Microscopic artificial swimmers

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Microscopic artificial swimmers

Rémi Dreyfus, Jean Baudry, Marcus L. Roper, Marc Fermigier, Howard A. Stone & Jérôme Bibette Nature 437, 862-865 (6 October 2005). Keywords:

Summary

The authors constructed a micro-scale swimming robot based on the behavior of swimming micro-ogranisms. Bacteria tend to use helical tail-like structures known as flagella that rotate in order to move through liquids, whereas eukaryotic cells tend to use flagella that undergo an oscillatory beating motion. The authors made their device from micron-size magnetic colloidal particles that were bound together using 100nm-long segments of DNA. This artificial flagella was used to propel a red-blood cell. To power this artificial swimmer, the researchers applied two magnetic fields: a steady magnetic field to lengthen the flegella and an oscillatory transverse field to cause the beating motion. A diagram is shown below:

Figure1.jpg

The crucial aspect of this technique was ensuring that the motion was cyclic, but no time-reversible. A symmetric motion would cause the device to simply oscillate back and forth due to the dominance of viscosity at such small length scales. When observed under a microscope, the authors saw the device move uni-directionally as planned, but with the tail first. They suspect this is due to whether the disturbances in the flagella propagate from the head to the free end (as in most natural cases) or in the opposite direction (which occurred in this case).

Soft Matter aspects

Although we have typically studied stationary, non-living systems in this course, novel behavior in complex fluids could be created by applying magnetic fields to specially constructed systems. One possibility would be to have magnetic beads dispersed throughout a polymer network.