Influence of the Processes Parameters on the Properties of The ...

Chapter 5.
Characterization <strong>of</strong> Scaffolds for Connective Tissue Engineering
<strong>of</strong> <strong>the</strong> new experiments <strong>of</strong> <strong>the</strong> Doehlert’ plan. All repeated results <strong>of</strong> <strong>the</strong> new Doehlert plan with <strong>the</strong> volume
constraint are presented in Table 5.21.
Table 5.21: Complementary Doehlert’ design experiments.
Exp. X 1 X 2 dP/dt (bar/s) P sat (bar) Pore Diameter (μm)
1 0 0 2.5 125 8.4
2 1 0 10 125 3.6
3 0.5 0.866 5 150 5.0
4 -0.5 0.866 1.25 150 26.9
5 -1 0 0.625 125 187.25
6 -0.5 -0.866 1.25 100 133.0 ; 127.9 ; 135.0
7 0.5 -0.866 5 100 52.35 ; 51.0 ; 54.0
In all cases, we have observed significant changes from <strong>the</strong> results <strong>of</strong> <strong>the</strong> initial Doehlert
experiments. These differences can be attributed to <strong>the</strong> change in <strong>the</strong> experimental setup. However, <strong>the</strong>
general observed behaviour for P sat and dP/dt is <strong>the</strong> same for initial and repetition experiments. The
maximum pore size is calculated according to <strong>the</strong> analysis <strong>of</strong> <strong>the</strong> Doehlert plan, and it has been found
255.7μm. P sat = 100 bar and dP/dt = 0.625 bar/s have been taken as <strong>the</strong> parameters which give <strong>the</strong> maximum.
This result is confirmed by <strong>the</strong> experiment that we had been carried out and presented in Table 5.20 for <strong>the</strong>
last sample. As shown in Table 5.22, we have found that <strong>the</strong> effect <strong>of</strong> all factors is statically significant but
<strong>the</strong> predominant factor is <strong>the</strong> factor 1 (dP/dt). The effect <strong>of</strong> <strong>the</strong> depressurization rate on <strong>the</strong> foams, reported
in Figure 5.18, is an example.
Table 5.22: Analysis <strong>of</strong> <strong>the</strong> Doehlert design: coefficients <strong>of</strong> <strong>the</strong> model.
â â
a 0 8.4 5.3
a 1 - 74.4 2.8 Significant
a 2 - 44.3 2.5 Significant
a 12 20.5 4.6 Significant
a 11 87.0 6.5 Significant
a 22 32.3 6.2 Significant
The modelling study was also carried out and <strong>the</strong> homogenous nucleation <strong>the</strong>ory presented in
chapter 2 has been used. As explained earlier, <strong>the</strong> total number <strong>of</strong> nuclei generated can be calculated as a
function <strong>of</strong> <strong>the</strong> saturation pressure. Once we have calculated <strong>the</strong> number <strong>of</strong> nuclei, we can calculate <strong>the</strong>
average pore diameter by using Equation (4.1). We have used <strong>the</strong> measured porosity data to convert <strong>the</strong>
number <strong>of</strong> nuclei to <strong>the</strong> average pore diameter.
These results are plotted in Figure 5.19-(A), toge<strong>the</strong>r with <strong>the</strong> experimental results <strong>of</strong> average pore
diameter. Figure 5.18 depicted as example for t sat = 60 min, T sat = 36.5°C and dP/dt = 5 bar/s, <strong>the</strong> variations
with saturation pressure toge<strong>the</strong>r experimental results and model <strong>of</strong> average pore diameter.
(a) 10 bar/s (b) 5 bar/s (c) 1.25 bar/s (d) 0.625 bar/s
Figure 5.18: <strong>Influence</strong> <strong>of</strong> dP/dt on <strong>the</strong> pore size <strong>of</strong> <strong>the</strong> foams processed at scCO 2 condition P sat = 100 bars,
T sat = 36.5°C and t sat = 60 min.
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