Skin Electroporation: Modeling Perspectives - Porous Media: Applications in Biological Systems and Biotechnology - page 348

change G occur at temperatures above 90 ◦ C and have been associated with
protein denaturation (Cornwell et al. 1996; Tanojo et al. 1999; Silva et al.
2006a). Secondary lipid melting has been associated with phase change, F, at
temperatures around 80 ◦ C and has been linked to lipids covalently bonded to
corneocytes (Cornwell et al. 1996; Tanojo et al. 1999).
So it is clear then that there exists a specific temperature range within
which the lipid barrier architecture is destroyed, and that the lipid thermal
behavior should be considered in any electroporation study in which the pulse
parameters are such that significant temperature rises are possible.
9.7 Skin Electroporation Models (Nonthermal)
The following section displays the models currently used to depict electropo-
ration. The reader should keep in mind that the physics underlying electro-
poration (even of a single bilayer) are not completely understood and that
the models used to describe electroporation are experimentally based (either
empirically or hypothetically). Whatever the models basis, its purpose it to
relate permeability (measure of porosity) to electroporation pulse parame-
ters, typically applied voltage, V app , and pulse time, τ P . With the structural
changes of electroporated SC come large increases in electrical conductiv-
ity of the SC , σ SC . Because electrical characteristics (conductivity, current,
and voltage drop) can be easily and precisely measured, they have tradition-
ally been used as parameters to show the transient increases in permeability.
Furthermore, because the current electroporation models have origins tied
to experimental findings (which monitor electrical behavior), it should come
as no surprise that the numeric and theoretic models used to describe skin
electroporation often use electric parameters to interpret the degree of per-
meability.
9.7.1 Single Bilayer Electroporation Modeling
We begin the discussion of using SC electrical behavior to describe electro-
poration with a description of single bilayer pore formation (recall that the
SC architecture consists of about 100 lamellar sheets made of these single
bilayer membranes.) The single bilayer models track the creation and growth
of small pores ( < 10 nm) in which the increase in permeability is based on
the local potential drop across the membrane, V m . To model single bilayer
electroporation, investigators keep track of each individual pore's transient
growth or decay. It is not di cult to imagine what a task this would become
when dealing with 100 bilayers interconnected by the corneocytes.
The models used to describe single lipid bilayer membrane electropore
creation are usually some extension of the Smoluchowski equation that links