The collaborative research study "Guiding Microscale Swimmers Using Teardrop-Shaped Posts" was featured on the cover of Soft Matter, and was picked up by NYU Research in a piece called, "Playing Traffic Cop with the Tiniest of Motors" (click here for this issue). Silver Professor of Chemistry Michael D. Ward collaborated with colleagues in various science and math departments at NYU, including Xiao Zhong and Takuji Adachi, who are members of the Chemistry Department's Molecular Design Institute. For the complete list of authors, and to download the full article, click here.
Abstract: The swimming direction of biological or artificial microscale swimmers tends to be randomised over long time-scales by thermal fluctuations. Bacteria use various strategies to bias swimming behaviour and achieve directed motion against a flow, maintain alignment with gravity or travel up a chemical gradient. Herein, we explore a 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 could enable artificial swimmers to transport cargo to desired locations.
This research was supported by the National Science Foundation, through its Materials Research Science & Engineering Center and other grants.