title: Shape control and compartmentalization in active colloidal cells.
abstract: Small autonomous machines like biological cells or soft robots can convert energy input into control of function and form. It is desired that this behavior emerges spontaneously and can be easily switched over time. For this purpose we introduce an active matter system that is loosely inspired by biology and which we term an active colloidal cell. The active colloidal cell consists of a boundary and a fluid interior, both of which are built from identical rotating spinners whose activity creates convective flows. Similarly to biological cell motility, which is driven by cytoskeletal components spread throughout the entire volume of the cell, active colloidal cells are characterized by highly distributed energy conversion. We demonstrate that we can control the shape of the active colloidal cell and drive compartmentalization by varying the details of the boundary (hard vs. flexible) and the character of the spinners (passive vs. active). We report buckling of the boundary controlled by the pattern of boundary activity, as well as formation of core-shell and inverted Janus phase-separated configurations within the active cell interior. As the cell size is increased, the inverted Janus configuration spontaneously breaks its mirror symmetry. The result is a bubble-crescent configuration, which alternates between two degenerate states over time and exhibits collective migration of the fluid along the boundary. Our results are obtained using microscopic, non-momentum-conserving Langevin dynamics simulations and verified via a phase-field continuum model coupled to a Navier-Stokes equation.
authors.affiliation: Department of Chemical Engineering, University of Michigan, Ann Arbor, MI 48109; Biointerfaces Institute, University of Michigan, Ann Arbor, MI 48109;
authors.forename: Matthew
authors.initials: M
authors.lastname: Spellings
authors.affiliation: Department of Chemical Engineering, University of Michigan, Ann Arbor, MI 48109; Biointerfaces Institute, University of Michigan, Ann Arbor, MI 48109;
authors.forename: Michael
authors.initials: M
authors.lastname: Engel
authors.affiliation: Department of Chemical Engineering, University of Michigan, Ann Arbor, MI 48109; Biointerfaces Institute, University of Michigan, Ann Arbor, MI 48109;
authors.forename: Daphne
authors.initials: D
authors.lastname: Klotsa
authors.affiliation: Department of Chemical Engineering, Pennsylvania State University, University Park, PA 16802;
authors.forename: Syeda
authors.initials: S
authors.lastname: Sabrina
authors.affiliation: Department of Chemical Engineering, Pennsylvania State University, University Park, PA 16802; Department of NanoEngineering, University of California, San Diego, La Jolla, CA 92093;
authors.forename: Aaron M
authors.initials: AM
authors.lastname: Drews
authors.affiliation: Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109;
authors.forename: Nguyen H P
authors.initials: NH
authors.lastname: Nguyen
authors.affiliation: Department of Chemical Engineering, Pennsylvania State University, University Park, PA 16802; kjmbishop@engr.psu.edu sglotzer@umich.edu.
authors.forename: Kyle J M
authors.initials: KJ
authors.lastname: Bishop
authors.affiliation: Department of Chemical Engineering, University of Michigan, Ann Arbor, MI 48109; Biointerfaces Institute, University of Michigan, Ann Arbor, MI 48109; Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109 kjmbishop@engr.psu.edu sglotzer@umich.edu.
authors.forename: Sharon C
authors.initials: SC
authors.lastname: Glotzer
keywords: active matter; colloids; confinement; emergent pattern