Page 68 - Tailoring Electrospinning Techniques for Regenerative Medicine - Marc Simonet

CHAPTER 3
Figure 3.6 Polymer mesh density for electrospun biopolymers collected at room temperature (le ) or using a dry ice cooled collection drum (right) and increasingly more humid air.
3.4.3 Ice particle deposition
The role of humidity in the surrounding air to supply vapor for the ice particle formation in the vicinity was further confirmed by investigating low-temperature electrospinning at increasing humidity. In relatively dry air, no di erence in mesh density could be observed either for polymer fibers collected at room temperature or on a dry ice cooled collection drum (see columns at 15% relative humidity, Figure 3.6). For higher humidity (30, 50 and 85% relative humidity), a much lower mesh density confirmed the incorporation of ice particles into the depositing polymer fibers during low-temperature electrospinning. This observation may be explained using a psychometric chart (Figure 3.7) depicting the
temperature dependence of the relative humidity. Since heat from the surrounding (room temperature) air continuously flows to the cooled collection drum, a temperature gradient is found at the vicinity of the drum surface. As a consequence, the air at the surface of the collection drum is colder, a ording an increase in relative humidity as indicated by the vertical lines in Figure 3.7. Once saturated, water precipitates from the humid air forming water droplets or particles that can deposit onto the collection drum. The here-used temperature (collection drum surface at below 220K) suggests the direct precipitation of ice particles from the humid air (snow) and rapid incorporation in the polymer fiber mesh.
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