DESIGNING NANOFIBROUS SCAFFOLDS FOR TISSUE ENGINEERING - Advanced Biomaterials: Fundamentals, Processing, and Applications - page 441

gauge (internal diameter of capillary) on the diameter of nanofi bers
and demonstrated a decrease in the average fi ber diameter with re-
duction in needle diameter [82]. Hence, needle gauge can have a
signifi cant infl uence on the fi ber diameter.
(b) Voltage plays a critical role in determining the fi ber diameter.
Since voltage is responsible for generation of charges on the poly-
meric droplet, an increase in voltage (or electric fi eld strength)
increases the charge density on the polymeric jet and hence repul-
sion. Higher charge repulsion causes an increased drawing effect on
the polymer jet that leads to the formation of fi bers with smaller
diameter [77] .
(c) Electrospinning distance (distance between the tip of the capillary
and the collector) determines the time taken by the jet (path length)
to reach the collector plate. Hence, the electrospinning distance can
indirectly infl uence the length of the ejected jets' trajectory [83,84].
Decreased electrospinning distances prevent complete solvent evap-
oration, thereby leading to agglomeration of the fi bers. It has been
reported by Lee et al. [84] that with the increase in the electrospin-
ning distance, the average fi ber diameter increases, due to reduction
in the effective fi eld strength (per unit distance) and hence reduced
thinning effect. However, in another study by Zhao et al. [85], it
was observed that average fi ber diameter decreased with increas-
ing distance. It was discussed that the increase in the distance pro-
vides greater opportunity for the jet to split and elongate. Although
the aforementioned studies [84,85] report contradictory results, it is
intuitive to believe that an increase in electrospinning distance will
lead to a decrease in nanofi ber diameter. However, increase in elec-
trospinning distance beyond a critical limit does not lead to the col-
lection of fi bers probably due to reduced infl uence of the electric
fi eld [85] .
(3) Ambient parameters
(a) Humidity in the electrospinning environment affects fi ber mor-
phology to a great extent without infl uencing the fi ber diameter. In-
creased humidity levels increase the pores on fi ber surface, which
ultimately coalesce to form non - uniform structures [86] . Humidity
also determines the rate of solvent evaporation from the jet that de-
posits in form of fi bers. High humidity levels interfere with solvent
evaporation, hence fi bers that would have otherwise dried in a con-
trolled humidity environment would not dry completely in a high
humidity environment.
Thus, the fi ber diameter and morphology of the electrospun nanofi bers can
be altered by manipulating the solution, system and ambient parameters.