Microfluidic Devices for Angiogenesis - Mechanical and Chemical Signaling in Angiogenesis - page 94

a b c d

UV UV UV

The coated SU-8
photoresist Silicon wafer

Mask

For the patterning, SU-8
photoresist is exposed with UV.

After baking and development,
SU-8 photoresist is developed.

Silicon wafer is placed on
a spin coater.

SU-8 photoresist is coated
onto silicon wafer.

e f g h

Petri dish

PDMS slab

Punched PDMS
slab

Patterned SU-8
master mold

PDMS

Cover slip

SU-8 master mold is placed
in Petri dish.

PDMS is poured onto master
mold in the Petri dish

Punched PDMS slab is bonded
by air plasma treatment.

After curing, the PDMS slab is
peeled off from the master molds.

Fig. 1 Schematic of Microfluidic Device Fabrication: The microfluidic chip is fabricated via
conventional soft lithography (a-d) and PDMS replica molding (e-h). a A silicon wafer is placed
on a spin-coater to achieve the desired SU-8 resist film thickness. b SU-8 photoresist is coated
onto the silicon wafer and baked on a hot plate. c For patterning, the SU 8 photoresist on the
silicon wafer is exposed to conventional UV (350-400 nm) radiation through a photomask.
d After baking, the SU-8 resist is developed with SU-8 developer, and an SU-8 master mold is
made. e The SU-8 master mold is placed in a large Petri dish for PDMS preparation. f PDMS is
poured onto the master mold in the Petri dish and degassed in the vacuum chamber. g After
curing (70 C), the PDMS replica is peeled away from the master mold. h For bonding, the
PDMS slabs are bonded with a cover slip after oxygen plasma treatment

1.3 The Advent of Microfluidics

Early fluidic devices were developed in the 1980s and used in studies of the effects
of shear stress on endothelial monolayers [ 19 - 21 ]. While not ''micro'' in scale,
they typically involved channels on the order of 10 -3 m; large enough to enable
easy fabrication by standard machining methods, yet small enough to limit the
need for large numbers of cells or large volumes of reagents. In parallel, micro-
fluidics emerged as a multidisciplinary research field since its inception at Stanford
University where the technology was first applied to the fabrication of gas chro-
matographic air analyzers [ 22 ] and for designing the nozzle component for the first
inkjet printers by IBM [ 23 ]. The foundation for microfluidic fabrication was laid
by the microelectronics industry that developed fabrication techniques for creating
high-resolution features in microelectronic components. Early microfluidic sys-
tems were fabricated in silicon or glass using standard photolithography (other
lithographic techniques include electron lithography, X-ray lithography, ion
lithography) and chemical etching methods [ 24 ]. In recent years, there has been a
shift towards elastomeric materials that permits rapid prototyping of microfluidic
systems, discussed further in Sect. 3 and illustrated in Fig. 1 [ 25 , 26 ].