Biomedical Engineering Reference
In-Depth Information
smart polymers based on chitosan. Grafted copolymerization, by CLRP methods, of mono-
mers such as NIPAM and acrylic acid (AA) (among others) will enable the preparation of a
variety of responsive graft copolymers with precise structure and molecular design to
give materials made up of tailored chitosan and synthetic polymers.
2.12 Chitosan-Dendrimer Hybrid
Dendrimers are attractive molecules owing to their multifunctional properties and have
useful applications as viral and pathogenic cell adhesion inhibitors. Increasing scientific
efforts have gone into the design and synthesis of dendrimers. Dendronized polymers, on
the other hand, are also attractive because of their rod-like conformation and nanostruc-
ture. Dendrimer-like hyperbranched polymers, a new class of topological macromolecules,
have recently been grafted onto chitosan. Tsubokawa and Takayama [317] reported the
surface modification of chitosan powder by the grafting of hyperbranched dendritic poly-
amidoamine (PAMAM). They found that PAMAM was propagated from the surface of
chitosan by the repetition of two processes: (1) Michael addition of methyl acrylate to the
surface amino groups and (2) amidation of the resulting esters with ethylenediamine to
give PAMAM dendrimer-grafted chitosan powder (Figure 2.42).
Sashiwa established the synthesis of a variety of chitosan-dendrimer hybrids, mainly by
two procedures (
Figure 2.43)
[318-320]. In method A, corresponding dendrimers bearing
aldehyde and a spacer are synthesized, and then these are reacted with chitosan by reduc-
tive N-alkylation. This procedure has the advantage of no cross-linking during the reaction.
Repeating the same steps
COOMe
1.
Chitosan
NH
2
2.
H
2
N
OH
O
O
O
HO
NH
2
O
N
O
H
2
N
O
HN
H
HN
O
N
O
N
N
H
HN
O
N
N
NH
O
NH
O
O
NH
2
O
H
2
N
NH
NH
N
N
N
O
NH
2
NH
O
O
O
NH
H
2
N
NH
H
2
N
H
2
N
Figure 2.42
Polyamidiamine dendrimer-grafted chitosan surface.
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