Biomedical Engineering Reference
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similar to the mechanism of pore resealing that the cell applies regardless of
the pore's origin (Steinhardt et al. 1994). Although the number of pores in
this stage is much smaller than, during the pulse and the molecular transport
has also decreased considerably, most of the important mass transfer occurs
during this stage. The short duration of the pulses, which are required to pre-
vent the cells membrane from completely disintegrating, make it very dicult
to obtain substantial molecular and ionic transport during the pulse duration.
The existence of the very large electric field also has an effect on the charge
molecules that may pass during the pulse duration, although this effect may
sometimes be constructive and sometime destructive depending on the charge
and the geometrical configuration.
The final stage of the process, the long-term recovery, may linger for sev-
eral hours, but it is probably the less important part of electroporation. Some
studies have shown that even 4 h after electroporation, when the pores have
long been resealed and the original permeability has been restored, the cell
may not return to its exact original state (Rols et al. 1995). For instance,
endocytosis and macropinocytosis were observed in electroporated cells even
though cells that were not treated with electrical pulses did not exhibit sim-
ilar behavior. Another long-lasting effect, which is not really a part of the
electroporation process but rather a consequence of this procedure, is the ter-
minal effect that electroporation may have on some of the cells. This is what
we have referred to as irreversible electroporation, and it is sometimes the
ultimate goal of the procedure.
In many cases irreversible electroporation is considered as an instance of
unresealable pores. This is certainly the case in several scenarios where the
applied voltage is very high or when the expansion of the pores persists for
a very long time to the point that the membrane ruptures and it is not able
to reseal. Sometimes the damage is too great even for the cytoskeletal mecha-
nisms of the cell to fix. The loss of membrane can only mean one thing—cell
death. However, another mechanism of irreversible electroporation exists, one
which may be just as important. In this case, the cell manages to keep the
membrane in tact and the pores do reseal, either spontaneously or with the aid
of the cytoskeleton, but homeostasis is lost and the cell is not able to recover
from this shock. This will lead to cell death but on a much longer time scale
and possibly with very different characteristics.
2.3 Mathematical Models of Ion Transport
during Electroporation
Many of the models developed for electroporation focused on the membrane
itself and often referred to a single cell (Abidor et al. 1979; Lewis 2003;
Krassowska and Filev 2007), but an important thing to consider in the case
 
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