Biomedical Engineering Reference
In-Depth Information
Glass scaffolds were fabricated by extruding the inks through a 100
m
syringe nozzle using a robotic deposition device. The viscosity of the ink
is critical. The inks were printed on an alumina substrate in a reservoir of
non-wetting oil. The scaffolds were air-dried for 24 hours and subjected
to a controlled heat treatment to decompose the organics and sinter the
glass particles (700
◦
C).
μ
12.5.7 Summary of Bioactive Glass Scaffold Processing
Bioactive glass scaffolds have been synthesised with foam-like pore
networks resembling the structure of cancellous bone. Compressive
strengths of 2-15MPa have been obtained in bioactive glass foam scaf-
folds while maintaining modal interconnect diameters above 100
μ
m
(
80% porosity). Using solid freeform fabrication, higher compressive
strengths were obtained (
>
150MPa at 60% porosity), but the architec-
ture was less similar to native bone. Although the compressive strength
of glass scaffolds may be suitable for bone grafts in applications where
the load is compressive and not cyclic, bioactive glass scaffolds suffer
similar problems to other bioceramics: they are brittle. For certain appli-
cations, and to replace the need for autografts, improved toughness is
needed.
>
12.6 THE FUTURE: POROUS HYBRIDS
Chapter 10 explains that bioactive glasses must be made more tough if
they are to be used in sites that will be under cyclic loading. Chapter 9
showed that there have been several attempts to combine bioactive
glasses with biodegradable polymers to create composite scaffolds with
degradability, bioactivity and toughness. Chapter 10 discusses how
conventional composites are flawed as synthetic bone grafts because the
bioactive particles are generally covered by the polymer matrix. The host
bone will therefore not come into contact with the glass. This may be
rectified as the polymer phase begins to degrade and the glass is exposed.
However, the polymer often degrades much more rapidly than the glass.
Sol-gel hybrids are different from composites in that the inorganic
and organic components are interpenetrating networks that are indis-
tinguishable above the sub-micrometre scale (Figures 10.1 and 12.14).
Because the sol-gel process is initially at room temperature, polymers can
be incorporated into the sol so that the polymer network is incorporated
as the silica network forms. This nanoscale interaction can produce
