Skin Electroporation: Modeling Perspectives - Porous Media: Applications in Biological Systems and Biotechnology - page 333

porous-media-based descriptions of passive transdermal transport. The sec-
ond half of this chapter focuses on one such method called electroporation
in which the skin is exposed to short (

s to ms) pulses that act to disrupt
the skin's barrier structure to allow increased permeability. Then the process
of electroporation is detailed to describe the primary and secondary effects of
exposing the skin to these intense electric pulses. Experimental skin electropo-
ration findings are given to add insight into the mechanics underlying current
hypotheses.
The following section is devoted to providing a basic physical description of
the skin and the obstacles that must be overcome to transport drugs through
its impermeable nature.

µ

9.3 The Skin as a Composite
Although the skin is the body's first defense against infection, in general, the
skin should not be treated as a homogenous medium. Even in a very basic
description, human skin is made of multiple constituent composite layers,
each providing specific function with varying thicknesses (see Figure 9.1).The
reader unfamiliar with the physiology of the skin may find the introductory
text (Millington and Wilkinson 1983) helpful.
The outer skin layer, the epidermis, (0.05-1.5 mm), is without vasculature
and acts as a protective barrier preventing molecular transport. The epidermis
is basically an assembly line of viable living cells at its base that transition to
flat dead cells at its outer surface. The outer layer of the epidermis provides
the skin's primary barrier to transport.

he Skin

Stratum
corneum

Epidermis

he Stratum Corneum

Sweat duct

Dermis

Corneocyte

Sweat gland
Hair follicle

Lipid bilayers

Blood
vessels

Subcutaneous
Tissue

Fat lobule

FIGURE 9.1
The skin.