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

Chapter 5.
Characterization <strong>of</strong> Scaffolds for Connective Tissue Engineering
4.9 <strong>Influence</strong> <strong>of</strong> Pellet Thickness on Foaming
To study <strong>the</strong> effect <strong>of</strong> polymer mass and o<strong>the</strong>r parameters pellets <strong>of</strong> different thickness ranging
between (0.2 − 1.8 mm) were made (cf. Table 5.25).
Table 5.25: Pellets <strong>of</strong> variable thickness and <strong>the</strong>ir foam data.
Pellet Dimensions Foam Dimensions Porosity
Diameter Thickness Mass Diameter Thickness Mass
d p (mm) ø p (mm) m p (mg) d f (mm) ø f (mm) m (mg)
(%)
12.93 0.25 28.60 23.63 0.92 28.90 91.8
12.85 0.43 63.30 25.05 1.49 63.10 92.4
12.90 0.62 96.00 25.08 2.06 96.10 92.0
12.94 0.83 126.70 32.13 2.12 126.10 93.7
12.92 1.10 165.00 24.59 4.72 164.90 93.6
13.00 1.23 203.00 23.00 5.52 202.80 92.9
12.94 1.37 230.70 20.81 5.76 230.70 90.8
12.90 1.62 273.10 20.23 6.14 272.20 89.3
12.95 1.82 298.60 20.79 6.33 297.60 88.9
The pellets were prepared at P = 150 bars, T = 60 o C and t = 20 min as per procedure described in
section 4.3 and illustrated in Figure 4.9-(B). Before and after scCO 2 treatment, <strong>the</strong> pellets and foams
diameter and thickness was measured by using a digital vernier caliper at eight different points (cf. Table
5.25). The mean values were considered during <strong>the</strong> calculation and analysis. Pellets were treated at
following supercritical CO 2 conditions: P sat = 120 bars, t sat = 20 min, T sat = 35°C and dP/dt = 3 bar/s.
Experiments were carried out in <strong>the</strong> SEPAREX ® SF200 pilot plant by adopting <strong>the</strong> setup-02 as described in
(cf. chapter 4, Figure 4.12-B).
4.9.1 Porosity and Cell Density
By using <strong>the</strong> dimensions <strong>of</strong> pellets and foams, geometric porosity <strong>of</strong> <strong>the</strong> foam was calculated. It
was above 88% for all <strong>the</strong> samples. Average porosity was calculated from <strong>the</strong> diameter, thickness and mass
<strong>of</strong> pellets and foams, <strong>the</strong>n data was considered for <strong>the</strong> calculation <strong>of</strong> cell density. (cf. Table 5.25 and Figure
5.28). Cell densities <strong>of</strong> <strong>the</strong> foams are presented in Figure 5.29 and corresponding images <strong>of</strong> obtained foams
are represented in Figure 5.30.
Foam Porosity ( %)
100
95
90
85
Foams Porosity Variation
Pore Density--Pores /(cm) 3
10 6 Cell Density <strong>of</strong> Pores
Micro Pores
Meso Pores
Macro Pores
10 5
10 4
10 3
80
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8
PLGA 50:50 Pellets Thicknesses (mm)
10 2
0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8
Pellet Thickness (mm)
Figure 5.28: Porosity <strong>of</strong> PLGA 50:50 foams for
pellets with different initial thickness.
Figure 5.29: Pore density <strong>of</strong> PLGA 50:50 foams with
different initial pellet thickness.
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