分级组装活性物质的自发运动
Spontaneous motion in hierarchically assembled active matter
摘要：
细胞以极高的精确度和可重复性，协调数千个纳米大小的分子马达的合作行动，以更大的长度尺度执行机械任务，如细胞运动、分裂和复制。除了它们的生物学重要性之外，这种固有的非平衡过程是从消耗能量以产生连续运动的微观组分开发仿生活性材料的灵感。由于受到主动驱动，这些材料不受平衡统计力学定律的约束，因此可以表现出非常受欢迎的特性，如自主运动性、内部产生的流动和自组织跳动。从可伸展的微管束开始，我们分层组装传统聚合物凝胶，液晶和乳液的活性类似物。在足够高的浓度下，微管形成一个具有内部驱动的混沌流动，流体动力学不稳定性，增强的运输和流体混合的特征的扩散活性网络。当被限制在乳液液滴中时，3D网络自发地吸附到液滴表面上以产生高度活性的2D液晶液晶，其流动流动由内部产生的断裂和自修复以及相反电荷的向错缺陷的解结合和湮灭控制。所得的活性乳剂表现出意想不到的性质，如自主运动，这是没有观察到在其被动类似物。总的来说，这些观察揭示了有生命的微观物体的组合如何表现出集体的仿生特性，这些特性与无生命的构建块组装的材料中发现的特性截然不同，这对我们提出了挑战，要求我们开发一个理论框架，以便系统地设计它们远离平衡的材料特性。
英文摘要：
With exquisite precision and reproducibility, cells orchestrate the cooperative action of thousands of nanometer-sized molecular motors to carry out mechanical tasks at much larger length scales, such as cell motility, division and replication. Besides their biological importance, such inherently non-equilibrium processes are an inspiration for developing biomimetic active materials from microscopic components that consume energy to generate continuous motion. Being actively driven, these materials are not constrained by the laws of equilibrium statistical mechanics and can thus exhibit highly sought-after properties such as autonomous motility, internally generated flows and self-organized beating. Starting from extensile microtubule bundles, we hierarchically assemble active analogs of conventional polymer gels, liquid crystals and emulsions. At high enough concentration, microtubules form a percolating active network characterized by internally driven chaotic flows, hydrodynamic instabilities, enhanced transport and fluid mixing. When confined to emulsion droplets, 3D networks spontaneously adsorb onto the droplet surfaces to produce highly active 2D nematic liquid crystals whose streaming flows are controlled by internally generated fractures and self-healing, as well as unbinding and annihilation of oppositely charged disclination defects. The resulting active emulsions exhibit unexpected properties, such as autonomous motility, which are not observed in their passive analogues. Taken together, these observations exemplify how assemblages of animate microscopic objects exhibit collective biomimetic properties that are starkly different from those found in materials assembled from inanimate building blocks, challenging us to develop a theoretical framework that would allow for a systematic engineering of their far-from-equilibrium material properties.
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