Page 43 - Tailoring Electrospinning Techniques for Regenerative Medicine - Marc Simonet

at 25 μL/min. A coaxial shield of chloroform rich air was used to prevent the needle exit from clogging by suppressing excessive solvent evaporation, as suggested by Larsen et al.40 Aside from these constant parameters, the solvent system of the solution, environmental conditions, collection speed of fibers and spinning time, were varied as follows according to the specific aspect of the electrospun sample that we aimed to study.
2.3.3 Polymer mesh characterization
Fiber diameter and surface morphology
Each sample was electrospun for 5 minutes, with a fiber uptake speed of 0.1 m/s (no fiber orientation occurs). Temperature was varied from 20°C to 40°C, increasing it by 5°C steps for the 15 wt% in CHCl3 solution, and by 10°C steps for all the other CHCl3/ THF ratios). Relative humidity was varied from 30% to 90%, increasing it by 10% steps for solution 15 wt% in CHCl3 and by 20% steps for the other solutions. Each condition was investigated with at least three specimens.
Fiber orientation
The relation between relative humidity and the minimum uptake speed for obtaining aligned fibers was studied at a constant temperature of 20°C at four di erent relative humidity’s (30%, 50%, 70%, and 90%). The uptake speed is defined as the tangential speed on the collector surface, expressing
the speed of fibers being winded-up on the rotating
collector. The spinning time was 5 minutes for all the
samples. By changing the rpm’s, the uptake speed
was increased to a maximum of 2.5 m/s, with 0.1 m/s
increments, in order to evaluate the critical value 2 of collecting speed that resulted in fiber alignment.
Each condition was investigated with at least three specimens.
Minimum uptake speed for fibers orientation
The critical uptake speed that is necessary for obtaining alignment was investigated at 20°C for four values of relative humidity (30%, 50%, 70%, 90%). The rotation speed of the cylindrical collector was increased up to 2.5 m/s for achieving fiber alignment. Fast Fourier Transformed (FFT) was used to quantify the degree of fiber alignment present in an original Scanning Electron Microscope (SEM) micrograph according to Ayres et al.41
The resulting FFT output image is a distribution of intensity in arbitrary units (a.u.), which reflects the fiber orientation in the sample analyzed. The intensity was integrated radially along a circular projection between 0° and 360° (azimuthal integration). The image analysis was performed in a MatLab script (The MathWorks, Inc., Natick, Massachusset, USA) in which all the FFT data are normalized to a baseline in order to have comparable results from di erent data sets. Because of symmetry of the system, the integrated intensity was plotted as a function of
ELECTROSPINNING POLY(Ε-CAPROLACTONE) UNDER CONTROLLED ENVIRONMENTAL CONDITIONS
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