Formation of Chitosan-Based Hydrogels Network - Chitosan Based Hydrogels: Functions and Applications - page 202

decrease with increasing the GA concentrations in the P-CS/GA gels and increasing the
viscosities of the P, P-CS, and P-CS/GA solutions.
The multifunctional chitosan-poly(methacrylic acid)-CdSe (chitosan-PMAA-CdSe)
hybrid nanogels are prepared in an aqueous solution via in situ immobilization of CdSe
quantum dots (CdseQDs) into the chitosan-PMAA semi-IPN nanogels, which should dis-
play the properties and functions from each building block, as schematically depicted in
Figure 4.14. The template chitosan-PMAA nanogel is formed either by noncovalent physi-
cal associations, such as secondary forces and physical entanglements, or by covalent
cross-linkages. The covalently cross-linked nanogels are very stable in both structure and
composition upon pH variation; the hybrid nanogels based on the physical associations
exhibited a significant change in structure and composition in response to a pH increase
to physiological conditions. The covalently cross-linked hybrid nanogels exhibit excellent
structural stability as well as reversible physical property change in response to a pH
variation cross the physiological condition, which can successfully integrate the optical
pH-sensing and cellular imaging ability, regulated drug delivery, and low-cytotoxicity
into a single nano-object. In contrast, the physically associated hybrid nanogels would not
be an ideal candidate for biosensing and drug delivery. It is important to achieve progress
in the development of multifunctional bionanomaterials by incorporation of functional
building blocks into a single individual nanoparticle [159].
The limited solubility of chitosan in water and common organic solvents has inhibited
extensive studies and utilization of chitosan. So modifications of chitosan with polymers
have been widely investigated to tune its properties to fulfill some requirements for spe-
cific applications. These are carried out either by physical blending, chemical grafting, or
cross-linking. For example, PEG/polydimethylsiloxane (PEG/PDMS) block copolymer,
prepared by a condensation reaction between PEG diacid and PDMS diol, is incorporated
into chitosan in order that good water swellability and wettability of chitosan were retained
due to hydrophilic PEG blocks, whereas PDMS block in the copolymers functioned as a
toughening modifier [160,161]. However, some macroscopic phase separation between the
copolymer and chitosan is still observed when a high percentage of the copolymer was
applied due to the absence of chemical bonding between these two phases. Therefore,
PDMS/PEG-chitosan semi-IPNs were prepared, where PDMS and PEG were selected to
represent hydrophobic and hydrophilic polymers, respectively, to investigate their effect
on the properties of chitosan hydrogels. They are interpenetrated and locked in place in
the chitosan structure, so that up to 20 wt% PDMS/PEG with high Mn (8000 g/mol) can be

-

-

-

-

Chitosan

Controlled
drug delivery

Biopolymer
chitosan

Drug

-

-

PMAA

pH-sensing
Tumor-cell
imaging

Uncross-linked Cross-linked

Optical code
(CdSe QDs)

Hybrid nanogel
(R h < 100 nm)

-
-

-

-

pH-sensitive
PMAA

pH-induced
structural changes

Stable
structure

Figure 4.14
Schematic representation of the concept for designing multifunctional chitosan-PMAA-CdSe hybrid nanogel
and its potential applications in the biomedical field. (From Wu, W. et al. 2010. Biomaterials 31: 8371-8381. With
permission.)