(706d) Surface Infusion Micropatterning of Elastomeric Substrates: A Novel Processing Method for Microfluidic Device Fabrication

The
last decade has witnessed revolutionary advances in the fields of
microfabrication and microfluidics because of a number of attractive attributes
of miniaturization, such as conservation of material in biological analyses.  Microfluidic devices have found applications
in a variety of fields including cell and molecular biology, medicine,
synthesis of novel materials, biosensors and food safety.  In recent years, microfabrication procedures
have shifted from materials such as silicon or glass toward inexpensive
polymers, which may be more amenable to low-cost mass production of disposable
devices. The development of accessible processing methods for microscale
patterning of soft elastomeric materials such as poly(dimethylsiloxane) (PDMS)
has led to an explosive growth in research in microfluidic devices and
microcontact printing devices.

Current
microfabrication processes for polymers include photolithography, casting,
injection molding, microthermoforming, and hot embossing. ?Soft lithography'
has revolutionized research in academic laboratories, where fabrication of PDMS
devices by simple casting protocols proves cost effective.  On the other hand, injection molding,
microthermoforming, and hot embossing are more adaptable to high-throughput
manufacturing.  However, these processes
are arguably less attractive to labs engaged in rapid prototyping of new
devices because of the prohibitive costs associated with repeated mold
tooling.  As a result, scale-up of new
devices from the prototype stage to the mass production stage can require a
change in both materials and equipment, a hindrance to commercialization.  A single process that allows rapid,
cost-efficient production of micropatterned polymer devices at both the lab
scale and the industrial scale could prove to be a critical advance in
microfabrication science and industry.

Surface
Infusion Micropatterning (SIM) is a new microfabrication process for surface
relief patterning of elastomeric substrates, including both chemically
crosslinked or vulcanized materials (e.g. polydimethylsiloxane, PDMS) and
thermoplastic elastomers (e.g., thermoplastic polyurethanes, TPUs).  The starting material (substrate) is an
optically transparent elastomeric material, which can be formed into flat
sheets by standard processing techniques prior to SIM.  The substrate may be either free-standing or
mounted as a surface layer on glass or another rigid material.  Patterning of the substrate by SIM is a
three-step process: 1) monomer infusion, 2) photopatterning, and 3) drying.  For the first time, SIM has been demonstrated
with two elastomeric materials, a crosslinked polydimethylsiloxane (PDMS) and a
thermoplastic polyurethane (TPU), to create micropatterned surface relief
features including a "checkerboard" well pattern and a microfluidic
channel system.  Surface micropatterns were
characterized by scanning electron microscopy, optical microscopy, and optical
profilometry to examine channel depth and shape.  High-resolution surface features of
dimensions as small as 10 micrometers can be obtained using an uncollimated,
broadband ultraviolet light source, making the technique amenable to low-cost
lab production.  SIM is most suitable for
producing shallow (low aspect-ratio) microfluidic channels in soft elastomeric
substrates.  After considering process
advantages and limitations, the potential for SIM to impact emerging microfluidic
manufacturing technologies will be discussed.