretic properties, which can be used for adaptation to mechanical stimuli.

中文翻译：

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肌动蛋白网络中的机械滞后†

从材料科学到生物学，了解复杂材料对外力的响应是至关重要的。在这里，我们描述了在F-肌动蛋白（一种在真核细胞中普遍存在的蛋白）的交联网络中的一种新型的机械适应。我们表明，即使在消除应力后很长时间，剪应力仍会改变网络的非线性机械响应。强迫历史的持续时间，大小和方向都会改变这种机械响应。机械滞后寿命长，但是可以通过反方向施加力简单地消除。我们进一步表明，观察到的机械适应性与组成丝的向列顺序的应力依赖性变化相一致。因此，这种机械滞后现象是由非线性响应的变化引起的，该响应是由应力引起的细丝取向变化引起的。这表明F-肌动蛋白网络可以表现出模拟读写机械迟滞特性，可用于适应机械刺激。