SYNTHETIC ENROUTES TO ENGINEER ELECTROSPUN SCAFFOLDS FOR STEM CELLS AND TISSUE REGENERATION - Micro and Nanotechnologies in Engineering Stem Cells and Tissues - page 121

most cases, they cannot be applied for tissue engineering. Cross-linking is carried out
by many researchers to maintain the structural integrity of the construct.
To improve the stability of the natural protein 3-24 or carbohydrate-based scaffolds
and to reduce the biodegradation rate of the scaffolds, cross-linking becomes
inevitable. The details of electrospun cross-linked polymeric scaffolds used for
tissue regeneration are also provided in this chapter.

5.1.1 Electrospun Nanofibrous Scaffolds for Tissue Engineering

Electrospinning has been recognized as an efficient and well-established technique
capable of producing nanofibers by electrically charging a suspended droplet of
polymer melt or solution. 25-32 Various polymers, including synthetic ones such as
poly(

-caprolactone) (PCL), poly(lactic acid) (PLA), poly(glycolic acid) (PGA),
poly(lactic-co-glycolic acid) (PLGA), polystyrene, polyurethane (PU), polyethylene
terephthalate (PET), and poly( L -lactic acid)-co-poly(

e

-caprolactone) (PLACL), and
biological materials, such as collagen, gelatin, and chitosan, have been successfully
electrospun to obtain fibers with diameters ranging from 3 nm to 5

e

m. Different
parameters control the electrospinning process, including the solution properties,
applied voltage, solution flow rate, humidity, and temperature. Using a simple and
inexpensive setup, this technique not only provides an opportunity for control over
the thickness and composition of nanofibers but also controls fiber diameter and
porosity of the electrospun nanofiber meshes. Typically, nanofibers are collected as
random, and aligned nanofibers with improved mechanical stability and degradation
properties are also produced for specific applications. Whereas deposition of nano-
fibers on a static plate produces randomly oriented nanofibrous (100-650 nm)
scaffolds, aligned nanofiber (250-650 nm) mats are fabricated using a rotating
cylinder or disk collector with a sharp edge as shown in Fig. 5.2a and b. Coaxial
electrospinning is a modification or extension of the traditional electrospinning
technique with a major difference being a compound spinneret used. Using the
spinneret, two components are fed through different coaxial capillary channels and
are integrated into core-shell structured composite fibers to fulfill different applica-
tion purposes. For example, bioactive composite scaffolds are fabricated using
collagen (imparting bioactivity) as the shell and PCL (synthetic polymer) as the
core (Fig. 5.2c).
Core-shell structured nanofibers (360-400 nm) prepared by coaxial electrospin-
ning, have the advantages of being able to control the shell thickness and manipulate
overall mechanical strength and degradation properties of the resulting composite
nanofibers without changing their biocompatibility. Alternatively, core-shell struc-
tured composite nanofibers are functionalized for potential use in drug or growth
factor encapsulation and release and development of highly sensitive sensors and
tissue engineering applications. Tissue engineering is the application of knowledge
and expertise from a multidisciplinary field to develop and manufacture therapeutic
products that use the combination of matrix scaffolds with viable human cell systems
or cell-responsive biomolecules derived from such cells for the repair, restoration, or
regeneration of cells or tissue damaged by injury, disease, or congenital defects.

m