Application of Chitosan-Based Biomaterials in Tissue Engineering - Chitosan Based Hydrogels: Functions and Applications - page 436

scaffolds have attracted much attention in cartilage tissue engineering. The addition of
GAGs does not obviously alter the physical properties of chitosan scaffolds. Conjugating a
single GAG species to chitosan is beneficial to chondrocyte culture and ECM production.
The inclusion of GAG in the scaffold may promote the adhesion, migration, proliferation,
and differentiation of chondrocytes. In addition, GAG can increase the water-binding
capacity of scaffolds. The rich water-binding capacity may have therefore influenced the
cell distribution and cluster formation, and the preservation of chondrocytes. For example,
chondrocytes attached to chitosan-chondroitin sulfate scaffold had largely maintained a
rounded or polygonal morphology and undergone only a modest degree of mitosis, main-
taining the synthesis of cartilage-specific collagens [141]. A homogeneous cartilaginous
tissue, which was similar to those of natural cartilage, formed when chondrocytes were
seeded in the ternary chitosan-collagen-chondroitin sulfate porous scaffold at 12 weeks
after implantation [142]. Similarly, ternary chitosan-collagen-hyaluronan scaffolds show
an improvement in the mechanical strength, degradation rate, and water-binding capacity.
And the chitosan-collagen-hyaluronan scaffolds reveal an increase in the total amount of
GAGs and contain significantly more newly synthesized GAGs than the chitosan-collagen
scaffolds alone [143]. Dermatan sulfate plays a very important role in cartilage engineer-
ing, and a low concentration of dermatan sulfate is beneficial for ECM production. However,
higher concentration could enhance the activities of metalloproteases [144] which degrade
ECM molecules and lead to lower GAGs and collagen production levels. Hu and coworkers
[145] found that a combination of 2.8 mg chondroitin 6-sulfate and 0.01 mg dermatan
sulfate in the chitosan scaffold (ca. 2.5 mg) is the optimal composite to modulate the behav-
iors of chondrocytes.
9.5.3.2.3 Chitosan-Polysaccharide Scaffolds
Some polyanion polysaccharides, whose structures are similar to GAGs, are also intro-
duced into the chitosan network to construct the artificial cartilages. Alginate, a family of
polyanionic copolymers, represents naturally occurring polysaccharides composed of
(1-4)-linked β-d-mannuronic acid (M units) and α-l-guluronic acid (G units) monomers.
The use of alginate may facilitate a uniform distribution of chondrocytes in the relatively
wide pores of the scaffold and prevent cells from floating out. Moreover, in vitro experi-
ments showed that alginate can stimulate the expression of the chondrogenic phenotype
[146]. Chitosan-alginate porous scaffolds have a highly porous structure with a fairly even
pore distribution and the surface of the scaffold is relatively rough and embedded with
small grooves. The chondrocyte on chitosan, alginate, and chitosan-alginate scaffolds
continued to increase with time. Moreover, the cell number on the chitosan-alginate scaf-
fold became notably higher than on the pure chitosan scaffold and alginate scaffold. And
the proliferation capacity of chondrocytes on chitosan-alginate (50/50 wt%) is higher than
that on the chitosan-alginate (30/70 wt%) scaffold [37,147-149]. Moreover, the chitosan-
alginate scaffold showed prolonged support for collagen type II production compared
with the chitosan scaffold. Compared with chitosan, chitosan-alginate showed better sup-
port of maintaining the phenotype of chondrocytes, presumably resulting from special
characteristics of alginate material in promoting chondrocyte recovery. At day 14, chon-
drocyte cells on chitosan and chitosan-alginate exhibited a spherical morphology. At day
21, however, the cells on the chitosan scaffold became more flattened and started to assume
a fibroblast-like morphology, while the cells on the chitosan-alginate scaffold remained
their initial spherical morphology ( Figure 9.29) [137]. When the chondrocyte-chitosan-
alginate-hyaluronate constructs are implanted into rabbit knee cartilage defects, partial
repair is observed after 1 month [150].