title: Swimming by reciprocal motion at low Reynolds number.
abstract: Biological microorganisms swim with flagella and cilia that execute nonreciprocal motions for low Reynolds number (Re) propulsion in viscous fluids. This symmetry requirement is a consequence of Purcell's scallop theorem, which complicates the actuation scheme needed by microswimmers. However, most biomedically important fluids are non-Newtonian where the scallop theorem no longer holds. It should therefore be possible to realize a microswimmer that moves with reciprocal periodic body-shape changes in non-Newtonian fluids. Here we report a symmetric 'micro-scallop', a single-hinge microswimmer that can propel in shear thickening and shear thinning (non-Newtonian) fluids by reciprocal motion at low Re. Excellent agreement between our measurements and both numerical and analytical theoretical predictions indicates that the net propulsion is caused by modulation of the fluid viscosity upon varying the shear rate. This reciprocal swimming mechanism opens new possibilities in designing biomedical microdevices that can propel by a simple actuation scheme in non-Newtonian biological fluids.
authors.affiliation: 1] Max Planck Institute for Intelligent Systems, Heisenbergstrasse 3, Stuttgart 70569, Germany [2] Institute of Bioengineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne CH-1015, Switzerland.
authors.forename: Tian
authors.initials: T
authors.lastname: Qiu
authors.affiliation: Max Planck Institute for Intelligent Systems, Heisenbergstrasse 3, Stuttgart 70569, Germany.
authors.forename: Tung-Chun
authors.initials: TC
authors.lastname: Lee
authors.affiliation: Max Planck Institute for Intelligent Systems, Heisenbergstrasse 3, Stuttgart 70569, Germany.
authors.forename: Andrew G
authors.initials: AG
authors.lastname: Mark
authors.affiliation: Faculty of Chemical Engineering, Technion-Israel Institute of Technology, Haifa 32000, Israel.
authors.forename: Konstantin I
authors.initials: KI
authors.lastname: Morozov
authors.affiliation: Institute of Applied Mathematics (LS III), TU Dortmund, Vogelpothsweg 87, Dortmund 44227, Germany.
authors.forename: Raphael
authors.initials: R
authors.lastname: Münster
authors.affiliation: Institute of Applied Mathematics (LS III), TU Dortmund, Vogelpothsweg 87, Dortmund 44227, Germany.
authors.forename: Otto
authors.initials: O
authors.lastname: Mierka
authors.affiliation: Institute of Applied Mathematics (LS III), TU Dortmund, Vogelpothsweg 87, Dortmund 44227, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Turek
authors.affiliation: 1] Faculty of Chemical Engineering, Technion-Israel Institute of Technology, Haifa 32000, Israel [2] Technion Autonomous Systems Program (TASP), Haifa 32000, Israel.
authors.forename: Alexander M
authors.initials: AM
authors.lastname: Leshansky
authors.affiliation: 1] Max Planck Institute for Intelligent Systems, Heisenbergstrasse 3, Stuttgart 70569, Germany [2] Institut für Physikalische Chemie, Universität Stuttgart, Pfaffenwaldring 55, Stuttgart 70569, Germany.
authors.forename: Peer
authors.initials: P
authors.lastname: Fischer
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D002465:Cell Movement; D008954:Models, Biological; D049897:Pectinidae / Q000737:chemistry* / Q000502:physiology*; D013550:Swimming; D014783:Viscosity