Introduction - In-Situ Gelling Polymers: For Biomedical Applications - page 2

[ 7 ], and as phase-transfer catalysts [ 8 ]. They have been widely investigated for
their potential biomedical applications, particularly in drug delivery [ 9 ]. Micelles
with their hydrophobic cores and hydrophilic coronas solubilize hydrophobic
compounds, encapsulating them within the micelle core. Bulkier materials such as
hydrogels can also be assembled from small molecules. Hydrogels are crosslinked,
three-dimensional macromolecular network of hydrophilic copolymers. Hydrogels
are widely used as wound dressings, soft contact lenses and soft tissue substitutes.
Physical or chemical crosslinking of hydrogels have been described. Chemical
crosslinks can take place with the incorporation of functional crosslinkers with
more than two reactive groups. Physical crosslinks can be formed via hydrophobic
interactions between polymer chains, host-guest complexation, metallo-mediated
binding or electrostatic approaches.
The delivery of drugs requires scientific and engineering manipulation of bio-
logically active components into practically implementable therapeutic modalities.
The most serious issue facing today's healthcare industry is the 'on-cue' release of
therapeutics to their designated target site in a safe, repeatable and patient-friendly
manner. Conventional therapy is fraught with obstacles, this happens regardless of
the route of administration. For example, the drug molecule could be degraded by
enzymes in the stomach, be absorbed drug molecules across intestinal epithelium,
cleared by the liver, be overwhelmed by the body's natural immune system result-
ing in a short plasma half-life and nonspecific tissue distribution. These natural
barriers are important for the upkeep of critical bodily functions and yet results
in the dilution of the therapeutic efficacy of the injected drugs. It is therefore very
important, in the field of drug delivery, to totally understand the limits of these
barriers and develop new strategies to overcome them.
As a result, an alternative administration by daily intravenous infusion is usu-
ally used to increase the bioavailability of the drug. Nevertheless, intravenous
injections raise the possibility of contamination at the localized site and systemic
adverse reactions that might result from a sudden high dosage of drug, such as,
in the instance of chemotherapeutic medications for the management of cancer.
To eliminate this complication, regulated drug release systems such as emulsions,
liposomes, biodegradable microspheres and micelles have been developed. Even
though effective for the intake of hydrophobic medications, these types of prod-
ucts have a variety of shortcomings, for example poor stability in vivo, prerequi-
site of organic solvents for the loading of drugs and inferior drug encapsulation
efficiencies. These limitations have restricted the utilization of these DDS for
the delivery of delicate curative agents such as, peptides and proteins. The use of
organic solvents denatures these beneficial peptides, removing these approaches as
the preference delivery agents of beneficial peptides. The significance and devel-
opment of the peptides as therapeutic agents cannot be ignored. For instance,
glucagon-like peptide-1 (GLP-1) is utilized for the management of diabetes, ghre-
lin for the management of obesity, gastrin-releasing peptide used in cancer treat-
ment options, defensin for antimicrobial use and growth factors used for wound
healing applications. Nonetheless, peptide delivery in vivo continues to be compli-
cated due to their brief residence half-life. An optimum peptide treatment requires