Higher order electrospun fiber organization using electrical field control and mechanical movement

Moving collector is commonly used to construct highly aligned nanofibers membrane. This is due to the movement of the collector pulling the solidifying electrospinning jet as it touches the collector. While there has been much research on the influence of a flat surface collector on electrospun fiber collection to obtain aligned fibers, there are much less on the effect of a moving collector with different shapes on fiber organization. It is important to note that as the shape of the collector changes, the electric field profile between the spinneret and the collector also changes. It is widely understood that the electrospinning jet is strongly influenced by the electric field profile. Various hybrid setups where the electric field is modified and mechanical movement are been used to construct membrane with ordered fibers.

A hybrid setup may also be used to construct higher ordered electrospun fibrous structure. In its simplest form, varying the rotation speed of a tube collector has allowed the construction of tubular fibrous scaffold comprising of layers of differing fiber organization. At a higher rotation speed, aligned fibers can be deposited along the circumference of the tube collector. Slowing down its rotation speed, a random layer of fibers can be deposited over the aligned fibrous layer. A more complex organization of fibers has been demonstrated by Zhu et al (2016) where they used a dumbbell shaped rotating collector to investigate fiber deposition behaviour. The dumbbell shape modified the electric field profile such that it resembles a parallel electrodes collector system where the ends of the dumbbells function as parallel electrodes. When the dumbbell collector is static or moving slowly, the fibers will preferentially deposit across the gap at the middle of the dumbbell shape collector. However, when the collector starts rotating around its axis, above a critical rotation speed, the fibers will be deposited with one end on one edge of the dumbbell, the middle touching the central spindle and the other end on the other edge of the dumbbell. This has been attributed to the slower deposition speed of the electrospinning jet such that part of the electrospun fibers wrapped around the central spindle. Starting with a higher rotating speed and progressively reduce the speed, separate layers of fibers with space in between can be deposited on the dumbbell collector.

Layered fibers constructed by varying the rotation speed of the dumbbell shape collector [Zhu et al. AIP Advances 2016; 6: 055304].

Schematic illustration of the influence of rotation speed on fiber deposition [Zhu et al. AIP Advances 2016; 6: 055304].

For direct electrospinning of more complex tube structures such as T-junction tubes, both the orientation of the base template and the electric field profile needs to be controlled. This is shown by Tejeda-Alejandre et al (2017) in their construction of a T-junction tube as vascular scaffold. The challenge of such structure is at the junction where the electrospun fibers have the tendency to cut across the corners. To reduce this effect, Tejeda-Alejandre et al (2017) changes the orientation of the template at an angle during electrospinning and insert an electrode in the tube. A porous template was used to increase the influence of the electrode in the lumen of the tube on the electrospinning jet. With this setup, they were able to show the influence of the orientation of the template and the corresponding strength of the electric field with the help of an additional electrode on the electrospinning jet. By altering the electric field profile and strength, the electrospinning jet is encouraged to deposit as close to the corner on the T-junction as possible.

(a) CAD design of the positioning device; (b) positioning device with compliant links (in blue) holding the mandrel (in red) and slip ring (in black); (c) positioning mechanism inside the electrospinning chamber. [Tejeda-Alejandre et al. Procedia CIRP 2017; 65: 207].

Electrospun fibers on bifurcated tubular scaffold (SEM imaging) [Tejeda-Alejandre et al. Procedia CIRP 2017; 65: 207].

 

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Content [Macrostructure Fabrication Methods]