Biomedical Engineering Reference
In-Depth Information
phenomenon is known as electrospinning. However, when charge is provided to
low molecular weight polymeric solution, it results in the formation of nano-
particles by the phenomenon of electrospraying [79].
Electrospinning is infl uenced by solution parameters namely viscosity, con-
ductivity, and surface tension [80,81]; system parameters namely capillary diam-
eter, electric potential at the tip, and the distance between the tip and the collection
plate [77,82-85]; and ambient parameters like temperature and humidity in the
electrospinning chamber [86].
(1) Solution parameters
(a) Solution viscosity plays a key role in affecting fi ber diameter and
morphology. Low solution viscosities can lead to the formation of
particles/beads whereas, higher solution viscosity, above a thresh-
old yields fi bers without beads [80]. Further, an increase in the solu-
tion viscosity results in an increase in the fi ber diameter. However,
beyond an upper limit of viscosity, the solution dries at the nozzle,
thereby preventing fi ber formation.
(b) Conductivity is another solution parameter that infl uences elec-
trospinning by generation of repulsive forces on the polymeric jet.
In general, a more conductive solution is easily drawn to form a
jet during electrospinning. Conductivity on the polymeric droplet
is governed by the type of polymer used and the solvent used to
dissolve it.
In a recent study, Choi et al. studied the infl uence of salts on nano-
fi brous structure [87]. Their study indicates that increased charges
on a polymer solution poly(3 - hydroxybutyrate - co - 3 - hydroxyvalerate
(PHBV) by addition of a salt benzyl trialkyl ammonium chloride led
to increased elongation forces caused by self repulsion of similar
charges that resulted in reduced fi ber diameter. Therefore, increase
in charges on a polymer solution can cause a signifi cant reduction in
fi ber diameter.
(c) Surface tension (closely linked to solution viscosity) plays an impor-
tant role from the point of initiation of the process where it holds the
hemispherical meniscus at the tip of the capillary. Surface tension is
directed opposite to the electrostatic charges thereby determining
the voltage threshold value responsible for jet formation. Excess sur-
face tension encourages the formation of beads. Choice of solvent
and polymer concentration can help alter surface tension and hence
the formation of nanofi bers/nanoparticles.
(2) System parameters
(a) The internal diameter of the needle closely refl ects the diameter of
the base of the Taylor cone and hence the diameter of the jet issuing
out of that Taylor cone. Katti et al. studied the infl uence of needle
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