Biomedical Engineering Reference
In-Depth Information
(a)
(b)
(c)
(d)
FIGURE 5.8
(a) SEM and fl uorescence images of electrospun PCL/Col fi bers doped with rhodamine.
(b) SEM and fl uorescence images of electrospun PEO fi bers doped with FITC. (c) Co-electrospinning of PCL/
Col and PEO. The two polymers exhibited mixing in the structure with PEO fi bers showing more irregular
fi ber morphology. FITC/rhodamine fl uorescence confi rmed the mixing of the two fi ber species. (d) Leaching
of PEO from the structure, leaving only rhodamine-doped PCL/Col.
solution that are directly related to the solvent used. In a study done by Lee et al., morphology
of PCL electrospun fi bers was highly dependent on the solvent composition. The addition of
N
,
N
-dimethylformamide (DMF) into methylene chloride (MC) improved the resulting conductivity
of the solution, thus resulting in much fi ner fi bers compared to MC alone [7]. Interaction between
the solvent and the polymer chains determines the fl exibility of the molecules. Orientation of the
polymer molecules and thus stretching of the jet is facilitated during bending instability, resulting
in thinner fi bers [8].
It is possible to electrospin two or more different species of polymers into a single nanofi brous
membrane structure. Figure 5.8 shows co-electrospinning of PCL/Col blend and PEO nanofi bers.
To visualize the distribution of both fi bers, PCL/Col solution was doped with rhodamine dye
(Figure 5.8a, red color) and PEO was doped with FITC dye (Figure 5.8b, green color). When
they were spun together using a two-syringe electrospinning system and rotating mandrel as a
collector, the two fi bers were intertwined in the fi nal nanofi ber mesh (Figure 5.8c). As PEO is a
water-soluble polymer, immersion of the mesh in an aqueous solution resulted in leaching of PEO
from the structure leaving only the PCL/Col component (Figure 5.8d).
5.2.1.2 Collection Systems
The collectors may have a range of shapes or confi gurations. The vast majority of electrospin-
ning systems use a single collection plate to collect the fi bers, while grounding a single rotating
cylindrical collector can collect fi brous mats, orient the fi bers in a thin sheet of fabric, or make a
tubular (bilayered) construct. Oriented fi bers can also be obtained using dual, grounded collection
plates, or rings. In this confi guration, the fi bers are suspended in a space between the two grounds.
Additionally, a ring of wire, when used horizontally as a collector, results in a thin membrane upon
which cells can be seeded. Collection systems may also be a hydrogel, water, a confl uent layer of
cells, or part of a living body.
5.2.1.3 Polymer Solutions
The major parameters controlling the fi ber diameter are the concentration of the spinning solu-
tion, the electric conductivity of the solution or melt, as well as the feeding rate of the spinning
