Biomedical Engineering Reference
In-Depth Information
22.5.1 Factors That Influence Protein Structure at Surfaces
22.5.1.1 Boundaries Shaping the Interface
The.nano-bio.interface.is.comprised.of.three.dynamic.interaction.components:
.
1.. Nanoparticle. surface:. Characteristics. are. determined. by. its. physicochemical.
composition.
.
2.. Solid-liquid/solid-gas. interface:. Changes. occur. when. the. particle. interacts. with.
components.in.the.surrounding.medium.
.
3.. Solid-liquid/gas.interface:.Contact.zone.with.biological.substrates.
In.a.given.medium,.the.most.important.nanoparticle.characteristics.that.determine.sur-
face. properties. are. the. material's. chemical. composition,. surface. ictionalization,. shape,.
angle.of.curvature,.porosity,.and.surface.crystallinity..Other.quantiiable.properties,.such.
as. effective. surface. charge. (zeta. potential),. particle. aggregation,. state. of. dispersion,. sta-
bility/biodegradability,. dissolution. characteristics,. hydration,. and. valence. of. the. surface.
layer,. inluence. its. interaction. with. biological. components.. Conversely,. protein. proper-
ties.that.inluence.interactions.include.hydrophobicity/hydrophilicity,.nonspeciic.attrac-
tive.forces.(electrostatics,.Van.der.Waals.(VDW)),.speciic.binding.(covalent),.protein.size,.
hydration,. side. group. charges,. protein. crystallization,. and. intraprotein. forces.. Many. of.
these.properties.can.be.inluenced.by.the.solution.environment,.such.as.pH,.ionic.strength,.
temperature,.and.the.presence.of.large.organic.molecules.like.detergents.(Table 22.2).
22.5.2 Forces at the Nano-Bio Interface
At.irst.glance,.interactions.between.nanoparticles.and.cells.seem.to.embody.some.of.the.
same.principles.as.those.between.colloidal.particles..VDW,.electrostatic,.solvation,.solvo-
phobic,.and.depletion.forces.still.apply,.but.they.require.special.consideration.for.events.
occurring. at. the. nanoscale.. For. example,. because. nanoparticles. contain. relatively. few.
atoms,.their.VDW.forces.are.dependent.on.the.positioning.of.their.surface.atoms.and.their.
standard.bulk.permittivity.functions.
Typical.interactions.between.SiO
2
.particles.in.water.involve.VDW,.electrostatic,.and.sol-
vation.forces..VDW.forces.result.from.the.quantum.mechanical.lux.of.the.electrons;.at.any.
moment,.their.luctuations.produce.a.small.but.important.dipole.in.the.particle,.thereby.
inducing.a.dipole.moment.in.the.atoms.of.the.adjacent.SiO
2
.particle.and.causing.an.attrac-
tive.force..The.electrostatic.force.in.the.system.results.from.surface.charges.that.inevita-
bly.arise.on.the.SiO
2
.particles..In.contact.with.water,.silanol.(Si-OH).groups.dissociate.to.
yield.negative.surface.charges,.which.will.generate,.at.least.transiently,.repulsive.electro-
static.forces.between.particles;.under.constant.surface.potential.conditions,.such.repulsion.
might.be.mitigated.by.surface.regulation..For.SiO
2
.particles,.the.sum.of.the.attractive.VDW.
and. repulsive. electrostatic. forces. yields. the. well-established. Derjaguin-Landau-Verwey-
Overbeek.(DLVO).theory.of.colloid.science
44,45.
(Figure 22.6).
22.5.2.1 Ionic Strengths
In. an. I
3
-
. electrolyte. solution,. the. ionic. strength. is. quite. high. relative. to. biological. envi-
ronments,. meaning. that. the. electrostatic. forces. are. most. likely. to. be. screened. within. a.
few.nanometers.of.the.surface..The.high.ionic.strength.also.obscures.the.zero-frequency.
