Biomedical Engineering Reference
In-Depth Information
phase.with.or.without.surfactant/stabilizer,.such.as.PVA,.gelatin,.poloxamer.188,.DPPC,.
TPGS,.etc..The.mixture.is.emulsiied.by.either.high-speed.homogenization.or.high-voltage.
sonicator,.leading.to.the.formation.of.an.oil-in-water.emulsion..After.a.stable.emulsion.is.
formed,.the.organic.solvent.is.evaporated.under.increased.temperature,.reduced.pressure,.
or.continuous.stirring.at.room.temperature..Further.processes,.including.multiple.centrif-
ugation/washing.and.lyophilization,.will.inally.result.in.dried.nanoparticles.
12,13
.Figure.
8.1(A). shows. the. ield. emission. scanning. electron. microscopy. (FESEM). image. of. PLGA.
nanoparticles.prepared.by.solvent.extraction/evaporation.method..The.nanoparticles.are.
in.spherical.shape.and.in.the.nanosized.range..The.pharmaceutical.characteristics.of.the.
nanoparticles. can. be. inluenced. by. many. factors. of. the. fabrication. process,. such. as. the.
polymer.concentration.in.the.solvent,.ratio.of.the.organic.to.the.aqueous.phase,.type.and.
concentration. of. emulsiiers,. drug. loading. ratio,. strength. of. the. mixing. energy. in. emul-
sifying. and. evaporation,. and. post-treatment. of. nanoparticles,. including. centrifugation,.
washing,.lyophilization,.sterilization,.pH.condition,.and.temperature.
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8.2.2.2 Dialysis Method
Dialysis.is.another.self-assembling.method.for.nanoparticle.fabrication,.in.which.nanopar-
ticles.can.be.fabricated.with.or.without.surfactant/additive/stabilizer..The.drug.and.poly-
mer.are.dissolved.in.a.water-miscible.organic.solvent..The.solution.is.then.transferred.into.
a.cellulose.membrane.bag,.which.is.then.immersed.in.a.container.illed.with.water.for.1.or.
2.days..The.water.is.exchanged.at.a.certain.interval.to.maintain.the.osmotic.pressure,.which.
removes.the.solvent.and.unloaded.drug.from.the.membrane.bag..The.nanoparticle.disper-
sion.is.then.centrifuged.to.further.eliminate.the.unloaded.drug..In.dialysis,.the.molecular.
weight. cutoff. (MWCO). of. the. membrane. is. one. of. the. additional. controlling. factors. that.
may.inluence.the.suitability.of.dialysis.for.some.polymers.
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.In.addition,.the.porosity.of.the.
membrane.controls.the.rate.at.which.the.organic.phase.is.dialyzed,.thus.affecting.the.size.
of.nanoparticles..The.main.limitations.of.the.dialysis.method.are.that.it.is.time-consuming.
and.a.large-volume.tank.is.required..Therefore,.large-scale.operation.may.not.be.feasible.
8.2.2.3 Nanoprecipitation Method
Nanoprecipitation. is. a. nanoparticle. synthesis. process. involving. solvent. displacement.
followed.by.interfacial.deposition.of.preformed.polymer..This.technique.was.developed.
by.Fessi.et.al.
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.The.oily.phase.commonly.used.is.water-soluble.organic.solvents.such.as.
acetone,.acetonitrile,.and.dimethylformamide..The.polymer.and.drug.are.dissolved.in.the.
organic.phase..When.the.organic.phase.is.mixed.dropwise.with.the.aqueous.phase.under.
gentle.magnetic.stirring,.an.emulsiication.is.formed.spontaneously..The.solvent.is.evapo-
rated. overnight. with. gently. stirring.. The. particles. are. collected. by. iltration. to. remove.
the.aggregation..The.iltrate.is.then.centrifuged.and.lyophilized..Figure.8.1(B).shows.the.
FESEM.image.of.PLGA.nanoparticles.prepared.by.the.nanoprecipitiation.method,.which.
are.more.uniform.in.size.than.those.shown.in.Figure.8.1(A).
8.2.3 Nanoparticles for Targeted Drug Delivery
Nanoparticle-based. drug. delivery. systems. have. considerable. potential
.
for. treatment. of.
various.diseases,.and.are.especially.attractive.for.dificult-to-treat.diseases.like.cancer.
Targeted.therapy.is.deined.as.a.type.of.treatment.that.uses.drugs.or.other.substances.to.
identify.and.attack.speciic.target.cells,.e.g.,.cancer.cells.(http://www.cancer.gov)..Targeted.
therapy.may.be.more.effective.and.have.fewer.side.effects.than.general.treatments.without.
