Skin Electroporation: Modeling Perspectives - Porous Media: Applications in Biological Systems and Biotechnology - page 353

Sigmoid dependence:

σ 0
1 + exp ( E 1 + E 0 −

σ 1 −

σ ( E )= σ 0 + (9.32)

E )

2 B

where B is a shape parameter.
Comparing the simplicity of the empirical model to the complexity of the
single bilayer models, it is clear that the benefit of using experimental results
to model electroporation lies in the ability to match the physical phenomenon
measured in the electrical skin behavior. Furthermore, these studies cleverly
use the experimental data to capture lateral variations in the SC . The limiting
factor of empirical models is that they require detailed data regarding tissue
electrical behavior during electroporation, which can be a problem when this
data does not exist. That is the motivation of the recently introduced ther-
modynamic approach to modeling skin electroporation.

9.8 Thermodynamic Approach
The increase in permeability associated with the formations of the LTR
has been linked to sudden local rises in temperature. We recall the findings
described in Section 9.6.3, which point toward the following trends associated
with long-pulse electroporation:

• The electroporated SC is not homogenous laterally but experiences local-

ized regions of higher permeability.

• The skin experiences local heat fronts that propagate radially outward

forming regions of high permeability (for medium pulse amplitudes these
originate in skin appendageal ducts).

• These local heating regions have been observed to reach temperatures

above 70 ◦ C.

That at temperatures above 60 ◦ C SC lipids have been shown to experience
thermal phase transitions that destroy the lamellar barrier architecture.

•

Figure 9.5 shows a representation of the SC prior to electroporation in
which a preexisting pore of radius, R P , at the axial center passes through the
SC . Before electroporation, the lipid structure connecting the corneocytes of
the SC is lamellar and uniform. During electroporation a large current density
through the pore causes local temperature rises within the SC . Figure 9.5
shows the lamellar structure in phase transition and that the effective pore
radius, R eff , extends to the region at which SC lipids are unaffected by the
temperature rises.