Biomedical Engineering Reference
In-Depth Information
connects preformed telechelic polymer chains and the trunk polymer at a particular site
by covalent bonding. Examples of different polymers grafted onto chitosan include
poly(isobutylvinyl ether), PEG, and the derivatives PEO-PPO-PEO (pluronic polyols or
poloxamers), poly(ethyleneimine), polyurethane, poly(dimethylsiloxane), and polylactide
(Figure 2.36). Of these, PEG is an important hydrophilic polymer commonly grafted
(PEGylated) onto chitin-chitosan. Several methods have been reported on the PEGylation
of chitin-chitosan using PEGs with various terminal reactive groups
(Table 2.4).
PEG can
be regioselectively grafted to obtain chitosan-
O
-poly(ethylene glycol) graft copolymers by
prior protection of amino groups [304]. Such etherification of chitosan was reported with
poly(ethylene glycol) monomethyl ether (MPEG) using triazine derivative as coupler and
with MPEG iodide without coupler [239] (
Figure 2.37)
.
Regioselective modification of chi-
tosan through the C-6 position of glucosamine units by PEG has been reported for the first
time using 6-oxo-2-
N
-phthaloylchitosan, 6-
O
-dichlorotriazine-2-
N
-phthaloylchitosan, and
3-
O
-acetyl-2-
N-
phthaloylchitosan intermediates with high DS [305].
Methods of immobilizing adhesive peptide ligands on nonfouling surfaces are impor-
tant because they allow us to study the effect of individual factors on cell adhesion, prolif-
eration, and differentiation without the confounding influence of protein adsorption from
the serum or the extracellular matrices produced by the cells themselves. Ying and cowork-
ers [306] engineered the RGD peptide on chitosan PEC using a three-tiered system
(
cf.
Figure 2.38).
The three-tiered system described in this work offers unique advantages.
First, the three-tiered system enabled the isolation of the effect of the ligand from the effect
of chitosan by interposing a nonfouling second tier between the underlying substrate (first
OH
NHR
N
NH
2
NHR
N
NH
2
O
HOC
CHO
N
3
NH
2
O
3
R
N
3
H
O
R
H
H
O
HO
N
NH
2
PEI-grafted chitosan
N
PEI
OHC
CHO
NH
2
RNH-PEI
PEI
NH
2
+
O
1.
O
O
O
2.
O
O
O
O
PHB
R
O
H
RNH
2
HO
UV irradiation
PHB-conjugated chitosan
O
PDMS
R
PDMS
PEO-PPO-PEO-pNP
H
O
OH
PDMS-grafted chitosan
BPA
O
HO
O
R
O
O
H
PEG-grafting
O
Poloxomer conjugated chitosan
NH
2
-PPG-NH
2
D-PAG
PPG-grafted chitosan
Protein grafted chitosan
Figure 2.36
Various synthetic routes to chitosans conjugated with different macromolecular pendant groups by the “graft-
ing onto” method. PEI: polyethyleneimine, PHB: poly(3-hydroxybutyrate), PEO: poly(ethylene oxide), PPO:
poly(propylene oxide), pNP:
p
-nitrophenyl, G-APG: gluadin APG (a partially hydrolyzed wheat gluten protein,
M
W
= 5000), PPG: poly(propylene glycol), BPA: bisphenol A residue, PDMS: poly(dimethylsiloxane).
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