Biomedical Engineering Reference
In-Depth Information
(A)
(B)
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Figure 8.3
Nanofiber and nanoparticle fabrication using (A) electrospinning, and (B) electrospraying.
Most electrospinning processes are carried out using a solution of polymer. Melt electro-
spinning is a modified version of the normal electrospinning process, where an electrical
heater maintains the temperature of the reservoir containing the molten polymer, which is
further pumped to the tip [32]. The parameters affecting the spinnability and physical prop-
erties of nanofibers are classified into polymer solution, processing, and ambient parame-
ters. Polymer solution parameters include the molecular weight of the polymer, viscosity
and conductivity of the solution, surface tension and dielectric constant of the solvent,
while the processing conditions include the applied voltage, feed rate, temperature, collector
geometry, and spinning distance. Ambient parameters such as humidity and pressure of the
electrospinning environment are also considered crucial for electrospinning [9]. Along with
the advantage of producing highly porous nanofiber meshes with a high surface area, elec-
trospinning is a relatively robust, simple, cost-effective technique to produce nanofibers
from a wide variety of natural and synthetic polymers, that makes it a very versatile method
[19]. Furthermore, this technique also offers the opportunity for controlling and improving
the physical, biological, and mechanical features of nanofibrous scaffolds. Thus electrospin-
ning remains the most widely used technique for production of nanofibers when compared
to other nanofiber formation techniques.
Indeed, electrospinning has originated from electrospraying [19]. Although the principles
of charged droplets are essentially the same for electrospinning and electrospraying, during
the electrospraying process (Figure 8.3B) the droplets undergo break-up into smaller drop-
lets at the micro- to nanoscales [33]. The most important variable distinguishing the electro-
spinning and electrospraying techniques is the chain entanglement density of the polymer
solution. Chain entanglement density mainly depends on the polymer solution concentration.
The critical chain overlap concentration, depending on the type of polymer solution, dic-
tates the behavior of electrospraying or electrospinning [33, 34].
Electrospinning and electrospraying are two major electrohydrodynamic techniques used for
the fabrication of fibers and particles, respectively with controllable dimensions through proper
selection of the polymer solution and processing parameters, especially in the field of biomed-
ical and tissue regeneration. Moreover, knowledge of the effects of chemical, physical, and
mechanical properties of particles and/or fibrous structures on the behavior of stem cells can
help researchers select appropriate material to cause a suitable stem-cell differentiation effect.
Table 8.1 summarizes the application of electrospun nanofibrous scaffolds for TE using
stem cells [35-64].
