Biomedical Engineering Reference
In-Depth Information
fabricated.stamps.using.a.thermoplastic.polymer.by.hot.embossing.and.printed.polar.inks.
including.proteins..Lee.et.al..(2006).prepared.stamps.using.a.mixture.of.poly(ethylene.glycol).
diacrylate.and.a.commercial.photocurable.adhesive..The.adhesive.allowed.tuning.of.the.
mechanical.properties.of.the.stamps.and.poly(ethylene.glycol).provided.a.polar.polymer.
network.that.rendered.the.stamp.hydrophilic..The.stamp.was.used.to.print.bovine.serum.
albumin. on. glass.. Stamps. have. also. been. prepared. using. hydrogel,. which. is. a. class. of.
materials.characterized.by.high.water.content..The.hydrogel.stamps.not.only.provide.ideal.
wettability.for.polar.inks,.but.also.offer.a.benign.environment.for.biological.macromolecules.
and. even. live. cells.. Martin. et. al.. (2000). used. a. copolymer. hydrogel. of. 6-acryloyl-β-O-
methylgalactopyranoside.and.ethylene.glycol.dimethacrylate.to.prepare.stamps..Similarly,.
Coq. et. al.. (2007). produced. hydrogel. stamps. by. cross-linking. 2-hydroxyethyl. acrylate.
and.poly(ethylene.glycol).diacrylate..Moreover,.agarose.gel.stamps.were.utilized.to.print.
bacteria.on.agar.plates.by.Weibel.et.al..(2005).and.human.osteoblast.cells.on.porous.tissue-
engineering.substrates.by.Stevens.et.al..(2005).
11.3.2 inks and Substrates
11.3.2.1 Self-Assembled Monolayers
Alkanethiols. are. the. irst. ink. materials. used. in. μCP. due. to. their. ability. to. form. SAMs.
on. metals. such. as. Au,. Ag,. Cu,. and. Pd. (Geissler. et. al.. 2003).. In. the. process. of. printing.
thiol.SAMs,.the.thiol.molecules.self-assemble.into.an.ordered.monolayer.on.the.substrate.
within.milliseconds.of.the.contact.between.the.stamp.and.substrate.(Helmuth.et.al..2006;.
Larsen. et. al.. 1997).. The. order. and. quality. of. the. SAMs. are. signiicantly. affected. by. the.
concentration.of.the.ink.solution..The.thiol.molecules.can.spread.laterally.from.the.contact.
areas.to.the.noncontact.areas.by.diffusion,.usually.resulting.in.blurred.patterns.(Sharpe.
et.al..2004)..However,.the.diffusion.can.be.utilized.to.generate.features.at.the.100.nm.scale.
(Xia. and. Whitesides. 1997).. In. addition. to. thiols,. silane. SAMs. were. printed. on. SiO
2
/Si.
substrates.(Jeon.et.al..1997;.Xia.et.al..1995),.docosyltrichlorosilane.(DTS).SAMs.on.indium.
tin.oxide.(ITO).(Koide.et.al..2003),.and.hexadecanephosphonic.acid.SAMs.on.Al.(Geissler.
et.al..2003).
11.3.2.2 Oligonucleotides
Considerable. efforts. have. been. devoted. to. the. use. of. μCP. to. produce. oligonucleotide.
microarrays.. Since. oligonucleotides. are. highly. negatively. charged. at. neutral. pH,. Lange.
et. al.. (2004). coated. PDMS. stamp. and. substrate. with. positively. charged. amino-silane.
to. enhance. adhesion. between. the. oligonucleotides. and. the. stamp. and. substrate.. Also.
using. a. positively. charged. stamp,. acetylene-modiied. oligonucleotides. were. printed. on.
an. azide-terminated. glass. slide. (Rozkiewicz. et. al.. 2007b).. Xu. et. al.. (2003). conjugated. a.
hydrocarbon.chain.to.an.oligonucleotide.to.form.a.surfactant.molecule..The.hydrocarbon.
chain. enabled. hydrophobic. interaction. between. the. ink. and. a. hydrophobic. substrate,.
and.the.interaction.was.strong.enough.for.DNA.hybridization..Thibault.et.al..(2005).later.
found.that.unmodiied.oligonucleotides.can.be.printed.using.an.unmodiied.PDMS.stamp.
with.submicron.resolution..The.hydrophobic.interaction.was.probably.responsible.for.the.
binding.of.the.oligonucleotides.to.the.stamp.surface..Different.from.the.methods.mentioned.
earlier,.a.stamp.was.grafted.with.single-stranded.oligonucleotides.with.known.sequences.
for. capturing. complementary. oligonucleotides. from. a. mixture. of. oligonucleotides. by.
hybridization.(Lin.et.al..2006;.Tan.et.al..2007;.Yu.et.al..2005)..The.ink.oligonucleotides.could.
be. dehybridized. and. printed. to. a. substrate. with. the. same. spatial. pattern. as. that. of. the.
