Biomedical Engineering Reference
In-Depth Information
Van der Waals
Solvation
solvophobic
Electrosteric
Electrostatic
Osmotic
depletion
Biomolecules
FIGURE 22.11
Interactions.between.nanoparticles..Traditional.forces.for.colloidal.fabrication.(for.example,.electrostatic,.VDW,.
covalent).and.other.important.interactions.(for.example,.solvation,.solvophobic,.biomolecular,.depletion).that.
occur.when.particles.are.suspended.in.biological.media.and.come.into.contact.with.proteins.
contribution.of.the.VDW.forces,.(Figure.22.11),.whereas.higher-frequency.dispersion.inter-
actions.remain.operative..Moreover,.solvation.is.another.phenomenon.that.is.important.for.
inorganic.and.other.hydrophilic.nanoparticles..The.water.molecules.adhere.to.the.particles.
with.suficient.energy.to.form.steric.bumper.layers.on.their.surfaces,.making.it.dificult.
for.pairs.of.particles.to.touch.or.adhere..Thus,.solvation.forces.increase.particle.stability.
through.hydration.pressure.or.hydrophilic.repulsion..Alternatively,.rapid.dehydration.and.
aggregation. will. occur. if. the. relative. afinity. of. two. interacting. surfaces. for. water. mol-
ecules.is.much.lower.than.that.between.the.water.molecules.themselves—a.hydrophobic.
attraction. or. hydrophobic. effect.. All. of. these. forces,. which. change. little. or. slowly. over.
time,.can.be.predicted.or.estimated.using.known.theories.
46
.These.experimental.measure-
ments.also.tend.to.be.fairly.consistent.
22.5.2.2 Particle Dissolution
So.far.it.has.been.assumed.that.proteins.are.the.only.component.that.would.be.affected.in.
such.a.bioinorganic.interface..However,.it.has.been.demonstrated.that.proteins.and.organic.
substances.increase.the.dissolution.rates.of.particles.of.ZnO,.CdSe,.iron.oxides,.aluminum.
oxides,.and.oxyhydroxides..The.negative.effects.of.this.dissolution.on.BSSC.eficacy.can.be.
inferred;.increased.dissolution.of.the.nanoscale.metal.oxide.structures.will.eventually.lead.to.
an.Ostwald.ripening.process.resulting.in.a.loss.of.surface.area..Furthermore,.such.a.dynami-
cally.changing.landscape.has.signiicant.effects.on.the.sensitizer.adsorption.kinetics.
This. bioenhanced. dissolution. has. been. shown. to. occur. through. at. least. two. mecha-
nisms:.aqueous.complexation.(that.is,.aqueous.species.complexing.free.ions.released.from.
the.material's.surface).and.ligand-enhanced.dissolution.(adsorbed.natural.organic.mate-
rial.and.organic.acids.extracting.surface.metal.atoms.from.nanoparticle.surfaces)..The.lat-
ter.mechanism.has.been.demonstrated.for.iron.and.aluminum.oxides.and.oxyhydroxides,.
and.is.also.likely.to.occur.for.ZnO.
