Hydrodynamics and Actuation of Magnetic Bacteria in Confined Geometries:Single cells to swarms

为了在环境中导航，许多细菌和其他活的微生物通过旋转鞭毛来游泳，鞭毛是一种细长的螺旋状附着物，与细胞体相连。在表面附近，这种旋转的鞭毛产生的尾流产生复杂的力和扭矩，作用于细菌。这就产生了一系列的运动，这些运动取决于细胞相对于表面的方向，以及它的旋转速度和物理几何形状。了解表面的这些相互作用对于研究单个活动细菌以及开发能够在流体环境中控制大型微生物种群的技术非常重要。拟议的研究将利用固有磁性细菌物种M. magneticum AMB-1的独特特征，即趋磁细菌（MTB）群。它们的天然磁性使它们能够被外部操纵，为探测表面附近产生的基于流体的力提供了一种新方法。探索细胞几何形状和方向、磁性含量和鞭毛推力的作用的实验将为结核分枝杆菌游泳行为和相关流体流动模式的模型的发展奠定基础。MTB也是生物动力微驱动和机器人技术的有希望的候选生物。在这种情况下，大规模电池组件允许开发几种基于磁场的设备，如“活液晶”显示器和细菌“传送带”。该项目将以每年夏季讲习班的形式为几名高中教师开展外联活动。通过这些活动，高中生将能够在一个有趣的，熟悉的设备，如Xbox控制器，和物理，环境科学，生物和工程学科（如磁学，细菌栖息地，微生物，阿基米德原理）在教室和实验室的概念之间建立联系。在微观层面上实现基于功能生物学的机器人技术，将在材料制造、纳米技术和医学等不同领域带来范式转变。通过研究具有固有磁性的模式细菌（M. magneticum AMB-1）的基本流体-表面相互作用，所提出的工作将在这个方向上取得重大进展。与微磁和微流体技术一起，它们的磁性细胞器允许单个活细菌和群体被限制和引导，以产生对其动力学至关重要的水动力和磁力以及扭矩的定量测量。这些定量参数将作为在从单个细胞到群体的尺度上发展其流体动力学模型的基础。在低雷诺数环境中集成生物体的驱动和控制将成为在微流体环境中运行的几种新型生物和生物混合机器的基础。通过设计的磁性表面模式对单个细胞的相对位置进行原位管理，为探索成对的细胞-细胞相互作用提供了一种新的手段，这种相互作用导致了新的集体行为的发现，如旋转丝状细菌簇、活液晶磁光调制器和在这些粘性力占主导地位的环境中产生动量的“传送带”轨迹。这些有鞭毛的游泳者的推进所产生的流场将被用来构建微观可调的泵、混合器和流体动力学组装器。该项目将为高中学生和教师开展刺激的推广活动，将物理、环境科学、生物和工程学科在课堂和实验室中联系起来。

In order to navigate their environment, many bacteria and other living micro-organisms swim by rotating a flagellum, a slender helix-shaped attachment connected to the cell body. Near surfaces, the wake produced by this rotating flagellum produces complex forces and torques that act on the bacterium. This gives rise to a range of movements that depend on the orientation of the cell relative to the surface, as well as its rate of rotation and physical geometry. Understanding these interactions at surfaces is important in the study of individual motile bacteria as well as in the development of technologies that can controllably manipulate large micro-organism populations in fluid environments. The proposed investigations will take advantage of the unique features of an inherently magnetic bacterial species, M. magneticum AMB-1, of the magnetotactic bacteria (MTB) group. Their natural magnetism allows them to be externally manipulated, providing a new means of probing the fluid-based forces arising near surfaces. Experiments that explore the role of cell geometry and orientation, magnetic content and flagellar thrust will underlie the development of models for the swimming behavior of MTB and associated fluid flow patterns. MTB are also promising candidate organisms for biologically powered micro-actuation and robotics. In this vein, large scale cell assemblies permit several magnetic field-based devices such as "living liquid crystal" displays and bacterial "conveyor belts" to be developed. The project will undertake outreach activities for several high school teachers in the form of an annual summer workshop. Through these activities, high school students will be able to create a connection between a fun, familiar device, an Xbox controller for example, and concepts in physics, environmental science, biology and engineering disciplines (e.g. magnetism, bacterial habitats, microorganisms, Archimedes principle) in the classroom and laboratory.The realization of functional biology-based robotics at the microscopic level would introduce a paradigm shift in areas as diverse as materials manufacturing, nanotechnology and medicine. The proposed work will make major advances in this direction by investigating fundamental fluid-surface interactions of a model bacterial species (M. magneticum AMB-1) with innate magnetic properties. Together with micro-magnetic and micro-fluidics techniques, their magnetic organelles allow individual living bacteria and swarms be confined and guided to yield quantitative measures of the hydrodynamic and magnetic forces as well as torques that are central to their dynamics. These quantitative parameters will serve as the foundation for developing models of their hydrodynamics on scales ranging from single cells to swarms. Integrating actuation and control of living organisms in low Reynolds number surroundings will serve as the basis to enable several novel biological and bio-hybrid machines that operate in a micro-fluidic environments. The in-situ management of the relative positions of individual cells through designed magnetic surface patterns provides for a novel means to explore pairwise cell-cell interactions that have led to the discovery of novel collective behavior such as rotating filamentary bacterial clusters, living liquid crystal magneto-optical modulators and momentum generating "conveyer-belt" tracks in these environments where viscous forces dominate. The flow fields generated by the propulsion of these flagellated swimmers will be managed to construct microscopically tunable pumps, mixers and hydrodynamic assemblers. The project will undertake stimulating outreach activities for high school students and teachers that link physics, environmental science, biology and engineering disciplines both in the classroom and laboratory.