Page 63 - Tailoring Electrospinning Techniques for Regenerative Medicine - Marc Simonet

3.3.3 Polymer mesh characterization
Gel permeation chromatography
The molecular weight distribution of the polymers was determined by gel permeation chromatography (GPC Viscotek, VE7510 degasser, VE1121 solvent pump, VE520 autosampler and Model 301 triple detector array) performed on a PL-gel MIXED-D column (Polymer Laboratories, 300*7.5 mm) calibrated with polystyrene standards (Polymer Laboratories, 1000 up to 475,000 Da). Prior to analysis, the polymer was dissolved as an 0.1 wt/vol% solution in tetrahydrofuran (THF, Acros Organics, for analysis) containing 0.25 vol% toluene (Riedel-de Haën, for analysis) as a flow-marker and examined using both conventional and multi-detector calibration.
Mesh morphology
Polymer mesh samples were sputter-coated (Baltec SCD 050) with a 5 nm Pt-layer prior to imaging and investigated by scanning electron microscopy (SEM) on a LEO 1530 microscope. The inter-fiber spacing of the resulting polymer meshes was estimated by randomly measuring the distance between two adjacent fibers in SEM images using at least 30 randomly chosen fiber pairs.
Polymer and mesh density
The polymer density ρ0 of PLGA and PEU was
measured at 25°C using a helium pycnometer (Ultrapycnometer 1000, Quantachrome) yielding 1.26
g /cm3 for PLGA and 1.15 g /cm3 for PEU, respectively.
The bulk densities ρ of the electrospun polymer
meshes were determined gravimetrically using the
weight of precisely cut mesh samples of defined 3 area and thickness. The overall mesh porosity ε was
calculated according to the following expression: (1)
Tensile properties
The breaking length of selected polymer meshes was measured at room temperature (Instron tensile tester, model 5864) at a crosshead speed of 12.6 mm/ min using a sample gauge length of 12.6 mm (100 % /min). The fibrous nature of the mesh was taken into account by converting the values of the tensile tests into breaking length according to the procedure proposed by Page et al.34,35
(2)
where T denotes the tensile strength expressed as breaking length [km], F the force [kN], ρa the area density of the mesh [kg/m2], w the sample width [m] and g the acceleration due to gravity [m/s2].
ULTRA-POROUS 3D POLYMER MESHES BY LOW-TEMPERATURE ELECTROSPINNING
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