(443a) Tunable Aggregation and Collective Hydrodynamics of Active Inclusions on Biological Membranes

We study the hydrodynamic interactions and collective modes of motion of active particles on viscous membranes. The typical cell membrane is a crowded assembly of molecular motors and biomolecules embedded in a 2D fluid mosaic. Active molecular motors perform complex cellular tasks by binding, releasing, and changing conformations, inducing hydrodynamic flows in the membrane and the surrounding fluid. These long-ranged hydrodynamic fields perturb neighboring inclusions, potentially leading to coordinated motion. We build on classic theories of Newtonian fluid dynamics of viscous membranes to illustrate unique nonlinear dynamics and aggregation of active membrane inclusions that exert hydrodynamic dipoles on the fluid interface. We illustrate these novel flow physics by theoretically examining the phase behavior of pairs of hydrodynamically interacting membrane inclusions. Pairs display oscillatory dynamics that disappear when the 3D fluid adjacent to the membrane is confined, which we rationalize as a consequence of hydrodynamic screening due to confinement. The phase behavior of the pair problem reveals the underlying mechanisms and suggests strategies for control of large-scale aggregation, which we verify using numerical simulations. We then build on these insights to examine the role of inclusion shape as well as the convection of passive tracers within the membrane. Traditional engineering of foreign inclusions in membranes has targeted interactions due to capillarity, curvature and electrostatics; we propose hydrodynamic confinement as an additional controllable parameter to tune collective motility and aggregation on lipid membranes.