Dresden 2011 – scientific programme

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BP: Fachverband Biologische Physik

BP 7: Posters: Statistical Physics in Biological Systems

BP 7.6: Poster

Monday, March 14, 2011, 17:15–20:00, P3

Upstream swimming of a model micro-swimmer in a microchannel — •Andreas Zöttl and Holger Stark — TU Berlin

Many microorganisms in the human body swim in confined environments like sperm cells in the Fallopian tube or E. coli bacteria in the colon. Also pathogens use narrow channels like the urethra to swim to their destinations. Micro-swimmers exhibit hydrodynamic interactions with bounding surfaces that change their swimming speeds and orientations. In particular, pushers and pullers show different behavior. Pushers such as sperm cells or bacteria propel themselves with flagella attached at the back of the cell body and get attracted by a wall. Pullers like the algae Chlamydomonas typically have a propelling apparatus in the front and are reflected by a wall.

As a simple model microorganism we use the so-called squirmer. It has a spherical shape with a prescribed axisymmetric tangential surface velocity, different for pushers and pullers. We model the hydrodynamics of squirmers including thermal noise using multi-particle collision dynamics. This method introduces ballistic and collision steps of effective particles in order to solve the Navier-Stokes equations. We systematically investigate the swimming behavior of both pushers and pullers in a cylindrical microchannel with an imposed Poiseuille flow. When the strength of the flow is sufficiently small, pushers swim upstream at the wall. Pullers can swim upstream between the walls when the channel width is small enough. Increasing the imposed flow strongly, pushers and pullers now swim downstream and tumble due to flow vorticity similar to passive particles.