Instant Membrane Stabilization by Damage‐Triggered Actin Polymerization in Giant Unilamellar Vesicles

Giant unilamellar vesicles (GUVs) rupture catastrophically when membrane pores expand under tension, because they lack cellular repair machinery. Here we present a minimal, damage-triggered stabilization mechanism based on rapid actin polymerization inside GUVs. ATP-activated G-actin was encapsulated in a divalent-cation-free lumen while high concentrations of Ca2+ or Mg2+ were supplied externally, creating a condition where membrane poration immediately drives cation influx. Upon poration, localized cation entry induces fast F-actin assembly that forms a cortical-like meshwork at the defect, mechanically arresting pore enlargement and preserving vesicle morphology for extended periods. The resulting actin plug does not restore full impermeability to small molecules, but it substantially increases vesicle survival against rupture and recapitulates the "plugging" aspect of single-cell membrane wound responses in a bottom-up artificial cell model.