Biomedical Engineering Reference
In-Depth Information
OCH
3
OCH
2
CH
3
OCH
2
CH
3
OCH
2
CH
3
CH
3
O
Si
CH
2
CH
2
CH
2
O CH
2
CH
3
CH
2
O
Si
O
OCH
3
(Tetraethoxysilane)
OCH
3
(Glycidoxypropyltrimethoxysilane)
OCH
2
CH
3
CH
3
O
Si
CH
2
CH
2
CH
2
NH
2
CH
3
CH
Si
CH
3
OCH
3
OCH
2
CH
3
(a)
(3-aminopropyltrimethoxysilane)
(Methylvinyldiethoxysilane)
O
OCH
2
CH
3
O
Si
O
OCH
2
CH
3
H
H
2
O
CH
3
O
Si
CH
3
CH
2
O
Si
OCH
2
CH
3
CH
3
CH
3
Si
CH
3
OCH
2
CH
3
OCH
2
CH
3
(Ormosil)
O
(b)
FIGURE 16.3
(a) TEOS and other commonly used ormosil monomers and (b) reaction scheme for
ormosil formation.
act as electron shuttles to transfer the electrons between electrode surface and redox
enzymes. The use of ormosils in bioencapsulation provides interesting properties to the
host matrixes from hydrophobic to hydrophilic (hydrogels) [26]. When hydrophobic
silica forming monomers are used, the resulting electrodes reject water, leaving only
segregated islands of carbon at the outermost surface in contact with electrolyte [27].
On the other hand, when hydrophilic monomers are used, there is an increase in
the water-wetted area of sol-gel glass. Thus the ratio of hydrophilic and hydrophobic
monomers in organically modifi ed sol-gel glass is crucial in the preparation of biocom-
patible matrices and sensor design [28]. The structure and properties of doped sol-gels
depend not only on the chemical compositions of the starting materials, but also on
many operational factors involved in the preparation such as water-silica molar ratio,
solvent, catalyst, pH, and temperature. These parameters highly infl uence the hydroly-
sis and condensation and allow the control of nano- and microstructure of the fi nal
materials [8]. Such control is essential for achieving a proper balance between non-
leaching of the entrapped bioactive molecules and its accessibility to the analyte. In
addition to these the sol-sitting time, gel-dying time, and the conditions under which
the gel is aged and dried (i.e. relative humidity) can also affect the long-term perform-
ance of these materials [9].
16.2.2 Progress in sol-gel process
Although the sol-gel process is highly convenient for the immobilization of bio-
molecules, a major limitation is the formation of alcohol as a by-product during the
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