Biomedical Engineering Reference
In-Depth Information
tained release. Controlled delivery systems are used to improve the
therapeutic e
cacy and safety of drugs by delivering them to the
site of action at a rate dictated by the need of the physiological envi-
ronment. A wide variety of polymeric materials have been used as
delivery matrices, and the choice of the delivery vehicle polymer is
determined by the requirements ofthe specific application.
41
Withtheavailabilityofmultiplegenedeliverysystems,theselec-
tionofthemostappropriategenedeliveryvehicletomeettheneeds
of a particular therapeutic application can be challenging. Viral-
and plasmid-based delivery vehicles are currently used for the pro-
duction of therapeutic proteins so as to elicit a desired biological
response.
42
This would especially be useful in the field of tissue
engineering, wherein it would be possible to cause the production
of a desired protein (growth factor) that can enhance the process
of tissue regeneration. Therefore, gene delivery systems have been
explored for applications in the engineering of a variety of tissues.
The most commonly used carrier-based systems for gene delivery
are cationic liposomes and condensing agents such as poly(ethyl-
enimine), and poly(l-lysine). More recently, biomaterial-based gene
deliverysystemshavebeenexploredandareprovingtobeapromis-
ing approach. Various biomaterials such as poly(ethylene glycol)
(PEG), PLGA, and PLA-PEG copolymers are currently being inves-
tigated for gene and protein delivery.
43
Scaffolds for gene deliv-
ery need to provide structural stability and site-specific delivery
of genes, along with protection of genes from the biological sys-
tem until they are released. Further, the released DNA needs to
retain its structural integrity until it is taken up by the desired
cells.
PLGA and PLA-PEG block copolymer-based nanofibrous scaf-
folds have been used for plasmid DNA delivery.
44
Recently,
α
-
chymotripsin was attached to electrospun polystyrene nanofibers
(120 nm) as a catalytic system and examined for its catalytic e
-
ciency in biotransformation.
45
This study indicated that the nanofi-
brous enzyme system had a higher hydrolytic activity (65%) than
the immobilized enzyme and three times more nonaqueous activ-
ity than immobilized
α
-chymotrypsin in organic solvents. In a
recent study, poly(vinyl alcohol) (PVA) electrospun nanofibers have
been studied for protein delivery.
46
The coated and uncoated PVA
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