Stokesian jellyfish: Viscous locomotion of bilayer vesicles

TL;DR

This paper theoretically investigates how shape-changing bilayer vesicles can achieve net swimming at low Reynolds number by modulating their volume and membrane composition, offering insights into alternative microswimmer designs.

Contribution

It introduces a numerical framework for analyzing shape-driven locomotion of vesicles, demonstrating net movement through non-reversible shape cycles in two classical models.

Findings

Net locomotion achieved via asymmetric shape changes.

Hydrodynamic efficiencies comparable to biological microswimmers.

Shape transitions enable propulsion without traditional flagella.

Abstract

Motivated by recent advances in vesicle engineering, we consider theoretically the locomotion of shape-changing bilayer vesicles at low Reynolds number. By modulating their volume and membrane composition, the vesicles can be made to change shape quasi-statically in thermal equilibrium. When the control parameters are tuned appropriately to yield periodic shape changes which are not time-reversible, the result is a net swimming motion over one cycle of shape deformation. For two classical vesicle models (spontaneous curvature and bilayer coupling), we determine numerically the sequence of vesicle shapes through an enthalpy minimization, as well as the fluid-body interactions by solving a boundary integral formulation of the Stokes equations. For both models, net locomotion can be obtained either by continuously modulating fore-aft asymmetric vesicle shapes, or by crossing a continuous shape-transition region and alternating between fore-aft asymmetric and fore-aft symmetric shapes. The obtained hydrodynamic efficiencies are similar to that of other low Reynolds number biological swimmers, and suggest that shape-changing vesicles might provide an alternative to flagella-based synthetic microswimmers.