Formation of Chitosan-Based Hydrogels Network - Chitosan Based Hydrogels: Functions and Applications - page 182

the aid of protein. For example, rat osteoblasts directly recognize the CS-PECs (which are
composed of phosphate and carboxymethylated chitin as a polyanion and chitosan as a
polycation) and adhere to them without the aid of fibronectin [14]. CS-PECs containing
carboxymethyl groups as anionic sites cause the human periodontal ligament fibroblast
(HPLF) to aggregate and promote differentiation because the carboxymethyl groups offer
similar conditions as in vivo to HPLF. On the contrary, PECs containing sulfate groups
cause HPLF to form a spreading morphology and proliferate well [15,16]. A higher adhe-
sion number of cells on the chitosan/chondroitin sulfate surface are better than that on
pure chitosan films [17]. This is explained by taking into account that complex formation
removes the individual charges of the polymers and the chemical structure of chitosan,
which is necessary for cell recognition changes.
Above all, the diversity of the structure and preparation method of CS-PEC results in a
change of the physicochemical and bioactive functions. Here, some typical CS-PECs and
their characteristics will be introduced.
4.2.1.1 Chitosan-Gelatin PECs
Gelatin is a partial denaturalization derivative of collagen. Its electrical nature can be
changed by the collagen processing method. The alkaline process through hydrolysis of
amide groups of collagen yields gelatin with a high density of carboxyl groups, which
makes the gelatin negatively charged, reducing the isoelectric point (p I ) to 5.0. Gelatin pre-
sumably retains informational signals, for example, the Arg-Gly-Asp sequence. These
informational signals could improve chondrocytes attachment [18]. A PEC film can be
formed via the electrostatic interaction between chitosan and gelatin. There occurs strong
interaction between gelatin and chitosan in aqueous medium, which is enough to form
PECs in situ . And the chitosan/gelatin PECs is only yielded at pH values higher than 4.7 and
below pH 6.2 [19]. The strong interactions between chitosan and gelatin replace the macro-
molecular chain-water interactions. Therefore, the bound water content of chitosan/gelatin
PECs decrease slightly when compared to chitosan. The free water content of chitosan films
increases when blended with gelatin, which indicates that the structure of chitosan films is
more rigid and compact than that of a composite film. The chitosan/gelatin PEC reaches the
optimum interactive ratio when the content of gelatin is about 60% [20,21].
Gelatin moieties provide biocompatibility. The cell cycle analysis is carried out to assess
the proliferation of L929 rat fibroblasts on chitosan/gelatin PEC films in comparison with
that on chitosan films. It is found that blending chitosan and gelatin can induce cells to
enter the cell cycle and to begin to proliferate. Chitosan/gelatin PECs can promote cell
proliferation and inhibit cell apoptosis. This effect may be attributed to the decline in posi-
tive charge density of chitosan that may benefit cell migration [22]. A chitosan/gelatin PEC
scaffold is fabricated by freezing and lyophilizing methods. Autologous chondrocytes
from pigs' auricular cartilage are seeded onto the scaffold, and elastic cartilages have
been successfully engineered at porcine abdomen subcutaneous tissue [23]. Moreover,
chondrocyte proliferation is more distinct in chitosan-gelatin-DNA PEC scaffolds [24].
These studies indicate that the chitosan/gelatin PECs can be used as a suitable scaffold
for tissue engineering.
4.2.1.2 Chitosan-Alginate PECs
Chitosan-alginate PECs are prepared by mix ing aqueous solutions of chitosan and
alginate. At a given pH, the composition of the PEC shifts to a lower alginate content as the