From Active to Smart Matter

该奖项支持理论和计算研究和教育，以研究活性物质中的紧急行为。活性物质是一个术语，用来描述自供电实体的集合，如鸟类、活细胞或工程微游泳者，它们从环境中获取能量，自发地组织和产生协调运动。本课题研究的一个例子是细菌悬浮液。每个单独的细菌都是一个活跃的粒子，通过消耗营养物质来推动自己通过介质。一群密集的细菌集体行为就像一种活的液体，可以自我组织成复杂的几何图案，表现出像漩涡一样的湍流运动，或者“冻结”成一种固体状的生物膜——一种细菌聚集体，就像我们牙齿之间形成的牙垢。这种类型的涌现行为，即许多相互作用的实体的集合在具有新颖宏观特性的状态下表现出大规模的空间或时间组织，在无生命或被动物质中很常见，例如，当温度降低时，从水到冰的转变。然而，它在主动系统中获得了一种新的未知的丰富性，这种系统不是由外部旋钮调节的，比如温度，而是由每个个体内部产生的能量来调节的。这个项目结合了理论和数值模拟来解决活性物质物理学中的几个开放问题。第一个目标是理解所谓的非互反相互作用在控制主动系统组装中的作用。牛顿第三定律是一个基本的物理学原理，它确定了两个实体之间的相互作用是相互的：每一个作用都有一个相等和相反的反应。但这条定律似乎经常在活跃物质、生物和社会环境中被违反。通过量化非互反相互作用如何驱动物质新动态状态的组装，该项目旨在确定材料设计的新途径。该项目的第二个目标是利用几何和限制来控制活跃流体的湍流。所研究的特定系统是一种活性流体，由从活细胞中提取的蛋白质组成，在没有外力的情况下自发流动，表现出类似于湍流中观察到的旋转混沌运动。PI将与加州大学圣巴巴拉分校的实验同事合作，控制和引导这种流动，并将其应用于微流体装置的设计。第三个目标的灵感来自于对大多数细菌在粘弹性流体中游动的观察，这种流体既可以像水一样流动，也可以像固体一样抵抗变形，这取决于它们被搅拌的速度。PI将研究悬浮流体的粘弹性对细菌集体行为的作用，这在细菌生物膜的形成中具有重要意义。研究的最后一个目标将是理解有源系统中的波传播与在某些工程机械材料和量子系统中看到的一类特殊的鲁棒激励之间的深层联系，目标是制定允许在活性和生物物质中进行鲁棒信号传播的规则。为了在物理学上取得根本性的进步，拟议的研究将有助于实现设计新型智能材料的策略，并将对从生物学到工程学等其他领域产生影响。它将成为培养物理学、工程学和生物学领域本科生、研究生和博士后研究人员的框架，并有助于发展多样化的STEM劳动力。该奖项支持理论和计算研究和教育，将理论连续体模型和数值模拟相结合，以解决活性物质物理学中的一些开放问题。该研究将围绕以下具体目标进行组织：量化非互惠相互作用，记忆和反馈对活性物质的紧急行为的作用。利用模拟和连续统理论，PI将研究非互反和时间延迟的相互作用如何影响物质活跃状态之间的涌现行为和相变的本质，并研究这些状态的特性。具体的重点将放在活性胶体的混合物上，其中有效的非互反相互作用是由流体中的化学反应介导的，并在粘杆菌中聚集。这项工作将导致一个预测的理论框架，用于量化非互易性在主动自组织中的作用，与从细菌物种进化到形态发生中基因表达调节的生物学背景相关，并对群体智能和机器人技术产生影响。探索拓扑激发在活性物质中的作用。在有源系统中，活度和耗散的结合自然导致非厄米动力学算符的出现。这表明有源系统中的线性波与非互易超材料和量子系统中拓扑保护的边界态之间可能存在对应关系。在她之前工作的基础上，PI将探索这种联系，以确定可以作为活跃和生物物质中强大信息传输管道的模式。利用拓扑、几何和活动界面来控制和指导活动流和活动物质的组织。通过与实验学家的合作，PI将研究主动向列线的界面特性，以及利用几何和空间和时间调制活动来控制主动流动。这项工作将植根于旨在促进活性材料设计的实验，并为理解活性结构流体的液-液相分离提供基础进展，这是当前细胞生物学中一个非常相关的问题。利用介质粘弹性同时控制主动悬架的时空组织。PI将研究悬浮介质的粘弹性在调节活性剂的有效惯性动力学和延时相互作用中的作用，特别关注细菌悬浮液，其中粘弹性在控制生物膜形成方面很重要。PI期望这项研究将在非平衡统计物理学中产生根本性的进步，为活性和可重构材料的设计和组装开辟新的策略，并开发与生物过程相关的理论模型，从伤口愈合到癌症侵袭。该项目具有教育成分，旨在培养学生和博士后在软物质和物理与生物学界面方面具有强大的定量技能和专业知识，并强调促进多样化和包容性的研究环境。PI将继续通过组织会议和高级学校在该行业中发挥重要作用。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

NONTECHNICAL SUMMARYThis award supports theoretical and computational research and education to study emergent behavior in active matter. Active matter is a term coined to describe collections of self-powered entities, such as birds, living cells, or engineered microswimmers, that take energy from the environment to spontaneously organize and produce coordinated motion. An example which is studied in this project is a bacterial suspension. Each individual bacterium is an active particle that propels itself though a medium by consuming nutrients. A dense swarm of bacteria behaves collectively as a living fluid and can self-organize in complex geometric patterns, exhibit swirling turbulent-like motion, or ``freeze” into a solid-like biofilm – a bacterial aggregate like the tartar that forms between our teeth. This type of emergent behavior, where a collection of many interacting entities exhibits large-scale spatial or temporal organization in a state with novel macroscopic properties, is familiar in inanimate or passive matter, for example the transition from water to ice as one lowers the temperature. However, it acquires a new unexplored richness in active systems that are tuned not by an external knob, such as the temperature, but by energy generated internally by each individual.This project combines theory and numerical simulations to address several open questions in active matter physics. The first aim is understanding the role of so-called non-reciprocal interactions in controlling the assembly of active systems. A fundamental physics principle is Newton's third law which establishes that interactions among two entities are reciprocal: for every action there is an equal and opposite reaction. But this law is often seemingly violated in active matter and in biological and social contexts. By quantifying how non-reciprocal interactions drive the assembly of new dynamical states of matter, this project aims at identifying new pathways for materials design. The second aim of the project is to exploit geometry and confinements to harness the turbulent-like flow of active fluids. The specific system studied is an active fluid composed of proteins extracted from living cells that flows spontaneously with no externally applied forces, exhibiting swirling chaotic motions similar to those observed in turbulent fluids. The PI will collaborate with experimental colleagues at UC Santa Barbara to control and direct such flows, with applications to the design of microfluidic devices in mind. A third aim is inspired by the observation that most bacteria swim in viscoelastic fluids that can both flow like water or resist deformations like a solid depending on how quickly they are stirred. The PI will examine the role of viscoelasticity of the suspending fluid on the collective behavior of bacteria, which is of great importance in the formation of bacterial biofilms. The last goal underlying the research will be to understand the deep connection between wave propagation in active systems and a special class of robust excitations seen in certain engineered mechanical materials and in quantum systems, with the goal to formulate the rules that allow robust signal propagation in active and biological matter.To lead to fundamental advances in physics, the proposed research will help enable strategies for the design of new smart materials and will have impact on other fields, from biology to engineering. It will serve as a framework for the training of undergraduate and graduate students and postdoctoral researchers at the interface of physics, engineering, and biology, and contribute tothe development of a diverse STEM workforce.TECHNICAL SUMMARYThis award supports theoretical and computational research and education to combine theoretical continuum models and numerical simulations to address a number of open questions in active matter physics. The research will be organized around the following specific objectives:Quantifying the role of nonreciprocal interactions, memory, and feedback on the emergent behavior of active matter. Using simulations and continuum theory, the PI will examine how non-reciprocal and time-delayed interactions affect the emergent behavior and the nature of phase transitions between active states of matter, and examine the properties of these states. Specific focus will be on mixtures of active colloids, where effective non-reciprocal interactions are mediated by chemical reactions in the fluid, and to aggregation in Myxobacteria. This work will lead to a predictive theoretical framework for quantifying the role of non-reciprocity in active self-organization, with relevance to biological contexts from evolution of bacterial species to regulation of gene expression in morphogenesis, and with implications for swarm intelligence, and robotics.Exploring the role of topological excitation in active matter. In active systems the combination of activity and dissipation naturally leads to the emergence of non-Hermitian dynamical operators. This suggests a possible correspondence between linear wave in active systems and topologicallyprotected boundary states in nonreciprocal metamaterials and quantum system. Building on her previous work, the PI will explore this connection to identify modes that could serve as conduits for robust information transmission in active and biological matter.Exploiting topology, geometry, and active interfaces to harness and direct active flows and the organization of active matter. Through a collaboration with experimentalists, the PI will investigate the interfacial properties of active nematics and the use of geometry and of spatial and temporal modulation of activity for controlling active flows. This work will be rooted in experiments aimed at facilitating active materials design and provide fundamental advances in the understanding of liquid-liquid phase separation of active structured fluids, a question of great current relevance in cell biology.Exploiting medium viscoelasticity for simultaneous control of the spatial and temporal organization of active suspensions. The PI will examine the role of viscoelasticity of the suspending medium in mediating effective inertial dynamics of active agents and time-delayed interactions, with specific focus on bacterial suspensions, where viscoelasticity is important in controlling biofilm formation. The PI expects that the research will engender fundamental advances in nonequilibrium statistical physics , open new strategies for the design and assembly of active and reconfigurable materials, and develop theoretical models relevant to biological processes, from wound healing to cancer invasion.This project has an educational component aimed at training students and postdocs with robust quantitative skills and expertise in soft-matter and at the interface of physics and biology, and emphasis on promoting a diverse and inclusive research environment. The PI will continue to play a significant role in the profession through the organization of conferences and advanced schools.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.