  Giant unilamellar vesicles subjected to pulsed direct-current (pulsed-DC)
fields are promising biomimetic systems to investigate the electroporation of
cells. In strong electric fields, vesicles undergo significant deformation,
which strongly alters the transmembrane potential, consequently the
electroporation. Previous theoretical studies investigated the
electrodeformation of vesicles in DC fields (which are not pulsed). In this
work, we computationally investigate the deformation of a deflated vesicle
under unipolar, bipolar, and two-step unipolar pulses and show sensitive
dependence of intermediate shapes on type of pulse and the pulse width.
Starting with the stress-free initial shape of a deflated vesicle, which is
similar to a prolate spheroid, the analysis is presented for the cases with
higher and lower conductivities of the inner fluid medium relative to the outer
fluid medium. For the ratio of inner to outer fluid conductivity,
$\sigma_\mathrm{r}$ = 10, the shape always remains prolate, including when the
field is turned off. For $\sigma_\mathrm{r} = 0.1$, several complex dynamics
are observed, such as the prolate-to-oblate (PO), prolate-to-oblate-to-prolate
(POP) shape transitions in time depending upon the strength of the field and
the pulse properties. In this case, on turning off the field, a metastable
oblate equilibrium shape is seen, that seems to be a characteristics of a
deflated vesicle leading to POPO transitions. When a two-step unipolar pulse (a
combination of a strong and a weak subpulse) is applied, a vesicle can reach an
oblate or a prolate final shape depending upon the relative durations of the
two subpulses.
