CAREER: Chiral active nematic liquid crystals

非技术摘要：我们生活的生物世界是手性的：我们有左手和右手，甲壳虫的壳是具有旋转方向的纤维层，DNA形成螺旋。活着的世界中的基本运动也是手性的：细菌像船螺旋桨一样摆动它们的鞭毛，细胞中的微管在滑动的同时旋转。一个要问的基本问题是，手性世界中的手性活动如何产生生物世界的大量有趣的结构、动力学和力学。为了回答这个问题，研究小组将开发并系统地研究一种名为手性活性液晶的新模型系统。该系统由生物兼容的液晶和细菌游泳器组成，它们通过螺旋运动自我推进，允许以受控的方式完成广泛的实验。该项目旨在揭示动力学层次的潜在机制，从单个细菌的运动如何受到手性环境的影响，到手性系统如何对手性压力做出反应。该项目的研究方面伴随着广泛的教育和外联活动，包括通过光学实验教育学校教师，帮助他们为K-12学生建立新的STEM演示，通过基于课程的研究经验提高本科生解决问题的技能，通过迷你课程为高级本科生的暑期研究做准备，以及指导来自不同背景和代表性较低群体的研究生。技术摘要：本研究旨在了解手性向列序活性物质中的多能级动力学。活性物质在驱动其运动的单个组成粒子的水平上不断消耗能量，从而远离热力学平衡。其中许多形成了取向有序的向列相液晶，但到目前为止，大多数实验研究都集中在无手性向列相上。在这项提议中，该团队将使用手性活性液晶作为模型系统来研究一种新的对称性，手性活性向列相。该体系是手性液晶和游动细菌的混合物。通过使用标准液晶和生物技术独立控制关键物理参数，如宿主的手性、细菌的活动和限制的边界条件，该团队将在多个层面上调查和了解动力学，从手性游泳者在手性环境中导航的个人运动，到由手性和非手性应力集体注入产生的全球模式和宏观性质。该团队还将进一步研究限制的影响，并了解几何和拓扑约束如何进一步塑造手性活性线虫的动力学。该项目的完成不仅将回答生物学中一系列跨尺度的问题，还将使自主材料的新设计机制成为可能，例如利用活性粒子发挥有用功能的新型生物机械杂化材料。这笔资金支持的教育努力，例如为K-12教师举办的光学讲习班和后续的STEM演示开发，本科课程中的新研究元素，为暑期研究学生提供的迷你课程，以及为来自不同背景和代表性不足的研究生提供的包容性指导，将在多个层面上促进STEM教育和平等。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 abstract: The biological world we are living in is chiral: we have left and right hands, shells of beetles are layers of fibers with a rotating orientation, and DNA forms helices. Basic motions in the living word are also chiral: bacteria swing their flagella like a boat propeller, and the microtubules in cells are rotating while sliding apart. A fundamental question to ask is how chiral activity in a chiral world produces a large range of interesting structures, dynamics, and mechanics of the biological world. To answer this question, the research team will develop and systematically investigate a new model system called chiral living liquid crystals. The system is composed of biocompatible liquid crystals and bacteria swimmers that self-propel through helical motion, allowing a wide range of experiments to be done in a controlled way. The project aims to reveal the underlying mechanisms of a hierarchy of dynamics, ranging from how individual bacteria motion is affected by chiral environments, to how chiral systems respond to chiral stresses. The research aspects of the project are accompanied by an extensive scope of educational and outreach activities, including educating schoolteachers with optics experiments, helping them setting up new STEM demos for K-12 students, improving undergraduate students’ problem-solving skills with course-based research experiences, preparing advanced undergraduates for summer research with mini-courses, and mentoring graduate students from a diverse background and underrepresented groups. Technical abstract: This study aims to understand the multi-level dynamics in active matter with chiral nematic order. Active matter is far from thermodynamic equilibrium by constant energy consumption at the level of individual constituent particles that drives their locomotion. Many of them form orientationally ordered nematic liquid crystals, but most experimental studies so far focus on achiral nematics. In this proposal, the team will investigate a new symmetry, the chiral active nematic, using the chiral living liquid crystal as a model system. The system is a mixture of chiral liquid crystals with swimming bacteria. By independently controlling the key physical parameters such as chirality of the host, the activity of the bacteria, and boundary condition of the confinement using standard liquid crystals and biological techniques, the team will investigate and understand dynamics at multiple levels, from individual motion of a chiral swimmer navigating through chiral environments, to global patterns and macroscopic properties generated by collective injection of chiral and achiral stress. The team will also further study the effect of confinement and understand how geometric and topological constraints further shape the dynamics of the chiral active nematics.Completion of the project will not only answer a cascade of questions in biology across scales, but also enable new design mechanisms of autonomous materials, such as new bio-mechanical hybrids that harness active particles for useful functions. The educational efforts supported by this grant, such as optics workshops for K-12 teachers and the following up STEM demo developments, the new research elements in undergraduate courses, the mini-courses for summer research students, and the inclusive mentoring for graduate students from a diverse and underrepresented background will enhance STEM education and equality at multiple levels.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.