Collective Hydrodynamics of Swimming Bacteria: A Living Fluid

游动细菌的集体流体动力学：一种活体液体

• 批准号: 0730579
• 负责人: Donald Koch
• 金额: $ 24万
• 依托单位: Cornell University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-08-01 至 2011-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0730579&HistoricalAwards=false
• 关键词: Collective; Hydrodynamics; Swimming; Bacteria; Living

National Science Foundation - Division of Chemical &Transport Systems ? Particulate & Multiphase Processes Program (1415)Proposal Number: 0730579 Principal Investigators: Koch, Donald Affiliation: Cornell University Proposal Title: Collective Hydrodynamics of Swimming Bacteria: A Living Fluid Suspensions of swimming micro-organisms such as the bacterium E. coli constitute a unique type of non-Newtonian fluid that can exhibit a negative-viscosity instability, enhanced mixing by secondary flows resulting from a negative first normal stress difference, break up due to concentration-gradient-induced stresses, and migration phenomena that facilitate novel separation methods. While the physical mechanism by which a single bacterium swims, pushing itself through the fluid with a flagella bundle that turns like a screw, is well understood, the equations of motion governing a suspension of bacteria have not been derived previously. In the proposed study, we will derive these equations starting from a fundamental description of bacteria-fluid interactions, solve the equations for several representative flows, and observe these flows experimentally. Intellectual Merit: A bacteria cell exerts a drag force on the fluid while its flagella exert an equal and opposite force, leading to a force dipole which on average creates a pressure in the direction of mean cell orientation. This situation may be contrasted with a stretched polymer which exerts a tension in the direction of its orientation. In a weak shear flow, a bacterium orients with the extensional axis of the flow and reinforces the extensional motion. Thus, above a critical cell concentration, the suspension has a negative viscosity and a quiescent suspension will be unstable to the formation of spontaneous fluid motion. We believe that this instability explains previous experimental observations of vortical motions in systems of swimming bacteria. We plan to use particle tracking of both bacteria and passive colloidal particles to probe this instability. The alignment of bacteria along streamlines in a strong shear flow will create a negative first normal stress difference (or streamline pressure) in contrast to the positive first normal stress difference (or streamline tension) for polymer solutions. Both non-Newtonian fluids can enhance mixing due to secondary flows caused by streamline curvature in a curved microfluidic channel, but, as we shall confirm, the vortices will be centered on the inside of a channel bend for bacteria and on the outside for a polymer solution. Broader Impacts: The applications of our studies include a novel method to separate bacteria based on their chemotactic behavior, a new ?active? fluid for micro-fluidic mixing whose activity can be modulated by biochemical inputs, and insights into the manner in which cells disperse or collect themselves into clusters as they respond to biochemical cues. People have a natural curiosity about the collective behavior of living things. Our studies which link such collective behaviors to the principles of momentum and mass transport and kinetic theory descriptions of suspensions will provide a means to engage and inspire students to think about connections between biology and engineering. We will exploit these opportunities in our undergraduate and graduate curricula and in the Nanobiotechnology Center's outreach program for high school teachers.

国家科学基金会 - 化学与运输系统部门？颗粒与多相过程计划 (1415) 提案编号：0730579 主要研究员：Koch, Donald 隶属关系：康奈尔大学 提案标题：游动细菌的集体流体动力学：活体流体 游动微生物（例如大肠杆菌）的悬浮液构成了独特的一种非牛顿流体，可以表现出负粘度不稳定性，通过二次流增强混合负第一法向应力差、由于浓度梯度引起的应力而破裂以及促进新颖分离方法的迁移现象。虽然单个细菌游泳的物理机制（通过像螺丝一样旋转的鞭毛束推动自身穿过液体）已被很好地理解，但控制细菌悬浮液的运动方程之前尚未导出。在拟议的研究中，我们将从细菌-流体相互作用的基本描述开始推导这些方程，求解几个代表性流动的方程，并通过实验观察这些流动。智力优点：细菌细胞对流体施加拖曳力，而其鞭毛则施加相等且相反的力，从而产生力偶极子，该力偶极子平均在平均细胞方向上产生压力。这种情况可以与在其取向方向上施加张力的拉伸聚合物形成对比。在弱剪切流中，细菌沿着流的延伸轴定向并增强延伸运动。因此，在临界细胞浓度之上，悬浮液具有负粘度并且静止悬浮液对于自发流体运动的形成将不稳定。我们相信这种不稳定性解释了之前对游动细菌系统中涡旋运动的实验观察。我们计划使用细菌和被动胶体粒子的粒子追踪来探测这种不稳定性。细菌在强剪切流中沿着流线排列将产生负的第一法向应力差（或流线压力），这与聚合物溶液的正的第一法向应力差（或流线张力）相反。由于弯曲微流体通道中的流线曲率引起的二次流动，两种非牛顿流体都可以增强混合，但是，正如我们将确认的那样，对于细菌来说，涡流将集中在通道弯曲的内部，而对于聚合物来说，涡流将集中在通道弯曲的外部。解决方案。更广泛的影响：我们研究的应用包括一种根据细菌的趋化行为（一种新的“活性”）分离细菌的新方法。用于微流体混合的流体，其活动可以通过生化输入进行调节，并深入了解细胞在响应生化信号时分散或聚集成簇的方式。人们对生物的集体行为有着天生的好奇心。我们的研究将这种集体行为与动量和质量传递原理以及悬浮的动力学理论描述联系起来，将提供一种方法来吸引和启发学生思考生物学和工程学之间的联系。我们将在本科生和研究生课程以及纳米生物技术中心针对高中教师的外展计划中利用这些机会。