Biomedical Engineering Reference
In-Depth Information
create.the.cationic.silica.signiicantly.reduced.the.contamination.from.phosphoproteins,.
which.preferentially.bind.to.metal.ions.
15.3.2.2 Nanostructured Materials for Bioseparations
The. most. commonly. used. nanostructured. materials. for. bioseparations. are. nanoporous.
membranes.. Nanoscale. membranes. employed. for. separating. biomacromolecules. or.
nanoparticles.can.be.fabricated.from.nanoporous.anodic.alumina.membranes.(AAM),.car-
bon.nanotube.membranes,.nanoporous.silicon.membranes,.or.one-dimensional.nanorod.
and. nanotube. membranes. (El-Safty. 2011).. Membrane. separations. can. be. based. on. size,.
charge,.afinity.separation,.or.some.combination.thereof..The.driving.force.can.be.either.
pressure.or.electrophoretic/electro-osmotic.
Size-based.separations.are.the.most.obvious.application.of.membranes,.and.membranes.
with.micrometer-.and.nanometer-size.pores.have.been.extensively.used.for.separation.of.
cells,. virus,. and. proteins,. typically. under. pressure-driven. low.. In. general,. these. mem-
branes.have.been.polymeric.(nitrocellulose,.nylon,.polysulfone,.etc.).with.fairly.broad.pore.
distributions,. leading. to. partial. retention. of. many. compounds.. In. addition,. these. mem-
branes. are. often. subject. to. clogging. and. the. rates. of. iltration. are. frequently. limited. by.
the. formation. of. a. gel. layer. that. resists. luid. low.. The. development. of. anodic. alumina.
membranes.(AAM,.discussed.in.Section.15.2.1.3).with.their.fairly.uniform.pore.size.and.
pore. distribution. has. created. new. opportunities. for. size-based. bioseparations.. El-Safty.
and.coworkers.synthesized.3D.mesocage.silica.NTs.perpendicular.to.the.longitudinal.axis.
of.the.nanochannels.in.AAM.and.then.used.this.nanoilter.to.ilter.solutions.containing.
myoglobin,.lysozyme,.β-lactoglobulin.or.hemoglobin..With.the.exception.of.hemoglobin.
(MW.68,000.Da),.all.the.proteins.showed.greater.than.90%.recovery.in.the.retentate.
Of.greater.challenge.than.size-based.separation.is.the.separation.of.molecules.by.charge,.
particularly.if.they.are.similarly.sized..Cheow.et.al..(2008).developed.a.platinum-coated.
alumina.membrane.and.demonstrated.selective.transport.of.bovine.serum.albumin.(BSA),.
lysozyme.(Lys),.and.myoglobin.(Mb),.using.an.applied.electric.ield.across.the.membrane..
The. platinum. was. sputter. coated. on. both. sides. of. the. membrane. with. pore. sizes. rang-
ing.from.∼90.nm.after.5.min.of.sputtering.to.∼20.nm.after.20.min.of.sputtering..However,.
the.20.nm.pores.were.impervious.to.water..A.compromise.of.60.nm.pores.obtained.from.
10.min. of. sputtering. was. selected. for. further. study.. By. varying. the. potential. across.
the. membrane,. they. were. able. to. alter. the. lux. of. the. different. species. and. change. the.
distribution. of. the. permeate. relative. to. the. rententate.. In. a. slightly. different. approach,.
Osmanbeyoglu.et.al..(2009).fabricated.thin.(0.7-1.μm).anodic.alumina.membranes.directly.
on. silicon. wafers,. providing. a. narrow. pore. distribution. (20-30.nm). and. pores. that. tra-
versed. the. entire. length. of. the. alumina. layer.. They. then. applied. a. solution. of. BSA. and.
bovine.hemoglobin.to.the.membrane.at.pH.4.7.and.observed.that.the.neutrally.charged.
BSA.had.approximate.40×.the.lux.through.the.membrane.as.the.positively.charged.hemo-
globin. due. to. the. repulsive. forces. of. the. net. positive. charge. on. the. alumina. membrane.
at. pH. 4.7.. They. also. noted. that. the. throughput. obtained. in. their. work. was. more. than.
three.orders.of.magnitude.greater.than.those.of.polymeric.membranes,.e.g.,.5.×.10
−8
.versus.
1.×.10
−11
.M. cm
−2
. s
−1
.. They. ascribed. this. dramatic. enhancement. of. throughput. to. the. very.
different.pore.density.(200.versus.6.μm
−2
).and.membrane.thickness.(∼0.6.versus.6.μm).
Other. studies. that. exploit. both. charge-. and. size-based. separations. have. employed.
carbon.nanotube.membranes.(Sun.et.al..2011).and.ultrathin.silicon.membranes.(Striemer.
et.al..2007)..Sun.and.coworkers.prepared.CNT.membranes.by.embedding.MWCNTs.in.an.