Biomedical Engineering Reference
In-Depth Information
a
TM
SGM
BEM
SHM
CDM-2T
CDM-4T
CDM-8T
1
0.9
CDM-8T
b
TM
SGM
BEM
SHM
CDM-2T
CDM-4T
CDM-8T
CDM-4T
0.8
0.7
0.6
70
µm
CDM-2T
30.6 µm
Advection
dominate
SHM
0.5
0.4
0.3
0.2
0.1
0
10
-2
Slanted grooves
BEM
Circulation
disturbance
micromixer
(CDM)
SGM
Diffusion dominate
TM
10
-1
10
0
10
1
10
2
Reynolds number
Yellow color dye liquor
Flow
c
Y~0 cm
Y~1.4 cm
Y~2.8 cm
Blue color dye liquor
Re = 2.38
SGM
CDM
FIGURE 3.102
Homogenizer.enhanced.by.a.circulation-disturbance.barrier..(From.Jing-Tang.Yang,.
Ker-Jer.Huang,.Kai-Yang.Tung,.I-Chen.Hu,.and.Ping-Chiang.Lyu,.“A.chaotic.micromixer.modulated.
by.constructive.vortex.agitation,”.
J. Micromech. Microeng.
.17,.2084-2092,.2007..Reproduced.with.
permission.from.the.Institute.of.Physics..Figure.contributed.by.Jing-Tang.Yang.)
3.10.2 Micromixers Incorporating Dynamic Elastomeric Microelements
In Section 3.9, we have already seen micromixer designs that are “dynamic,” in the sense that
their performance could be changed with time—for example by changing the low rate. However,
that performance could not be changed unless the user changed the low going into the mixer. In
this section, we will see several designs in which the performance of the mixer can be tuned by
controlling elastomeric microelements integrated into the device.
3.10.2.1 Microvalve-Based Mixers
A simple way to control mixing in a microdevice is to incorporate microvalves and micropumps
that can be programmed to do the mixing on a desired schedule. Stephen Quake and cowork-
ers at Caltech, then designed a microluidic “formulator” that looks like a rotary mixer, which
accepts plugs of several inputs through a multiplexer (
Figure 3.105
); note that if the plugs do not
rotate, the difusion path to achieve homogenization is the whole circle. However, as the plugs
rotate, Taylor dispersion typical of the parabolic low proile encountered in microchannels (see
Figure 3.2
in Section 3.2.4.2) greatly speeds up mixing, because the plugs get ensheathed within
each other and the difusion path is now limited to the width of the channel. Complete mixing
takes an impressive 3 seconds.
A diferent concept, originally presented by Quake's group, also achieves mixing but uses
only nanoliter-sized chambers that communicate via microvalves. he power of the approach is
that groups of valves are operated simultaneously using the same pneumatic channel, so it is pos-
sible to create titrations in parallel on a very small scale. his system is now commercialized by
