近日，英国爱丁堡大学的Tyler N. Shendruk及其研究小组取得一项新进展。经过不懈努力，他们揭示活动向列流中的自发自约束现象。相关研究成果已于2024年1月18日在国际知名学术期刊《自然—物理学》上发表。

该研究团队通过研究活动向列膜中的集体流动和缺陷动力学，揭示了一种自约束机制的存在。这种自约束表现为活动驱动的流动边界等值面与中尺度向列结构之间，存在一种自发产生的双向关系。研究人员发现，自运动缺陷被严格约束于粘度表面，这是沿涡度和应变率平衡的等值线。这揭示了自运动缺陷在沿着单个粘性表面移动时破坏镜像对称性的现象。这一现象可归因于粘度表面与弯曲壁之间的相互依赖关系，其中弯曲壁在方向场中呈现为细长的窄扭结。

这些发现表明，缺陷不能被视为孤立点，而是与其相关的中尺度变形紧密相关，这种中尺度变形是流体动力流动的稳态耦合的关键。这种中尺度交叉领域的自约束为解决复杂的三维主动湍流问题、设计动态控制的仿生材料以及理解生物系统如何利用主动应力进行动态自组织提供了一个框架。

据悉，活动过程驱动着各种尺度的生物动力学，包括亚细胞细胞骨架重塑、胚胎形成中的组织发育以及细菌菌落的种群级扩张。在每一种情况下，生物功能都需要在保持自组织结构的同时发生集体流动。然而，活动流如何自发地约束其动态以保持结构的机制尚待明确。

附：英文原文

Title: Spontaneous self-constraint in active nematic flows

Author: Head, Louise C., Dor, Claire, Keogh, Ryan R., Bonn, Lasse, Negro, Giuseppe, Marenduzzo, Davide, Doostmohammadi, Amin, Thijssen, Kristian, Lpez-Len, Teresa, Shendruk, Tyler N.

Issue&Volume: 2024-01-18

Abstract: Active processes drive biological dynamics across various scales and include subcellular cytoskeletal remodelling, tissue development in embryogenesis and the population-level expansion of bacterial colonies. In each of these, biological functionality requires collective flows to occur while self-organised structures are protected. However, the mechanisms by which active flows can spontaneously constrain their dynamics to preserve structure are not known. Here, by studying collective flows and defect dynamics in active nematic films, we demonstrate the existence of a self-constraint, namely a two-way, spontaneously arising relationship between activity-driven isosurfaces of flow boundaries and mesoscale nematic structures. We show that self-motile defects are tightly constrained to viscometric surfaces, which are contours along which the vorticity and the strain rate are balanced. This in turn reveals that self-motile defects break mirror symmetry when they move along a single viscometric surface. This is explained by an interdependence between viscometric surfaces and bend walls, which are elongated narrow kinks in the orientation field. These findings indicate that defects cannot be treated as solitary points. Instead, their associated mesoscale deformations are key to the steady-state coupling to hydrodynamic flows. This mesoscale cross-field self-constraint offers a framework for tackling complex three-dimensional active turbulence, designing dynamic control into biomimetic materials and understanding how biological systems can employ active stress for dynamic self-organisation.

DOI: 10.1038/s41567-023-02336-5

Source: https://www.nature.com/articles/s41567-023-02336-5