Biomedical Engineering Reference
In-Depth Information
Exploded view of single valve
a
d
Control
Input
c
Output
Cross-section
Valve seat
Control
Input
Output
Input
channel
Output
channel
Control
Closed
PDMS
membrane
Input
Output
Bottom wafer
facing up
Top wafer
facing down
Complete
latching valve
Displacement
chamber
Displacement
chamber
Atmospheric pressure
PDMS
membrane
Set pulse input
Open
e
Pressure
valve
Assembled valve
Output
channel
b
Vacuum
valve
Input
channel
Vacuum applied
Latching
valve
Vent
PDMS
membrane
Control
channel
Valved fluid channel
FIGURE 3.44
Latching.microvalves..(From.William.H..Grover,.Robin.H..C..Ivester,.Erik.C..Jensen.
and.Richard.A..Mathies,.“Development.and.multiplexed.control.of.latching.pneumatic.valves.using.
microluidic. logical. structures,”.
Lab Chip
. 6,. 623,. 2006.. Reproduced. with. permission. from. The.
Royal.Society.of.Chemistry.)
3.8.1.10 Electrically Actuated PDMS Microvalves
Note that all the previous designs require the connection of the device to a vacuum supply (and
sometimes also a pressurized air source), so they are not portable while functioning. Ideally,
one would like to generate the pressure with minimal power and using electrical circuits,
which can be readily patterned and addressed with computers. With that in mind, Christopher
Backhouse's group at the University of Alberta in Canada has introduced a temperature-
sensitive polymer, which could be PEG or wax, into the control channel of a doormat design
valve (
Figure 3.45
). To low, the polymer has to be introduced in the molten phase (expands in
volume), so when it cools down to room temperature it opens the valve. Upon local heating of
the valve seat, the polymer in the control channel expands, causing closure of the valve. Note
b
a
70 µm
Control layer
Open
c
Flow layer
3 mm
Closed
FIGURE 3.45
Microvalve. based. on. thermal. expansion. of. PEG.. (From. Govind. V.. Kaigala,. Viet. N..
Hoang,.and.Christopher.J..Backhouse,.“Electrically.controlled.microvalves.to.integrate.microchip.
polymerase. chain.reaction.and. capillary. electrophoresis,”.
Lab Chip
.8,.1071,.2008.. Reproduced.
with.permission.from.The.Royal.Society.of.Chemistry.)
