Page 42 - Tailoring Electrospinning Techniques for Regenerative Medicine - Marc Simonet

CHAPTER 2
structures oriented perpendicularly to the collector, and noticed that their occurrence is strongly dependent on the relative humidity in the spinning environment.32 They addressed this phenomenon to the ability of high relative humidity to increase the charge on the surface of the fibers. Yan et al. studied the self-assembly of polymer fibers under di erent environmental conditions, concluding that 3D structuring is a phenomenon that arises from electrostatic forces acting on deposition of fibers, so relative humidity can play a role in controlling it.33
The overall goal of our work is to study the e ect of relative humidity and temperature variations on electrospun poly(ε-caprolactone) fibers. PCL is a widely studied polymer with many applications as a biomaterial due to its biocompatibility and biodegradability.34–36 Also in our group PCL is already used since many years as a sca old material for tissue engineering applications.30,37–39 However, in this paper we will focus on the reproducibility of producing fibers in relation with the environmental conditions and not on these applications. Fibrous mats features we addressed are fiber diameter, surface morphology and orientation. Concerning the study on surface morphology, we compared two solvents of di erent water miscibility but similar boiling points, in order to investigate the former parameter while minimizing the di erences that can arise from solvents of di erent volatility. In addition, we studied how relative humidity can influence
the minimum uptake speed which is necessary for obtaining oriented fibers, and we present, to our knowledge, a never reported self-assembly in which fibers are deposited on the collector as vertical monolayers, allowing porous aligned structures.
2.3 Materials and Methods
2.3.1 Materials
Poly(ε-caprolactone) (PCL) was supplied by Solvay (CAPA 6800, MW ~ 80 kDa) and used as received. Chloroform (CHCl3) (>99,8%, stabilized with Ethanol) was purchased from Acros Organic; Tetrahydrofuran (THF) (reagent grade, stabilized with 0.025% BHT) was purchased from Fisher Chemicals.
2.3.2 Electrospinning
Solutions were prepared by mixing the polymer with the solvent at room temperature and stirring overnight. The following concentrations and solvent systems were used: 15 wt% in CHCl3, 15 wt% in CHCl3/THF 90/10 wt, 20 wt% in CHCl3/THF 50/50 wt, 20 wt% in CHCl3/THF 10/90 wt and 20 wt% in THF. Electrospinning was performed on an IME Technologies EC-CLI equipment (IME Technologies, Geldrop, The Netherlands), fibers were collected on a rotating cylindrical target (diameter 20 mm) wrapped with Aluminum foil. Applied voltage was 15 kV on the electrospinning nozzle (1.0*0.8 mm), and –0.5 kV on the rotating collector, solution flow rate was set
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