Biomedical Engineering Reference
In-Depth Information
100 nm
Figure 12.12
SEM image of the nanotopography of a 70S30C (70mol% SiO
2
,
30mol% CaO) sol-gel derived bioactive glass.
takes around three days, and for a foaming process, a few minutes is
needed. Hydrofluoric acid is the gelling agent of choice because, when
gelation occurs, it occurs rapidly, allowing the porous foam to gel
homogeneously.
On gelation, the spherical bubbles become permanent in the gel. As
drainage occurs in the foam struts, the gel shrinks and the bubbles merge,
interconnects open up at the point of contact between neighbouring
bubbles.
The sol-gel foam scaffolds have a hierarchical structure of intercon-
nected macropores (Figure 12.2 and see Figure 14 in colour section),
which mimic the porous structure of cancellous bone and allow the
scaffold to act as a 3D template for tissue growth, and a nanoporosity
that allows control of degradation (Figure 12.12).
Cell response studies on the bioactive glass foam scaffolds have found
that primary human osteoblasts lay down mineralised immature bone
tissue, without the need for additional growth factors or hormones.
Glass compositions are usually 58S (60mol% SiO
2
, 26mol% CaO and
4mol%P
2
O
5
) or 70S30C (70mol% SiO
2
, 30mol% CaO). However,
other network modifiers can be used for added functionality, such as
strontium (anti-osteoporosis) or silver (antibacterial).
