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Bacteria use various strategies to bias swimming behavior and achieve directed motion against a flow, maintain alignment with gravity or travel up a chemical gradient. NYU MRSEC investigators devised purely geometric means of biasing the motion of artificial nanorod swimmers. These artificial swimmers are bimetallic rods, powered by a chemical fuel, which swim on a substrate printed with teardrop-shaped posts. The artificial swimmers are hydrodynamically attracted to the posts, swimming alongside the post perimeter for long times before leaving. The rods experience a higher rate of departure from the higher curvature end of the teardrop shape, thereby introducing a bias into their motion. This bias increases with swimming speed and can be translated into a macroscopic directional motion over long times by using arrays of teardrop-shaped posts aligned along a single direction. This method provides a protocol for concentrating swimmers, sorting swimmers according to different speeds, and it could enable artificial swimmers to transport cargo to desired locations.



M.S.D. Wykes,  X. Zhong,  J. Tong, T. Adachi,  Y. Liu, L. Ristroph,  M.D. Ward, M.J. Shelley  and  J. Zhang

Soft Matter 2017,13, 4669-4800.








Highlight: Guiding biased motion of microscale swimmers using teardrop-shaped posts

Figure. Sketch of artificial Au-Pt nanorod swimmers interacting with teardrop-shaped posts. Rods swim with the Pt-end leading when placed in a solution of hydrogen peroxide fuell. After encountering a post, swimming rods tend to travel in proximity to the perimeter, then preferentially depart from the tip where the curvature is highest.