Biomedical Engineering Reference
In-Depth Information
2.5
2.0
1.5
1.0
0.5
0
1.9 2.0 2.1 2.2 2.3
Network Connectivity
2.4 2.5 2.6 2.7 2.8 2.9
Figure 2.2
Effect of NC on rate of apatite formation in simulated body fluid on
phosphate-free soda. (Plotted from data in Ref. [11].)
For 45S5 Bioglass, NC
is equal to:
[2
×
46
.
13]
−
[(2
×
24
.
35)
+
(2
×
26
.
91)]
+
(2
×
2
.
6
×
3)
NC
=
2
+
.
[46
13]
=
2
.
22
(2.5)
Glasses that have NC (rather than NC
) greater than 2.4 are not
likely to be bioactive. Figure 2.2 shows how NC affects HCA formation
on SiO
2
-CaO-Na
2
O glass discs in simulated body fluid (SBF). Above
NC
2, the rate of HCA layer deposition decreases rapidly.
This trend can also be seen for
in vivo
bone ingrowth for particles
implanted in a bone defect (Figure 2.3). The percentage of new bone
formed (osteoconduction) drops off rapidly for glasses where NC
=
2.
Other properties can be predicted from NC, such as tendency for
crystallisation, as glasses with NC
>
2 will generally have a higher
energy barrier to overcome for crystallisation than glasses with NC
>
<
2
owing to the stabilising effect of cross-linking the silicate chains.
2.3 ALTERNATIVE BIOACTIVE GLASS
COMPOSITIONS
Research groups worldwide have developed a large number of bioactive
glass compositions using the 45S5 composition as a guide or starting
