Melt over the outcome of the structures. By

electrospinning is a recent approach which has been developed to combat the
problems associated with traditional solvent electrospinning. Research on melt
electrospinning is most certainly still in its infancy which is mainly due to
the fact that building a melt electrospinning device is considerably more
complex than building a device for solution electrospinning. The melt
electrospinning process is similar to that of solution electrospinning in that
a polymer is pushed through a small spinneret while a high voltage is applied
to the droplet to charge and accelerate the jet towards the grounded collector.
The main difference between the two processes is the fact that, as its name
suggests, the melt electrospinning process melts the polymer before it leaves
the syringe. This results in the polymer melt cooling down and solidifying as
it moves towards the collector, as opposed to evaporating as it does in
solution electrospinning 46. This results in significantly less deviation of the polymer jet due
to lack of electrical instabilities which eliminates the ‘whipping’ (unstable
region) present in solution electrospinning, enabling a stable continuous jet
which allows greater control over the produced structures. This is illustrated
in Figure 2.5 below where the stable jet produced by melt electrospinning is
compared to the unstable jet produced by electrospinning.


2.5: Traditional electrospinning (left) and melt electrospinning writing
(right). The use of a polymer melt instead of a polymer solution results in a
stabilized jet and greater control over the deposition of the fibres 47.

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Control over the
structures can be improved further by using melt electrospinning writing in a
direct writing mode. This process, dubbed melt electrospinning writing (MEW),
involves moving the grounded collector at speeds faster than the speed of the
electrostatically charged jet to produce fibres with a defined microscopic and
macroscopic architecture. Additionally, the use of a high viscosity and low
conductivity polymer melt results in a straight melt flow with a more
predictable path over much greater distances 48. This
is illustrated in Figure 2.5 above. The movement and design of the collector
are important in the MEW process, with movement in the x-y direction and the
use of a rotating collector proving to have profound effect over the outcome of
the structures. By collecting the MEW fibres onto a rotating collector, a 3-dimensional
tubular structure can be produced. The specific architecture of this tubular
structure can then be controlled by altering the rotation and translation
speeds of the collector to produce both straight and coiled tubular structures.
An example of these tubular structures which can be produced is illustrated in
Figure 2.6 below.

2.6: Tubular structure created by Jungst et al by MEW onto a 2mm diameter
rotating collector where (A) is an overview of the image, (B) is a magnification
of the central part of the tube and (C) is a magnification of the edge of the
tube 9.

The tubular
scaffold in Figure 2.6 above was fabricated by MEW onto a 2mm diameter rotating
collector with a rotational speed of 8 rpm and a translational speed of 598

This illustrates the precise level of control which the MEW approach can have
over the fabrication of tubular scaffolds and the unique architecture produced
is of research interest for various areas of tissue engineering including
vascular tissue engineering. In light of this, the purpose of this project is
to investigate whether the layers of native vessels can be reproduced via MEW
onto a small diameter rotating collector. A custom-made MEW device is used,
which has been designed previously, in addition to a designed apparatus which
facilitates the collection of these 3-dimensional tubular structures. The
design of this apparatus and the approach to fabricating these scaffolds is
discussed in the sections below. 


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