Biomedical Engineering Reference
In-Depth Information
PDMS
prepolymer
200 µm
Cap +
Fill mold
Cure
Stencil
Lift cap
FIGURE 1.29
Fabrication. of. PDMS. stencils. by. microluidic. molding.. (From. Tourovskaia,. A.,. T..
Barber,.B..Wickes,.D..Hirdes,.B..Grin,.D.G..Castner,.K.E..Healy,.and.A..Folch,.“Micropatterns.of.
chemisorbed.cell.adhesion-repellent.ilms.using.oxygen.plasma.etching.and.elastomeric.masks,”.
Langmuir
,.19,.4754,.2002..Reprinted.with.permission.)
Apply Mylar sheet
and glass
Cast PDMS against
SU-8 master
Clamp and cure
PDMS in oven
Multilayer SU-8
photoresist
Glass
Mylar sheet
Si wafer
PDMS
Release PDMS from mold
Oxygen plasma PDMS
and glass/PDMS substrate
and bring them together
PDMS stencil
on substrate
Peel off Mylar sheet
from PDMS
FIGURE 1.30
Fabrication.of.PDMS.stencils.by.exclusion.molding..(From.Hsu,.C.-H.,.C..Chen,.and.
A..Folch,.“.'Microcanals'.for.micropipette.access.to.single.cells.in.microluidic.environments,”.
Lab.
Chip
.,.4,.420,.2004..Reproduced.with.permission.from.The.Royal.Society.of.Chemistry.)
must be sot enough to form a good contact and hard enough to bridge features in the
master without sagging. A solution to this problem has been the use of multilayer cov-
ers; however, the layer that comes into contact with the master is made of a thin sheet
of plastic, and pressure is applied to the plastic by a hard surface such as a glass slide.
Mylar (acetate ilm) happens to stick particularly well to cured PDMS; when Mylar is
used as the cover for exclusion molding, cured PDMS—surprisingly enough—prefers
the lat Mylar surface to the microstructured surface of the master, even though the
PDMS is not irreversibly bound to the Mylar (i.e., the PDMS stencil can still be peeled
of the Mylar).
