Nanotoxicity - The Nanobiotechnology - page 608

residue.numbers.and.binding.surface.areas.exhibited.the.same.order:.BFg.>.γ-Ig.>.Tf.>.BSA,.
in.agreement.with.the.experimental.indings..Further.analysis.showed.that.the.π-π.stacking.
interactions.between.SWCNTs.and.aromatic.residues.(Trp,.Phe,.Tyr).play.a.critical.role.in.
their.binding.capabilities..These.different.protein-coated.SWCNTs.will.then.have.different.
cytotoxic.affects.by.inluencing.the.subsequent.cellular.responses.(Ge.et.al..2011a).
Human.skin.is.the.largest.organ.of.the.body.and.functions.as.a.strict.barrier.with.respect.
to. the. external. environment.. The. skin. is. constructed. of. three. layers:. the. epidermis,. the.
dermis,.and.the.subcutaneous.layers..It.does.not.appear.to.be.easy.for.nanoparticle.exposure.
to.result.in.penetration.of.intact.skin..Sporadically,.penetration.into.the.dermis.is.reported.
for. QD. nanoparticles. (Ryman-Rasmussen. et. al.. 2006,. Zhang. and. Monteiro-Riviere. 2008,.
Jeong.et.al..2010,.Li.and.Chen.2011)..Especially.in.damaged.skins,.the.interactions.between.
nanoparticles. with. epidermal. and. dermal. cells. may. cause. cytotoxicity. and. undesired.
immune. responses,. which. will. further. promote. the. entering. of. nanoparticles. to. deeper.
sites.or.even.lymphatic.or.blood.circulation.(Romoser.et.al..2011,.Unnithan.et.al..2011).
The.gastrointestinal.and.respiratory.tracts.are.the.most.important.portals.of.entry.for.
exogenetic.toxicants..Nanomaterials.are.now.widely.produced.and.used.in.various.com-
modities,. industrial. products,. agricultural. products,. and. biomedical. applications,. etc..
They. will. enter. the. human. body. by. intended. use. or. by. unintended. exposure.. There. is.
much.evidence.to.conirm.that.nanoparticles.could.be.taken.up.via.these.tracts.and.enter.
both.lymphatic.and.blood.circulation.systems..After.entering.the.circulation.systems,.the.
nanoparticles.can.reach.and.cause.effects.on.different.organs.in.vivo.
27.4 Target Organs and Toxicological Effects of Nanoparticles
The.special.physicochemical.characteristics.of.nanoparticles.present.the.possibilities.of.
cellular.uptake.as.well.as.the.blood.and.lymph.circulation,.reaching.organs.and.physi-
ological.structures.such.as.the.lungs,.liver,.spleen,.heart,.bone.marrow,.and.even.brain..
This.may.cause.negative.effects.such.as.undesired.accumulation.and.toxicity.in.various.
body.tissues.
27.4.1 respiratory System
The. respiratory. system. is. a. principal. interface. between. the. organism. and. outer.
environment..As. a. dominant. part. of. the. respiratory. system,. the. lungs. have. the. largest.
epithelial. surface. area. of. the. human. body. in. direct. contact. with. outside. atmosphere..
The. lungs. contain. two. different. parts:. airways. and. alveolar. structure.. The. alveolar.
surface.area.is.connected.in.parallel,.where.the.structural.barrier.between.air.and.blood.
is.reduced.to.about.a.1.or.2.μm.thin.layer..Although.this.structure.is.required.for.eficient.
gas. exchange,. it. also. makes. alveoli. less. well. protected. against. possible. environmental.
damage..The.effect.of.nanoparticles.on.the.respiratory.system.has.been.mainly.studied.
in.view.of.the.health.risks.posed.by.ambient.airborne.particulate.material.(PM;.Li.et.al..
2007)..The.particle.size.can.be.deined.as.aerodynamic.diameter,.which.is.the.diameter.of.a.
spherical.particle.with.a.density.of.1.g/cm 3 .with.the.same.settling.velocity.as.the.particle..
PM.with.an.aerodynamic.diameter.of.<10.μm.(PM 10 ).is.categorized.into.coarse,.ine,.and.
ultraine.particles.with.aerodynamic.diameters.between.2.5.and.10.μm,.<2.5.μm.(PM 2.5 ),.
and.<0.1.μm.(PM 0.1 ),.respectively.(Hinds.1999)..With.respect.to.the.size,.the.smaller.the.