Formation of Chitosan-Based Hydrogels Network - Chitosan Based Hydrogels: Functions and Applications - page 197

The cross-linking of the chitosan/chondroitin sulfate composite ECMs with GA and
EDC/NHS shows no obvious change in the morphology of 3D porous scaffolds. However,
the cross-linking of the chitosan/chondroitin sulfate composite with Ca 2+ produces a sig-
nificant change in its porous structure. The Ca 2+ -cross-linked chitosan/chondroitin sulfate
composite ECMs have smaller pore size than GA- and EDC/NHS-cross-linked counter-
parts [139]. GA cross-links at the C-2 amine of glucosamine units in chitosan via imide
bonds formation. However, the functional groups on chondroitin sulfate are not easy to
react with GA. This suggests that the cross-linking of the chitosan/chondroitin sulfate
complex with GA may produce a composite structure like semi-interpentrated networks,
whereas EDC/NHS cross-linking results in the formation of amide bonds between car-
boxylic acid groups on chondroitin sulfate and amine groups on chitosan. Chondroitin
sulfate will become cross-linked with the chitosan macromolecular chain, which is to form
real chitosan/chondroitin sulfate interpenetrated networks. Calcium ions coordinated
by oxygen atoms on carboxylate and sulfate groups on chondroitin sulfate are at short
distances to form cross-linked networks. The chitosan/chondroitin sulfate networks show
different swelling behavior due to the different cross-linked structure. The swelling ratios
of the Ca 2+ -cross-linked chitosan/chondroitin sulfate network are significantly lower than
those of the GA-cross-linked ones. And different cross-linking types have different effects
on the adsorption of bFGF ( cf. Figure 4.11) [140]. In addition, the release rate of these GFs
can be controlled by varying the composition of chondroitin sulfate in the sponge or initial
loading content. For example, Lee and coworkers [141] found that the release rate of
platelet-derived growth factor BB (PDGF-BB) increases with decreasing the chondroitin
sulfate content of the system. And chitosan/chondroitin sulfate can improve the migration
and proliferation of osteoblasts as compared with the chitosan scaffold alone. Furthermore,
the release of PDGF-BB from the chitosan/chondroitin sulfate network scaffold signifi-
cantly enhances osteoblast proliferation.
Chitosan can provide initial attachment and spreading of osteoblasts preferentially over
the fibroblast [142]. Gelatin is derived from type I collagen, which plays a central role in the
new bone formation from progenitors cells [143]. Moreover, chondroitin sulfate, which is
the main GAG in bone, in association with collagen fibers, promotes in vitro mineraliza-
tion[144]. Based on the advantages of these, a 3D chitosan/gelatin/chondroitin sulfate
porous scaffold was cross-linked with EDC. A rat MSC scaffold was cultured with the
osteogenic medium. The results demonstrated that the 3D structure provides a good envi-
ronment for the osteogenic process and enhances cellular proliferation [145].
4.3.1.2.2 Chitosan/HA Network
HA is a major component of the PGs in the cartilage. Chitosan/gelatin/HA hybrid
cross-linked networks were prepared via cross-linking with EDC/NHS and MES ( cf.
Figure 4.12). For studying the biocompatibility of these films, the cell cycle and apoptosis
of L929 cells were evaluated. The results show that incorporated HA shortens the adapta-
tion period of cells on the film surface, and then cells enter the normal cell cycle quickly.
Moreover, the added HA would not trigger necrosis; it inhibited cell apoptosis on chitosan/
gelatin films [146]. The concentration of HA in the chitosan/gelatin/HA-cross-linked net-
work has an influence on the physical and mechanical properties and cytocompatibility
of the network film. It is only the HA concentration in the range of 0.01-0.1% that benefits
the ternary film [147].
A two-layer chitosan/gelatin/HA scaffold cross-linked with EDC has been constructed
using the freeze-drying method. The asymmetric scaffold with different pore size layers
is used for coculturing human fibroblasts and keratinocytes. The scaffold provides a