Biomedical Engineering Reference
In-Depth Information
9.1 Introduction
The subject of this chapter concerns modeling and treatment of mass trans-
port through biological tissues, specifically the skin. To the reader unfamiliar
with the physiological aspects of the skin, a basic description of the skin and
each of its composite layers is provided. The treatment of the skin as a porous
medium is then addressed. The chapter continues by introducing current meth-
ods used to describe nondestructive transdermal transport of low-molecular
weight hydrophilic and hydrophobic solutes. This provides a glimpse of the
current approaches of the porous media perspective of transdermal transport,
and presents access to a list of these models.
The second half of the chapter covers the subject of electroporation (a
structure altering electrokinetic means of transport in which the skin is
exposed to a series of intense, short-duration electric pulses). A review of
experimental findings and observations regarding the electrically induced cre-
ation of local transport regions (LTRs) is presented. This is done to familiarize
the reader with clinical and experimental results that link the thermal aspects
of the applied pulse to the thermal behavior of the skin. Furthermore the
review points out a thermodynamic basis to the creation of these local sites
of increased permeability. A description of various methods used to describe
electroporation of the skin (both empirical and mechanistic) is also provided.
9.2 Transdermal Drug Delivery
Traditional systemic drug delivery methods often result in low ecacy and
unintentional treatment of healthy tissue. Oral intake may result in drug
denaturation in the body's gastro-intestinal tract: drugs consisting of water-
soluble molecules may degrade in the digestive tract before reaching intended
locations of treatment. Injection of drugs into the circulatory system results
in a lower selectivity level of the region of drug influence. For drugs with a
high toxicity, for example, those used in chemotherapy, systemic delivery is
associated with a high risk of unintentional damage to healthy tissues. Tar-
geted drug delivery refers to any method of drug administration designed to
ensure and enhance a drug's transfer rate to specific location (rather than the
entire body as in systemic delivery). Transdermal drug delivery is one method
that allows for localized delivery by transporting the drug directly through
the skin to the drug's desired target.
This chapter begins with a general physical description of the skin
and
its
barrier
properties.
This
is
followed
by
a
review
of
current
 
Search WWH ::




Custom Search