Biomedical Engineering Reference
In-Depth Information
OCH
3
O
O
O
H
H
S
S
n
a
a
b
NC
NC
b
O
O
O
O
m
OCH
3
S
S
m
O
O
O
O
d
n
3
r
4
n
g
|
3
HO
O
O
OH
O
OH
HO
O
P
O
O
P
O
O
HO
O
HO
OH
O
O
OH
O
O
O
O
OH
HO
OH
O
OH
O
OH
N
N
OH
OH
OH
O
O
O
HO
Figure 12.4 Molecular
structure of a methoxy group-containing PRX block
co-polymer.
From this point of view, a polyrotaxane (PRX) is considered as a proper
materials to provide dynamic nature on the polymer surfaces. PRX is a
molecular assembly consisting of a host molecule, e.g., a-cyclodextrin
(a-CD), threaded by a linear guest molecule, e.g., polyethylene glycol (PEG).
23
a-CD and PEG form a non-covalent inclusion complex due to intermolecular
hydrogen bonding of neighboring CD molecules as well as van der Waals
interaction between the cavities of CD with PEG chains. For this reason,
threaded a-CD molecules in PRX are expected to freely slide and rotate along
a linear PEG backbone after diminishing the intermolecular hydrogen
bonding of CD by chemical modification.
24
By taking advantage of this
highly movable inclusion complex, it is expected that a polymer surface with
a broad range of Mf values could be achieved. To this end, an ABA-type block
co-polymer was recently reported to develop dynamic polymer surfaces.
Figure 12.4 shows the representative molecular structure of the PRX block
co-polymer. A random co-polymer composed with 2-methacryloyloxyethyl
phosphorylcholine (MPC) and n-butyl methacrylate (n-BMA) (PMB) is intro-
duced at both ends of the PRX segment for the stable forming PRX segment
on the substrate surfaces. The PMB is a well-known surface anchoring group
which can be immobilized on the various surfaces by hydrophobic inter-
action induced by n-butyl segment.
25
Furthermore, effective suppression of
non-specific protein adsorption could be achieved due to the cell membrane
mimic anti-fouling phosphorylcholine group.
26
Because a-CD molecules in
PRX segment is covered with 18 hydroxyl groups, various functional groups
could be introduced on the dynamic PRX segment by chemical modification
such as carbonyldiimidazole-mediated chemistry.
27
The hydrophobic
methoxy group is one of the most commonly used chemical groups to pro-
vide hydrophobic property onto PRX segment. The change in Mf value is
observed when the hydrophobic methoxy group was introduced on PRX
segment (mPRX) (Figure 12.5). Of particular interest is the independent
manner of the Mf values on PRX block co-polymer surfaces with those of the
surface free energy. While most of the prepared polymer surfaces show
similar level of surface free energy, i.e., within a narrow range of surface free
.
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