Chemistry Reference
In-Depth Information
6.4 CHAINS BONDED TO OR EMBEDDED IN SURFACES
6.4.1 Tethering
Tethered chains can be placed at the surface of another polymer to change
its surface characteristics. The placement can be through covalent bond-
ing or by a physical process such as adsorption or embedding. It is also
possible to tether quaternary ammonium salts to PDMS to enhance anti-
fouling and antimicrobial characteristics.
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The embedding approach is
likely to be more robust.
One example is the silanization of the PDMS surface in the channels of
a microfluidic devices such as biosensors.
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The goal was to make the sur-
face less hydrophobic and therefore less likely to absorb proteins. An or-
ganosilane was used to attach thiol groups on the surface, which were
then reacted with modified DNA chains to give surface-immobilized
chains of DNA oligomers. Oligomer reactions with target DNAs and an
alkaline phosphatase conjugated with streptavidin then provides a plat-
form for assaying some biologically important substances. DNA has also
been bonded to maleimide-activated PDMS surfaces.
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PDMS coatings in the channels of microfluidic devices have also been
modified with a perfluorinated alkoxysilane for selectivity toward fluorine-
tagged peptides.
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A more general approach employs a vinyl-terminated
initiator with some H atoms on a dimethyl-methylhydrogen polysiloxane
copolymer.
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The polysiloxane surface activates to the extent that hydro-
philic chains can be bonded onto it. Another biologically interesting mate-
rial, heparin, has similarly been bonded to PDMS surfaces through a
heterobifunctional poly(ethylene glycol) spacer to suppress the adsorption
of molecules such as fibrinogen.70
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In related work, acrylamide was grafted onto a PDMS surface using
plasma polymerization. After this treatment, cell attachment to the
PDMS surface became negligible.
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6.4.2 Grafting
One grafting approach involved peroxide-containing PDMS, using
radical catalyzed thiol-ene chemistry to produce cross linkable poly-
mers.
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Another study focused on functionalization of surface-grafted
poly(methylhydrosiloxane) thin films with alkyl side chains.
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In some
cases, the alkyl chains were long enough to undergo crystallization.
Crystallization was also involved in the study of polypropylene-graft-
polydiphenylsiloxane copolymers.
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