Biomedical Engineering Reference
In-Depth Information
(a)
1 mm
(b)
600
μ
m
200
μ
m
(c)
(d)
300
μ
m
Figure 12.5
Images of porous bioactive glasses produced by the space holder
method, using PMMA microspheres (diameter
m) at a glass-to-polymer ratio
of 50 : 50. (a) Low-magnification SEM image showing isolated spherical pores.
(b) SEM image showing isolated pores (not interconnected). (c) 3D reconstruction
from X-ray microtomography (
∼
500
μ
μ
CT) imaging, showing irregularity of pores. (d)
2D
CT projection showing isolated pores. (Images by Zoe Wu and Sheng Yue.
Copyright (2012) Zoe Wu and Sheng Yue.)
μ
12.5.2 Polymer Foam Replication
Interconnectivity is improved through using sacrificial polyurethane
foams rather than spheres. Polyurethane foams are used to make com-
mon open-pore (open-cell) foams such as those used in sofas and
armchairs. They are readily available in different ranges of pore sizes,
although they are usually quoted in pores per inch. Figure 12.6(a) shows
a scanning electron microscope (SEM) image of a polyurethane foam.
The struts are thin and the pores are large and well connected, so much
so that it is difficult to tell what is an interconnection and what is a
pore. The polymer foam can be immersed in slurries of glass or ceramic
particles so that the particles coat the polymer foam. The aim is that,
after sintering, the glass will take the shape of the foam. The main
challenge in the process is to ensure that the polymer is well coated but
not full of excess particles. If there are excess particles, they will block
the pores. The common way to remove excess powder is to squeeze it
