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Abstract: Pharmaceutical gels are well known as
dense networks of fine particles dispersed in suitable
media. Based on the types of dispersion phases, they are
sub classified as hydrogels, alcogels and organogels,
which are dispersions of polymeric materials in water,
alcohol, and organic solvents, respectively. Aerogel,
having more than 15 entries in Guinness Book of World
Record, is a very low-density solid-state gel which is
derived by replacing the dispersion phase of a gel with
gas. Aerogels can be made with a density only three
times larger than that of air. This novel material has
many desired properties, such as low thermal
conductivity, refractive index, along with thermal
stability, large surface area and biocompatibility,
which make it a potential candidate as a drug carrier. A
striking number of applications have been developed for
aerogels like catalysts, thermal insulators, and
particle detectors and so on. Pharmaceutical
applications of aerogels are being investigated for more
than a decade, e.g., as flow enhancing materials,
filler, drug carriers and so on.
Introduction
Aerogel, world’s lightest solid material and drug
delivery system, was first created by Steven Kistler in
1931. Kistler competed with Charles Learned to see if
one of them could replace the liquid inside a jelly jar
with gas without causing any shrinkage. Kistler won the
bet, and published his findings in 1931. Aerogel is a
low-density solid-state material derived from gel in
which the liquid component of the gel has been replaced
with gas. Aerogels are produced by extracting the liquid
component of a gel through super-critical drying. This
allows the liquid to be slowly removed without causing
the solid matrix in the gel to collapse due to capillary
action, as would happen with conventional evaporation.
The first aerogels were produced from silica gels.
Kistler’s later work involved aerogels based on alumina,
chromia and tin oxide. Carbon aerogels were first
developed in the early 1980s.
Aerogel is a concept of pulmonary drug delivery from a
very light weight and highly transparent polymer
material which is also known as “Frozen Smoke”, “Blue
Smoke”, or “Solid Smoke”. These names suggest its hazy
blue appearance as a solid. It has emerged out as one of
the most promising means of drug delivery during the
past few years.
Superiority of Aerogel to Aerosol
Porous gels are prepared from a material which is
soluble in pulmonary surfactant. The lower the density
difference between the floating particle and the air,
the higher are the chances the particle will stay afloat
at a given level of air motion. Since the aerogel
particles are highly porous (up to 95% filled with the
air), they are much lighter than a solid particle and
they have much better chances of remaining afloat
reaching the innermost alveoli of the lungs and settling
on the pulmonary surfactant rather than on the mucous
membranes along the way. Since human lungs have an
equivalent surface area of a tennis court, it is
advisable to take advantage of as much of the surface of
the lungs as possible for efficient drug delivery. The
air suspension characteristics of the micron and
submicron size aerogel particles are determined using a
small chamber with a paddle fan.
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