Biomedical Engineering Reference
In-Depth Information
these materials are synthesized using surfactants which play the role of a
template, allowing the production of materials with ordered porosity, in the
nanometre size range, and amorphous silica pore walls.
the application of this synthesis methodology to the production of bioactive
glasses leads to amorphous silica materials, which are highly reactive and have
ordered mesoporosity. this stage leads in turn to the synthesis of templated
glasses.
151
these templated glasses exhibit spectacular textural properties when
compared with traditional bioactive sol-gel glasses; specific surface values, for
instance, are twice as large.
they are bioactive and, owing to their more open
texture, the bioactive response is evidenced after much shorter periods of time;
the best bioactive response data in traditional sol-gel glasses is obtained after
3 days, while 1 hour suffices in the mesoporous templated glasses.
151
these
templated glasses exhibit high
in vitro
reactivity when in contact with SBF. the
transformation path starts with the formation of an amorphous calcium phosphate,
which then evolves to octacalcium phosphate and subsequently to calcium
deficient carbonate hydroxyapatite. The whole sequence is performed in just 8
hours
152
and its most interesting feature is its similarity to the biomineralization
processes which take place in natural bone.
On the other hand, mesoporous microspheres have been recently investigated
for biomedical applications. thus, bioactive glass microspheres with accelerated
deposition rates of HCA and hemostatic efficacy153
153
and magnetic silica microspheres
for drug targeting have been reported.
154, 155
7.4.2 Organic-inorganic hybrid materials
the synthesis of bioactive organic-inorganic hybrid materials able to bond
osseous tissues and to host molecules with biological activity is an important
task in the biomedical engineering field.156
156
Hybrids are synthesized by sol-gel
processes at temperatures close to ambient that do not destroy the organic
component. this method makes possible the production of hybrid materials in
different forms: as bulk, coatings, fibres, and so on. Inorganic components of
hybrids are often based in SiO
2
-CaO glasses because they supply many surface
silanol groups and release Ca
2+
ions into solution, both effects promoting the
bioactive response. With respect to the organic component, several biocompatible
polymers were investigated in order to tailor the hybrid materials properties. For
instance, bioactive hybrids with mechanical features comparable to natural bone
were obtained.
157
In addition, polymers with specific functionality (i.e. amino
groups) able to interact with biological entities, have been used as the organic
component of hybrids.
28
Several organic-inorganic systems were investigated for clinical uses as
bioactive or degradable materials. in some hybrid systems, only weak physical
interactions between inorganic and organic domains are present. examples
include hybrids containing poly(vinyl alcohol) (PVA),
158, 159
or poly(hydroxyethyl
