Biomedical Engineering Reference
In-Depth Information
Polypeptide chain
NH
H
+−
−+
H
−+
H
Si
−+
H
H
+−
H
+−
−+
H
−+
H
−+
H
−+
H
H
+−
H
+−
H
+−
Covalent coupling
H
+−
−+
H
−+
H
Si
−+
H
H
+−
H
+−
NH
H
+−
−+
H
−+
H
−+
H
−+
H
−+
H
Si
H
+−
H
+−
NH
−+
H
H
+−
H
+−
H
+−
−+
H
−+
H
Figure 10.6
Schematic of polypeptide-silica hybrids, for example, gelatin-silica,
where GPTMS is used to couple the polypeptide to the silica network formed by a
TEOS-based sol-gel process.
Using TEOS to produce a silica network and GPTMS as the coupling
agent allows control of the degree of coupling independent of the total
inorganic-to-organic ratio, which provides a greater ability to control
properties but also creates a complex system. By using this method,
properties can be tailored such that the hybrid is as flexible as a polymer
or as stiff as a glass, or anywhere in between. The hybrids also degrade
congruently (silica is lost at a similar rate to the polymer). Poly(glutamic
acid) has also been used as a simpler polypeptide in similar systems.
10.7 MAINTAINING BIOACTIVITY IN SOL-GEL
HYBRIDS
In terms of a hybrid for bone regeneration, there is little point creating a
hybrid if it is not bioactive. A key part of the bone bonding mechanism
is spontaneous deposition of a layer of HCA (§§10.2) on the surface
when the materials contact with blood plasma. The mechanism of HCA
layer formation is described in Chapter 2. It is important to remember
