title: Active multi-point microrheology of cytoskeletal networks.
abstract: Active microrheology is a valuable tool to determine viscoelastic properties of polymer networks. Observing the response of the beads to the excitation of a reference leads to dynamic and morphological information of the material. In this work we present an expansion of the well-known active two-point microrheology. By measuring the response of multiple particles in a viscoelastic medium in response to the excitation of a reference particle, we are able to determine the force propagation in the polymer network. For this purpose a lock-in technique is established that allows for extraction of the periodical motion of embedded beads. To exert a sinusoidal motion onto the reference bead an optical tweezers setup in combination with a microscope is used to investigate the motion of the response beads. From the lock-in data the so called transfer tensor can be calculated, which is a direct measure for the ability of the network to transmit mechanical forces. We also take a closer look at the influence of noise on lock-in measurements and state some simple rules for improving the signal-to-noise ratio.
authors.affiliation: Institute of Experimental Physics, Ulm University, Albert-Einstein-Allee 11, 89081 Ulm, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Paust
authors.affiliation: Institute of Experimental Physics, Ulm University, Albert-Einstein-Allee 11, 89081 Ulm, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Neckernuss
authors.affiliation: Institute of Experimental Physics, Ulm University, Albert-Einstein-Allee 11, 89081 Ulm, Germany.
authors.forename: Lina Katinka
authors.initials: LK
authors.lastname: Mertens
authors.affiliation: Institute of Experimental Physics, Ulm University, Albert-Einstein-Allee 11, 89081 Ulm, Germany.
authors.forename: Ines
authors.initials: I
authors.lastname: Martin
authors.affiliation: Department of Internal Medicine I, Ulm University, Albert-Einstein-Allee 23, 89081 Ulm, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Beil
authors.affiliation: Central Electron Microscopy Facility, Ulm University, Albert-Einstein-Allee 11, 89081 Ulm, Germany.
authors.forename: Paul
authors.initials: P
authors.lastname: Walther
authors.affiliation: Institute of Applied Physics and Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), Wolfgang-Gaede-Strasse 1, 76131 Karlsruhe, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Schimmel
authors.affiliation: Institute of Experimental Physics, Ulm University, Albert-Einstein-Allee 11, 89081 Ulm, Germany.
authors.forename: Othmar
authors.initials: O
authors.lastname: Marti
keywords: cytoskeleton; intermediate filaments; lock-in technique; microrheology; optical tweezers