Biomedical Engineering Reference
In-Depth Information
(a)
200
μ
m
(b)
200
μ
m
(c)
100
μ
m
(d)
100
μ
m
Figure 12.10
SEM images from the gel-cast foaming process of a bioactive glass
after sintering: (a, b) low magnification; and (c, d) higher magnification. (Images by
Zoe Wu. Copyright (2012) Zoe Wu.)
factor in getting a good foam: too little glass means the particles are not
in contact with each other, and the foam will slump before sintering can
occur; and too much glass is difficult to foam. Particle size is also impor-
tant: small particles sinter more easily as they have a higher surface area.
However, as crystallisation of the glass is surface nucleating, a higher
surface area also means crystallisation can occur at lower temperatures
in smaller particles.
The gel-cast foaming process produces excellent scaffolds, but up-
scaling for production is challenging. Another challenge is that, in order
for a surfactant to function, water has to be present, so the glass has to
be in a slurry of water. This means the glass will start to react with the
water. Although the amount of time the glass is exposed to the water
is short, it can trigger crystallisation of the glass to occur at a lower
temperature.
12.5.5 Sol-Gel Foaming Process
The sol-gel process involves the hydrolysis of alkoxide precursors to
create a sol (Chapter 3). The sol can be considered as a solution of silica
