Biomedical Engineering Reference
In-Depth Information
should structural modifications affect drug activities, gelation abilities, or enzyme
activities restricted due to stereoelectronic effects, these problems may be over-
come by linking the drug to the gelator through a self-immolating spacer molecule
[18]. The specificity in enzyme-mediated activation of prodrug-gelator conjugates
can be exploited for targeted delivery of drugs to specific sites. For example, a
prodrug-gelator conjugate with peptide linkage specific for tyrosinase would be
able to target melanoma where tyrosinase is present only in melanoma cells [19].
In another work also involving enzymes and supramolecular hydrogels, the
research group utilized alkaline phosphatase to convert ionic group on an amino
acid derivative to neutral group to form a small-molecular hydrogelator, which
resulted in the formation of hydrogels [20]. The process uses enzymes for bond
cleavage instead of formation reactions as mentioned earlier. Nonetheless the
bond breaking reaction requires enzyme specificity, hence facilitates targeted
delivery and site formation of supramolecular hydrogels. In a later work by the
same investigator, application of enzyme-mediated formation of supramolecular
hydrogels using phosphatase, thermolysin, and
β
-lactamase was further illustrated,
which suggested new avenue for detecting activity of enzymes and screening for
enzyme inhibitors [21].
3.3
Organogels in Pharmaceutical Applications
An organogel is easily prepared by warming a gelator in organic liquid until the
solid gelator completely dissolves, and then cooling the solution to below the
gelation transition temperature [22]. Small-molecular-weight organogelators have
higher organogelation abilities than polymer organogelators. Various classes of
small-molecular-mass gelators have been identified which include fatty acid deriva-
tives, steroid derivatives, anthryl derivatives, amino acid-type, and organometal-
lic compounds [22]. Some examples of small-molecular-weight and polymeric
organogelators are listed in Table 3.1.
The pharmaceutical industry has taken increase interest in organogels due to
the discovery of biocompatible organogelators in recent years. As compared to its
hydrogel counterpart, organogels offer more as they are thermodynamically stable
at ambient conditions and thermoreversible under suitable conditions. In addition,
Examples of organogelators.
Table 3.1
Small molecular weight
Polymeric
Lecithin [23-25]
Polylactide [26-30]
Sorbitan monostearate [31]
Polyethylene vinyl alcohol [32]
Glyceryl palmitostearate [33]
Polystearyl acrylate-acrylic acid [34]
Hydroxystearic acid [35]
Search WWH ::
Custom Search