Biomedical Engineering Reference
In-Depth Information
can be unplugged and transported to a diferent location with all the luids safely stored in
microchambers.
Note that the doormat microvalve is limited to a monolithic PDMS architecture—unless
the valves are implemented on a diferent level. his mandate for an “all-PDMS architecture”
can be a hurdle for biological applications, especially cell culture studies, in which it is desir-
able to have a glass surface. Glass ofers better control over the surface chemistry, has superior
optical clarity, and is rigid even when it is very thin (an advantage for high-resolution optical
microscopy). he Quake microvalve, on the other hand, can be used either as a stand-alone
device, that is, it can be
applied to a surface
, or be fabricated entirely in PDMS. Also, devices
that can be applied to a surface can, in principle, be used to deposit patterns on the surface.
he Mathies laboratory has reported a doormat microvalve design made in PMMA (except
the PDMS membrane); to bond the PDMS membrane to the PMMA layers, both the PMMA
and the PDMS surfaces were exposed to a UV ozone treatment, which generated -OH groups
on their surface.
3.8.1.6 PDMS Microvalve: The “Sidewall Design”
Andrew Berlin and colleagues at the University of Wisconsin (Madison) have presented a PDMS
valve design that places the pneumatic actuators on the lateral walls of the microchannels
(
Figure 3.41
). his design decision incurs a considerable cost in chip real estate, making high-
density microvalve arrays very diicult, but enables the fabrication of valves with a single-mask
process. Here, one or more of the sidewalls of the microchannel is fabricated thin enough that,
when pressure is applied on the other side, the wall delects into the volume of the microchannel;
this scheme cannot produce strong seals but, nevertheless, alternatively actuated “leaky” valves
were shown to produce pumping.
3.8.1.7 PDMS Microvalve: The “Curtain Design”
he “curtain design” by the Toner group from Harvard University in 2006 overcomes the main
limitation of the doormat microvalve design: here, the membrane constitutes the microchan-
nel's roof (as in the Quake design), which lits a wall like a curtain to open a normally closed
channel (unlike the Quake microvalves). he curtain design is fabricated entirely in SU-8 and
can be assembled as a stand-alone device on a glass surface (
Figure 3.42
), making it ideal for
cellular applications. It is to be expected that, as the PDMS membrane in the curtain design
must displace a larger mass than in the doormat design, the response time of the doormat design
should be faster.
Actuation of deformable membrane
units on the left or right branch outlets
Outlet to
bin 1
Outlet to
bin 2
Operating
channels
0.03 s
Sheath Sheath
Sample
0.03 s
6 µm bead directed to left
or right branch outlets
(a)
(b)
FIGURE 3.41
PDMS. microvalves. implemented. in. the. sidewall.. (From. Narayan. Sundararajan,.
Dongshin. Kim,. and. Andrew. A.. Berlin,. “Microluidic. operations. using. deformable. polymer. mem-
branes.fabricated.by.single.layer.soft.lithography,”.
Lab Chip
.5,.350-354,.2005..Reproduced.with.
permission.from.The.Royal.Society.of.Chemistry.)
