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Niveau: Supérieur, Doctorat, Bac+8
Lire la première partie de la thèse

  • psat

  • pellets prepared

  • tsat

  • both wet

  • between both

  • dry method

  • wet method

  • initial taguchi

  • pore diameter


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Language English
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Lire lapremièrepartie de la thèse
Chapter 6
Chapter 6
Optimization of Pore Morphology of Scaffolds for Connective Tissue Engineering
This chapter consist of two parts, first two PLAs and two PLGAs were foamed by using the wet and dry method techniques in order to see the difference in pore morphology, structure and anisotropy. The influence of scCO2foaming parameters was studied in detail with respect to each polymer and process. The effect of each process parameter was taken into account to analyze the scaffolds and optimize their porosity and equivalent pore diameter. The mechanical properties of the optimized foams were also tested. Second we will present the optimized foaming results obtained by adding surface modifier to the polymer by co-grinding to improve the surface adhesion of the blend foam. A focus on pore morphology and their characteristics will be emphasized as it plays an important role in cell seeding, differentiating and growth in the scaffold.
1Optimization of PLA’s Foams Processed by Wet and Dry Methods
® In this chapter, we have used PL,DLA (PABR L 68), PL,DLLA (Resomer LR 704), PLGA85:15(DL-PLG), and PLGA50:50(PDLG 5010). These polymers have been characterized in detail in chapter 5.
First, pellets prepared by both methods were foamed with supercritical fluid to make scaffolds. Secondly, a comparative study was made to analyze the porosity and pore morphology created by wet and dry method. In the first part, we will discuss the two PLAs in which, one is amorphous while the other is semi-crystalline.
1.1Experimental Procedure
1.1.1Preparation of Pellets by Wet and Dry Methods
A soluble solvent, acetone, was used to make a homogenous solution with polymer powders. Transparent solution was poured in petri dish of 7cm diameter. The solution was dried for 48 hrs and then pellets of 12mm diameter and ~1 1.2mm thickness was cut with die cutter. Further details of the wet
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Chapter 6. Optimization of Pore Morphology of Scaffolds for Connective Tissue Engineering
method pellet preparation are reported in chapter 4 section 1.5. In parallel pellets of 13 mm diameter and ~1.2 mm thickness were also prepared by dry method as described earlier in section 1.4, chapter 4.
1.1.2
Taguchi’ Design for Foaming
Taguchi’ design was considered for these experimentations. We have chosen L9table. As a result, 4 process parameters were optimized: the pressure, the temperature, the time of saturation and the rate of depressurization. The domain of definition of this Taguchi design is presented in Table 6.1. A wide range of all the four parameters were kept in the initial plan.
Table 6.1:Initial Taguchi plans for scCO2foamingof pellets prepared bywet and dry method.Nr 1 2 3 4 5 6 7 8 9 o Tsat( C)5040 40 40 45 45 45 50 50 Psat(bar)100 200 300 100 200 300 100 200 300 tsat(min)30 40 20 40 20 30 20 30 40 dP/dt (bar/s)11 3 5 5 1 3 3 5
® SEPAREX SFC6 scCO2plant was used for foaming scaffold during this laboratory experimentation. As the pressure chamber capacity is 6 liters, multiple pellets were placed inside the chamber for one process condition. Single perforate plate was adopted for foaming process by placing 4 pellets (2 wet plus 2 dry) for one process condition.
1.2PL,DLA Foams Processed by Wet and Dry Methods: Initial Taguchi Plan
Foams of PL,DLA pellets, prepared by wet and dry methods, were produced by adapting initial Taguchi plan. After making the dimensional observations for geometric porosity calculations, SEM analysis for all the foams was done. Four to six micrographs were taken for each foam at different magnifications at different positions on the sample.
® The equivalent pore diameter obtained from SCION Image analysis of the SEM micrographs and the geometric porosity calculated from the dimensional data of pellets and foams are reported on Table 6.2. The highlighted and underlined values in the table are the optimum values. SEM micrographs of PL,DLA foams are presented in Figure 6.1. The process conditions for foams in the micrograph are saturation temperature, saturation pressure, saturation time and depressurization rate.
Table 6.2:PL,DLA foams pore data of wet and dry method by initial Taguchi’ plan.scCO2Parameters Geometric Equivalent PorosityDiameter Pore PL,DLATsat Psat tsat dP/dt P (%)de(m)(°C) (bar) (min) (bar/s) Wet Dry Wet Dry P16055.8 50 1 56.5 40 100 30 P263.3 15 3 59.1 4040 200 40 P368.9 20 2540 300 20 5 69.3 P4655 63.5 83.6 25 45 100 40 P51 74.4 45 200 20 5057.1 20 P645 300 30 8059.5 10 3 75.2 P712572.5 100 3 77.2 50 100 20 P85 91.6 57.8 10 50 200 30 50 P950 300 40 1 64.8 63.0 20 25
The pore diameter was heterogeneous (small and large) in the foams obtained hence the maginification was different for some of the foams. Higher and low magnification was done for foam
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Chapter 6. Optimization of Pore Morphology of Scaffolds for Connective Tissue Engineering
micrographs with small and large pore diameters. Most of the images presented in Figure 6.1 are of magnification 100× and 250×.
Wet Method
Condition:01--200× o [40 C - 100 bars - 30 min - 1 bar/s]
Condition:03--100× o [40 C - 300 bars - 20 min - 5 bar/s]
Condition:05--100× o [45 C - 200 bars - 20 min - 1 bar/s]
Condition:07--100× o [50 C - 100 bars - 20 min - 3 bar/s]
Dry Method
Condition:01--100× o [40 C - 100 bars - 30 min - 1 bar/s]
Condition:03--100× o [40 C - 300 bars - 20 min - 5 bar/s]
Condition:05--50× o [45 C - 200 bars - 20 min - 1 bar/s]
Condition:07--50× o [50 C - 100 bars - 20 min - 3 bar/s] Wet Method
Wet Method
Condition:02--250× o [40 C - 200 bars - 40 min - 3 bar/s]
Condition:04--250× o [45 C - 100 bars - 40 min - 5 bar/s]
Condition:06--100× o [45 C - 300 bars - 30 min - 3 bar/s]
Condition:08--100× o [50 C - 200 bars - 30 min - 5 bar/s] Dry Method
Dry Method
Condition:02--100× o [40 C - 200 bars - 40 min - 3 bar/s]
Condition:04--100× o [45 C - 100 bars - 40 min - 5 bar/s]
Condition:06--100× o [45 C - 300 bars - 30 min - 3 bar/s]
Condition:08--100× o [50 C - 200 bars - 30 min - 5 bar/s]
Condition:09--100× Condition:09--100× o o [50 C - 300 bars - 40 min - 1 bar/s] [50 C - 300 bars - 40 min - 1 bar/s] Figure 6.1:Micrographs of PL,DLA foams processed by wet and dry methods.
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