Biomedical Engineering Reference
In-Depth Information
Adsorb
photoinitiator
Photoinitiator
Add monomer
Monomer
Photopolymerize
Polymer
Detach
top half
Stain with
toluidine blue
30 µm
FIGURE 3.26
Grafting. of. PDMS. channels.. (From. Shuwen. Hu,. Xueqin. Ren,. Mark. Bachman,.
Christopher.E..Sims,.G..P..Li,.and.Nancy.L..Allbritton,.“Surface-directed,.graft.polymerization.within.
microluidic.channels,”.
Anal. Chem.
.76,.1865,.2004..Reprinted.with.permission.of.the.American.
Chemical.Society..Figure.contributed.by.Nancy.Allbritton.)
making clever use of the fact that PDMS behaves like a “sponge” when it is exposed to strong
organic solvents (
Figure 3.26
). When exposed to a solution of the photoinitiator benzophenone
in acetone, the benzophenone penetrated into the swollen PDMS and remained there (inside
or adsorbed on the surface) ater abundant rinsing with water. Next, a monomer solution was
introduced into the channel and exposed to UV light for photopolymerization, which started
at the benzophenone-covered surface but extended into the bulk of the material. his process
is applicable to a variety of monomers and produces very stable layers, which could be useful in
ields such as capillary electrophoresis (enhanced electrophoretic mobility was demonstrated),
tissue engineering, and cell biology.
3.6 Operation of Microluidic Channels: Practical Concerns
Filling and running low through a microchannel is not as trivial as illing a pipe and opening a
faucet. Measuring low velocity is even more diicult. hese can be tedious, but it must be done
if we are to do
something
with the microchannels. Here, we review practical methods to operate
microluidic channels.
3.6.1 Filling a Microchannel: The “Bubble Curse” and Methods to Jinx It
For a few reasons, illing a microluidic channel can be harder than illing a garden hose. Even
if the viscosity of the luid is low as is the case of most biomedically interesting aqueous bufers,
