Elastic Torques about Membrane Edges: A Study of Pierced Egg Lecithin Vesicles

The shape of mechanically pierced giant vesicles is studied to obtain the elastic modulus of Gaussian curvature of egg lecithin bilayers. It is argued that such experiments are governed by an apparent modulus, kappa(app), not the true modulus of Gaussian curvature, kappa. A theory of kappa(app) is proposed, regarding the pierced bilayer vesicle as a closed monolayer vesicle. The quantity measured, i.e. kappa(app)/kappa, where kappa is the rigidity, agrees satisfactorily with the theory. We find kappa(app) = -(1.9 +/- 0.3) . 10(-12) erg (on the basis of kappa = (2.3 +/- 0.3) . 10(-12) erg). The result may have implications for bilayer fusion.