Soft Matter Composites Interfacing with Biomolecules, Cells, and Tissues - Bioinspired Approaches for Human-Centric Technologies - page 47

Fig. 2.10 (a, upper panel ) swelling behavior of pure hydrogel, ions-loaded hydrogel, and
nanohydrogels. (b, lower panel ) (a) plain hydrogel. (b) Ag+ ions-loaded hydrogel. (c) Ag
nanocomposite hydrogels (Reddy et al. 2013 )
such as hydrophilicity, existence of functional amino groups, and a net cationic
charge have made chitosan a suitable polymer for the intelligent delivery of
macromolecular compounds, such as peptides, proteins, antigens, oligonucleotides,
and genes. Chitosan hydrogels have been prepared with a variety of different
shapes, geometries, and formulations that include liquid gels, powders, beads,
films, tablets, capsules, microspheres, microparticles, sponges, nanofibrils, and
inorganic composites. In each preparation, chitosan is either physically associated
or chemically cross-linked to form the hydrogel. As a hydrogel, chitosan networks
should satisfy the following: (1) interchain interactions must be strong enough to
form semipermanent junction points in the network and (2) the network should
promote the access and residence of water molecules within. Gels that meet these
demands may be prepared by non-covalent strategies that rely on electrostatic,
hydrophobic, and hydrogen bonding forces. Figure 2.12 shows the schematics of
four major physical interactions (i.e., ionic, polyelectrolyte, interpolymer complex,
and hydrophobic associations) that lead to the gelation of a chitosan solution
(Bhattarai et al. 2010 ). Because the network formation by all of these interactions
is purely physical, gel formation can be reversed. Due to cationic amino groups of