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

Chapter 5.
Characterization <strong>of</strong> Scaffolds for Connective Tissue Engineering
pore size, PLGA 50:50 must be used instead <strong>of</strong> PLGA 85:15 . These results are in conformation with <strong>the</strong>
observations <strong>of</strong> Tai et al. [2007b]. These authors found that when greater depressurization times are applied
(actually very low, approximately 1 to 2 hours), <strong>the</strong> pore size is increasing with increasing LA composition
<strong>of</strong> <strong>the</strong> PLGA co-polymer.
Table 5.14: Coefficients <strong>of</strong> <strong>the</strong> 2 4 model for <strong>the</strong> PLGA 85:15 and <strong>the</strong> PLGA 50:50.
â 50-50 â 85-15
a 0 83.4 111.1
a 1 -55.3 3.0
a 2 -117.1 -46.5
a 3 -1.2 -31.8
a 12 4.4 12.9
a 13 -48.3 28.4
a 23 -60.2 36.4
Average Pore Diameter (m)
500 Psat = 100 PLGA bars 50:50 + PLGA 85:15 Blend
T
400 sat = 36.5 °C
t sat = 20 min
dP/dt = 25 bar/s
300
200
100
0
0 20 40 60 80 100
PLGA50:50 Fraction (%)
Figure 5.13: Average pore diameter as a function <strong>of</strong> PLGA 50:50 ratio in <strong>the</strong> PLGA 50:50 /PLGA 85:15 blends.
The comparison between <strong>the</strong> first order model <strong>the</strong>ory and experimental data has been realized and
<strong>the</strong> Fisher-Snedecor test has been applied. The critical value with <strong>the</strong> error probability alpha <strong>of</strong> 5% and one
degree <strong>of</strong> liberty at both <strong>the</strong> numerator and <strong>the</strong> denominator variance give F c = 161.4. The average pore
value is equal, in <strong>the</strong> PLGA 50:50 model to 222.4 and <strong>the</strong> PLGA 85: 15 model to 1.1. This first order model is not
statistically well suited in <strong>the</strong> PLGA 50:50 model. As various process parameters are correlated, it is necessary
to control <strong>the</strong>ir effects by using a multifactor design.
3.2.2 Model with a Taguchi’ Design for PLGA 50:50 Foaming
Taguchi’ design is a screening plan which helps at <strong>the</strong> determination <strong>of</strong> <strong>the</strong> more influent
parameters for <strong>the</strong> experimental plan. We have chosen a L 9 table and decided to continue only with <strong>the</strong>
PLGA 50:50 . Thus, it has left us 4 process parameters to optimize: <strong>the</strong> pressure, <strong>the</strong> temperature, <strong>the</strong> time <strong>of</strong>
saturation and <strong>the</strong> rate <strong>of</strong> depressurization. The domain <strong>of</strong> definition <strong>of</strong> this Taguchi design is presented in
Table 5.15.
Table 5.15: Domain <strong>of</strong> definition for <strong>the</strong> Taguchi’ design.
Factors T sat (°C) P sat (bar) t sat (min) dP/dt (bar/s)
Level 1 36.5 120 20 3
Level 2 45 150 45 5
Level 3 60 200 90 10
Figure 5.15 represents <strong>the</strong> variation <strong>of</strong> <strong>the</strong> effects <strong>of</strong> <strong>the</strong> four process factors on <strong>the</strong> corresponding
pore diameter. The pore diameter at a given level is estimated by taking <strong>the</strong> average <strong>of</strong> <strong>the</strong> average pore
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