Biomedical Engineering Reference
In-Depth Information
K
+
HCO
3-
Mg
2+
Na
+
So
2-
4
Cl
-
Simulated
body fluid
H
3
O
+
Ca
2+
H
3
O
+
Ca
2+
Ca
2+
OH
Ca
2+
OH
Ca
2+
OH
HPO
2-
HPO
2-
HPO
2-
4
4
4
Apatita
Apatita
Apatita
Hydroxyapatite
O
O
O
HO
OH
HO
OH
HO
OH
Si
Si
Si
O
O
O
O
O
O
Bioactive glass
nanoparticles
Si
Si
Si
O
O
O
O
O
O
O
O
O
Si
Si
Si
O
O
O
O
O
O
FIGURE 15.3
Schematic drawing of the formation process of hydroxyapatite layer. It shows the formation of hydroxyapatite
layer after interaction of the bioactive glass with simulated body fluid.
to form hydroxyl carbonate apatite (HCA) Ca
5
(PO
4
CO
3
)
3
(OH) layers. Once apatite nuclei forms,
crystals grow by consuming calcium and phosphate ions from the simulated body fluid.
Several in vitro and in vivo studies show that a series of reactions occur that lead to the forma-
tion of a carbonated HA layer on the bioactive glass surface (
Figure 15.4
). Parameters such as sur-
face charge, composition, structure, and morphology will be important in the formation of the Ca/P
layer as well as in the interaction between the material surface and the surrounding medium, pro-
teins, and cells
[9,28
33]
.
Several theories have been proposed to explain the formation of this layer. The HA layer is
spontaneously formed in the surface of bioactive glass of the CaO
SiO
2
P
2
O
5
system after
exposure to body fluids
[27
30,34,35]
. Studies have shown that apatite is preferentially formed on
a surface material composed mainly of CaO and SiO
2
because the Ca
2
1
ions released from the
glass increase the degree of saturation of the apatite in relation to surrounding fluid. In addition,
the Si
OH groups of the hydrated silica gel formed on the surface induce a heterogeneous
nucleation of apatite. These crystals grow by consuming calcium and phosphate ions from the body
fluid and those that migrate from the bulk to the surface of the glass.
Compared with microparticles, bioactive glass nanoparticles have advantages in bone repair and
regeneration, with the decrease in grain size promoting an increase in cellular adhesion, enhanced
osteoblast proliferation and differentiation, and an increase in the biomineralization process
