(111f) Surface Topography Influences Driven Filament Alignment and Controls Swarm Formation

Driven colloids and proteins, like actin filaments, play a crucial role in cytoskeletal rearrangement and cell motility. When bound to molecular motors, colloidal rods are self-propelled along surfaces due to the conversion of chemical energy into mechanical work. It is known that membrane bound actin can form polar and nematic swarms, even when the particle interactions exhibit only nematic symmetry. Furthermore, surface topography allows for the creation and control of these coherent flows, as seen when directing the generation of forces along a cell surface to undergo cell migration. Despite the importance of this topography – swarming coupling, we have little theoretical understanding of how curved surfaces modulate the motion of individual self-propelled particles, or how that propagates into bulk behavior.

We use theory and experiments to determine how boundaries and topography influence the phase behavior and direction of these emergent swarms. Using both a Langevin-based particle description and a Smoluchowski-based field description, we develop a linear stability analysis in the mean field limit to predict the onset of swarming as a function of activity and surface topography. Our work provides new insight on the coupling of surface topography with active forces at 2D interfaces and provides new techniques to control the spatial and temporal onset of dynamical phase transitions in active nonequilibrium systems.