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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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.
Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests.
This document describes the physics of the motion of the magnetic filament attached to a red blood cell. (DOC 84 kb)
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)
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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