Page 44 - Tailoring Electrospinning Techniques for Regenerative Medicine - Marc Simonet

CHAPTER 2
the angle between 0° and 180°. The width of the peak at half height (WHH) decreases with increasing fiber alignment. Critical uptake speed for obtaining aligned fiber structure was defined at the minimum WHH for each relative humidity.
Scanning Electron Microscopy (SEM)
Samples were analyzed with a FEI Quanta 600F scanning electron microscope, in high vacuum atmosphere, without any further treatment. Dimensions of fibers were measured with the so ware ImageJ (U. S. National Institutes of Health, Bethesda, Maryland, USA), with a minimum of at least 90 measurement points.
2.3.4 Statistical analysis
All data are presented as mean ± standard deviation. Statistics were performed using GraphPad Prism (GraphPad So ware, La Jolla, California, USA) by mean of an unpaired t test. Di erences were considered significant for p-values <0.05.
2.4 Results and Discussion
2.4.1 Fiber dimension
Already a few authors described a change in fiber diameter caused by variations in the electrospinning environment, mainly by changes in the relative humidity. Most of them report an increase in fiber diameter with a higher relative humidity’s,9,10,42 while Pelipenko et al. reported a decrease in the average
fiber diameter with increasing relative humidity.17 They electrospun poly(vinyl alcohol) dissolved in water and the observed e ect was addressed to a decreased evaporation rate of water while spinning in a more humid environment, allowing a longer elongation of the jet. On the other hand, the studies reporting an increase in fiber diameter with increasing relative humidity were performed with non-water soluble polymers in organic solvents as tetrahydrofuran and N,N-dimethylformamide (DMF). These authors explained their findings either with a precipitation of the polymer due to water di usion into the elongating jet10 or with an increased discharge potential of the polymer solution jet in a more humid environment, reducing the repulsive force between needle and collector that is responsible for the jet elongation.9,42 Additionally these studies mention a broader fiber diameter distribution with increasing relative humidity.10,17
In contrast with these observations our experiments resulted in almost constant diameter and diameter range of fibers spun from a same solution regardless of the employed set of environmental conditions. Table 2.1 reports the average fiber dimension obtained by electrospinning the five di erent PCL solutions in the 20°C - 40°C temperature range and 30% - 90% relative humidity range. Within each of the di erent solution group, there was no significant di erence in fiber diameter over the tested temperature and humidity range.
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