Figure 2
Left and center: Scanning electron microscope images of fibers produced with the ultrasound-enhanced electrospinning (USES) device at low, mid and high ultrasonic power. Top row corresponds to the test and the lower row to a re-test. Low ultrasonic power exhibited fibers with minor “beading”, whereas beading was most pronounced in fibers generated with high ultrasound power and with the reference technique (conventional electrospinning). The images suggest that the visual appearance of fibers was similar in the test compared to the re-test. Ultrasonically enhanced fibers appear thicker than those produced with the reference method. The results suggest that the appearance of the topography of fibers generated with USES can be repeatedly modified. Right: Distribution of fiber diameters produced at high, mid or low ultrasound power in test/re-test -experiments. All methods produced nanofibers with 50–500 nm diameter. Ultrasound-enhanced fibers were qualitatively thicker and statistically different in diameter (p < 0.0001) than those produced with the reference method. The fibers produced using high ultrasound power were qualitatively thinner and statistically significantly different (p < 0.0001) than those produced with ‘mid’ or ‘low’ ultrasound power. The ‘mid’ ultrasound exposure produced a narrower fiber distribution than the low power, but low power produce thinner fibers in the 50–200 nm range. The results suggest that the distribution in fiber diameter can be modified by changing the ultrasound power, without changing the chemical composition of the source polymer. The reference fibers were produced with conventional needle electrospinning. For comparability the area of each histogram was normalized to 1. For statistical analysis, non-parametric Kruskall-Wallis for pairwise comparison with Bonferroni adjustment was used. Scale bars for 1800× and 15 000× magnifications corresponds to 30 μm and 3 μm, respectively.
