Effect of the Waveform of the Pulsed Electric Field on the Cylindrical Deformation of Uncharged Giant Unilamellar Vesicles

Abstract

High-speed imaging of giant unilamellar vesicles (GUVs) in recent years has shown significant shape deformation of these vesicles under electroporating direct current (DC) pulsed electric fields, possibly altering the surface distribution of transmembrane potential (TMP) and, thereby, the location and extent of electroporation on the bilayer membrane. The development of TMP, the corresponding shape deformation, and the extent of electroporation depend upon the waveform of the applied electric field. In this work, the deformation of vesicles was carried out under a high-intensity, single cycle of a sinusoidal pulsed electric field (SSPEF) and a square wave pulsed electric field (SWPEF). The cylindrical shape deformations of vesicles were observed for both SSPEF and SWPEF and were dependent upon the ratio of conductivity of the inner medium to the outer medium, α. For α = 1 and α > 1, the vesicles deformed into prolate cylinders as a result of Maxwell stress, whereas they were compressed into oblate cylinders for α < 1. Vesicles subjected to a SSPEF relaxed following either the pore closure dominated t 2 or the efflux and lipid loss dominated, slow t 3 mechanism depending upon the value of α. For α = 1 and α < 1, the relaxation of the vesicles was found to be predominantly dependent upon pore closure. On the other hand, a majority of vesicles gained excess area during poration when α > 1, which can be attributed to a higher TMP and faster charging of the membrane. The predictions of the approximate model for the deformation of vesicles agreed with the experiment, with deviations between the two as a result of the simplicity of the model. Moreover, the degree of deformation of vesicles [measured by the aspect ratio (AR)] and shape deformations of vesicles were found to be dependent upon the pulse width (T P) and amplitude (E 0) of the SSPEF. The specific temporal variation of pore-forming tendencies of SSPEF and SWPEF, with their associated peculiarities, can be judiciously used for controlling electroporation in cells and vesicles.