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

Chapter 5.
Characterization <strong>of</strong> Scaffolds for Connective Tissue Engineering
One can see <strong>the</strong> effects <strong>of</strong> all <strong>the</strong> process parameters on <strong>the</strong> pore size. Increasing T sat ultimately
improves <strong>the</strong> pore diameter, and pore diameter is decreased by increment <strong>of</strong> P sat and dP/dt. There was a
slight increase in <strong>the</strong> pore diameter <strong>of</strong> foam by increment <strong>of</strong> t sat . So <strong>the</strong> process parameters have been
improvised by performing <strong>the</strong>se experiments. A foam was <strong>the</strong>n produced at this optimized condition and
from analysis, <strong>the</strong> porosity obtained was 93% and diameters for micro, meso and macro pore was 14m,
97m and 276 m respectively.
5 Conclusion
Different types <strong>of</strong> polylactides including polylactic acid and poly(lactic co-glycolic acid) have
been characterized in details. The composition <strong>of</strong> each polymer was also discussed as it has a pivotal role on
<strong>the</strong> properties <strong>of</strong> <strong>the</strong> final porous scaffolds produced. Foams were made with pure polylactic acid and with
blends <strong>of</strong> polylactic acid and polylactic co-glycolic acid in order to analyze <strong>the</strong> effect <strong>of</strong> LA/GA
composition during <strong>the</strong> foaming process and porosity <strong>of</strong> <strong>the</strong> foam. Different experimental designs were used
to attain optimized porosity and pore size distribution.
Firstly, we must admit that <strong>the</strong> consideration <strong>of</strong> <strong>the</strong> results <strong>of</strong> <strong>the</strong> 2 4 , Taguchi and initial Doehlert
plan is difficult. During <strong>the</strong>se experiments, we have not noticed <strong>the</strong> important effect <strong>of</strong> <strong>the</strong> volume constraint
and <strong>the</strong> position <strong>of</strong> <strong>the</strong> pellet. Indeed, <strong>the</strong>se two parameters affect <strong>the</strong> pore size. We have encountered
important heterogeneities within <strong>the</strong> cross-sections micrographs and very different pore sizes for <strong>the</strong>
scaffolds which were processed in <strong>the</strong> same chamber. For this reason, we have decided to change <strong>the</strong>
experimental setup. We have removed <strong>the</strong> Teflon isolation to gain volume and we have filled <strong>the</strong> chamber
with small glass balls. After that, only one pellet has been placed on <strong>the</strong> holed grill which has been
positioned above <strong>the</strong> glass balls. For <strong>the</strong> following experiments, we have found that <strong>the</strong> pore size increases
with decreasing saturation pressure and depressurization rate. Best results have been achieved within <strong>the</strong>
range <strong>of</strong> 128 and 138μm for P sat = 100 bar, T sat = 36.5°C, t sat = 60 min. and dP/dt = 1.25 bar /s.
Finally, detailed emphasis was laid down on <strong>the</strong> effect <strong>of</strong> process parameters such as saturation
pressure, saturation temperature and saturation time and depressurization rate during foaming process.
Optimum thickness <strong>of</strong> <strong>the</strong> pellet was finalized for <strong>the</strong> experimentation process.
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