Rogowski, Louis WilliamAli, JamelZhang, XiaoWilking, James N.Fu, Henry C.Kim, Min Jun2022-05-092022-05-092021-02Rogowski, L.W., Ali, J., Zhang, X. et al. Symmetry breaking propulsion of magnetic microspheres in nonlinearly viscoelastic fluids. Nat Commun 12, 1116 (2021). https://doi.org/10.1038/s41467-021-21322-02041-1723https://scholarworks.montana.edu/handle/1/16768Microscale propulsion impacts a diverse array of fields ranging from biology and ecology to health applications, such as infection, fertility, drug delivery, and microsurgery. However, propulsion in such viscous drag-dominated fluid environments is highly constrained, with time-reversal and geometric symmetries ruling out entire classes of propulsion. Here, we report the spontaneous symmetry-breaking propulsion of rotating spherical microparticles within non-Newtonian fluids. While symmetry analysis suggests that propulsion is not possible along the fore-aft directions, we demonstrate the existence of two equal and opposite propulsion states along the sphere’s rotation axis. We propose and experimentally corroborate a propulsion mechanism for these spherical microparticles, the simplest microswimmers to date, arising from nonlinear viscoelastic effects in rotating flows similar to the rod-climbing effect. Similar possibilities of spontaneous symmetry-breaking could be used to circumvent other restrictions on propulsion, revising notions of microrobotic design and control, drug delivery, microscale pumping, and locomotion of microorganisms.en-UShttp://creativecommons.org/licenses/by/4.0/Article