Formation of Chitosan-Based Hydrogels Network - Chitosan Based Hydrogels: Functions and Applications - page 215

design of the prodrugs. It is Lu and Hu [231] loaded positively charged myoglobin (Mb) in
the interior of PEM films of chitosan/HA. The electrostatic interaction may be the main
driving force for Mb to be loaded into multilayer films. However, other interactions, such
as the hydrophobic force and hydrogen bonding, cannot be ruled out completely.
The chitosan/HA-cross-linked multilayer coating exhibits nonadherence to NIH-3T3
fibroblasts, but this nonadherence is not due to the cytotoxic effect. These chitosan/HA
PEM surfaces appear to be promising as a potential new noninteractive coating for inva-
sive medical devices (e.g., catheters) and are also useful for the culture of naturally nonad-
herent cells (e.g., chondrocytes) [232]. Osteoblast adhesion onto the Ti surface, which is
modified using chitosan/HA PEMs, is inhibited due to the presence of the HA chains.
However, the immobilization of RGD (Arg-Gly-Asp) on the surface of such functionalized
substrates tries to counteract this adverse effect. The immobilized RGD has a profound
beneficial influence on osteoblast adhesion and proliferation, and retains high antibacte-
rial efficacy [233]. The chitosan/HA PEM can also be constructed on damaged and healthy
aortic porcine arteries using a perfusion chamber matching closely the conditions achiev-
able in vivo . Strong adhesion of the coating onto the artery is ensured by depositing the
first chitosan layer, a polycation exhibiting excellent bioadhesive properties toward nega-
tively charged surfaces such as those presented by damaged arteries. The multilayer has
an effective protective effect against platelet adhesion onto damaged arteries. Moreover,
this effect can be improved when the l-arginine are introduced into multilayers [234].
4.5.2.2.2 Chitosan-Alginate PEM
Both chitosan and alginate are weak polyelectrolytes, and thus their charge density can be
easily tuned by pH. The chitosan-alginate assembly systems are commonly developed as
a complex planar membrane and microcapsule ( cf. Figure 4.20) [235,236]. Their multilayer
films are formed by the LBL method. There are small globules on the surface of chitosan-
alginate PEM. In addition, with increasing the assembly pH, the size of the globules
becomes larger and larger. Different assembly pH values induce a change of the conforma-
tion of the chitosan molecules. When the assembly pH of alginate is 3, the assembled struc-
ture is relatively homogeneous, which means that the alginate molecules are adsorbed
homogeneously on the surface. At higher assembly pH values, chitosan develops a loopier
and globular conformation, weakens the electrostatic repelling, and induces the aggrega-
tion of chitosan molecules. Thus, chitosan assembly with alginate molecules produces a
more globular complex ( cf. Figure 4.20).
The multilayer films can load antibody with pI 6.0-6.5 on the active site of the negatively
charged multilayer film surface. Its loading capacity decreases with increasing assembly
pH of alginate [235]. Shen and coworkers [237] employed mercaptoacetic acid (MAA) to
form a self-assembled monolayer (SAM) on the gold electrode surface of the quartz-crystal
microbalance (QCM), which resulted in a negatively charged surface through the formula-
tion of the MAA-SAM layer. The HSA antibodies were coupled to alginate via activation
with EDC-NHS, which prepared the negatively charged alginate-HSA antibodies. The
immobilization of the antibodies on QCM is achieved with a positively charged chitosan
layer used as the double-sided linker to attach the negatively charged alginate-HSA anti-
bodies to the negatively charged MAA-SAM layer ( cf. Figure 4.21) . The aforementioned
immobilization methodology was applied as a piezoelectric immunosensor for detecting
HSA in human serum.
Chitosan-alginate assembly nanotubes are prepared by the LBL assembly technique by
depositing chitosan and alginate onto the inner pores of a polycarbonate template alter-
nately [238]. Their nanotubes form after the removal of the template. The thickness of the