Biomedical Engineering Reference
In-Depth Information
80
70
60
50
40
30
20
3.0
2.5
2.0
1.5
1.0
0.5
0.0
10
46
48
50
52
54 56
Porosity (%)
58
60
62 64
46
48
50
52
54 56
Porosity (%)
58
60
62
64
(a)
(b)
FIGURE 4.7
(a) Compressive strength and (b) modulus of plotted CPC scaffolds with different porosity (n =
5). Scaffolds with a size of 10 mm × 10 mm × 10 mm were tested by using an Instron 5566 testing
machine with a 10 kN load cell and a constant rate of 1 mm/min.
material but are also strongly affected by the pore parameters including size,
morphology, distribution, and orientation. In case of scaffolds fabricated by
RP technologies, the influence of macroporosity and scaffold architecture,
predefined by the CAD data set, on mechanical strength has been clearly
demonstrated by several studies (Hutmacher et al. 2001; Zein et al. 2002;
Sobral et al. 2011). The mechanical properties of the plotted CPC scaffolds
are, to a certain extent, adaptable by design and changing the pore param-
eters. Generally, a uniform and continuous pore structure and orientation
improves the mechanical strength (Wu et al. 2008, 2011) and in this respect,
scaffold fabrication applying the technique of 3D plotting has an advantage
over other conventional methods.
The 3D plotted CPC scaffolds set in water were mechanically weaker than
those sintered at high temperature. We studied the modulus of the plot-
ted CPC scaffolds with and without sintering and found that the plotted
CPC scaffolds produced with an additional sintering step (1250°C for 3 h)
acquired a modulus of about 330 MPa, which is nearly seven times higher
than that of samples with the same geometry produced without sintering
(Figure 4.8a). As apparent from SEM investigations (Figure 4.8b,c), high tem-
perature sintering results in highly crystalline materials with, compared to
cements, bigger particles that are connected to each other by sinter necks.
This structural feature is accompanied by a higher mechanical strength. In
contrast, CPC consists of smaller, mostly nanocrystalline particles that were
formed and became entangled during the precipitation reaction providing
mechanical rigidity (Bohner 2000). Accordingly, the SEM image shown in
Figure 4.8a reveals that the surface of the nonsintered CPC strands is highly
porous with plenty of small particles that seem to be bonded weaker com-
pared to the more dense counterparts produced by sintering.
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