International Research Fellowship Program: Driving Fluids with Rotating and Beating Semiflexible Polymers

国际研究奖学金计划使美国科学家和工程师能够在国外进行三到二十四个月的研究。该计划的奖项提供了联合研究的机会，并利用国外独特或互补的设施、专业知识和实验条件。该奖项将支持阿尔弗雷多·亚历山大-卡茨博士与德国慕尼黑大学的罗兰·内茨博士合作的为期24个月的研究奖学金。这个项目将得到数学和物理科学局多学科活动办公室的支持。大自然已经开发出各种方法来在粘性介质中移动微生物。在这种情况下产生流体动力阻力的典型策略包括：(A)旋转聚合物螺旋(鞭毛)或(B)击打通常形成相当密集接枝区域(纤毛)的半柔性聚合物。在这个项目中，PI将对移动聚合物(以及与支撑细胞表面)内的弹性性质和流体动力相互作用之间的复杂耦合进行理论研究，这将导致在大驱动力下的形状变形。虽然基本的流体动力学方程是线性的，但与弹性自由度的耦合导致了非线性，这些非线性对于定向阻力的产生起着重要的和迄今被忽视的作用。在项目的第一阶段，PI将分析和了解旋转的鞭毛和跳动的纤毛这两种生物相关的情况，并具体计算作为施加扭矩的函数的聚合物的形状变形。该项目的第二部分将以仿生方式开发策略，使用节拍的合成纤毛或磁力驱动旋转半柔性聚合物(单丝或聚合物刷子)在微流控芯片中泵送或混合流体。

The International Research Fellowship Program enables U.S. scientists and engineers to conduct three to twenty-four months of research abroad. The program's awards provide opportunities for joint research, and the use of unique or complementary facilities, expertise and experimental conditions abroad.This award will support a twenty-four month research fellowship by Dr. Alfredo Alexander-Katz to work with Dr. Roland Netz at the University of Munich, in Germany. This project will be supported by the Math and Physical Sciences Directorate's Office of Multidisciplinary Activities.Nature has developed a variety of methods to move microorganisms within viscous media. Typical strategies for producing hydrodynamic drag in this regime involve either (a) rotating polymeric spirals (flagella) or (b) beating semiflexible polymers that normally form quite densely grafted areas (cilia). Within this project, the PI will perform a theoretical study of the intricate coupling between the elastic properties and the hydrodynamic interactions within the moving polymer (and with the supporting cell surface), which leads to shape deformations at large driving forces. Although the underlying hydrodynamic equations are linear, the coupling to elastic degrees of freedom leads to non-linearities that play an important and hitherto neglected role for the production of directed drag. In the first stage of the project, the PI will analyze and understand the two biologically relevant situations of a rotating flagella and beating cilia, and in specific calculate the resulting shape deformations of the polymers as a function of applied torque. The second part of the project will be destined to develop in a biomimetic fashion strategies for pumping or mixing fluids within micro-fluidic chips using beating synthetic ciliae, or magnetically driven rotating semiflexible polymers (either single filaments, or polymer brushes).