Biomedical Engineering Reference
In-Depth Information
network, the bubbles must be large and touching each other in the
solution until gelation. On gelation, the surfactant films must rupture,
opening up interconnecting channels between the bubbles, which now
become the pores. After gelation, the foam is a composite of glass
particles within the newly formed polymer matrix (Figure 12.9).
In order to make the porous glass, the polymer has to be removed.
Polymer removal and sintering occur in the same heat treatment pro-
cedure. The composite is usually held at around 300
◦
C to remove the
polymer. At this point, the particles are effectively balancing on each
other in the shape of a foam. As the temperature increases above
T
g
,
the particles begin to sinter together. The sintering temperature depends
on the sintering window of the glass composition being used, but is
usually around 700
◦
C. A 3D image of a gel-cast foam scaffold can
be seen in Figure 12.2. The scaffolds have large interconnecting pores
without hollow struts. Figure 12.10 shows SEM images of a bioactive
glass scaffold after sintering. Note the smoothness of the foam surface
at higher magnification after sintering, which shows that sintering has
run to completion. The amount of glass loading in the slurry is a critical
(a)
(b)
200
μ
m
200
μ
m
50
μ
m
(d)
10
μ
m
(c)
Figure 12.9
SEM images from the gel-cast foaming process of a bioactive glass
after foaming and gelation of glass particles dispersed in a polymer foam: (a, b) low
magnification; and (c, d) higher magnification, showing individual particles in the
polymer matrix. (Images by Zoe Wu. Copyright (2012) Zoe Wu.)
