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

Chapter 5.
Characterization <strong>of</strong> Scaffolds for Connective Tissue Engineering
fulfills <strong>the</strong> requirement for tissue engineering applications. A Taguchi’ plan will be applied to see <strong>the</strong> effect
<strong>of</strong> process parameters on <strong>the</strong> foam.
To study <strong>the</strong> effect <strong>of</strong> different parameters, we opted to make complementary pellets <strong>of</strong> 0.6 mm
diameter by weighing ~100 mg <strong>of</strong> PLGA 50:50 . The pellets were prepared at P = 150 bars, T = 60 o C and t = 20
min as per procedure described in chapter 4. Before and after scCO 2 treatment, <strong>the</strong> pellets and foams
diameter and thickness was measured and mean dimensional values were considered during <strong>the</strong> calculation
and analysis.
Twelve pellets <strong>of</strong> same diameter were manufactured. Experiments were carried out in <strong>the</strong>
SEPAREX SF200 pilot. Pressure chamber without Teflon isolation material was filled with small glass
marbles to <strong>the</strong> ~2/3 <strong>of</strong> <strong>the</strong> height as described in setup-02 and presented in Figure 4.12-B. The four process
parameters P sat , t sat ,T sat dP/dt were varied (cf. Table 5.26) and geometric porosity was determined. The ratio
<strong>of</strong> <strong>the</strong> micro, meso and macro pores <strong>of</strong> <strong>the</strong> corresponding foams was obtained by SCION ® image analysis. In
this chapter, for <strong>the</strong> Taguchi plan for PLGA 50:50 (RG 504) best process conditions was P sat = 120 bars, t sat =
20 min, T sat = 35°C and dP/dt = 3 bar/s. A special experimental plan was not applied; however values <strong>of</strong> <strong>the</strong>
four parameters were changed slightly to see <strong>the</strong>ir effects fur<strong>the</strong>r on <strong>the</strong> foam porosity and pore size.During
<strong>the</strong> experimentation variation in temperature a,pressure and dP/dt was observed which can slightly affect <strong>the</strong>
final results obtained.
Table 5.26: ScCO 2 process conditions for foaming <strong>of</strong> PLGA 50:50.
<strong>Parameters</strong> A 1 A 2 A 3 A 4 A 5 A 6 A 7 A 8 A 9 A 10 A 11 A 12
P sat (bar) 120 120 120 120 120 120 110 120 130 120 120 120
t sat (min) 20 20 20 20 20 20 20 20 20 15 20 25
T sat ( o C) 35 35 35 32.5 35 37.5 35 35 35 35 35 35
dP/dt (bar/s) 4 3 2 3 3 3 3 3 3 3 3 3
4.10 Discussion on Foam Morphology
Porosity <strong>of</strong> <strong>the</strong> foams obtained under <strong>the</strong> different conditions has been calculated and is presented.
Three foams were made for each condition, average values were taken into account and is presented in
Figure 5.32. Geometric porosity was above 90% except in one case where <strong>the</strong> P sat was 130 bar, it was 84%.
We can see that as dP/dt decreases from A1-A3 <strong>the</strong> porosity increases gradually. While from A4-A6 <strong>the</strong>
porosity increases gradually as saturation temperature increases. From A7-A9, by increasing saturation
pressure, porosity drop trend is visible. In <strong>the</strong> last three samples <strong>the</strong>re is again a slight increase in porosity
due to an increase in saturation time.
100
Foams Porosity Variation
Foam Porosity ( %)
95
90
85
80
A1
A2
A3
A4
A5
A6
A7
A8
A9
A10
A11
A12
Pellets Thickness (0.6mm)
Figure 5.32: Variation in PLGA 50:50 foams geometric porosity for different process parameters.
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