Biomedical Engineering Reference
In-Depth Information
Step 1: Engraving
Step 2: Stacking
a
1st layer
2nd layer
Step 3: Final device after shrinking
Input 2
Etching
3rd layer
Input 1
Drain
4th layer
200 µm
Un-shrunk
b
d
Shrunk
200 µm
c
FIGURE 3.11
“Shrinky-dinks”. microluidics.. (From. Chi-Shuo. Chen,. David. N.. Breslauer,. Jesus. I..
Luna,. Anthony. Grimes,. Wei-chun. Chin,. Luke. P.. Lee,. and. Michelle. Khine,. “Shrinky-dink. micro-
luidics:. 3D. polystyrene. chips,”.
Lab Chip
. 8,. 622,. 2008.. Reproduced. with. permission. from. The.
Royal.Society.of.Chemistry.)
device is very expensive, indeed. As a consequence, researchers have generally avoided injection
molding, but manufacturers of disposable devices oten must convert a design to one that can be
injection-molded to keep the cost-per-device as low as possible.
he inherent shrinkage property of biaxally prestressed thermoplastic sheets (e.g., the toy
“Shrinky-Dinks”) has also been leveraged for miniaturization: on heating, engraved grooves
(using syringe tips or digital cutters) will shrink only in one plane, becoming narrower and
deeper (
Figure 3.11
).
3.5.1.3 A New Kid on the Block: PDMS
As we have seen already in Section 1.6, PDMS has many excellent qualities as a polymer for micro-
luidics, so it is widely used today. he development of inexpensive methods for patterning PDMS
molds, the idelity with which PDMS can reproduce even nanometer-scale small features in those
molds, its ability to be sealed to itself and other oxide-covered surfaces, and its optical transparency
have made it the material of choice for researchers. he fact that PDMS is permeable to gases and
even to water vapor has proven very useful in some biological applications of microluidics, as well,
although in some cases it could be seen as a liability. he fact that PDMS is a very mobile polymer
allows the surface of PDMS to readily change its composition from hydrophobic to hydrophilic
and back again. his is not necessarily an advantage. Also, as of this writing, PDMS has not been
very amenable to inexpensive mass production (although it is possible, especially if one redeines
“mass production”), but has been used in a few commercialized microluidic devices.
