Membrane-Mediated Force Transduction Drives Stick-Slip Motion of Lipid Vesicles.

How internal forces are transduced into motion through soft, fluid membranes remains a fundamental question in the study of active systems. This is investigated using a minimal system: a ferromagnetic particle encapsulated inside a lipid vesicle with controlled membrane composition and phase behavior. A rotating magnetic field drives particle rotation, generating internal flow. This flow propels the particle along the inner membrane leaflet and induces local membrane slip, with regions closer to the particle exhibiting faster motion relative to the substrate. When the particle approaches the vesicle bottom, this slip produces a shear gradient across the lubrication gap, resulting in vesicle propulsion through a stick-slip cycle. Vesicle motion depends on membrane elasticity, excess area, and phase coexistence. Deformations and fluctuations dissipate stress, while line tension deflects the particle and reorients membrane structure. The results demonstrate how lipid membranes mediate force transduction and motion, offering new avenues for the bottom-up design of soft, membrane-based active systems.