Page 53 - Tailoring Electrospinning Techniques for Regenerative Medicine - Marc Simonet

Indeed, electrospinning for 20 minutes with a rotation speed that provided aligned fibers in a flat mesh when electrospinning for only 5 minutes also resulted in this self-assembled structure. A er 20 minutes the thickness of the electrospun material deposited as vertical monolayers reaches more than 1 mm, increasing significantly the uptake speed on the surface of the electrospun material, which is already on the collector. During the investigation about fiber orientation at di erent RHs, it was noticed that an increase of 0.1 m/s in the uptake speed can be enough to change from random to aligned fibers (Figure 2.3b-d), confirming that the rapidly raising thickness of the self-assembly of fibers might enhance its further occurrence. This could mean that they depend on uptake speed up to 5 minutes of electrospinning and can be shut down by setting a constant rotation speed of the collector that allows avoiding them, while still providing aligned fibers. While this might be di icult to control, one could also use a target with a much larger diameter, such that a diameter change of 100 to 200 μm doesn’t have much e ect on the circumferential speed. This might also explain the reason that these self-assembled structures aren’t jet reported, since studies for aligned fibers generally resort to much larger drums.
Di erent kind of 3D morphologies have been reported in literature, most frequently flu y45–47 or honeycomb-like structures.33,48,49 The former is made
of random non-wovens that grow perpendicularly to the collector, the latter involves uniaxial aligned fibers.
The main causes of the self-assembling of fibers
are most probably of electrostatic nature, especially 2 when the obtained structure is highly ordered like our
vertical monolayers or honeycombs. This hypothesis
is corroborated by results of Bonino et al.,32 who
electrospun a solution of PEO and sodium alginate,
an anionic polyelectrolyte capable to respond to
the electric field in the environment, which was
detected mainly on the surface of fibers in a core-
shell distribution of the two components in the
bulk of the material. They postulated a mechanism
of like-charge Coulombic repulsion between fibers,
enhanced by the presence of the charged component
on their surface. The self-assembly principle of our
found vertical structures are probably based on the
same charge dissipation principle as the stationary
collected honeycomb structures. Yan et al.33 and
Airwal et al.49 postulate that these thick fibers stack
on top of each other since they are still partial wet,
allowing a better charge dissipation towards the
collector. This electrically most balanced way of
deposition and the fast rotating target caused these
vertical monolayers meshes, is reported here for the
first time. Such structures could well be a potential
sca old for e.g. muscle or nerve tissue engineering,
combining highly aligned structures with a lot of void
spaces for cells ingrowth.
ELECTROSPINNING POLY(Ε-CAPROLACTONE) UNDER CONTROLLED ENVIRONMENTAL CONDITIONS
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