Biomedical Engineering Reference
In-Depth Information
and passed through 300 meshes. Using this method, regular nanochannels
with diameters of around 5 nm were formed in the Ca-Si-P bioglass particles,
which enhance the specific surface area making this material attractive for
drug-loading applications by increasing the binding capability and sus-
tained release ability (Xia and Chang 2006).
For preparation of the plotting pastes, β-CaSiO
3
and Ca-Si-P bioglass pow-
der were further sieved to reduce the particle size to less than 45 µm and
mixed with a 15 wt% aqueous PVA solution. As previously described, the bio-
compatible polymer PVA is ideally suited to prepare bioceramic pastes with
excellent injectability. After stirring the mixtures (with adjusted powder-
to-liquid ratio) to become homogeneous pastes and loading into a printing
cartridge, the plotting process was carried out as described earlier. Plotted
scaffolds were dried at 40°C overnight, and then heated to 150°C for 30 min
to induce heat-activated cross-linking of PVA. Afterward, the obtained scaf-
folds were stable in dry state as well as in aqueous solutions like cell culture
medium without a second high-temperature sintering step. In this system,
PVA works as a binder to bond the bioceramic particles. The molecular
weight of PVA was 130,000 and after cross-linking, the crystallinity of PVA
was increased and solubility therefore diminished (Chun et al. 2010). A PVA
content of only 12 wt% for plotted CaSiO
3
and 14 wt% for plotted mesopo-
rous Ca-Si-P scaffolds in dry state was enough to bind the ceramic powders.
In further studies we have revealed that the 3D plotted silicon-based bio-
ceramic scaffolds with PVA as binder had excellent apatite deposition ability
after incubation in SBF
in vitro
and new bone formation ability
in vivo
(Wu
et al. 2012). No negative effect of PVA on the bioactivity has been observed.
The pore size and morphology of the two types of plotted silicon-based
bioceramic scaffolds were characterized microscopically (Figure 4.16). With
the control of CAD, scaffolds with defined geometry and porosity were pre-
pared of both pastes. However, concerning the surface structure, certain dif-
ferences are visible: the surface of the CaSiO
3
scaffold was rough and porous,
and that of the mesoporous bioglass scaffolds was smooth and dense. Those
differences were related to the powder particle size (β-CaSiO
3
particles were
bigger than those of mesoporous Ca-Si-P) and the higher specific surface
area of the Ca-Si-P scaffolds was due to the mesoporosity of the bioglass.
The compressive strength of plotted scaffolds was tested by exerting the
force in z-direction using an Instron 5566 testing machine equipped with
a load cell of 10 kN at a crosshead speed of 0.5 mm/min. The stress-strain
curves and morphologies of scaffolds before and after compression are
shown in Figure 4.17. The maximal compressive strength and modulus of
plotted β-CaSiO
3
scaffolds with a porosity of 65% were 3.6±0.1 and 39.5±7.7
MPa, respectively. Compressive strength and modulus of plotted mesopo-
rous Ca-Si-P scaffolds with a porosity of 60.4% were 16.1±1.5 and 155.1±14.9
MPa, respectively. The compressive strength and modulus of these scaffolds
were significantly higher than that of silicon-based bioceramic scaffolds
of similar porosity, prepared by conventional methods, especially for the
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