Table 1.

Electrospinning parameters and their effects.

Process Parameters	Increase	Decrease
Voltage [4,8,10,11]	-Smaller Taylor cone, thinner fibres, smaller pores. -Very high voltage causes multiple jets and may result in the formation of beads.	-Larger Taylor cone, thicker fibres, larger pores. -Voltage below spinning threshold stops jet formation.
Flow rate [4,8,10,12]	-Thicker fibres, larger pores. -Excessive flow rate causes a bloated Taylor cone and wet fibres.	-Thinner fibres, smaller pores -Too little causes the Taylor cone to retreat into the nozzle.
Tip-to-collector distance (TCD) [4,10,13]	-Causes an effective decrease in electrical density, resulting in thicker fibres. -A large TCD may not be suitable for solvents with fast evaporation.	-Decrease in TCD causes an effective increase in electrical density. -A minimum distance is required for the formation of fibres.
Solution Parameters	Increase	Decrease
Polymer concentration [4,10,14]	-Thicker fibres, larger pores. -Very high concentration stops electrospinning. -A medium concentration gives a combination of beads and fibres.	-Thinner fibres, smaller pores. -Very low concentration results in the formation of beads. -If the polymer is sufficiently conductive, electrospraying is possible at fairly low concentrations.
Conductivity [4,10,15]	-Thinner fibres, smaller pores. -Solutions with extremely high conductivities may be unstable during electrospinning and are likely to produce multiple jets.	-Thicker fibres, larger pores produced. -A minimum conductivity is required for electrospinning.
Viscosity [4,14,16]	-Thicker fibres, larger pores -Extremely viscous solutions cannot be electrospun.	-Thinner fibres, smaller pores -Very low viscosity causes the formation of beads.
Surface tension [4,14,17,18]	-Makes it harder to electrospin and results in instability of jets. -Solutions with very high surface tension cannot be electrospun.	-Very low surface tension increases the tendency of jet breakage and results in drops.
Molecular weight [4,11,15]	-Beads reduced if any, thicker fibres produced.	-Fibre thickness decreases. -Very low molecular weight forms beads.
Ambient Parameters	Increase	Decrease
Temperature [4,10,19]	-Fibre diameter decreases.	-Fibre diameter increases.
Humidity [4,10,19,20,21,22]	-Higher humidity causes thinner fibres due to slower solvent evaporation. -Increases the incidence and size of circular pores on fibres. -No useable fibres produced over a critical limit	-Lower humidity allows for better and faster solvent evaporation, resulting in thicker fibres.
Other Parameters	Effect
Total spinning time	-Longer spinning times result in the accumulation of ions in the vicinity of the jet, resulting in instabilities in the process.
Scaffold thickness	-Very thick scaffolds can induce impedance, causing fibres to be deflected off the target. -Extremely thin samples can be easily electrospun, but it may not be feasible to remove these samples properly from the collector or process them for further testing.
Solvent vapour partial pressure [10,23]	-Solvents with high vapour partial pressure evaporate faster and tend to produce thinner fibres.
Polymer relaxation time [24]	-Polymer relaxation time needs to be above a particular threshold for the polymer to be spinnable. -If the polymer relaxation time is sufficiently large, electrospinnability may be improved even with dilute polymer solutions.
Relative collector velocity [25,26]	-Increase in this velocity results in a lower fibre diameter and degree of orientation distribution up to a critical velocity.
Spinning orientation	-Effects discussed in this paper.