Biomedical Engineering Reference
In-Depth Information
− Bulk.polymerization
− Emulsion.polymerization
− Suspension.polymerization
. . By. using. these. routes,. polymeric. nanoparticles. carrying. bioactive. or. imaging.
agents.could.be.prepared.
•.
Lipid-basednanoparticles:
Lipid-based.nanoparticles.are.useful.tools.for.drug.
delivery. and. gene. transfer. since. they. protect. their. content. from. being. cleared.
by. the. circulatory. system. while. also. protecting. the. nontarget. tissues. from.
adverse. effects. of. the. bioactive. agent.. More. importantly,. they. can. be. metabo-
lized. and. removed. from. the. body. without. leaving. any. by-products. behind..
Nanoparticles. made. of. phospholipids. can. be. spontaneously. self-assembled. or.
prepared. by. similar. processes.. Depending. on. their. preparation. method,. lipid.
nanoparticles.can.take.different.shapes.and.forms,.such.as.micelles,.bilayers,.and.
hexagonal. vesicles.
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. Lipid-based. nanoparticles. can. have. a. wide. range. of. sizes.
(i.e.,. 20-1000. nm),. because. of. the. different. methods. used. in. their. preparation..
Liposomes. are. a. special. category. of. lipid. nanoparticles,. and. their. ield. of. use.
in.biotechnology.is.determined.by.physicochemical.characteristics.such.as.com-
position,. size,. loading,. and. stability,. in. addition. to. their. interaction. with. cells..
For.drug.delivery.purposes.liposomes.can.be.formulated.in.a.suspension,.as.an.
aerosol,.or.in.a.semisolid.form,.such.as.cream,.gel,.or.dry.powder.
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.In.addition.
to.different.methods.of.lipid-based.nanoparticle.preparation,.there.also.are.large.
numbers. of. methods. for. active. and. passive. loading. of. drugs. in. these. nanopar-
ticles.. For. example,. hydrophilic. drugs. can. be. encapsulated. in. the. aqueous. core.
while.hydrophobic.ones.can.be.embedded.in.the.bilayer.of.the.phospholipids..For.
speciic.purposes,.conventional.liposomes.can.be.modiied;.they.can.be.PEGylated.
(poly(ethylene. glycol). modiied). or. targeted. or. designed. to. be. charged. through.
the.use.of.functional.groups.or.molecules..These.modiications.alter.their.interac-
tions.and.control.their.distribution.in.the.body.
•.
Inorganic nanoparticles:
Inorganic. nanoparticles. are. preferred. in. nanobio-
technology. due. to. their. durability,. magnetic. properties,. luorescence,. and. radio.
opaqueness.
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.Calcium.phosphate,.gold,.carbon.materials,.silicon.oxide,.iron.oxide,.
cadmium. selenide,. and. zinc. selenide. are. some. examples. of. inorganic. nanopar-
ticles..Among.the.metallic.nanoparticles,.gold.nanoparticles.are.very.commonly.
used.for.delivery.purposes.since.they.can.be.shaped.and.brought.to.the.desired.
size,.and.their.surface.can.be.modiied.by.coating.with.a.variety.of.molecules..All.
inorganic.nanoparticles.can.be.surface.modiied.to.be.multifunctional.and.used.
in. targeting. a. tissue. in. drug. delivery,. to. avoid. the. immune. system,. and. also. to.
luoresce.for.imaging.
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11.2.1 Liposomes as Drug Delivery Systems
Liposomes.form.spontaneously.when.phospholipids.are.hydrated..Bangham.et.al..in.1965.
demonstrated. that. phospholipids. form. closed. structures. when. dispersed. in. water,. and.
these.structures.are.relatively.impermeable.to.entrapped.material.
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.After.Bangham.et.al.,.
there.was.a.great.expansion.in.the.use.of.liposomes.as.models.for.biomembranes,.for.gene.
delivery,.and.as.drug.delivery.systems.
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.The.main.constituents.of.liposomes.are.phospho-
lipids,.which.have.an.amphiphilic.structure;.they.have.polar.and.nonpolar.regions..The.
polar.regions.contact.with.the.aqueous.phase.inside.and.outside.the.liposomes,.and.the.
