Future - Chitosan Based Hydrogels: Functions and Applications - page 469

siRNA or miRNA both in vitro and in vivo . Such feasibility has been shown by Howard
et al., who significantly reduced the number of enhanced green fluorescence protein-
expressing epithelial cells in the bronchiole (43% and 37% reduction compared to the
untreated and mismatch control, respectively) of mice via daily nasal administration of
interpolyelectrolyte siRNA-chitosan complexes.
Interpolyelectrolyte complexes between chitosan and siRNA were used to form nano-
particles for siRNA delivery and gene silencing applications. Physicochemical properties
such as size, zeta potential, and complex stability of the nanoparticles were shown to be
highly dependent on the structural parameters M w and the degree of deacetylation (DD) of
the chitosan polymer. It was found that chitosan/siRNA nanoparticles formed using high
M w (114 and 170 kDa) and DD (84%) chitosan formed at N:P 150 were the most stable and
exhibited the highest (about 80%) in vitro gene knockdown, which was comparable to the
best we have observed using other commercial reagents. This work demonstrates the
application of chitosan as a nonviral carrier for siRNA and the pivotal role of polymeric
properties in the optimization of gene silencing protocols.
10.2.4 extension of Application Potential
Chitosan and its derivatives have great potential to be used in other biomedical applica-
tions. As a result of the biocompatible properties such as good blood compatibility and cell
growth efficiency, grafted chitosan materials have potential to be used in cardiovascular
applications [19]. It has been demonstrated that the permeability of chitosan membranes
grafted with hydroxyethyl methacrylate (HEMA) may be controlled through plasma treat-
ment that has the potential to be used in dialysis [20].
Stimuli-responsive hydrogels have shown an improved drug-loading capacity and a sus-
tained release behavior [21]. In particular, systems that combine chitosan and poly( N -iso-
propylacrylamide) (PNIPAAm) have shown drug release profiles that can be controlled by
both pH and temperature, constituting very promising materials [22,23]. This kind of
smart system has also been proposed for gene delivery. Our previous research [24] coupled
a carboxyl-terminated NIPAAm-vinyl laurate (VL) copolymer with chitosan (PNVLCS)
and examined the gene expression of PNVLCS-DNA complexes in C 2 C 12 cells against tem-
perature change. The results indicated that the transfection efficiency of PNVLCS-DNA
complexes was improved by dissociation of the gene from the carrier by temporarily reduc-
ing the culture temperature to 20°C. By contrast, naked DNA and Lipofectamine did not
demonstrate thermoresponsive gene transfection.
In addition to applications in controlled drug release, PNIPAAm-grafted chitosan-based
materials have been exploited for controlling cell adhesion/detachment by changing the
incubation temperature above or below its LCST [5,25]. Temperature-responsive chitosan-
graft-PNIPAAm [5] were applied for culturing MSCs. Chitosan-g-PNIPAAm copolymers
with chondrogenic MSCs showed promising potential for clinical applications, particu-
larly as cell therapy technologies for treating vesicoureteral reflux [25].
10.3 Challenges Due to Interactions of Chitosan-Based Gels
Hydrogels are comprised of cross-linked polymer networks that have a high number of
hydrophilic groups or domains. These networks have a high affinity for water, but are