CAREER: Topological dynamics of three-dimensional active fluids

自发的集体运动可以在自然界的不同尺度上看到：鸟群、迁徙的蚂蚁，甚至是我们自己体内的细胞集体运动来闭合伤口。这个研究项目的目标是通过使用简单的三维仿生材料来更好地理解这些集体运动是如何出现的。这些活性物质是由蛋白质组成的，它们可以通过从环境中获取能量来自我推进。将研究两种类型的3D液晶，其中推进由分子马达驱动或由一端生长而另一端收缩的生物丝驱动，概括了活细胞迁移所采用的两种基本机制。该研究项目将解决如何将微观尺度上产生的力与3D中出现的集体特性联系起来，这是机器人或生物工程应用中新型活性材料预测设计的关键一步。在教育方面，该项目将改善从幼儿园到高等教育各个学术水平的多样性和保留代表性不足的少数民族。首席研究员将利用活性物质的有形性质，1)创建一本双语儿童科学书籍，2)每月科学/披萨讲座，3)在当地学校进行互动演示，4)每年为REU学生举办一次活性物质训练营。技术摘要由生物聚合物组成的简单仿生材料已成为研究自发流动的活性流体的一个范例。在宏观尺度上，这些流动常常驱动运动奇点（如拓扑缺陷）的成核。在3D中研究这种拓扑动力学提出了新的概念和实验挑战。此外，需要将这些系统大小的拓扑特征与微观驱动力联系起来，以严格测试活性流体的流体动力学理论。该奖项旨在阐明介观活动应力的大小和对称性如何驱动具有定向顺序的3D活动流体的新兴拓扑动力学，特别关注3D活动向列和3D极性流体。总之，这两个互补的研究项目提供了三维运动拓扑缺陷的非平衡流体动力学的全面描述。他们将为制造具有类似生命特性的先进仿生材料奠定基础。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。

Non-Technical AbstractSpontaneous collective motion can be witnessed at different scales in nature: flocks of birds, migrating ants, and even cells within our own body moving collectively to close a wound. The goal of this research project is to better understand how these collective motions appear by employing simple three-dimensional biomimetic materials. These active materials are composed of proteins that can self-propel by harvesting energy from their environment. Two types of 3D liquid crystals will be investigated where the propulsion is driven by either molecular motors or by biofilaments that grow from one end and shrink from the other, recapitulating two fundamental mechanisms employed by living cells to migrate. This research project will address how to relate the forces generated at the microscopic scale to the emergent collective properties in 3D, a critical step towards the predictive design of novel active materials for robotic or bioengineering applications. On the educational side, this project will improve diversity and retainment of underrepresented minorities at each academic level, from Kindergarten through postsecondary education. The principal investigator will leverage the tangible nature of active matter to i) create a bilingual science children’s book, ii) monthly Science/Pizza talks and iii) interactive demonstrations in local schools, and iv) an annual active matter bootcamp for REU students.Technical abstractSimple biomimetic materials composed of biopolymers have become a paradigm for studying active fluids that spontaneously flow. At the macroscale, these flows often drive the nucleation of motile singularities such as topological defects. Investigating such topological dynamics in 3D presents novel conceptual and experimental challenges. In addition, connecting these system-sized topological features to the microscopic driving forces is required to rigorously test hydrodynamic theories of active fluids. This CAREER award aims to elucidate how the magnitude and the symmetry of mesoscopic active stresses drive the emergent topological dynamics of 3D active fluids with orientational order, with a particular focus on 3D active nematics and 3D polar fluids. Together, these two complementary research projects provide a comprehensive description of the out-of-equilibrium hydrodynamics of motile topological defects in 3D. They will set the foundations for building advanced biomimetic materials endowed with life-like properties.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.