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

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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).