Biomedical Engineering Reference
In-Depth Information
60
50
40
R
2
=
0.96
30
20
10
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 2.3
Effect of NC on osteoconduction
in vivo
.(Plottedfromdatain
Ref. [11].)
point. Because glass is a random arrangement of units, such as the silica
tetrahedra, there is space for a large number of therapeutic ions. The ions
can be incorporated into the chemistry without significant alteration of
properties. 45S5 crystallises rapidly when it is heated above
T
g
.This
presents a problem if engineers want to process the glass in its more fluid
form. This could be sintering (fusing) particles together to make large
pieces of glass, porous constructs or scaffolds (Chapter 12) or it could
be coating metal implants with glass (Chapter 8). Another problem with
making coatings using Bioglass is that the thermal expansion coefficients
(TECs) of the glass and metal (e.g. titanium or cobalt-chrome alloy)
do not match, which causes the glass coating to shrink away from the
metal surface during the coating process. Ions such as zinc, magnesium
and boron can be added to the glass to stabilise the working range to
enable viscous flow sintering and to alter the TEC to match those of
metal alloys for coatings [5, 12]. Potassium and fluorine can be added
for dental application when slow release of fluoride ions is desired. Silver
can also be added for bactericidal action. Strontium has been shown
to be beneficial for healthy bone growth, and glass particles containing
strontium are now commercially available as StronBone
(RepRegen
Ltd, UK). The release of these ions can be controlled by altering the NC
and particle size of the glasses. Table 2.3 summarises some important
bioactive glass compositions reported in the literature.
Figure 2.4 shows the effect of the addition of strontium on the thermal
properties using differential thermal analysis (DTA) in a bioactive glass
series [4]. DTAmeasures thermal changes as the temperature is increased,
™
