Biomedical Engineering Reference
In-Depth Information
sufficiently high molecular weight polyester. Few of the studies associated with aliphatic polyester
conducted the molecular weight studies.
3.2.4
Electrospinning
An alternate technique to fabricate polymer/CNT composite fibers is electrospinning. This tech-
nique allows the alignment of the CNTs along the fiber axis. The diameter of electrospun polymeric
fibers ranges from tens of nanometers to several microns. Many biologically functional molecules
and cells often interact at the nanoscale level making these electrospun matrix attractive for tissue
engineering. A number of CNT/polymer composites (mostly consisting of MWNT) have been
successfully electrospun making it a versatile fiber processing technique. The alignment of the
CNT in the polymer enhances the aspect ratio for reinforcing and increases the area for interfacial
bonding
[88]
.
The elements of a basic electrospinning unit include an electrode connected to a high voltage
power supply that is inserted into a syringe-like container containing the polymeric solution.
Connected to the syringe is a capillary. The syringe
capillary setup can be mounted vertically
[89]
, horizontally
[90]
, or tilted at a defined angle
[91]
. A grounded collector plate, which is
connected to the other end of the electrode, is placed at a distance of 10
30 cm from the tip of the
capillary (
Figure 3.1
).
The polymer solution at the end of the capillary upon the application of high voltage becomes
charged. As the voltage is increased, a charge is induced on the surface of the liquid. Mutual charge
repulsion leads to the development of force directly opposite to the surface tension. A jet is ejected
Taylor cone
Whipping
instability
Syringe pump
High-voltage
DC supply
HVDC
Rotating and translating
grounded collector
FIGURE 3.1
Schematic of a typical electrospinning system. If the electrostatic charge is able to overcome the surface
tension, the Taylor cone is formed and the solution is ejected from the apex of the needle. Whipping instability
depicted here further thins the fiber. It is collected on the drum which can be rotated to further align the fiber.
From Ref.
[92]
.
