Estimation of mechanical strength of unilamellar and multilamellar AOT/water vesicles and their rupture using micropipet aspiration.

Vesicles prepared from surfactant sodium dioctyl sulfosuccinate (AOT) were characterized by micropipet aspiration for determining membrane bending rigidity and area expansion modulus and mechanism of rupture. Unilamellar vesicles (ULV) and multilamellar vesicles (MLV) were studied. The mechanical properties calculated using micropipet aspiration for ULV were found to be 5-10 k(B)T, K(a) = 100 +/- 20 mN/m and for MLV were 8-15 k(B)T, K(a) = 120 +/- 30 mN/m. These properties fall with the range of lipid (PC) membrane measurements (values). However, the membrane rigidity of multilamellar vesicles was found to be approximately 3 times larger than that of unilamellar vesicles. The apparent area expansion moduli of multilamellar vesicles are of the order 1.4 times, sustained far greater areal strain before rupture compared to that of unilamellar vesicles. A dynamic structural change in MLV is demonstrated upon stress by micropipet aspiration. MLV at stress undergoes various stages of deformation. The fluctuation in size and shape of MLV led to separation of bilayers from the stack and decrease in vesicle diameter facilitating in formation of new equilibrium MLV, for it to sustain the specified membrane tension, a new mechanism that is demonstrated experimentally.