Biomedical Engineering Reference
In-Depth Information
Photoresist
pattern
Pour PDMS
pre-polymer
Cure
and peel off
SU-8
master
PDMS
replica
PDMS
30 µm
FIGURE 1.19
PDMS.micromolding..The.linewidth.of.the.letters.“CEMGH”.is.50.
μ
m..Red.arrows.
point.to.PDMS.structures.that,.because.of.their.high.aspect.ratios.(>5:1.height/width),.have.not.
replicated.well..(Figure.contributed.by.the.author.)
exceptionally faithful—features smaller than 100 nm can be replicated; importantly, extremely
lat surfaces in the master are also replicated as extremely lat PDMS surfaces. For some features
such as long, high aspect ratio trenches, the direction in which the replica is peeled of the mas-
ter can be important to avoid tearing the PDMS. High aspect ratio (>5 or so) columns or walls
have very low integrity and can collapse against the surface (
Figure 1.20
).
W = 20 µm
H/W = 2
W = 5 µm
W = 10 µm
H/W = 3.8
H/W = 7.5
15 µm
100 µm
25 µm
20 µm
FIGURE 1.20
Structural.integrity.of.PDMS.walls..The.ridges.on.the.PDMS.walls.were.present.on.
the.walls.of.the.trenches.from.which.these.structures.were.replicated..W.indicates.width.and.H/W.
indicates.height-to-width.“aspect”.ratio..(From.Folch,.A.,.A..Ayon,.O..Hurtado,.M.A..Schmidt,.and.
M..Toner,.“Molding.of.deep.polydimethylsiloxane. microstructures.for.microluidics. and.biological.
applications,”.
J. Biomech. Eng.
,.121,.29,.1999..Figure.contributed.by.the.author.)
