Biomedical Engineering Reference
In-Depth Information
hydrogel.showed.a.new.opportunity.for.cell.manipulation.and.immobilization.
64
.Though.
DEP. is. effective. to. separate. cells. with. different. sizes. in. luids,. biological. damages. due.
to.high.electric.ield.and.the.additional.process.for.electrode.formation.restrict.its.wide-
spread.application.in.microluidic.systems.
Mechanical. manipulation. of. cells. is. typically. applied. to. cell. sorting. by. implementing.
mechanical.constriction.structures.inside.microluidic.systems.to.separate.cells.of.interest.
based.on.their.mechanical.properties,.such.as.size..Contrary.to.other.methods,.this.approach.
uses.passive.structures.inside.microluidic.systems,.leading.to.numerous.advantages,.such.
as.simple.cell.manipulation.fabrication,.easy.procedures,.and.high.throughput..The.modi-
ied.application.of.mechanical.manipulation.is.cell.trapping.and.docking.inside.microwell.
arrays.to.investigate.cell-soluble.factors'.interaction.with.different.conditions.or.cell.types..
C-shaped. microwell. arrays. showed. successful. cell. docking. with. a. uniform. number. of.
cells.
65
.Double.grooves.underneath.microluidic.channels.also.can.effectively.capture.cells.
by.microcirculation.of.luids.
66
12.4.2 Microfluidic Systems for Gradient Generation of Soluble Factors
Generation.of.gradient.is.essential.in.cell-related.studies.implemented.for.investigation.of.
cellular.responses.according.to.different.combinations.and.concentrations.of.soluble.fac-
tors..Microluidic.systems.make.it.possible.to.generate.different.types.of.static.or.dynamic.
gradients.on.chips.
The.simplest.way.to.create.gradients.in.microluidic.channels.is.by.combining.two.or.more.
input.channels.into.one.gradient.channel.to.generate.combinatorial.gradients.of.different.bio-
logical.solutions.
67
.This.method.is.reproducible.and.quantitative,.but.consumes.a.consider-
able.amount.of.expensive.reagents,.and.the.cells.inside.channels.inevitably.experience.shear.
stress.caused.by.the.low..Complex.shapes.of.gradients.can.be.obtained.by.using.branched.
structures. that. control. diffusive. mixing. of. liquids,. depending. on. branch. conigurations.
68
.
This. technique. provides. lexible. and. fast. generation. of. gradients,. but. drawbacks. include.
large.dead.volumes,.single.axis.gradient,.and.rapid.clearance.of.cell-secreted.factors.before.
gradient.stabilization..The.parallel.low.gradient.generator,.having.physical.walls.between.
adjacent.streams,.uses.orthogonal.diffusion.at.disconnected.points.of.the.walls.in.order.to.
generate. various. types. of. stream. proiles. (Figure 12.6).
69
. Like. the. branch-structured. gen-
erator,.this.technique.may.consume.a.large.volume.of.reagents.that.are.possibly.expensive..
Recently,.gradient.range.and.linearity.in.a.passive.diffusive.gradient.were.improved.by.the.
addition.of.backward.low.inside.a.microluidic.channel,
70,71
.which.is.a.simple.and.effective.
approach.to.obtain.a.long-range.gradient.up.to.a.few.centimeters.inside.a.single.channel.
The. stabilization. of. generated. gradients. is. also. important. to. analyze. cell-soluble. fac-
tor.interactions.inside.a.localized.and.stabilized.microenvironment..Many.of.the.papers.
about.gradient.generation.mention.that.cells.may.be.able.to.interact.with.soluble.factors.
inside.microluidic.channels.where.chemical.or.biological.gradients.are.dynamically.gen-
erated.. Kim. et. al.. showed. that. microluidic. devices. can. produce. a. logarithmic. scale. of.
low.rates.and.a.logarithmatic.concentration.of.gradients.
72
.Based.on.these.gradients,.it.has.
been.shown.that.the.morphology.and.proliferation.of.ESCs.varies.
72
.These.approaches.are.
easy.and.convenient.for.testing.cellular.response,.but.a.number.of.drawbacks.exist,.such.
as.large.consumption.of.soluble.factors,.exposure.of.cells.to.shear.stress,.leading.to.false.
response,. and. cross-contamination. between. combinatorial. conditions.. One. solution. for.
this.purpose.is.to.implement.different.microluidic.pathways.for.cell.loading.and.media.
perfusion.
73
.Individual.addressability.to.chambers.by.bridge.and.underpass.architecture.
has.made.this.possible..Upadhyaya.and.Selvaganapathy.utilized.a.nanoporous.membrane.
