Symmetry breaking propulsion of magnetic microspheres in nonlinearly viscoelastic fluids

• Published in: Nature communications 2021-02, Vol.12 (1), p.1116-1116, Article 1116
• Main Authors: Rogowski, Louis William, Ali, Jamel, Zhang, Xiao, Wilking, James N., Fu, Henry C., Kim, Min Jun
• Format: Article
• Language: English
• Subjects: 147/135; 639/166/988; 639/766/189; Acrylic Resins - chemistry; Asymmetry; Broken symmetry; Drug delivery; Drug development; Elasticity; Fertility; Fluid dynamics; Fluid flow; Humanities and Social Sciences; Humans; Locomotion; Magnetic Phenomena; Microorganisms; Microparticles; Microspheres; Microsurgery; Mucins - chemistry; Mucins - ultrastructure; multidisciplinary; Newtonian fluids; Non Newtonian fluids; Nonlinear Dynamics; Propulsion; Reynolds number; Rheology; Rotating spheres; Rotation; Science; Science (multidisciplinary); Symmetry; Viscoelastic fluids; Viscoelasticity; Viscosity; Viscous drag
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-021-21322-0

Microscale 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. A self-propelling agent at small Reynolds numbers usually requires a fore-aft asymmetry in order to circumvent the scallop theorem. Here Rogowski et al. show that this need not be true for motion in non-linear viscoelastic fluids, where an initial symmetry may be broken spontaneously.