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

为了在环境中导航，许多细菌和其他微生物通过旋转鞭毛来游动，鞭毛是一种连接到细胞体的细长螺旋形附件。在靠近表面的地方，由这种旋转的鞭毛产生的尾流产生了作用于细菌的复杂的力和扭矩。这产生了一系列的运动，这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。了解这些相互作用的表面是很重要的研究个别能动的细菌，以及在技术的发展，可以可控地操纵大型微生物种群在流体环境中。拟议的调查将利用一种固有的磁性细菌物种，M。magneticum AMB-1，属于趋磁细菌（MTB）组。它们的天然磁性使它们能够被外部操纵，提供了一种探测表面附近产生的基于流体的力的新方法。探索细胞几何形状和方向，磁含量和鞭毛推力的作用的实验将成为MTB游泳行为和相关流体流动模式模型发展的基础。 MTB也是生物动力微致动和机器人的有前途的候选生物。在这种情况下，大规模的细胞组装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，高中生将能够在有趣，熟悉的设备（例如Xbox控制器）与物理，环境科学，生物和工程学科的概念之间建立联系（例如磁性、细菌栖息地、微生物、阿基米德原理）在课堂和实验室中的应用。功能生物学的实现-在微观层面上的基于机器人的技术将在材料制造、纳米技术和医学等不同领域带来范式转变。拟议的工作将通过研究模型细菌物种（M. magneticum AMB-1）具有固有的磁性。与微磁和微流体技术一起，它们的磁性细胞器允许个体活细菌和群体被限制和引导，以产生对它们的动力学至关重要的流体动力学和磁力以及扭矩的定量测量。这些定量参数将作为基础，发展其规模从单细胞到成群的流体动力学模型。在低雷诺数环境中集成活生物体的致动和控制将作为使几种新型生物和生物混合机器能够在微流体环境中操作的基础。通过设计的磁性表面图案原位管理单个细胞的相对位置提供了探索成对细胞-细胞相互作用的新手段，所述成对细胞-细胞相互作用已经导致发现新的集体行为，例如在粘性力占主导地位的这些环境中旋转的寄生细菌簇、活的液晶磁光调制器和产生动量的“腰带”轨道。由这些鞭毛虫游泳者的推进产生的流场将被管理，以构建微观可调泵，混合器和流体动力组装器。该项目将为高中学生和教师开展激励性的外联活动，在教室和实验室将物理学、环境科学、生物学和工程学科联系起来。

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.