Biomedical Engineering Reference
In-Depth Information
intended effect. Furthermore, hybrid organogels would allow hydrophobic and
hydrophilic compounds to be harmoniously incorporated into separate particulate
compartments within the same gel formulation. The benefit of a hybrid formulation
is exemplified in dermal applications, where it translates to the ease of applying a
single preparation for the combined therapeutic effects of otherwise incompatible
gel preparations. In addition, hybrid organogel formulations will potentially provide
a more sustained therapeutic effect, as drug compounds can be gradually released
from the particles after the initial burst release from the gel matrix.
In actual fact, the ideology of hybrid organogels is not new. Murdan and co-
workers experimentedwith organogels containing niosomes as a delivery vehicle for
vaccine antigens more than a decade ago [31]. Light microscopy of their organogels
prepared using the non-ionic surfactant sorbitan monostearate as the gelator
showed a suspension of niosomes dispersed in a tubular network of surfactant
aggregates. Model antigens, bovine serum albumin, and hemagglutinin were
entrapped within the niosomes. Although immunogenicity studies showed that the
niosomes-containing gels possess immunoadjuvant properties, they unfortunately
did not elicit the expected higher antibody titers. This may be due to the low amount
of niosome suspension in the gel, as well as the low entrapment efficiency of the
niosomes during preparation.
An investigation into the role of an
in situ
implant that incorporates superpara-
magnetic iron oxide nanoparticles as a form of minimally invasive treatment of
cancer lesions by magnetically induced local hyperthermia was recently carried out
by Le Renard and co-workers [32].
In vitro
and
in vivo
comparison studies were
made among hydrogel, single-solvent organogel, and co-solvent organogel, which
had concentrated single-solvent organogel diluted with low-toxicity hydrophilic
solvent during gel preparation. It was found that the organogel formulations
gave the most favorable result, where 8% poly(ethylene-vinyl alcohol) in dimethyl
sulfoxide (DMSO) containing 40% w/v of magnetic microparticles formed the
most suitable implants in terms of localization to tumor center and periph-
ery, as well as heat delivery. Co-solvent organogels showed promising results
and are clinically more appealing due to better safety profile than single-solvent
organogels. However, high viscosity of the co-solvent formulations resulted in
limited syringeability. It is hoped that further development will pave the way for
clinical applications of magnetic microparticles-containing organogels in tumor
treatments.
In recent years, characteristics of organogels with carbon nanotubes dispersed
within the gel matrix have been studied [61, 62]. It was found that organogels con-
taining 0.2% w/w of carboxylated nanotubes have increased mechanical strength
by a factor of 4, and organogels with 0.2% w/w of pristine carbon nanotubes incor-
porated had electrical conductivity enhancement of 6 orders of magnitude [62]. This
finding will have value in the development of fuel cells and energy. Presently, stud-
ies on hybrid gels are relatively limited. However, considering the benefits of using
organogels alone and the potential extra advantages of using hybrid gels, research
work in the area of hybrid organogels is expected to be favored in the future.
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