Formation of Chitosan-Based Hydrogels Network - Chitosan Based Hydrogels: Functions and Applications - page 203

incorporated. Without the formation of semi-IPN structure, hydrophobic PDMS with high
Mn and high content tends to macrophase separate from chitosan continuous phase. PDMS
and PEG in the chitosan semi-IPNs generally promote water swelling ability and water
vapor permeability of the modified chitosan films. It is hypothesized that PEG enhanced
these properties due to its hydrophilic characteristics, while in the case of PDMS-chitosan
semi-IPNs, this is attributed to the formation of PDMS microphase, allowing the materials
to have more polymer-air interfaces and more contact with water. Addition of PDMS/PEG
to chitosan semi-IPNs slightly enhances their thermal stability and surface hydrophobic-
ity, while their tensile properties are sacrificed [162].
4.3.2.2 Full-IPNs
Fang and coworkers [163] reported a kind of full-IPN chitosan/poly( N -isopropylacry-
lamide) (CS/PNIPAM) hydrogel that is formed by chemical combination of methylene
bis-acrylamide-cross-linked PNIPAM network with a formaldehyde (HCHO)-cross-
linked chitosan network. It is demonstrated that the properties of the hydrogels, includ-
ing the extractability of PNIPAM within it, the phase transition behavior, the swelling
dynamics in aqueous phase, the swelling behavior in ethanol/water mixtures, and even
the microstructure, are quite different from those of the semi-IPN CS/PNIPAM hydro-
gels, in which PNIPAM is simply embedded. Like the semi-IPN CS/PNIPAM hydrogels,
however, the full-IPN hydrogel is also temperature sensitive; that is, the hydrogel is
transparent below 30°C, but opaque above that temperature. It is expected that this
hydrogel may find some uses in separation science and in the design and preparation of
new soft machines.
PVA has hydrophilic groups, which are employed in biomedical applications because
of its easy preparation, excellent chemical resistance and physical properties and
because it is biocompatible. Full-IPN hydrogels based on PVA and chitosan were pre-
pared by using UV irradiation and the swelling ratio, free water content and bound
water content of the IPN hydrogels were measured by Kim et al. [164]. All hydrogels
swell rapidly and reach equilibrium within 1 h. The swelling ratio and free water
contents increase with increasing molar ratio of hydrophilic groups of chitosan in IPNs.
The PVA/chitosan IPN hydrogels exhibit swelling change in response to external stimuli
such as pH and temperature, and can be useful as a novel modulation system in the
biomedical field.
Considering that conventional nonporous hydrogels swell slowly and exhibit low load-
ing capacities, which restrict their use in effective drug delivery, superporous hydrogel
(SPH) containing poly(acrylic acid-co-acrylamide)/carboxymethyl chitosan (P(AA-co-AM)/
O-CMC) IPNs (SPH-IPNs) are synthesized to enhance the mechanical strength, in vitro
muco-adhesive force, and loading capacity of SPHs. The swelling ratios of SPH-IPNs
decrease with increasing the O-CMC content, the GA amount, and the cross-linking time.
After the introduction of the full-IPN structure, mechanical properties, in vitro muco-
adhesive force and loading capacities of the SPH-IPNs are significantly improved and can
be modulated by varying the O-CMC content. The SPH-IPNs will also be biocompatible
considering the biocompatibility of both P(AA-co-AM) and O-CMC. Such characteristics
suggest that the SPH-IPN may be an advantageous candidate for the mucosal drug deliv-
ery system, especially for effective peroral delivery of peptide and protein drugs [165].
SPH-IPN is also evaluated as the oral delivery vehicle for insulin, emphasizing the effect
of polymer integrity on insulin absorption mechanisms. Compared to powdered SPH-IPN
(P-SPH-IPN), integral SPH-IPN (I-SPH-IPN) has a higher swelling ratio, a stronger water