Biomedical Engineering Reference
In-Depth Information
the.narrowing.of.the.jet.is.caused.by.the.instability.of.the.whipping.process..In.this.case,.
instability. refers. to. the. jet. transforming. from. a. straight. line. into. an. inconsistent. bend..
This.is.attributed.to.the.electrostatic.interactions.between.the.applied.electric.ield.(external).
and.the.surface.charges.on.the.jet..It.is.within.this.instability.zone.that.iber.formation.is.
possible.by.stretching.and.accelerating.the.luid.
14.2.2 Parameters involved in electrospinning
Another.attractive.quality.of.electrospinning.is.the.capability.to.inluence.the.parameters.
involved. in. the. design. of. a. speciic. system.. There. are. several. variables. that. affect.
electrospinning,.which.can.be.broken.down.into.solution.properties,.governing.variables,.
and.ambient.parameters.(Li.and.Xia.2004)..Solution.properties.include.viscosity,.elasticity,.
conductivity,.and.surface.tension.(Son.et.al..2004,.Tan.et.al..2005a)..Governing.variables.
refer. to. hydrostatic. pressure. in. the. capillary. tube,. electric. potential. at. the. tip,. and. the.
distance. between. the. tip. and. the. collector.. Lastly,. ambient. parameters. simply. refer. to.
temperature,. humidity,. and. air. velocity. in. the. electrospinning. area.. By. tuning. these.
properties,.it.is.possible.to.determine.the.optimal.conditions.for.a.laundry.list.of.polymer.
solutions..It.is.critical.because.different.applications.have.different.polymer.speciications..
Other. factors. to. take. into. account. during. fabrication. include. diameter. consistency,.
defects,. and. continuity. of. a. single. nanoiber.. In. terms. of. the. iber. diameter,. the. main.
contributor.is.solution.viscosity,.which.is.directly.proportional.to.iber.diameter.(Huang.
et.al..2003,.Mit-uppatham.et.al..2004,.Gupta.et.al..2005,.Thompson.et.al..2007)..Thus,.the.
higher.the.viscosity.of.the.solution,.the.larger.the.iber.diameter.will.be..Another.factor.
that.inluences.the.diameter.is.the.applied.electrical.voltage..A.higher.applied.potential.
concludes.in.a.larger.iber.diameter.due.to.an.increase.in.the.amount.of.luid.in.the.jet.
(Zhang. et. al.. 2005,. Chang. et. al.. 2008).. In. addition,. the. increase. of. the. applied. potential.
makes.rougher.ibers.(Huang.et.al..2003).
As.with.any.operation,.there.can.be.defects.that.form.while.electrospinning..The.term.
defects. in. electrospinning. usually. refers. to. bead. formation,. as. shown. in. Figure. 14.2..
Typically,. an. increase. in. polymer. concentration. results. in. a. decrease. in. bead. formation.
(Huang.et.al..2003)..There.are.also.theories.involving.charge.density,.surface.tension,.and.
polymer.chain.entanglements.affecting.bead.formation..Beads.are.considered.to.be.a.defect.
because.they.interrupt.the.uniformity.of.the.nanoibers.and.could.be.easily.confused.for.
cells.in.biomedical.applications.
Figure 14.2
SEM.image.of.electrospun.nanoibers.with.bead.formation.
