Page 62 - Tailoring Electrospinning Techniques for Regenerative Medicine - Marc Simonet

CHAPTER 3
drum for fiber deposition. The polymer solutions were delivered at 4 ml/h (Racel Scientific Instruments) to a spinning head consisting of a central stainless steel tube (Angst & Pfister AG, Switzerland; inner diameter: 1.0 mm, wall thickness 0.3 mm) connected to a DC high voltage supply (Glassman, EH-series) operated at 20 kV. A coaxial jacket of chloroform saturated air prevented the needle exit from clogging by suppressing excessive solvent evaporation as proposed by Larsen et al.33 The polymer fibers were collected for two hours on a rotating, hollow, cylindrical aluminum drum (length 100 mm, diameter 80 mm, wall thickness 5 mm) equipped with removable end covers. In normal operation, the drum was grounded and successively covered by polymer fibers. For low-temperature electrospinning, at the cold external cylinder surface (see Figure 3.1).
the drum was loaded with dry ice (frozen CO2; Pan Gas, technical grade, average temperature 195K) which resulted in the rapid deposition of ice crystals
The distance between the needle and the collector drum was maintained at 20 cm. For the comparison of normal and low-temperature electrospinning, all spinning parameters were kept constant while only changing the collection drum temperature (300K versus 200-220K). The relative humidity (measurement accuracy: +/- 2.5%) and air temperature during polymer processing were recorded on a Testo 625 thermohygrometer. The environmental relative humidity was measured at a distance of 5 cm, the sca old temperature and relative humidity at a distance of 5 mm next to the collection drum surface.
Figure 3.1 Dry ice cooled collection drum at the end of an electrospinning run, covered by an intimate mixture of ice crystals and polymer fibers. 60