Biomedical Engineering Reference
In-Depth Information
CH 3
CH 3
O
O
CH 2
CH 2
CH
C
O
C
O
CH
CH 2
3-HB
x
3-HV
y
FIGURE 11.4
Molecular.structure.of.PHBV..x.and.y.can.be.in.the.range.of.several.thousands.
In.the.current.research.activities.in.many.biomaterials.laboratories,.both.types.of.these.
important.biomedical.polyesters.are.used.to.construct.carriers.for.various.bioactive.agents..
The.followings.are.results.from.studies.carried.out.in.our.laboratories.
11.2.2.2.1 Preparation and Characterization of Nano-Microspheres
Designed for Controlled Release Purposes
11.2.2.2.1.1 Preparation PHBV. and. PLGA. nano-microspheres. were. prepared. by. an. oil-
in-water. (o/w). emulsion. technique.. These. polymers. are. dissolved. in. an. organic. solvent.
such.as.dichloromethane,.which.is.immiscible.with.water..Bioactive.agents.are.dissolved.
in.the.organic.solvent,.and.this.organic.solution.is.added.to.an.aqueous.solution.to.form.an.
o/w.emulsion,.and.thus.the.droplets..The.aqueous.phase.generally.contains.an.emulsiier.
such.as.poly(vinylalcohol).(PVA),.Tween,.or.Span.to.provide.stabilization.of.the.droplets..
Emulsiication.is.achieved.by.sonication,.and.continuous.mixing.prevents.cluster.formation.
before.the.solvent.evaporates.at.room.temperature..Ultracentrifugation.is.generally.used.to.
collect.the.nano-microspheres..Excess.aqueous.and.organic.solvents.are.removed.by.wash-
ing.the.nano-microparticles,.and.they.are.dried.in.a.vacuum.oven.or.by.lyophilization.
11.2.2.2.1.2 Characterization of PLGA and PHBV Nano-Microspheres The. various. nano-
microspheres. of. PHBV. and. PLGA. were. characterized. for. their. size,. size. distribution,.
and.surface.topography.using.various.methods.such.as.a.particle.size.analyzer,.scanning.
electron.microscopy.(SEM),.and.an.image.analysis.program.(e.g.,.Scion.Image.of.National.
Institutes. of. Health. (NIH)),. and. luorescence. microscopy. for. luorescent. agent-loaded.
nano-microspheres.
In.FigureĀ 11.6,.the.inluence.of.the.drying.method.on.the.quality.of.recovery.of.PLGA.
(50:50).nano-microspheres.is.presented..It.can.be.seen.that.even.a.simple.stage.of.the.pro-
cess.has.a.signiicant.inluence.on.the.nano-microspheres.obtained.
Nanocapsule
Nanosphere
FIGURE 11.5
Schematic.representation.of.nanospheres.and.nanocapsules.carrying.drugs.in.their.structure.
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