Biomedical Engineering Reference
In-Depth Information
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Figure 5.1
Three strategies for functionalization of HBPs.
5.2.2.1 Terminal Modification
The terminal groups of HBPs occupy a great proportion in the macro-
molecules compared with linear polymers, so the alteration of the terminals is
capable, to a considerable degree, of transforming the characteristics of HBPs.
Nowadays, the numerous terminal groups of HBPs have been used to realize
their functionalization, thus revealing the great influence of the terminal
groups on the attributes of HBPs. Generally speaking, the terminal
modification is mainly based on the functional groups at the periphery of
HBPs, such as hydroxyl, carboxyl, amine, thiol, and halide terminals. Through
these various end-groups, many specific functional components can be grafted
onto the periphery of HBPs, including different functional end-groups, small
molecules (drug, organic dye, folic acid, etc.),
31,32
oligomers or polymers (so-
called ''graft to'' method),
10
or directly initiating the grafting polymerization of
functional monomers (so-called ''graft from'' method) to prepare block HBPs
and further obtain self-assemblies of HBPs. The interactions between terminal
groups and modified components vary from covalent bonds to noncovalent
bonds, thus affording many modified methods. Such a synthetic methodology
of functionalizing HBPs is termed as ''terminal groups replacing'' (TGR).
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Figure 5.2 summarizes the primary approaches to TGR; how to obtain the
expected
functions
through
TGR
will
be
discussed
in
the
section
on
functionality of delivery (Section 5.3).
5.2.2.2 Hybrid Modification
The driving force of hybrid modification mainly stems from host-guest
interaction, complexation interaction, hydrogen bonding interaction, and
electrostatic attraction. By means of these weak interactions, the external
components such as metal ions can be settled into the cavities of HBPs, thus
