Biomedical Engineering Reference
In-Depth Information
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Figure 4.2
Structure of chitosan hydrogels formed by (a) chitosan cross-linked with itself; (b) HPN; (c) semi-interpenetrat-
ing network; and (d) ionic cross-linking of chitosan. (From Bergera, J. et al. 2004.
Eur J Pharm Biopharm
57: 19-34.
With permission.)
structure, charge density, hydrophilicity/hydrophobicity balance, stereo-regularity, and
compatibility, as well as the reaction conditions, for example, the pH, ionic strength,
concentration, mixing ratio, and temperature [13]. The properties of PECs are mainly
determined by the degree of interaction among individual polymers. PECs depend
essentially on the polymers' global charge density and this determines their relative
composition in the PEC. The lower the charge density of the polymer, the higher the
polymer proportion in the PEC, since more polymeric chains are required to react with
other polymers. A PEC can be formed via two ionizable polymers with opposite charges
individually. This means that PEC formation reaction can only occur at pH values in the
vicinity of the p
K
a
interval of the two polyelectrolytes. The concomitant release of cor-
responding counterions is the main driving force of the reaction because it corresponds
to an increase in entropy of the system. Other interactions may be involved in the forma-
tion of PEC structures, such as hydrogen bonding, hydrophobic interaction, or van
der Waals interactions. PECs can be prepared in various forms such as film, hydrogel,
microcapsule, or scaffold.
Cell attachment, morphology, and proliferation are influenced by physicochemical prop-
erties of the CS-PECs surface. The surface chemical composition of PECs is important in
cell events because the cell could directly recognize the PECs and adheres to them without
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