Biomedical Engineering Reference
In-Depth Information
Silicon. and. silica. have. many. unique. properties. that. allow. these. materials. to. be. so.
versatile..In.the.case.of.porous.silicon,.pore.sizes.can.be.varied.with.ease.and.precision..
These.pores.also.allow.for.high.surface.area.and.therefore.high.loading.capabilities.(Low.
et.al..2006)..Porous.silicon.is.also.biodegradable.in.aqueous.solutions,.breaking.down.to.
silicic.acid.(Canham.1995)..Since.porous.silicon.has.these.properties,.it.is.an.ideal.material.
for. cell. culture. and. for. size-. and. charge-based. biomolecule. separations.. The. surface. of.
porous.silicon.has.been.modiied.with.different.chemistries.and.characterized.to.observe.
how. cells. attach. (Low. et. al.. 2006).. Three. different. chemistries. were. used. to. modify.
the. silicon. surface:. ozone. oxidation,. silanization,. or. coating. with. serum. or. collagen..
The. surfaces. with. collagen. and. the. surfaces. that. were. amino-silanized. promoted. cell.
attachment,. while. those. that. were. ozone. oxidized. or. silanized. with. PEG. did. not. result.
in.much.cell.attachment..Another.study.explored.porous.nanocrystalline.silicon.(pnc-Si).
membranes.as.a.cell-culture.substrate.(Agrawal.et.al..2010)..Immortalized.ibroblasts.and.
primary.vascular.endothelial.cells.were.cultured.on.thin.pnc-Si.membranes.and.placed.in.
their.appropriate.media..The.membranes.degraded.after.a.couple.of.days.in.media,.which.
was.accelerated.by.the.addition.of.cells..This.dissolution.had.no.cytotoxic.effects.on.the.
cells,.illustrating.the.material's.biocompatibility..In.order.to.expand.cell-culture.longevity.
on.the.pnc-Si.membranes,.the.density.of.the.supericial.oxide.was.increased.by.applying.
heat.. By. increasing. the. density. of. the. supericial. oxide. on. this. membrane,. the. stability.
was. increased,. thereby. reducing. the. degradation. rate. of. the. membranes. in. cell. media..
Although.there.were.not.large.differences.in.cell.growth.and.adhesion.between.the.pnc-Si.
and.the.controls.(glass,.tissue.culture.polystyrene),.they.determined.that.pnc-Si.could.still.
be.useful.as.a.cell-culture.substrate.
Silica.is.also.highly.biocompatible.since.it.is.produced.naturally.in.many.plant.species.
(Neethirajan.et.al..2009)..Silica.is.also.found.naturally.in.diatoms,.which.are.unicellular,.
eukaryotic.photosynthetic.algae.composed.of.amorphous.clear.silica.glass..Diatom's.silica.
shells.are.used.for.many.nanotechnology.applications..These.applications.include.drug/
gene.delivery,.biophotonics,.and.microluidics.(Gordon.et.al..2009),.molecular.separations,.
and.biosensing.(Dolatabadi.and.de.la.Guardia.2011)..The.formation.of.nanoparticles.with.
silica.has.been.used.to.immobilize.enzymes.on.their.surface.(Liu.et.al..2009)..Porous.silica.
glass. has. been. used. to. encapsulate. and. protect. proteins,. which. also. prevented. protein.
aggregation.and.improved.overall.protein.stability.when.compared.with.proteins.in.free.
solution.(Domach.and.Walker.2010)..Studies.have.also.shown.that.enzymes.encapsulated.
in. silica. matrices. can. be. used. for. biosensing. applications. (Ramanathan. et. al.. 2009).. To.
better.understand.protein.adsorption.(bovine.serum.albumin.and.lysozymes).on.silica,.a.
study.was.conducted.using.ordered.mesoporous.silica.substrates.(SBA-15).and.evaluated.
using.low.microcalorimetry.(Katiyar.et.al..2010)..This.study.revealed.that.when.protein-
surface.interactions.were.attractive,.exothermic.events.were.observed..They.also.discov-
ered. that. enthalpies. of. protein. adsorption. on. SBA-15. decreased. as. the. surface. coverage.
increased.for.primary.protein-surface.interactions..They.believe.this.illustrates.an.increas-
ing.trend.in.repulsion.between.the.protein.molecules..Overall,.this.study.concluded.that.
protein.structure.and.solution.conditions.have.a.large.effect.on.how.proteins.conform.to.
the.silica.surface.
15.2.1.3  Metal Oxides
Metal. oxides. are. compounds. formed. between. metals. and. oxygen,. typically. an. oxygen.
anion. and. metal. cation.. Depending. on. the. metal. associated. with. the. oxide,. the. physi-
cal. and. chemical. properties. of. that. material. can. be. different.. Metallic. oxides. are. large.
