Biomedical Engineering Reference
In-Depth Information
stamp.and.the.substrate..As.a.result,.the.ink.is.transferred.to.the.surface.of.the.substrate.
only.from.the.protruding.areas.of.the.stamp,.producing.the.same.two-dimensional.(2D).
pattern.as.the.relief.features.of.the.stamp..Three.interactions.are.critical.to.μCP,.including.
the. ink-stamp. interaction,. the. cohesive. force. among. the. ink. ingredients,. and. the. ink-
substrate.interaction..While.the.irst.two.are.responsible.for.inking.the.stamp,.one.of.them.
must.be.surpassed.by.the.third.in.order.for.the.ink.to.be.transferred.from.the.stamp.to.
the.substrate..Various.types.of.interactions.ranging.from.nonspeciic.van.der.Waals.force,.
electrostatic.interaction,.and.hydrophobic.interaction.to.highly.speciic.antigen-antibody.
binding.and.base.pairing.between.complementary.DNA.have.been.utilized.in.μCP.
It.is.important.to.note.that.Figure.11.1.does.not.represent.all.versions.of.μCP..Regarding.
the.stamp,.it.can.not.only.be.a.monolithic.piece.of.slab.bearing.relief.features.but.also.have.
a. layered. structure. (Schmid. and. Michel. 2000). and. lat. surface,. respectively. (Coyer. et. al..
2007;.Geissler.et.al..2000;.Rozkiewicz.et.al..2007a)..The.way.of.inking.the.stamp.also.varies.
signiicantly.among.different.μCP.methods,.producing.not.only.a.continuous.ink.layer.but.
also.isolated.structures.on.the.stamp.(Wang.et.al..2001)..Moreover,.the.ink.can.be.loaded.
into. the. recessed. regions. of. a. stamp. (Kraus. et. al.. 2007). or. even. loaded. inside. a. stamp.
(Balmer.et.al..2005;.Xu.et.al..2009).
11.3 Key Elements of μCP
Stamp,.ink,.and.substrate.are.the.key.elements.of.μCP..In.principle,.any.solid.material.that.
allows.carrying.a.substance.and.releasing.it.by.contact.can.be.used.to.prepare.the.stamp..
Various.materials.have.already.been.used.for.this.purpose,.among.which.poly(dimethyl.
siloxane). (PDMS). is. the. irst. (Kumar. and. Whitesides. 1993). and. remains. the. dominant.
one.. The. following. section. introduces. the. properties. of. PDMS,. the. common. process. of.
preparing.the.PDMS.stamps,.surface.modiications.of.the.PDMS.stamps,.and.alternative.
stamp. materials.. Selection. of. an. ink. and. a. substrate. in. a. μCP. process. is. typically.
determined.by.its.target.application..While.an.extremely.wide.range.of.ink.materials.have.
been.printed,.much.fewer.substrates.have.been.used..However,.ink.and.substrate.materials.
are.frequently.tailored.for.each.other.in.a.speciic.μCP.process..They.are.thus.introduced.
together. in. the. latter. section,. which. is. divided. into. subsections. based. on. the. different.
types.of.the.ink.materials.
11.3.1 Stamps
11.3.1.1 Properties of PDMS
PDMS. possesses. a. number. of. properties. that. make. it. suitable. for. μCP.. First,. it. is.
commercially.available.and.affordable.by.regular.labs..The.most.commonly.used.PDMS.
for. μCP. is. Sylgard. 184. manufactured. by. Dow. Corning. Corporation.. Second,. PDMS. is.
elastomeric. with. Young's. modulus. of. PDMS. around. ∼1.5.MPa. (Kaufmann. and. Ravoo.
2010)..It.is.thus.soft.enough.to.allow.conformal.contact.between.a.stamp.surface.and.even.
a.relatively.rough.substrate,.but.still.stiff.enough.to.reproduce.the.patterns.of.the.stamp.
features. in. the. submicron. range.. Third,. PDMS. is. chemically. inert. and. thermally. stable.
(Camino. et. al.. 2001),. which. renders. it. compatible. with. various. ink. materials,. solvents,.
and.printing.processes..Fourth,.PDMS.is.hydrophobic.with.a.surface.energy.∼20.erg/cm
2
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