Page 69 - Tailoring Electrospinning Techniques for Regenerative Medicine - Marc Simonet

The apparent indi erence of the polymer mesh porosity on high humidity (similar mesh densities for 30, 50 and 85% humidity in Figure 3.6) can be explained on the basis of a typical heat/mass transfer limitation. Once condensation had started, the latent heat release from the condensing water determined the amount of water deposited and suggested that the here presented process was heat transfer limited.43,44 A further increase in water availability (higher humidity than 30%) did therefore not significantly increase the amount of ice particles and thus did not a ect the mesh density.
3.4.4 Tensile properties of the porous meshes
A er synthesis, the polymer/ice layer was removed and dried in a conventional desiccator yielding the porous polymer meshes as shown in Figure 3.2 to
Figure 3.4. The dry meshes were further characterized for their tensile properties in terms of breaking length and modulus.
The modulus of the PEU meshes is around 40 times lower than in the PLGA-meshes and a considerable di erence between the meshes spun at room temperature and at low-temperature is observed (Figure 3.8), although the mesh architecture is taken into account by the calculation of the mechanical properties. This loss in mechanical sti ness found for low-temperature spun samples may be attributed to the fact that the fibers are less entangled due to the presence of ice crystals during the formation of the meshes. During tensile deformation, individual fibers are torn out of the PLGA meshes spun at low- temperature, which may explain the increase in strain at break recorded for these systems.
ULTRA-POROUS 3D POLYMER MESHES BY LOW-TEMPERATURE ELECTROSPINNING
Figure 3.7 Psychrometric chart of moisture in air at 101.3 kPa displaying the 3 estimated relative humidity and temperature ranges close to the collection drum.
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