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

Chapter 5.
Characterization <strong>of</strong> Scaffolds for Connective Tissue Engineering
sorption value at 125 bars and 20 minutes (cf. Table 5.8). Thus, we can state that <strong>the</strong>re is not any difference
to process a PLGA 50:50 at 125 bars for 20 minutes or at 76.2 bars for 120 minutes.
One <strong>of</strong> <strong>the</strong> most important issues <strong>of</strong> <strong>the</strong> foaming phenomena is <strong>the</strong> depression <strong>of</strong> <strong>the</strong> glass
transition <strong>of</strong> <strong>the</strong> polymer by <strong>the</strong> sorption <strong>of</strong> CO 2 . As presented in <strong>the</strong> Figure 5.9, as <strong>the</strong> weight fraction <strong>of</strong>
CO 2 is greater than 0.02 at ~36.5°C, <strong>the</strong> saturation process is happening in plasticized state. We have
observed that, when <strong>the</strong> same depressurization rate is applied to <strong>the</strong> system (5 bar/s), <strong>the</strong> temperature at <strong>the</strong>
gas output <strong>of</strong> <strong>the</strong> pressure chamber is dropping to approximately 17°C and ~26°C when 100 bars and 200
bars <strong>of</strong> saturation pressure are applied respectively. According to <strong>the</strong> T g -w diagram and <strong>the</strong> desorption data,
<strong>the</strong> polymer saturated at 200 bars is closer to <strong>the</strong> vitrification point when <strong>the</strong> depressurization is finished.
However, <strong>the</strong> polymer processed at 100 bars remains in plasticized state until <strong>the</strong> end <strong>of</strong> <strong>the</strong>
depressurization. On <strong>the</strong> o<strong>the</strong>r hand, we have experimented that <strong>the</strong> swelling continues approximately 2-3
minutes after finishing <strong>the</strong> depressurization <strong>of</strong> <strong>the</strong> chamber which correspond to <strong>the</strong> plasticized state <strong>of</strong> <strong>the</strong>
polymer.
Figure 5.9: The depression <strong>of</strong> PLGA 50:50 T g as a function <strong>of</strong>
<strong>the</strong> weight fraction <strong>of</strong> sorbed CO 2 : (♦) 100 bars; (●) 200 bars.
3 <strong>Influence</strong> <strong>of</strong> <strong>the</strong> Process <strong>Parameters</strong> on <strong>the</strong> Microstructure <strong>of</strong> Scaffolds
3.1 Effect <strong>of</strong> Polymer Blend Compositions
3.1.1 Blends <strong>of</strong> P L,DL LA and PLGA 50:50
First experiments on polylactides were carried out to understand which polymer is more suitable
to use in tissue engineering. Foaming experiments are performed on blends <strong>of</strong> P L,DL LA (LR-704) and
PLGA 50:50 (RG-504), with different ratios, as given in <strong>the</strong> Table 5.10.
Table 5.10: Blends <strong>of</strong> PLGA 50:50 and P L,DL LA.
Blend w/w w/w w/w w/w w/w
PLGA 50:50 100% 75% 50% 25% 0%
P L,DL LA 0% 25% 50% 75% 100%
The following scCO 2 parameters are kept constant: saturation pressure P sat = 150 bars, saturation
time t sat = 60 minutes, saturation temperature T sat = 36.5 o C and depressurization rate dP/dt = 25 bar/sec and
<strong>the</strong> SEM images <strong>of</strong> <strong>the</strong> corresponding scaffolds are presented in Figure 5.10.
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