Polymer adsorption in shear

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Nature has developed a multitude of methods to move cells and animals within a viscous medium, or, which is in many cases an analogous problem, to move fluids within an animal. Of particular interest to the Schwerpunktprogramm is the Nano- to Micrometer scale, where inertia forces are typically small compared to viscous forces, defining the so-called small-Reynolds-number regime. Typical strategies of producing hydrodynamic drag involve either a) rotating polymeric spirals (so called flagellae) or b) beating straight and semiflexible polymers that normally form quite densely grafted areas (so-called ciliae). We will theoretically study the intricate coupling between the hydrodynamic interactions within the moving polymer (and with the supporting cell surface) and the elasticity of the polymers, which leads to shape deformations at large driving forces. Although the underlying hydrodynamics equations are linear in the low-Reynolds-number regime, 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 part, we 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. These calculations will be done using a Brownian-Dynamics-code including full hydrodynamic interactions. In the second part of the project we will in a biomimetic fashion develop strategies for pumping fluids within micro-fluidic chips using beating synthetic ciliae. These can for example be formed by thiol-bound DNA-oligomers, which are periodically moved using an electric potential applied from the grafting surface.