Biomedical Engineering Reference
In-Depth Information
Capillary valve
Hydrophobic valve
Siphon valve
Sacrificial valve
Crest
LD on
Pumping
Meniscus
front
Normally closed LIFM:
closed to open state
Hydrophobic
patch
Constriction
Vent
Chamber
Pressure
(a)
(b)
(c)
(d)
Normally closed LIFM:
closed to open state
FIGURE 3.36
Microvalving.strategies.used.in.centrifugal.microluidics..(From.Robert.Gorkin,.Jiwoon.
Park,.Jonathan.Siegrist,.Mary.Amasia,.Beom.Seok.Lee,.Jong-Myeon.Park,.Jintae.Kim,.Hanshin.Kim,.
Marc.Madou,.and.Yoon-Kyoung.Cho,.“Centrifugal.microluidics.for.biomedical.applications,”.
Lab
Chip
.10,.1758-1773,.2010..Reproduced.with.permission.from.The.Royal.Society.of.Chemistry.)
Fluid flow
(a)
(b)
Valve closed
Valve open
Sample
Reagent
Outlet
P
1
P
2
> P
1
FIGURE 3.37
Flap. microvalve.. (From. Joel. Voldman,. Martha. L.. Gray,. and. Martin. A.. Schmidt,.
“An integrated.liquid.mixer/valve,”.
J. Microelectromech. Syst.
.9,.295,.2000..Figure.contributed.by.
Joel.Voldman.)
if reversed pressure is increased. he only way to reopen the valve is to make the downstream
pressure lower than the upstream pressure (plus whatever force, e.g., a spring or gravity, is press-
ing the valve against the seat). Check valves can be implemented on the micron scale using tra-
ditional silicon micromachining techniques. A team at MIT led by Martin Schmidt developed
a micromechanical lap integrated at the end of a silicon nozzle (see
Figure 3.37
) to control bio-
chemical reactions of two compounds. he nozzle led to a reaction chamber, which had another
input nozzle (for the second reactant) and one output. When the irst reagent was pressurized at
a pressure higher than the chamber pressure (determined by the pressures at the outlet and at
the other inlet), the lap would delect upward (
Figure 3.37b
), opening the valve and producing
the chemical reaction in the chamber.
Micromachined
check microvalves
are expensive to develop but extremely inexpensive to
commercialize (i.e., batch manufacturing results in low cost per device). Issues of concern are
cost of disposal (must be disposed of with sharp objects such as needles) and sensitivity to dust
(the valve seat being a hard material, the seal is unforgiving to contamination, so the luids
must be carefully iltered). his device highlights a common problem in the miniaturization of
microluidic assays: the diiculty of metering micron-scale volumes. In macro-scale assays, this
problem does not exist because solution volumes are straightforwardly measured with a ruler
(by eye) or with a balance—pressure and low imbalances worry no one in the macro-world.
3.8.1.4 PDMS Microvalve: The Pinch Valve Design or “Quake Microvalve”
Pinch valves
use mechanical force to reduce the diameter of a section of the elastomeric
tubing through which the f luid is f lowing. In 2000, Stephen Quake's group, then at Caltech,
