Beppu Kazusa, Maeda Yusuke T
Department of Physics, Kyushu University, Fukuoka 819-0395, Japan.
Biophys Physicobiol. 2022 May 12;19:1-9. doi: 10.2142/biophysico.bppb-v19.0020. eCollection 2022.
Ordered collective motion emerges in a group of autonomously motile elements (known as active matter) as their density increases. Microswimmers, such as swimming bacteria, have been extensively studied in physics and biology. A dense suspension of bacteria forms seemingly chaotic turbulence in viscous fluids. Interestingly, this active turbulence driven by bacteria can form a hidden ensemble of many vortices. Understanding the active turbulence in a bacterial suspension can provide physical principles for pattern formation and insight into the instability underlying biological phenomena. This review presents recent findings regarding ordered structures causing active turbulence and discusses a physical approach for controlling active turbulence via geometric confinement. When the active matter is confined in a compartment with a size comparable to the correlation length of the collective motion, vortex-like rotation appears, and the vortex pairing order is indicated by the patterns of interacting vortices. Additionally, we outline the design principle for controlling collective motions via the geometric rule of the vortex pairing, which may advance engineering microdevices driven by a group of active matter. This article is an extended version of the Japanese article, Ordered Structure and Geometric Control of Active Matter in Dense Bacterial Suspensions, published in SEIBUTSU BUTSURI Vol. 60, p. 13-18 (2020).
随着一群自主运动的元素（即活性物质）的密度增加，会出现有序的集体运动。微游动体，如游泳细菌，已在物理学和生物学领域得到广泛研究。细菌的密集悬浮液在粘性流体中会形成看似混乱的湍流。有趣的是，这种由细菌驱动的活性湍流可以形成许多隐藏的涡旋集合。理解细菌悬浮液中的活性湍流可以为模式形成提供物理原理，并深入了解生物现象背后的不稳定性。本文综述了关于导致活性湍流的有序结构的最新研究成果，并讨论了通过几何限制来控制活性湍流的物理方法。当活性物质被限制在一个尺寸与集体运动的相关长度相当的隔室中时，会出现类似涡旋的旋转，并且相互作用的涡旋模式表明了涡旋配对顺序。此外，我们概述了通过涡旋配对的几何规则来控制集体运动的设计原则，这可能会推动由一群活性物质驱动的工程微器件的发展。本文是发表于《生物物理》第60卷，第13 - 18页（2020年）的日文文章《密集细菌悬浮液中活性物质的有序结构与几何控制》的扩展版本。
