Developing quantitative continuum theories of composite active fluids

非技术总结该奖项支持理论、计算和数据密集型研究，以开发一种理论来描述包含自供电元件的生物和其他流体中的流动现象。自然界和工程系统中的流动现象通常是由重力和压力梯度等外力驱动的。连续介质力学是一种数学语言，它允许我们描述这种流动，从而预测和设计它们。在生物系统中，如细胞骨架，流动现象是由内部驱动产生的，由蛋白质和其他消耗化学能量的生化机器提供动力。近年来，连续介质力学描述已经被开发并应用于这种内部驱动的生物流体，并取得了巨大的成功。到目前为止，工作主要集中在对这些系统的单一组件描述上。事实上，这些都是多组分系统。开发用于内部驱动流体的多组分连续介质理论需要克服几个技术挑战。该项目使用多尺度理论和数据驱动技术来解决这些技术挑战，从而开发多组分生物流体的模型。这个项目是朝着理解在自然和合成生物系统中发挥作用的物理机制迈出的一步。从实用的角度来看，设计和控制内部驱动流体是设计可快速重构的仿生材料的关键，这些材料在机器人、微流体和自适应光学等领域的应用非常广泛。除了科学成果外，这项研究还与教育和宣传活动结合在一起，包括：(I)软材料理论高级本科课程的内容--这满足了本科生在物理和生物学之间进行跨学科研究的教育需求，以及(Ii)在Brandeis社区内实施、测试和确定基准的多样性、教育和包容性倡议，可以作为可广泛分享给学术界的模型输出。技术概述该奖项支持理论、计算和数据密集型研究，以开发建立复合活性流体的预测性连续介质描述的理论框架。活性流体是由消耗能量和作用力的微观实体组成的。这一范例包括各种系统，从细菌悬浮液到由分子马达推动的细胞骨架细丝和合成的弥漫胶体。对这些流体动力学的连续描述在确定可转移的概念方面具有强大的作用，这些概念使我们能够理解、控制甚至预测性地设计活性流体。到目前为止，研究主要集中在活性物质的单组分流体动力学描述上。但实验现象学清楚地表明，需要多组分描述，允许不同组分中的密度梯度。即使在传统的平衡流体的背景下，建立多组分体系的宏观理论也是具有挑战性的。要确定守恒量动力学中不同通量之间的关系，需要考虑到互易性和熵产生。天生不平衡的活性流体可以从这些限制中解放出来。该项目通过开发一种多管齐下的方法来解决这些挑战，该方法将数据驱动的模型开发与软材料物理的标准技术相结合。一方面，唯象连续介质力学将与系统的非平衡统计力学相结合，以确定在决定复合活动流体中涌现行为的可能机制。另一方面，开发了一种补充数据驱动的方法，该方法利用来自体外细胞骨架悬浮实验的实验数据来指导模型发现。该项目旨在对活性复合流体中的非互易交叉扩散过程及其在紧急行为中的作用提供基本的理论见解。这项工作是理解导致生物系统功能的物理机制的第一步。从实用的角度来看，设计和控制主动应力是设计可快速重构的仿生材料的关键，在机器人、微流体和自适应光学等领域都有应用。在这个项目中开发的理论框架将提高我们设计材料中主动应力的能力。与研究工作相结合，这项计划将通过以下举措在社会和物理教育中产生影响：(I)开发和分发软材料理论高级本科课程的内容-这满足了我们本科生在物理和生物交界处进行跨学科研究的需要。(Ii)沃尔瑟姆社区内外的推广活动--这使我们能够与URM学生合作，并接触到发展中国家的学生，使他们接触到正在进行的软材料和生物物理学方面的工作。(Iii)布兰代斯社区内的多样性、教育和包容性倡议，将成为可与更广泛的受众分享并在其他机构实施的典范。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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, computational, and data-intensive research to develop a theory to describe flow phenomena in biological and other fluids that contain self-powered elements. Flow phenomena in nature and in engineered systems are typically driven by external forces such as gravity and pressure gradients. Continuum mechanics is the mathematical language that allows us to describe such flows and hence predict and design them. In biological systems, such as the cell cytoskeleton, flow phenomena are generated by internal driving, powered by proteins and other biochemical machines that consume chemical energy. Continuum mechanical descriptions have been developed and applied to such internally driven biological fluids in recent years with great success. So far, efforts have centered around single-component descriptions of these systems. In actuality, these are multicomponent systems. Developing multicomponent continuum theories for internally driven fluids requires overcoming several technical challenges. This project uses multi-scale theory coupled with data driven techniques to address these technical challenges and hence develop models for multi-component biological fluids. This project is a step toward understanding physical mechanisms that lead to function in natural and synthetic biological systems. From a practical perspective, designing and controlling internally driven fluids is key to engineering rapidly reconfigurable life-like materials, with applications in fields as diverse as robotics, microfluidics, and adaptive optics. In addition to the science outcomes, the research is integrated with education and outreach initiatives including : (i) content for an advanced undergraduate course on soft materials theory – this fills a need in the education of undergraduate students to undertake interdisciplinary research at the interface of physics and biology and (ii) Diversity, Education and Inclusion initiatives implemented, tested and benchmarked within the Brandeis community that can be exported as models shared widely with the academic community. TECHNICAL SUMMARY This award supports theoretical, computational, and data-intensive research to develop a theoretical framework for building predictive continuum descriptions of composite active fluids. Active fluids are composed of microscopic entities that consume energy and exert forces. This paradigm includes diverse systems from bacterial suspensions to cytoskeletal filaments propelled by molecular motors and synthetic diffusophoretic colloids. Continuum descriptions of the dynamics of these fluids have been powerful in identifying transferable concepts that allow us to understand, control, and even predictively design active fluids. Research to date has focused on single component fluid dynamic descriptions of active materials. But experimental phenomenology clearly shows the need for multi-component descriptions that allow for density gradients in different components. Building macroscopic theories of multi-component systems is challenging even in the context of traditional equilibrating fluids. One needs to invoke considerations of reciprocity and entropy production to determine relationships between different fluxes in the dynamics of conserved quantities. Active fluids, being inherently out of equilibrium are liberated from these constraints. This project addresses these challenges by developing a multi-pronged approach that integrates data driven model development with the standard techniques of soft materials physics. On the one hand, phenomenological continuum mechanics will be combined with systematic nonequilibrium statistical mechanics to identify possible mechanisms at play in determining the emergent behavior in composite active fluids. On the other hand, a complementary data-driven approach is developed, that leverages experimental data from in-vitro cytoskeletal suspension experiments to guide model discovery.This project is aimed to yield fundamental theoretical insights into non-reciprocal cross diffusion processes and their role in emergent behavior in active composite fluids. This effort is a first step in understanding physical mechanisms that lead to function in biological systems. From a practical perspective, designing and controlling active stresses is key to engineering rapidly reconfigurable life-like materials, with applications in fields as diverse as robotics, microfluidics and adaptive optics. The theoretical framework developed in this project will advance our ability to engineer active stress in materials. Integrated with the research effort, this project will produce impact in the community and in physics education through the following initiatives: (i) The development and distribution of content for an advanced undergraduate course on soft materials theory – this fills a need in the education of our undergraduates to undertake interdisciplinary research at the interface of physics and biology. (ii) Outreach initiatives in the Waltham community and beyond – this allows us to work with URM students and reach students in developing countries to expose them to ongoing work in soft materials and biophysics. (iii) Diversity, Education and Inclusion initiatives within the Brandeis community that will serve as a model that can be shared with a wider audience for implementation at other institutions.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.