Biomedical Engineering Reference
In-Depth Information
polymer consisted of 40% w/v of poly(ethylene glycol)-diacrylate (PEG-DA), with 2% w/v of
Irgacure 2959 as photoinitiator. For clarity of visualization, PEG-DA in each cycle was doped
with a combination of green, red, and blue luorescent dyes.
A common misconception is that microluidics is simply “assisting” the process because the
actual patterning is performed with light. Note, however, that the microchannel is used to deine
the height of the microstructure, which allows for bypassing the traditional photoresist spin-
coating step and, as a result, the whole clean room operation—clearly, the microchannel is not
merely assisting but
enabling
. Moreover, it is possible to produce more complex structures and
organize them downstream if the microchannel contains a guide (groove) on the roof, so the
laser-fabricated structures can be directed downstream with a system of “rails” (
Figure 1.26
).
Another variation of stopped-low lithography, called
lock-release lithography
(
Figure 1.27
),
uses a microchannel with a very thin roof that is “inlated” on completion of the chemical reac-
tion to release the microstructures. By sequential illing of the microchannel with diferent
chemistries (
Figure 1.28
), it is possible to fabricate composite particles.
In summary, microluidic patterning is inferior to photolithography in pattern idelity and
inferior to microstamping in convenience and resolution. As microstamping, it is pattern-
dependent (unlike photolithography, the procedures used to produce one pattern may have to be
changed for another pattern, and not all patterns are possible) but it is superior to photolithog-
raphy in cost-efectiveness and materials versatility. For biological patterning, the absence of a
need for further processing (e.g., obviating the protein drying step as needed for microstamp-
ing) can be invaluable with respect to traditional protocols.
Three-way
valve
Pressure
source
“Closed”
“Open”
Lock
Release
P = 0 psi
P = 5 psi
UV
Collect
FIGURE 1.27
“Lock-release.lithography”.in.microchannels..Scale.bars.are.100.
μ
m..(From.Bong,.
K.W.,.D.C..Pregibon,.and.P.S..Doyle,.“Lock.release.lithography.for.3D.and.composite.microparti-
cles,”.
Lab. Chip.
,.9,.863,.2009..Reproduced.with.permission.from.The.Royal.Society.of.Chemistry.)
