Page 86 - Tailoring Electrospinning Techniques for Regenerative Medicine - Marc Simonet

CHAPTER 4
same average SFD of 45 μm and the SFD reaching a maximum of 100 μm. These results are in accordance with the model of Eichhorn and Sampson stating that in conventional electrospinning, the fiber diameter mainly determines the spatial fiber distance.9
In contrast to the observation above, the polymer choice played a significant role when using LTE spinning. The maximum SFD increased from 100 μmto200μmforaPCL-andto300μmforaPLA sca old when using LTE-compared to conventional spinning. Also the average SFD increased. The use of PLA resulted in sca olds with an average SFD of 152 μm compared to the 123 μm found for the 8.5 times so er PCL. Likewise, a larger volume of SFD over 100 μm is measured for PLA sca olds as can be seen on the inserted cube pictures of the calculated SFD’s in Figure 4.3.
For the conventional spun sca olds nearly 70 % of the sca old voids have a SFD smaller than 50 μm and no SFD above 100 μm is found (Figure 4.4). In contrast, the low-temperature electrospun sca olds have less than 10 % of their voids in the smallest size range of 0-50 μm, and more than 60% of their voids have a SFD of 100 μm and above. Using a
polymer with a higher Young’s modulus shi s the SFD towards higher values when the sca olds are LTE spun. This leads to the distinctive di erence that is found between PCL- and PLA LTE-spun sca olds: the latter features less than 5 % of their SFD’s below 50 μm, but nearly 20 % are above the 200 μm.
4.4.3 Influence of fiber sti ness on 3D sca old porosity
We also investigated why a minor decrease in porosity is observed for LTE-spun sca olds when they were spun for a longer period of time (Figure 4.1). Since the ice crystal growth rate generally remained linear for a given spinning time and ambient parameters (data not shown), the additional polymer material deposited may have caused the sca old to collapse due to its own weight during the drying process, leading to denser structures. In order to scrutinize this hypothesis and learn how to exploit this feature, we explored how variations in the fiber diameters (see Figure 4.5), and hence the fibers’ sti ness (see Table 4.1), a ects the void spaces in LTE electrospun sca olds.
84