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

Chapter 5.
Characterization <strong>of</strong> Scaffolds for Connective Tissue Engineering
Table 5.20: Variation in <strong>the</strong> average size <strong>of</strong> pores with different dP/dt values at P sat = 100 bars.
Height <strong>of</strong> <strong>the</strong> glass
balls in <strong>the</strong> chamber
dP/dt (bar/s)
Pore Diameter
(µm)
Average Diameter
Pore (µm)
~2/3 10
19.0
18.9
18.9
~2/3 5
50.7
54.0
52.4
~2/3 1,25
138.0
127.9
133.0
~2/3 0,625 255.7 255.7
3.2.3.2 Discussion on <strong>the</strong> Effect <strong>of</strong> <strong>the</strong> Various CO 2 Process <strong>Parameters</strong>
As shown in Figure 5.17, for dP/dt = 5 bar/s, <strong>the</strong> estimated geometrical porosity (equation 3.11) is
decreasing when <strong>the</strong> dP/dt is increasing and it reaches a plateau at 92%, and 89.3% for saturation pressures
<strong>of</strong> 100 and 125 bars. The very close porosity values at 5 bar/s and 10 bar/s can also be explained by <strong>the</strong>
coalescence <strong>of</strong> <strong>the</strong> pores during CO 2 desorption. Our observations on pore size and <strong>the</strong> porosity (<strong>the</strong>
swelling) <strong>of</strong> <strong>the</strong> polymer has shown us that with great pore sizes comes great porosity and with small pore
size comes small porosity. This behaviour is in agreement with <strong>the</strong> literature [Beckman, 2004]. To our
knowledge, it is impossible to create big pores with small polymer volume or small pores with important
polymer swelling.
Porosity[1-( f
/ p
)] ( %)
98
96
94
92
90
88
PLGA 50:50
Porosity Variation
P sat
100 bar
P sat
125 bar
0 2 4 6 8 10 12
dP/dt (Bar/s)
Figure 5.17: Variation <strong>of</strong> <strong>the</strong> porosity <strong>of</strong> <strong>the</strong> foams as a function <strong>of</strong> depressurization rate.
The physical shapes <strong>of</strong> <strong>the</strong> scaffolds prepared without volume constraint were perfectly circled
and visually homogenous. On <strong>the</strong> o<strong>the</strong>r hand, <strong>the</strong> shape <strong>of</strong> <strong>the</strong> scaffolds processed with volume constraint
was corrupted. We have also observed homogeneity on <strong>the</strong> SEM images. As shown in Figure 5.18, <strong>the</strong> pore
size is smaller in high rates <strong>of</strong> depressurization and it increases with dP/dt increases. On <strong>the</strong> o<strong>the</strong>r hand,
according to micrographs <strong>the</strong> interconnectivity and homogeneity are observed in <strong>the</strong> cross-section
micrographs <strong>of</strong> <strong>the</strong> scaffolds. However, <strong>the</strong> SEM images are not sufficient to have a real characterization <strong>of</strong>
interconnectivity.
As mentioned previously, we have observed that both <strong>the</strong> volume <strong>of</strong> <strong>the</strong> pressure chamber and <strong>the</strong>
position <strong>of</strong> <strong>the</strong> pellet are important factors, which affect <strong>the</strong> pore size. For this reason, <strong>the</strong> 5 remaining
experiments are carried out in order to re-complete <strong>the</strong> Doehlert’ plan according to <strong>the</strong> new experimental
setup with glass balls. The height <strong>of</strong> <strong>the</strong> glass balls was at ~2/3 <strong>of</strong> <strong>the</strong> height <strong>of</strong> <strong>the</strong> pressure chamber for all
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