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

Chapter 5.
Characterization <strong>of</strong> Scaffolds for Connective Tissue Engineering
using <strong>the</strong> Mark-Houwink Relationship (MHR) with K = 2.2610 -5 dl/g and a = 0.796, <strong>the</strong> molecular weight
we obtain: M vis = 2 637 540 g/mol.
1.1.2 Discussion on <strong>the</strong> Molecular Mass
Experimental results have been compared with values given in data sheets with <strong>the</strong> different
polylactides. All <strong>the</strong> values, reported on Table 5.4, are in <strong>the</strong> range <strong>of</strong> <strong>the</strong> specifications. Moreover, <strong>the</strong>
separation between <strong>the</strong> two main medical applications <strong>of</strong> <strong>the</strong> polylactides seems to be governed by <strong>the</strong>
intrinsic viscosity range <strong>of</strong> <strong>the</strong> polymers. Below a certain molecular mass (i.e. <strong>the</strong> critical mass), oligomers
are used as controlled release and above this critical mass polymers can be used as medical device. As
shown on Table 5.4, differences between polylactides <strong>of</strong> <strong>the</strong> same inherent viscosities range are not
significant; <strong>the</strong>y can be chosen whatever <strong>the</strong>ir origin (Lactel, Purac, Boehringer).
Table 5.4: Comparison between molecular weight <strong>of</strong> various polylactides.
Polylactides
Data Sheet* Experiments M w Deduced
inh (dL/g) inh (dL/g) from MHR
Applications
P L,D LA (PABR L 68) 2.33 2.24 163 971 Packaging
P L,DL LA (Resomer ® LR 704) 2.0 − 2.8 2.68 201 169 Medical device
PLGA 85:15 (Resomer ® RG 858S) 1.3 − 1.7 1.62 57 529 Controlled release
PLGA 85:15 (DL-PLG) 0.55 − 0.75 0.72 18 943 Controlled release
PLGA 50:50 (PLG 8523) 2.27 2.21 88 033 Medical device
PLGA 85:15 (PLG 8531) 3.11 2.96 131 366 Medical device
PLGA 85:15 (LG 857 S) 5.0 − 7.0 6.63 396 495 Medical device
PLGA 50:50 (Resomer ® RG 504) 0.45 − 0.60 0.59 14 756 Controlled release
PLGA 50:50 (PDLG 5010) 1.03 0.97 28 494 Medical device
1.1.3 Characterization <strong>of</strong> Polylactide Powders by DSC
The <strong>the</strong>rmograms <strong>of</strong> <strong>the</strong> different PLAs and PLGAs are presented in <strong>the</strong> Figure 5.2, Figure 5.3 and
Figure 5.4. The <strong>the</strong>rmograms are representative <strong>of</strong> <strong>the</strong> second scan run.
Figure 5.2: Thermograms <strong>of</strong> various PLAs.
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