Biomedical Engineering Reference
In-Depth Information
Keywords:
Liposomes, passive targeting, active-targeting, dual-targeted
liposomes, antibody-targeted liposomes, multifunctional liposomes, drug
delivery, drug carriers
3.1 Introduction
Liposomes are artii cially prepared bilayered nanoparticles and are
mainly composed of phospholipids thus conferring upon them a high
degree of biocompatibility. Liposomes were discovered by Bangham
et
al.
in 1965 and were i rst described as 'phospholipid liquid crystals'[1].
Soon at er, their use as drug carriers was recognized [2]. Since then the
i eld of liposomal drug delivery has made signii cant progress and as
a result a number of liposomal formulations have entered the clinic
[3] (See table 3.1). Many of the current drug therapies like anticancer
therapy etc. are fraught with toxicity issues resulting from non-specii c
drug accumulation in healthy cells. Liposomes are fast becoming the
carrier of choice for a number of 'promiscuous' drug candidates and
the liposomal encapsulation of these drugs can help address most of
these issues. Hydrophilic drugs can be trapped in their aqueous interior
while hydrophobic drugs remain associated in their lipid bilayer. h is
allows for improved solubility of the drug, sustained release kinetics,
protection from the degrading action of enzymes in the body thereby
increasing the drug's half-life and accumulation at the target site and
allowing for therapeutic ef ects at lower doses. In addition, drug-loaded
liposomes can be surface modii ed to incorporate added functions like
longevity, triggered release, and specii c targeting of dif erent tissues,
cell types and intracellular organelles amongst others.
One of the i rst attempts to review the developments in the i eld of lipo-
somes as drug carriers was done by Gregoriadis [4]. Since then there have
been a number of developments and numerous reviews have been pub-
lished in order to keep abreast [5, 6].
To further the development of this i eld, the current state and trends in
research need to be identii ed. h e aim of this chapter is to equip the reader
with a clear knowledge of the dif erent types of liposomes and highlight
the specii c use of these in dif erent disease models thus demonstrating the
versatility of these drug carriers. In order to better understand the direc-
tion in which the i eld of liposomal drug delivery is heading, it is important
to be well aware of the current developments and strategies being used by
researchers, as well as to address the associated challenges [7]. With this in
mind this chapter has mainly focused on the developments in liposomal
drug delivery within a six-year window.
