Theoretical Studies of Mechanics in Active Matter

非技术总结该奖项支持位于物理和生物学交界处的机械可激发活性固体的理论研究、推广和教育。在跳动的心脏中，被称为心肌细胞的细胞以协调的方式收缩，产生从心脏的一端到另一端的收缩波阵面，每次跳动都会推动血液通过心脏。成人心脏中的心肌细胞利用涉及离子的电信号刺激其他细胞收缩。然而，在早期胚胎心脏中，PI及其合作者提出，一个细胞收缩产生的机械应力向其他细胞发出收缩信号。因此，胚胎心脏是一种机械可兴奋的固体，在这种固体中，称为心肌细胞的活性成分对周围组织施加压力，从而刺激其他心肌细胞的收缩(从而产生更多的压力)。就像它们更简单的近亲--化学可兴奋系统一样，机械可兴奋的活性固体可以表现出丰富的行为，如心脏收缩波前的波前传播，条纹或斑点等图案的形成，或混乱行为。在这个项目中，PI将研究可机械激发的活性固体的物理学，如胚胎心脏。机械可激发的活性固体是一类活性物质--系统包含许多小组件，例如心肌细胞，它们彼此之间相互作用很强，并为系统提供能量。活性物质的物理学可以从根本上不同于传统的被动物质的物理学，在传统的被动物质中，单个微观成分不能提供能量。该奖项支持培养物理学研究生，在他们的研究过程中，他们将汇集凝聚态物理学许多子领域的想法和技术，并与生物学家密切互动。他们的工作不仅将拓宽物理学中对活性物质的研究，而且将为心脏的工作带来新的视角，并可能导致将新的合成材料设计为活性固体。技术总结该奖项支持关于活性物质与生物学界面的理论研究和教育。活性物质是一种通过在微观尺度上注入能量而保持不平衡的物质形式。一个典型的例子是活动粒子的活性流体。这个项目的重点是可兴奋的活性固体，其中的成分通过产生压力来注入能量。心脏跳动就是一个例子，在心脏跳动中，心肌细胞通过协调收缩来向组织注入能量，从而产生一个收缩的波前，在每次跳动时穿过心脏泵血。在成人心脏中，收缩波前被理解为在化学-电兴奋性问题中的波前传播。一个细胞的离子会触发下一个细胞的钙释放，从而启动其收缩。然而，在胚胎心脏中，主要研究人员和合作者提出，收缩波前是一种机械兴奋性现象：当细胞收缩时产生压力，有效地在弹性粘性组织中扩散，并在下一个细胞中触发离子释放，导致其收缩。心脏表现出活性物质的反向能量级联特征：通过波前传播的非线性动力学，心肌细胞收缩注入的能量被传递到宏观器官尺度，在那里它导致集体功能-心脏的泵浦作用。这个理论项目有三个主要目标：(1)建立一个关于活性固体的理论描述，在微观水平上通过应力产生注入能量；(2)构建一个与实验观察一致的心脏内力-电反应-扩散的连贯理论框架，并了解其对心脏发育和进化的影响；(3)利用化学反应扩散系统的非线性动力学领域发展起来的理论技术，更全面地了解机械反应扩散系统。这里的目的是计算稳态行为和暂态现象的相图。这样的相图可能有表示的区域，波前传播，图案形成，时间振荡，或静止行为。该奖项将支持物理学研究生在软物质物理，机械生物学和生理学的界面上工作。在研究过程中，这些学生将汇集凝聚态物理学许多子领域的想法和技术，并与生物学家密切互动。他们的工作不仅将拓宽软物质物理学中活性物质的研究，而且将为早期发展和早期进化的心脏带来新的视角，并可能导致将新的合成材料设计为活性固体。

NONTECHNICAL SUMMARYThis award supports theoretical research, outreach and education on mechanically-excitable active solids that lie at the interface of physics and biology. In the beating heart, cells called cardiomyocytes contract in a coordinated fashion to generate a contractile wavefront that crosses from one end of the heart to the other, pushing blood through the heart with each beat. Cardiomyocytes in the adult heart excite other cells to contract using electrical signals involving ions. In the early embryonic heart, however, the PI and collaborators have suggested that the mechanical stress resulting from the contraction of a cell signals other cells to contract. The embryonic heart is therefore a mechanically-excitable solid in which active components called cardiomyocytes exert stresses on surrounding tissue that excite contraction of other cardiomyocytes (and therefore the generation of more stress). Like their simpler cousins, chemically-excitable systems, mechanically-excitable active solids can show rich behavior, such as wavefront propagation as in the contractile wavefront of the heart, the formation of patterns such as stripes or spots, or chaotic behavior. In this project, the PI will investigate the physics of mechanically-excitable active solids such as the embryonic heart.Mechanically-excitable active solids are a class of active matter--systems that contain many small components, for example cardiomyocytes, that interact strongly with each other and that supply energy to the system. The physics of active matter can be fundamentally different from the physics of traditional passive matter, in which individual microscopic components cannot supply energy. This award supports training physics graduate students who, in the course of their research, will bring together ideas and techniques from many subfields of condensed matter physics and interact closely with biologists. Their work will not only broaden the study of active matter within physics, but will bring a new perspective to the workings of the heart and may lead to the design of new synthetic materials as active solids.TECHNICAL SUMMARYThis award supports theoretical research and education on active matter at the interface with biology. Active matter is a form of matter maintained out of equilibrium by energy injected at the microscopic scale. A canonical example is an active fluid of motile particles. This project focuses on excitable active solids, in which constituents inject energy by generating stress. An example is the beating heart, in which cardiomyocyte cells inject energy into the tissue by contracting in a coordinated fashion to create a contractile wavefront that traverses the heart with each beat to pump blood. In the adult heart, the contractile wavefront is understood as wavefront propagation in a chemo-electrical excitability problem. Ions from one cell trigger calcium release in the next cell to initiate its contraction. In the embryonic heart, however, the principal investigator and collaborators proposed that the contractile wavefront is a mechanical excitability phenomenon: stress is generated when a cell contracts, effectively diffuses through elastoviscous tissue, and triggers ion release in the next cell to cause its contraction. The heart exhibits the reverse energy cascade characteristic of active matter: energy injected at the cellular scale by cardiomyocyte contraction is transduced, via the nonlinear dynamics of wavefront propagation, up to the macroscopic organ scale, where it leads to a collective function - the pumping action of the heart.This theoretical project has three main goals: (1) to develop a theoretical description for active solids in which energy is injected at the microscopic level via stress generation; (2) to construct a coherent theoretical framework for mechano-electrical reaction-diffusion in the heart that is consistent with experimental observations, and to understand its implications for development and evolution of the heart; (3) to understand mechanical reaction-diffusion systems more generally, using theoretical techniques developed in the nonlinear dynamics community for chemical reaction-diffusion systems. Here the aim is to calculate phase diagrams for steady-state behavior and transient phenomena. Such a phase diagram might have regions denoted, wavefront propagation, pattern formation, temporal oscillations, or quiescent behavior.This award will support physics graduate students to work at the interface of soft matter physics, mechanobiology and physiology. In the course of their research, these students will bring together ideas and techniques from many subfields of condensed matter physics and interact closely with biologists. Their work will not only broaden the study of active matter within soft matter physics, but will bring a new perspective to early developing and early evolving hearts and may lead to the design of new synthetic materials as active solids.