Biomedical Engineering Reference
In-Depth Information
Organic
polymer
chains
H
+
−+
H
H
+−
H
+−
H
−+
−+
H
H
+ −
−+
H
−+
H
H
+ −
−+
H
200 nm
H
+ −
Figure 10.1
Schematic representation of the structure of a hybrid of inorganic silica
and an organic polymer. Inset shows an example of the silica network.
a composite is the combination of two or more distinguishable com-
ponents. Although hybrids are a relatively new type of material, they
have had several names such as Ormosil, Ceramer, and hybrid. Some
(incorrectly) call them nanocomposites because of the nanometer (or
sub-nanometer) scale interactions between the components. At the time
of writing, there are no medical devices approved for clinical use that are
hybrids, but their properties mean that they are a material of the future
and they have massive potential in a variety of biomedical applications.
10.2 HYBRIDS IN MEDICINE AND WHY THEY
SHOULD BE SILICA-BASED
When a foreign substance is introduced into our body, cells, blood
proteins, and other physiologically active molecules quickly settle on
the surface to form a biological film-like layer. When ordinary artificial
materials, such as metals, bio-inert ceramics, and organic polymers
(synthetic), are implanted, our body produces a fibrous tissue on
the surface, and expels the foreigner away. In contrast, bioactive
ceramics, for example, hydroxyapatite (HA) and
β
-tricalcium phos-
-TCP), bioactive glasses (e.g. Bioglass
®
), and glass-ceramics
(e.g. Cerabone
®
and Bioverit
®
) form a calcium phosphate layer after
exposure to body fluid, instead of forming the fibrous tissue. When
implanted into bone defects, they can strongly and directly bond to
the surrounding bone tissue. Bioglass (45S5) has the glass composition
45SiO
2
-24.5CaO-24.5Na
2
O-6.0P
2
O
5
(wt%) (see Chapter 2). Bioverit
stands for a series of glass ceramics (crystallized glass, Chapter 7)
with a typical composition 45SiO
2
-30Al
2
O
3
-12MgO-9(Na
phate (
β
K)
2
O-4F
(wt%). 45S5 Bioglass, the most active bioactive material, bonds to hard
+
