Biomedical Engineering Reference
In-Depth Information
PEG hydrogel micropatterns have been fabricated by photopolymerization through a micropatterned
photomask (photolithography)
[24]
. Soft-lithography, as mentioned earlier, is a technique by which
micropatterns can be fabricated on a substrate using poly(dimethyl siloxane) stamp (PDMS)
[11]
.
11.5
SOFT-PHOTOLITHOGRAPHY OF HYDROGEL MICROPATTERNS
Soft-photolithography, a combination of photolithography and soft-lithography using a PDMS is
described in the following sections. UV embossing has been used to fabricate poly(ethylene glycol)
hydrogel-diacrylate (PEG-DA) micropatterns varying from 50 to 500 μm
[25]
. The spatial organiza-
tion of cells and their response to minute hydrogel patterns of subcellular dimensions less than 40 μm
could serve as a crucial element in understanding cell behavior in tissue culture experiments and
in their biomedical applications ranging from tissue engineering, BioMEMS, and biosensors. Using
the soft-photolithography technique, PEG hydrogel micropatterns were fabricated on a silicon sub-
strate of varying dimensions from 40 μm to as finer as 10 μm within the same substrate. The micro-
fabrication steps employed for the fabrication of the PEG micropatterns as small as 10 μm using
soft-photolithography as follows.
11.5.1
Fabrication of PDMS Stamp
11.5.1.1
Design of the Photomask
The design for the photomask to be used for the PDMS stamp fabrication was designed using the
“Clewin” software (PhoeniX Technologies, The Netherlands). Different patterns including squares,
circles, lines, and diamonds were designed of varying dimensions from 10 to 40 μm (
Figure 11.1
).
These patterns were repeated in quartets throughout the mask design. From this mask design, a
5
5 inch chrome/sodalime photomask was manufactured by Deltamask Co. (The Netherlands). The
micropatterns on the fabricated photomask as visualized under a light microscope (Olympus BX37,
London, UK) is represented in
Figure 11.2
.
11.5.1.2 Fabrication of “Master” or Negative Mould
The “master” or negative mould was produced on a silicon wafer using the conventional photolithog-
raphy technique (
Figure 11.3
).
The silicon wafer was silanized with hexa methyl disilazane (HMDS) in YES oven (Sanjose,
CA, USA) at 150°C and the photoresist was spincoated at 3,500 rpm for 60 s in an EVG101 resist
spincoater (Schaerding, Germany). The photoresist was soft baked for 5 min at 95°C in a preci-
sion hotplate (Electronic Microsystems, Boerne, TX, USA) and was exposed to UV light 365 nm,
10 mW/cm
2
for 15 s through a chrome/sodalime photomask in an EVG620 mask aligner (Schaerding,
Germany). The exposed photoresist was developed in an EVG103 developer with Shipley MF-26A
(Marlborough, MA, USA) developer solution for 2 min. The pattern of the photoresist on the negative
mould was visualized under a light microscope (
Figure 11.4
).
11.5.1.3 Fabrication of PDMS
The Sylgard 184 base silicone elastomer and Sylgard 184 curing agent for the fabrication of the
poly(dimethyl siloxane) (PDMS) stamp was purchased from Dow Corning GmbH (Weisbaden,
