Biomedical Engineering Reference
In-Depth Information
O
CH
3
O
CH
2
C
O
CH
C
O
x
y
GA
LA
FIGURE 11.2
Molecular.structure.of.poly(lactic.acid-co-glycolic.acid).block.copolymer..x.and.y.can.be.in.the.range.of.several.
thousands,.and.the.x:y.ratio.could.vary.between.100:0.and.0:100.
properties..These.polymers.and.their.degradation.products.have.been.shown.to.be.nontoxic.
and. biocompatible,. and. products. made. using. these. polyesters. have. been. awarded. FDA.
approval.
For.more.than.three.decades,.linear.polymers.of.lactide.and.glycolide.have.been.used.in.
various.medical.applications..Use.of.these.polymers.as.carriers.for.controlled.delivery.of.a.
wide.range.of.bioactive.agents.for.human.and.animal.use.has.been.an.attractive.research.
area.
75
. The. properties. of. these. linear. polyesters. have. been. modiied. by. making. copoly-
mers. and. by. varying. the. ratios. of. the. monomers. in. the. copolymer. with. respect. to. each.
other..Therefore,.copolymers.such.as.poly(lactide-co-glycolide).(PLGA).(Figure 11.2).have.
been. extensively. investigated. for. various. medical. applications,. including. drug. delivery.
devices,.scaffolds.for.tissue.engineering,.surgical.sutures,.bone.pins,.and.stents.
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.PLGA.
was.shown.to.be.biocompatible.in.many.applications.and.degrades.into.the.nontoxic.and.
natural.products.lactic.acid.and.glycolic.acid,.which.can.be.eliminated.from.the.body.as.
they.are.or.after.conversion.into.CO
2
.and.H
2
O.
77
PHAs.(Figure 11.3),.on.the.other.hand.are.the.most.commonly.used.natural.biotechno-
logical.polymers,.because.they.are.made.by.bacteria.as.well.as.by.other.organisms,.some.of.
which.are.transgenic.
78
.They.are.rapidly.hydrolyzed.in.the.environment,.but.more.slowly.
in.the.human.body,.and.this.rate.could.be.regulated.by.varying.the.composition,.form,.and.
size.of.the.biomedical.device.
The. best. known. polymer. of. the. PHA. family. is. poly(β-hydroxybutyrate). (P3HB).. The.
mechanical.properties,.crystallinity,.and.solubility.of.the.polyesters.can.also.be.controlled.
by. their. composition,. molecular. weight,. and. heterogeneity. index. (the. molecular. weight.
distribution.in.a.given.batch).
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11.2.2.2 Nanoparticles
Nanoparticles.have.a.diameter.in.the.range.of.5-1000.nm..They.can.be.irregular.in.shape.
or.spherical..Spherical.nanoparticles.can.be.full.in.the.interior.with.the.matrix.material.or.
empty..Nanospheres.are.nanoparticles.that.are.spherical.and.full,.and.hollow.spherical.sys-
tems.are.called.nanocapsules,.where.a.core.is.surrounded.by.a.membrane.(Figure 11.5).
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R
O
CH
(CH
2
)
m
C
O
n
FIGURE 11.3
Molecular.structure.of.poly(hydroxyalkanoates)..When.m.=.1.and.R.=.CH
3
,.the.product.is.poly(3-hydroxybu-
tyrate).(P3HB).
