Soft Matter https://doi.org/cpz9 (2018)
A fan-filled stadium is perhaps the most obvious place to find a metachronal movement — known to many as the Mexican wave (pictured) after it was popularized at the 1986 FIFA World Cup. Millipedes support them too, as do the cilia found on animal cells, which were the inspiration that led Srinivas Hanasoge and colleagues to come up with a biomimetic magnetic system capable of generating metachronal waves.
Hanasoge et al. attached thin magnetic filaments to a substrate and submerged it in a viscous fluid, using a rotating magnetic field to deform the cilia to the point at which their elasticity prompted a recovery. By engineering a length differential between filaments, they were able to induce a phase difference in the movements of neighbouring cilia. The ensuing metachronal motion emerged solely from the filaments’ magnetic and elastic properties, setting it apart from the hydrodynamically mediated waves observed in natural cilia. And as the latter can triple cellular propulsion speeds, there’s hope for future devices based on their magnetic counterparts.
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Klopper, A. Metachronal magnets. Nature Phys 14, 528 (2018). https://doi.org/10.1038/s41567-018-0174-0