Biomedical Engineering Reference
In-Depth Information
morphology.and.release.characteristics..They.found.that.increasing.heparin.concentration.
caused.the.iber.diameter.to.decrease..Normally,.the.proliferation.of.VSMC.cells.is.higher.
in.the.irst.week.after.injury.and.can.continue.for.14-28.days,.depending.on.the.severity.
of.injury..Thus,.the.sustained.release.of.heparin.from.these.iber.mats.over.at.least.14.days.
was.suitable.for.vascular.repair..Moreover,.these.iber.mats.did.not.induce.an.inlamma-
tory.response.in.macrophage.cells.in.vitro,.and.the.release.of.heparin.was.effective.in.pre-
venting.the.proliferation.of.VSMC.cells. 68 .In.2007,.Kim.et.al. 69 .developed.a.blend.mixture.
of.poly(ethylene.oxide).(PEO).and.poly(L-lactic.acid).(PLLA),.poly(ε-caprolactone).(PCL),.or.
poly(D,L-lactic-co-glycolic.acid).(PLGA).at.a.ratio.of.7/3.wt%.and.loaded.it.with.lysozyme.in.
order.to.prepare.lysozyme-loaded.iber.mats..PEO.was.used.to.improve.compatibility.with.
the.encapsulated.lysozyme.because.it.is.a.hydrophilic.and.biocompatible.polymer..Among.
the.three.blend.ibers,.the.PEO/PCL.iber.mat.showed.the.lowest.amount.of.burst.release,.
with.a.more.sustained.release.proile.during.a.1-week.period,.while.the.PEO/PLLA.and.
PEO/PLGA.iber.mats.showed.a.higher.amount.of.burst.release.with.less.sustained.release.
proiles..Additionally,.the.PEO/PLGA.iber.mat.exhibited.a.very.large.dimensional.change.
in.aqueous.medium,.whereas.the.PEO/PCL.iber.mat.maintained.its.original.dimension..
Hence,.the.PEO/PCL.iber.mat.was.used.for.further.investigations..The.PEO/PCL.blends.
with.various.ratios.(i.e.,.9/1,.7/3,.and.5/5).were.further.prepared,.and.the.release.behaviors.
of. lysozyme. were. investigated. from. these. blends.. Kim. et. al.. found. that. the. amount. of.
lysozyme.release.was.higher.with.an.increased.amount.of.PEO.in.blends..Moreover,.the.
amount.of.initial.burst.release.was.higher.when.the.blended.iber.mats.contained.a.higher.
amount.of.PEO..This.implied.that.the.lysozyme.release.rate.was.controlled.by.the.dissolu-
tion.rate.of.PEO.domains.that.were.separated.in.the.iber.phase. 69
However,. the. major. disadvantage. of. conventional. electrospinning. shows. the. initial.
burst.release,.which.leads.to.reducing.the.effectiveness.of.the.formulation. 70 .In.addition,.
the.loss.of.bioactivity.during.the.preparation.of.the.spinning.solution.and.electrospinning.
process.due.to.the.long.time.exposure.of.biological.agents.to.harsh.organic.solvents.may.
be.a.concern..To.overcome.these.problems,.coaxial.electrospinning.is.employed.to.encap-
sulate. drug. into. polymeric. materials.. This. technique. provides. some. advantages,. such.
as. easily. incorporating. the. drug. into. the. polymeric. matrix. with. high. loaded. eficiency.
and. capacity,. mild. preparation. conditions,. and. relatively. steady. release. characteristics..
Jiang. et. al. 71 . fabricated. an. electrospun. poly(ε-caprolactone). (PCL). core-shell. structure.
and.incorporated.bovine.serum.albumin.(BSA).and.lysozyme.containing.poly(ethylene.
glycol).(PEG).into.a.core.part.by.using.the.coaxial.electrospinning.technique..The.thick-
ness. of. the. core. and. the. shell. could. be. controlled. by. varying. the. feed. rate. of. the. inner.
dope..The.obtained.diameters.of.both.the.shell.and.core.were.increased.as.the.feed.rate.
increased..The.release.behaviors.of.protein.from.the.iber.mats.were.carried.out.in.0.05.
M.phosphate.buffer.solution.(pH.7.4).at.37°C..A.slight.burst.release.was.observed.on.the.
irst.day,.followed.by.a.relatively.steady.release..The.result.showed.an.increase.in.protein.
release.when.the.feed.rate.increased..This.implies.that.the.release.rate.can.be.controlled.
by.varying.the.feed.rate.of.the.PEG/protein.solution..In.2009,.Yan.et.al. 72 .also.investigated.
core-shell.structure.iber.mats.prepared.by.coaxial.electrospinning.from.PLLACL.solu-
tion.for.the.shell.and.phosphate.buffered.saline.(pH.7.4).solution.containing.BSA.or.nerve.
growth.factor.(NGF).for.the.core.for.use.in.the.nerve.tissue.engineering.application..They.
compared. the. release. characteristic. of. BSA. from. the. mix. PLLACL. iber. mats. with. that.
from.the.coaxial.PLLACL.iber.mats..The.results.showed.that.the.release.characteristics.
of.BSA.from.the.mix.PLLACL.iber.mats.exhibited.two.stages:.an.initial.fast.release.fol-
lowed.by.a.constant.release..On.the.other.hand,.the.release.characteristics.of.BSA.from.the.
coaxial.PLLACL.iber.mats.showed.a.relatively.stable.release..However,.there.was.some.
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