Vesicle deformation and poration under strong dc electric fields

Abstract

When subject to applied electric pulses, a lipid membrane exhibits complex responses including electrodeformation and electroporation. In this work, the electrodeformation of giant unilamellar vesicles under strong dc electric fields was investigated. Specifically, the degree of deformation was quantified as a function of the applied field strength and the electrical conductivity ratio of the fluids inside and outside of the vesicles. The vesicles were made from L-α-phosphatidylcholine with diameters ranging from 14 to 30 μm. Experiments were performed with field strengths ranging from 0.9 to 2.0 kV/cm, and intra-to-extra-vesicular conductivity ratios varying between 1.92 and 53.0. With these parametric configurations, the vesicles exhibited prolate elongations along the direction of the electric field. The degree of deformation was, in general, significant. In some cases, the aspect ratio of a deformed vesicle exceeded 10, representing a strong-deformation regime previously not explored. The aspect ratio scaled quadratically with the field strength, and increased asymptotically to a maximum value at high conductivity ratios. Appreciable area and volumetric changes were observed both during and after pulsation, indicating the concurrence of electroporation. A theoretical model is developed to predict these large deformations in the strongly permeabilized limit, and the results are compared with the experimental data. Both agreements and discrepancies are found, and the model limitations and possible extensions are discussed.

Deformation but not migration and rotation – a model study on vesicle biomechanics in a uniform DC electric field

“…The spherical vesicle model is based on several previous works, [18,24] which consider the vesicle in aqueous solution to have a permeable, conducting membrane with zero thickness. The model contains a homogeneous sphere (i) placed inside the conductive medium (o).…”

“…[16,17] It was found that the vesicles primarily underwent membrane deformation under electric fields. For example, Sadik et al [18] reported that the vesicles exhibited elongation along the direction of the electric field. Riske and Dimova [16] reported that vesicles subjects to DC electric pulses could be deformed into elliptical or cylindrical shapes.…”

“…Interestingly, there is no evidence of vesicle migration and rotation in these experiments, even if the field intensity was as large as 2.0 kV/cm, when electroporation could be observed. [18] In order to theoretically understand vesicle deformation under the electric field, simplified vesicle models have been built to analyze vesicle biomechanics. [19][20][21] Hyuga et al suggested that interactions between the field and charges that accumulate on the vesicle surface could generate membrane deformation.…”

“…[16,18] The phosphatidylcholine headgroup is a neutral molecule as a whole, since it contains a positively charged choline group and negatively charged phosphate and carbonyl groups. [25] In contrast, biological cells carry charged membrane proteins, which reside in the lipid headgroups within the membrane.…”

“…We adopted the common assumption among different theoretical models that the vesicle is a leaky dielectric particle of fixed shape, [18,22] and treated the vesicle as a spherical structure with certain conductance and dielectricity. [29,30] The membrane thickness is taken to be zero and the electrical resistance of the membrane is assumed to be negligible, [18,22] to account for the poration and leakage under strong electric field intensity. Our model generated analytical expression of the radial pressure on the membrane, and confirmed the experimental observation that the shape of deformation depended on the intra-to-extra-vesicle conductivity ratio.…”