Influence of the Processes Parameters on the Properties of The ...
Influence of the Processes Parameters on the Properties of The ...
Influence of the Processes Parameters on the Properties of The ...
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Chapter 5.<br />
Characterizati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> Scaffolds for C<strong>on</strong>nective Tissue Engineering<br />
chamber. Since <str<strong>on</strong>g>the</str<strong>on</strong>g> polymer swells during desorpti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> CO 2 , when <str<strong>on</strong>g>the</str<strong>on</strong>g> polymer has swelled approximately<br />
by 50%, <str<strong>on</strong>g>the</str<strong>on</strong>g> edges <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> polymer c<strong>on</strong>tact <str<strong>on</strong>g>the</str<strong>on</strong>g> wall <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> chamber. Since <str<strong>on</strong>g>the</str<strong>on</strong>g> polymer is very s<str<strong>on</strong>g>of</str<strong>on</strong>g>t, due to <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
depressi<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> glass transiti<strong>on</strong>, <str<strong>on</strong>g>the</str<strong>on</strong>g> chamber walls block desorpti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> CO 2 from <str<strong>on</strong>g>the</str<strong>on</strong>g> edges <str<strong>on</strong>g>of</str<strong>on</strong>g> polymer,<br />
which results in <str<strong>on</strong>g>the</str<strong>on</strong>g> expanding <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> pores in that regi<strong>on</strong>. Indeed, this expansi<strong>on</strong> corresp<strong>on</strong>ds to <str<strong>on</strong>g>the</str<strong>on</strong>g> increase<br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> molecular volume <str<strong>on</strong>g>of</str<strong>on</strong>g> CO 2 molecules which are no l<strong>on</strong>ger in supercritical state.<br />
(A) Sample 1-C (dP/dt = 2.5 bar/s).<br />
(B) Sample 5-B (dP/dt = 0.625 bar/s).<br />
Figure 5.16: Micrographs <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> cross-secti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> foams processed at P = 125 bars.<br />
One can say that <str<strong>on</strong>g>the</str<strong>on</strong>g>re is a significant difference <str<strong>on</strong>g>of</str<strong>on</strong>g> pore size depending <strong>on</strong> where <str<strong>on</strong>g>the</str<strong>on</strong>g> pellet is<br />
positi<strong>on</strong>ed. In <str<strong>on</strong>g>the</str<strong>on</strong>g> same Doehlert’ experiment (Nr 7), we have obtained a pore diameter ranging between 128<br />
and 223 μm. If <str<strong>on</strong>g>the</str<strong>on</strong>g> pellet is positi<strong>on</strong>ed in <str<strong>on</strong>g>the</str<strong>on</strong>g> low positi<strong>on</strong>, <str<strong>on</strong>g>the</str<strong>on</strong>g> average pore diameter and <str<strong>on</strong>g>the</str<strong>on</strong>g> porosity are<br />
found smaller than in <str<strong>on</strong>g>the</str<strong>on</strong>g> upper positi<strong>on</strong>. It can be explained by <str<strong>on</strong>g>the</str<strong>on</strong>g> faster vitrificati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> polymer in <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
low positi<strong>on</strong> which stops <str<strong>on</strong>g>the</str<strong>on</strong>g> growth <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> pores. As explained earlier, <str<strong>on</strong>g>the</str<strong>on</strong>g> bottom part <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> pressure<br />
chamber is always colder than <str<strong>on</strong>g>the</str<strong>on</strong>g> upper part after depressurizati<strong>on</strong>.<br />
Since, we have noticed that two supplementary factors affect <str<strong>on</strong>g>the</str<strong>on</strong>g> pore size (<str<strong>on</strong>g>the</str<strong>on</strong>g> c<strong>on</strong>straint <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
volume <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> experimental setup and <str<strong>on</strong>g>the</str<strong>on</strong>g> positi<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> pellet in <str<strong>on</strong>g>the</str<strong>on</strong>g> chamber), we have decided to remove<br />
<str<strong>on</strong>g>the</str<strong>on</strong>g> circle <str<strong>on</strong>g>of</str<strong>on</strong>g> Tefl<strong>on</strong> which was placed in <str<strong>on</strong>g>the</str<strong>on</strong>g> pressure chamber. After that, we have filled <str<strong>on</strong>g>the</str<strong>on</strong>g> pressure<br />
chamber with small glass marbles as described in chaptet 4, Figure 4.12, setup-02. <strong>The</strong>n, a pellet <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
PLGA 50:50 has been placed in <str<strong>on</strong>g>the</str<strong>on</strong>g> chamber. <strong>The</strong> carried out repetiti<strong>on</strong>s experiments and corresp<strong>on</strong>ding results<br />
are reported in Table 5.19. For <str<strong>on</strong>g>the</str<strong>on</strong>g> repetiti<strong>on</strong>s, we have obtained 52.4 and 26.5 μm, as <str<strong>on</strong>g>the</str<strong>on</strong>g> average diameter<br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> pores.<br />
Table 5.19: Repetiti<strong>on</strong>s experiments <str<strong>on</strong>g>of</str<strong>on</strong>g> Doehlert’ design (P sat = 100 bars and dP/dt = 5 bar/s).<br />
Height <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> Glass<br />
Balls in <str<strong>on</strong>g>the</str<strong>on</strong>g> Chamber<br />
Pore Diameter<br />
(µm)<br />
Average Diameter <str<strong>on</strong>g>of</str<strong>on</strong>g> Pores<br />
(µm)<br />
~ 1/3<br />
24.3<br />
28.7<br />
26.5<br />
~ 2/3<br />
50.7<br />
54.0<br />
52.4<br />
<strong>The</strong> variati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> pore diameter with dP/dt is reported in Table 5.20 and illustrated by <str<strong>on</strong>g>the</str<strong>on</strong>g> series <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
micrographs given in Figure 5.18. We have found that <str<strong>on</strong>g>the</str<strong>on</strong>g> pore size is decreasing with <str<strong>on</strong>g>the</str<strong>on</strong>g> increasing rate <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
depressurizati<strong>on</strong>.<br />
<strong>The</strong> variati<strong>on</strong> to <str<strong>on</strong>g>the</str<strong>on</strong>g> pore size estimated by image analysis, is ranging from 18.9 µm, for dP/dt = 10<br />
bar/s to 255.7 µm, for dP/dt = 0.625 bar/s. <strong>The</strong>se experiments were carried out at high depressurizati<strong>on</strong> rate<br />
(10 bar/s). Thus, we expect to find smaller pores. However, we have observed small (10−20 µm) and big<br />
pores [~ 150 − 200 µm] toge<str<strong>on</strong>g>the</str<strong>on</strong>g>r. So that, we can state that <str<strong>on</strong>g>the</str<strong>on</strong>g>re is a coalescence phenomen<strong>on</strong> occurring<br />
during <str<strong>on</strong>g>the</str<strong>on</strong>g> pore growth.<br />
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