Microscopic artificial swimmers

Abstract

Microorganisms such as bacteria and many eukaryotic cells propel themselves with hair-like structures known as flagella, which can exhibit a variety of structures and movement patterns1. For example, bacterial flagella are helically shaped2 and driven at their bases by a reversible rotary engine3, which rotates the attached flagellum to give a motion similar to that of a corkscrew. In contrast, eukaryotic cells use flagella that resemble elastic rods4 and exhibit a beating motion: internally generated stresses give rise to a series of bends that propagate towards the tip5,6,7. In contrast to this variety of swimming strategies encountered in nature, a controlled swimming motion of artificial micrometre-sized structures has not yet been realized. Here we show that a linear chain of colloidal magnetic particles linked by DNA and attached to a red blood cell can act as a flexible artificial flagellum. The filament aligns with an external uniform magnetic field and is readily actuated by oscillating a transverse field. We find that the actuation induces a beating pattern that propels the structure, and that the external fields can be adjusted to control the velocity and the direction of motion.

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Figure 1: Schematic representation of a flexible magnetic filament.
Figure 2: Beating pattern of the motion of a magnetic flexible filament attached to a red blood cell.
Figure 3: Sequence of deformation of the end of a free filament.
Figure 4: Scaled velocity as a function of Sp.

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Acknowledgements

We thank the Imphy Company for providing us with free Mumetal. We also thank A. Ajdari, J. Prost, J.-B. Salmon and D. Weitz for discussions, and C. Gosse, A. Koenig, F. Montel and C. Goubault for help in material preparation.

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Correspondence to Rémi Dreyfus.

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Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests.

Supplementary information

Supplementary Methods

This document describes the physics of the motion of the magnetic filament attached to a red blood cell. (DOC 84 kb)

Supplementary Video 1

This movie shows the dynamics of a filament tethered to a red blood cell on a single period of magnetic field (f=10Hz, Bx=9mT, By=14.5mT). The frame rate is 440 frames/s. One can clearly see how the filament bends to follow the direction of the magnetic field. (MOV 311 kb)

Supplementary Video 2

This movie shows the dynamics of the same filament on 25 periods of magnetic field (f=10Hz, Bx=9mT, B>y=14.5mT). The frame rate is 40 frames/s. The filament is moving towards the direction of the free extremity at a velocity corresponding to the red cell size per second. (MOV 770 kb)

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Dreyfus, R., Baudry, J., Roper, M. et al. Microscopic artificial swimmers. Nature 437, 862–865 (2005). https://doi.org/10.1038/nature04090

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