BLOOD VESSEL REGENERATION - 3D Bioprinting and Nanotechnology in Tissue Engineering and Regenerative Medicine - page 150

and the systems used to generate these scaffolds have been well characterized ( Shapira et al., 2014 ;
Hashi et al., 2010 ; Wu et al., 2010 ; Rayatpisheh et al., 2014 ; Hadjizadeh et al., 2013 ; Fu et al., 2014 ;
Han et al., 2013 ; Lai et al., 2014 ). However, this system is not compatible with live cells due to the
solvents typically used.
Typically, an electrospinning setup is comprised of a few main components: (1) a syringe filled with
the desired polymer, (2) a syringe pump, (3) a high voltage power supply, and (4) a grounded collection
plate/collector ( Figure 7.2 ). The syringe pump allows for the control of the flow rate, and can therefore
impact the size of the electrospun fibers. The syringe itself can have different types/gauges of needles
to modulate the stream of the polymer being ejected from the syringe. Also, the voltage applied can
be modulated to control the fiber diameter and provides the driving force due to electrostatic repulsion
to encourage the polymer solution to flow toward the collection plate. There are additional external
variables to consider, such as the temperature and humidity in the electrospinning chamber.
By modifying the applied voltage, the rotation velocity, and the solvent/polymer mixture, properties
of the graft such as orientation and fiber diameter (hundreds of nanometers to micrometers) and density
can be controlled. This allows for the control of properties such as porosity, mechanical strength, fiber
alignment, and surface area ( Fridrikh et al., 2003; Deitzel et al., 2001 ).
In the case of polycaprolactone (PCL), groups have shown that using either a high- rotation (2000
RPM) or low-rotation (20 RPM) speed resulted in either aligned fibers or randomly deposited nano-
fibers, respectively. Furthermore, to better mimic the native vasculature and to recapitulate the layer
variation as a function of radial distance, groups have shown that by simultaneously controlling the
applied voltage and rotation speed, they are able to generate vascular graft material that is comprised
of distinct layers with varying fiber orientation and alignment ( Wu et al., 2010 ). This sort of elec-
trospun tissue- engineered blood vessel has the potential of impacting future designs of electrospun
grafts for vascular applications because each layer's orientation can be controlled. Thus, this allows
the graft to physically mimic the orientation of the tunica intima and the tunica media, which in turn
can modulate the response of endothelial and vascular smooth muscle cells. By mimicking the mor-
phology of the native tissue, these scaffolds show great promise for impacting vascular regeneration in
FIGURE 7.2 Electrospinning.
A typical electrospinning apparatus has four main components: (1) A high voltage power supply provides the
potential difference required for the electrospinning process. The applied voltage can be modulated to vary
the physical dimensions of the resulting fibers during the deposition process. (2) A syringe filled with the polymer
solution. (3) A syringe pump provides the materials for the electrospinning process and controls the stream produced
via the flow rate and the needle gauge/type. (4) A collection plate or cylinder is where the deposited nanofiber mesh
is deposited. By depositing directly onto a cylinder, the implants' size can be directly controlled and potentially used
directly for blood vessel regeneration. If a flat collection plate is used, then the resulting electrospun fiber can be
rolled into a cylinder of appropriate dimensions for use in the desired application.