Biomedical Engineering Reference
In-Depth Information
PDMS chains
−+ H
H +−
CH 3
CH 3
H +−
H +−
H
−+
-Si-
O-
O
-Si-
−+ H
H + −
CH 3
CH 3
−+ H
−+ H
−+ H
H + −
H + −
CH 3
O
PDMS/ Silica interface
-Si -
OO
-Si -
O
CH 3
Figure 10.4 Schematic of the nanostructure of Ormosils. Inset shows an example
of the silica network.
with those on the silica blocks. The calcium ions, if added to the starting
solutions, are probably present near the silica block surface or inside the
blocks, being electrostatically bound to Si-O , but the oxygen atoms in
the PDMS blocks are less negatively charged, and hence cannot stabilize
the calcium ions.
A number of silanes are applicable as the starting materials for the
hybrids, including derivatives of TEOS that have some reactive organic
groups substituted for ethoxy (-OEt) groups. Sometimes they involve
active groups at either end. Table 10.1 lists such examples of bifunctional
silanes. Among those, vinyl and methacryloxy groups are primarily
subjected to homo-polymerization to form the
skeleton, while
the glycidoxy group is likely to be attacked by nucleophiles (having lone-
pair electrons): when, for example, the organic component contains an
amino group, -NH-O-C-C- bonds will be formed. Especially reactive
are mercaptans, which are easily hydrolyzed to give R -OH together
with H 2 S as the by-product:
>
C-C
<
R -SH
R -OH
+
H 2 O
+
H 2 S
(10.2)
The -SH group is one of the key sources for highly biological activity
of those mercaptans. In addition, some mercaptans can also attack Au
to form anchoring R -S-Au bonds, and hence they are strongly fixed on
Au coatings, particles, or films. They are sometimes arranged to yield
SAMs as shown in Figure 10.3.
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