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Preventing Depletion of a Catalyst within a Microfluidic Network

IP.com Disclosure Number: IPCOM000015228D
Original Publication Date: 2002-Jan-13
Included in the Prior Art Database: 2003-Jun-20
Document File: 5 page(s) / 46K

Publishing Venue

IBM

Abstract

Microfluidic networks (µFN) made from poly(dimethylsiloxane) (PDMS) are useful to perform reactions in confined volumes with consumption of only tiny amounts of reactants. This is especially important for the patterning of expensive materials like biochemicals or specialty polymers. Many chemical or biochemical reactions make use of some kind of catalyst (e.g. enzyme) or initiator (e.g. polymerization initiator) which is only present as a fraction of the amount of the other reactants. Any compound that is necessary in catalytic amounts for a reaction in µFNs may be subject to depletion during filling of the network, even if it only has little affinity towards the µFN material [1]. The desired reaction may then only take place in a very constricted volume at the entrance of the channels (Fig. 1). Figure 1: Depletion of a catalyst in a µFN. Only in the filling pad and at the entrance of the channel the reactant solution contains the catalyst. After depletion of the catalyst the solution is not reactive anymore. Microfluidic networks can be filled with a polymerizable liquid which is then cured into a polymer by UV light, heat or some other means. This polymer then is structured according to the pattern given by the microfluidic network. If the PDMS-µFN is removed from the substrate the structured polymer may stay within the network or it may be left on the surface of the substrate. The later method called MIMIC (Micromolding in Capillaries) is known [2] . By releasing the polymer in the second step from the underlying substrate even freestanding polymeric microstructures can be made. The MIMIC technique can be applied for the fabrication of patterned color filters and color converter materials for the fabrication of displays.

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Page 1 of 5

Preventing Depletion of a Catalyst within a Microfluidic Network

    Microfluidic networks (µFN) made from poly(dimethylsiloxane)
(PDMS) are useful to perform reactions in confined volumes with
consumption of only tiny amounts of reactants. This is especially
important for the patterning of expensive materials like
biochemicals or specialty polymers. Many chemical or biochemical
reactions make use of some kind of catalyst (e.g. enzyme) or
initiator (e.g. polymerization initiator) which is only present
as a fraction of the amount of the other reactants. Any compound
that is necessary in catalytic amounts for a reaction in µFNs may
be subject to depletion during filling of the network, even if it
only has little affinity towards the µFN material [1]. The
desired reaction may then only take place in a very constricted
volume at the entrance of the channels (Fig. 1).

Figure 1: Depletion of a catalyst in a µFN. Only in the filling
pad and at the entrance of the channel the reactant solution
contains the catalyst. After depletion of the catalyst the
solution is not reactive anymore.

Microfluidic networks can be filled with a polymerizable liquid
which is then cured into a polymer by UV light, heat or some
other means. This polymer then is structured according to the
pattern given by the microfluidic network. If the PDMS-µFN is
removed from the substrate the structured polymer may stay within
the network or it may be left on the surface of the substrate.
The later method called MIMIC (Micromolding in Capillaries) is
known [2] . By releasing the polymer in the second step from the
underlying substrate even freestanding polymeric microstructures
can be made.

The MIMIC technique can be applied for the fabrication of
patterned color filters and color converter materials for the
fabrication of displays.

1

[This page contains 2 pictures or other non-text objects]

Page 2 of 5

In another example it is desirable to have a hydrophilic polymer
fixed in the channels when the network is peeled off the
substrate. After such an operation the µFN represents a flat but
chemically patterned stamp having areas with different
wettability. In order to prepare such systems the µFN is placed
on a glass support and filled with a solution containing the
monomer(s) or macromonomer(s) and a photoinitiator. Some
combinations of monomer or macromonomer, solvent, and initiator
however face the problem that polymerization only occurs in a
very small zone at the entrance of the network. The major part of
the filled network stays unpolymerized and the uncured solution
spills over the PDMS-µFN during lift off. There was hence a need
for an improved procedure in order to guarantee complete
polymerization over the whole array of channels.

The effect of incomplete polymerization within the channels is
explainable by depletion of the initiator during filling of the
network, because the initiator has some affinity towards the
stamp material and it is only present in low concentration
(0.2%). With the procedure...