Biomedical Engineering Reference
In-Depth Information
(a)
Enter
Exit
(b)
(c)
(d)
Figure 4.3
Physical.guidance.of.microtubules.using.low.geometries..(a).Strategies.that.couple.ixed.kinesin.tail.domains.to.
tracks.contained.within.physical.structures.are.used.to.optimize.microtubule.directional.guidance..(b).Maze.con-
igurations.act.as.complex.tests.of.physical.guidance.in.terms.of.number.of.microtubules.entering.versus.exiting.and.
analysis.of.most.successfully.negotiated.versus.problematic.geometries..(c).In.this,.circular.concentrator.microtu-
bules.are.directed.toward.the.center,.limiting.exit..(d).An.“arrowhead”.design.used.as.a.direction-correcting.physical.
feature..A.microtubule.that.veers.in.the.wrong.direction.will.be.redirected.into.the.path.of.low.preventing.any.loss.
of.product..(c.and.d:.Adapted.from.Nitta,.T..et.al.,.
Lab Chip
.6.(7),.881,.2006.)
4.4.4 Directional guidance
Directional. guidance. of. microtubule. shuttles. has. utilized. physical,. chemical,. electric,.
magnetic,. and. low. ields.. One. means. of. physical. guidance. is. to. pattern. a. surface. with.
channels.to.create.microscale.walls.to.redirect.the.leading.end.of.colliding.ilaments.back.
along.the.channel.(Figure.4.3)..Channel.patterning.has.also.been.used.to.implement.unidi-
rectional.low.through.the.use.of.“arrowheads”.(Hiratsuka.et.al.,.2001;.Nitta.et.al.,.2006)..In.
this.method,.the.arrowhead.point.is.toward.the.desired.direction.of.travel..A.microtubule.
that.begins.to.travel.in.the.wrong.direction.will.run.into.the.backside.of.the.“arrowhead”.
and.be.redirected..Chemical.methods.to.pattern.a.surface.take.into.account.the.nature.of.
charged.proteins.to.interact.more.strongly.with.hydrophilic.versus.hydrophobic.surfaces..
When.used.in.conjunction.with.physical.patterning,.motors.and.microtubule.motility.can.
be.further.guided..Without.some.selectivity.of.where.motors.adhere,.it.is.possible.for.lex-
ible. microtubules. to. move. up. and. out. of. a. channel. instead. of. being. directed. along. its.
length..Modern.lithographic.processes.that.are.common.in.integrated.circuit.fabrication,.
including.E-beam.lithography.that.can.provide.nanometer.scale.resolution,.can.be.applied.
to.create.smaller.scaled.detailed.features.(Liddle.and.Gallatin,.2011)..An.important.advan-
tage.to.this.approach.is.the.ability.to.apply.smaller.microtubule.lengths.and.prevent.travel.
in.an.improper.direction.due.to.closer.coninement.to.the.proper.orientation.
