Biomedical Engineering Reference
In-Depth Information
that here the doormat design is open at rest, which may be an interesting variation on its own
for certain applications.
For biochemical reactors (e.g., PCR devices) or cell culture systems, which are operative only
on a very limited range of temperature, heat-based actuation naturally raises serious concerns.
hese concerns may be addressable by placement of the valves away from critical sites and by
designing heat sinks.
3.8.1.11 PDMS Microvalves Actuated by “Braille” Pins
hese valves also belong to the pinch valve class, but with two key diferences compared with
the PDMS valves reviewed previously: (a) instead of being based on the deformation of a thin
PDMS membrane next to the luid-carrying microchannel, they are based on the deformation
of the bulk of PDMS that forms the device; and (b) instead of being based on the remote genera-
tion of pressure—which keeps the Quake, doormat, curtain, and plunger designs tethered to a
vacuum-supplying wall—they are based on the local generation of pressure via mechanical pins.
An inexpensive, easily programmable source of pins is found in Braille displays universally used
by the blind to communicate, hence, the name of the valves. One limitation is that the pinch-
ing points cannot be very close, with the smallest distance ultimately dictated by the thickness
of the device (even if pin arrays smaller than Braille displays can be fabricated). However, the
pinching points need not be the valving points. As shown in
Figure 3.46
, each pin presses onto a
liquid-illed reservoir (~150 μm high, ~900 μm diameter), which acts as a “piston” that transmits
the pressure to a membrane-based pinch valve (in this case, a Quake microvalve) at a remote
location, even centimeters away.
Figure 3.46c
shows a top-down view of four intersections of
pressurized control (red) and luidic (green) microchannels (9 μm high and 100 μm wide except
for the 40-μm-wide control channel on the bottom right, which is not pinched because it is
narrower.
his “remote hydraulic piston” could, in principle, be implemented with actuation stimuli
other than displacement, such as light or temperature, that can also cause expansion and retrac-
tion in certain materials but are oten cumbersome to apply at the site of the valve.
a
Control
channel
Piston
100 µm
Braille
pin
Fluidic
channel
b
100 µm
c
100 µm
FIGURE 3.46
Braille-actuated.microvalves..(From.Wei.Gu,.Hao.Chen,.Yi-Chung.Tung,.Jens-Christian.
Meiners,.and.Shuichi.Takayama,.“Multiplexed.hydraulic.valve.actuation.using.ionic.liquid.illed.soft.
channels. and. Braille. displays,”.
Appl. Phys. Lett.
. 90,. 033505,. 2007.. Reprinted. with. permission.
from.the.American.Institute.of.Physics..Figure.contributed.by.Shuichi.Takayama.)
