Biomedical Engineering Reference
In-Depth Information
Flow sensor
Intersections
X
Microvalve
Y
Microfluidic channel
Compressed air
S-shaped micropump
FIGURE 3.65
Serpentine.channel.micropumps..(From.C.-H..Wang.and.G.-B..Lee,.“Pneumatically.
driven. peristaltic. micropumps. utilizing. serpentine-shape. channels,”.
J. Micromech. Microeng.
. 16,.
341-348,.2006..Reproduced.with.permission.from.the.Institute.of.Physics.)
at 20°C, but the reality is that the pneumatic channel expands, so the walls behave like a capaci-
tor (and so do the membranes), and the channel itself ofers some aerodynamic resistance,
R
—
all of which slows down the response of the line by more than two to three orders of magnitude.
(he capacitance,
C
, is a function of volume,
V
, and pressure,
P
, expressed as
C
= d
V
/d
P
, and
the resistance,
R,
is expressed by
Equation 3.12
.) In 2008, Gwo-Bin Lee studied how serpentine
pumps (with 1, 5, and 10 mm pneumatic channel lengths) behave using high-speed cameras and
determined that the total time needed to complete the activation and deactivation processes was
26, 38, and 106 ms (for the 1, 5, and 10 mm-length pumps, respectively); by comparison, sound
in a rigid pipe would have taken a mere 2.9, 14.5, and 29 μs to travel the same lengths, respec-
tively, and thus, clearly, the lexibility of PDMS plays a big (advantageous) role in slowing down
the pressure wave. If PDMS were rigid, the serpentines would have to be three to four orders of
magnitude longer. Still, serpentine design occupy a large amount of chip real estate.
he author's group at the University of Washington (Seattle) has investigated a design prin-
ciple that is based on the universal mechanical principle that small membranes respond faster
than larger membranes, so they can be connected to the same pneumatic line (
Figure 3.66
),
eliminating delay lines. On arrival of the pressure pulse, the irst valve to close is always the
Valve seat
Control channel
Fluidic channel
Valve pad
300 µm
FIGURE 3.66
Compact. PDMS. peristaltic. pump. actuated. by. a. single. pneumatic. channel..
(From Hoyin.Lai.and.Albert.Folch,.“Design.and.characterization.of.“single-stroke”.peristaltic.PDMS.
micropumps,”.
Lab Chip
.11,.336-342,.2011..Reproduced.with.permission.from.The.Royal.Society.
of.Chemistry..Figure.contributed.by.Hoyin.Lai.)
