Berlin 2008 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 27: Micro and Nano Fluidics II: Slipping + soft objects in flow

CPP 27.7: Talk

Thursday, February 28, 2008, 15:30–15:45, C 264

Cross-Streamline Migration of Semiflexible Actin Filaments in Microflow — •Dagmar Steinhauser, Heather M Evans, and Thomas Pfohl — Max-Planck-Institut für Dynamik und Selbstorganisation, Göttingen

Actin filaments, aside from their biological roles in cellular motility and mechanical stability, also provide an ideal system with which to study, more generally, the properties of semi-flexible polymers. Our experiments investigate the behavior of single actin filaments flowing inside symmetric microchannels with a Poiseuille velocity profile. Fluorescence microscopy using stroboscopic laser light illumination is utilized in order to visualize the moving actin filaments. The dimensions (width and depth) of the channels are in the same order of magnitude as the persistence length as well as the contour length of the filaments. A detailed analysis of the center-of-mass probability distribution along a cross-section of the channel is reported. Depletion layers, found at the walls, can be explained by migration due to hydrodynamic interactions with the walls. In addition, the conformation of the actin filaments in flow depends on the shear stress, which increases towards the walls for Poiseuille flow. The resulting spatially-varying diffusivity leads to a striking migration of filaments away from the center and consequently to a minimum in the center-of-mass distribution at the channel center. Analyzing the change in diffusivity from the measured conformations, the Fokker-Planck equation can be solved and the center-of-mass distributions can be described quantitatively for different velocities.