Collaborative Research:Fundamental Principles of Swimming in Viscoelastic Media

细胞运动在许多生物过程中起着核心作用，如受精、细菌感染以及体内粘液和液体的运输。运动细胞遇到的复杂液体充满了聚合物。当被游动细胞变形时，聚合物拉伸，除了流体的粘性阻力外，还产生弹性阻力。生物材料的微观结构往往也是各向异性的。本研究的目的是利用理论和实验模型来建立粘弹性介质（如粘液和生物膜）中游泳的基本原理。为了研究受控环境下的游泳力学，pi将开发一系列桌面宏观尺度实验。这些实验将确定游泳速度如何取决于游泳者规定泳姿的粘弹性特性，粘弹性力如何改变跳动丝的形状，以及粘弹性在跳动纤毛的流体动力学同步中的作用。pi将为这些现象发展新的理论，并研究非牛顿效应如何改变附近游泳者与边界之间的水动力相互作用，以及密集游泳者群体集体运动的本质。微生物在牛顿流体（如水）中游动的基本流体动力学理论已基本建立。然而，该领域仍然非常活跃，因为许多问题，如细胞之间的流体动力学相互作用，同步纤毛跳动和鞭毛的驱动只是部分理解。微生物的自然环境主要是非牛顿的，这个理论的每一个基本要素都必须重新考虑。我们的工作还将建立所需的设计原则，以建立能够通过粘弹性和粘性流体的人工微游泳者。pi将与布朗MRSEC外展计划中的K-12教师培训计划合作，开发细胞运动的新演示。法律与公正党将继续发扬其招募代表性不足群体的成功历史。最后，这项工作的基本原理有可能影响人类生育、细菌感染和囊性纤维化等疾病的治疗以及牲畜的人工授精等应用。

Powers0854108Cell movements play a central role in a host of biological processes, such as fertilization, bacterial infection, and transport of mucus and fluid in the body. The complex fluids that motile cells encounter are laden with polymers. When deformed by a swimming cell, the polymers stretch, leading to an elastic resistance in addition to the viscous resistance of the fluid. The microstructure of biological materials is often anisotropic as well. The goal of this research is to use theory and experimental models to establish the fundamental principles of swimming in viscoelastic media such as mucus and biofilms. To study swimming mechanics in a controlled environment, the PIs will develop a series of table-top macroscopic scale experiments. These experiments will determine how swimming speed depends on viscoelastic properties for a swimmer with a prescribed stroke, how viscoelastic forces can alter the shape of a beating filament, and the role of viscoelasticity in the hydrodynamic synchronization of beating cilia. The PIs will develop new theories for these phenomena, and also study how non-Newtonian effects change the hydrodynamic interactions between nearby swimmers and boundaries, and the nature of the collective motion of dense populations of swimmers. The basic hydrodynamic theory for microorganisms swimming in a Newtonian liquid such as water has been largely established. Nevertheless, the field continues to be very active since many issues such as hydrodynamic interactions between cells, synchronized ciliary beating, and the actuation of flagella are only partially understood. The natural environments of microorganisms are predominantly non-Newtonian, and every basic element of the theory must be considered anew. Our work will also establish the design principles required to build artificial microswimmers capable of negotiating viscoelastic as well as viscous fluids. The PIs will work with the K-12 Teacher Training program within the Brown MRSEC outreach program to develop new demonstrations of cell motility. The PIs will continue to build on their successful history of recruiting under-represented groups. Finally, the fundamental principles of this work have the potential to impact applications such human fertility, the treatment of bacterial infections and diseases such as cystic fibrosis, and the artificial insemination of livestock.