Biomedical Engineering Reference
In-Depth Information
OR
RO
Si
OR
+
Basic catalyst
(such as NH
4
OH)
OR
where R is -CH
3
or -CH
2
CH
3
, normally
OR
OR
OH
(1)
RO
O
H
+
RO
O
-
+
H
2
O
Si
Si
OR
OR
OR
OR
OR
OR
O
−
+
(2)
RO
Si
RO
Si
OH
OH
−
+
RO
Si
O
Si
OR
OR
OR
OR
OR
FIGURE 4.2
General synthesis of silica nanoparticles under basic conditions: (A) silica precursor and catalyst are added in
an alcoholic solution, if R is a methyl group, the precursor is TMOS and if R is an ethyl group, the precursor
is TEOS. (B) The precursor is then hydrolyzed by a hydroxyl ion (hydrolysis, B1) and the activated precursor
is condensed with another activated precursor or precursor (condensation, B2). (C) As a result of hydrolysis
and condensation, silica nanoparticles are generated.
4.3.2
Dispersibility and purification
Dispersibility, generally defined as a uniform distribution in solution, not to be confused with solu-
bility, is an important factor for both biomaterials and biomedical applications, with monodispersed
often being the most desirable. The sol
gel process can generate highly dispersible products,
whereas fumed products do not generate a good polydispersion index, a measure of dispersibility.
Silica's characteristics such as size distribution, surface charge, and porosity will vary depending
on their synthetic method and it is therefore important to select the synthesis method based on
application, irrespective of whether fabricated in the laboratory or purchased commercially.
