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Nat Commun. 2014 Sep 19;5:4829. doi: 10.1038/ncomms5829.

Gravitaxis of asymmetric self-propelled colloidal particles.

Author information

Institut für Theoretische Physik II: Weiche Materie, Heinrich-Heine-Universität Düsseldorf, D-40225 Düsseldorf, Germany.
2. Physikalisches Institut, Universität Stuttgart, D-70569 Stuttgart, Germany.
SUPA, School of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 3JZ, UK.
Department of Mathematics, University of Hawaii at Manoa, Honolulu, Hawaii 96822, USA.
1] 2. Physikalisches Institut, Universität Stuttgart, D-70569 Stuttgart, Germany [2] Max-Planck-Institut für Intelligente Systeme, D-70569 Stuttgart, Germany.


Many motile microorganisms adjust their swimming motion relative to the gravitational field and thus counteract sedimentation to the ground. This gravitactic behaviour is often the result of an inhomogeneous mass distribution, which aligns the microorganism similar to a buoy. However, it has been suggested that gravitaxis can also result from a geometric fore-rear asymmetry, typical for many self-propelling organisms. Despite several attempts, no conclusive evidence for such an asymmetry-induced gravitactic motion exists. Here, we study the motion of asymmetric self-propelled colloidal particles which have a homogeneous mass density and a well-defined shape. In experiments and by theoretical modelling, we demonstrate that a shape anisotropy alone is sufficient to induce gravitactic motion with either preferential upward or downward swimming. In addition, also trochoid-like trajectories transversal to the direction of gravity are observed.


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