Biomedical Engineering Reference
In-Depth Information
6.9 Microluidics for Studying Cellular Dynamics
Time is a crucial parameter in most cellular processes. Rapid changes are ever-present dur-
ing development, reproduction, cell migration, and healing, to mention a few key phenomena
that are central to life. During these processes, cells change through activation of genetic pro-
grams by extracellular signals and cells, in turn, change their environment by secretion of more
extracellular signals. Microluidic systems, in combination with recent advances in imaging
and biochemical readouts, provide an ideal platform for the quantitative stimulation of cells
under precise spatiotemporal control conditions. We have already seen a variety of microluidic
cell culture systems for general cell maintenance in Section 5.4. Here we will cover systems that
allow for a great spatiotemporal control of the cellular microenvironment (while obtaining some
particular readout).
Owe Orwar's group from the Chalmers University of Technology in Goteborg (Sweden) has
found a very practical way of modulating solution composition around a single cell very quickly
and at high throughput (
Figure 6.81
). he cell is held at the tip of a probe and held stationary
with respect to a stage, which holds a microluidic device and is scanned with respect to the cell.
he microluidic device simply produces an outlow of 16 parallel laminar lows into a large open
reservoir area (accessible to the pipette); the mixing of the solutions away from the outlets is
irrelevant to the experiment. he experimenter decides which solutions and which mixtures are
introduced into which wells, so that as the cell passes in front of the outlets in sequence, it “sees”
a “chemical waveform.” By varying the trajectory of the probe with respect to the stage (varying
the stage speed or the stage-probe distance), it was possible to create very complex waveforms
even with simple input concentration proiles (e.g., using only two diferent concentrations, or
a binary input). he probe could also be used to obtain electrical (patch clamp) measurements
from the cell while agonist or antagonist substances to ion channel receptors were applied. (A
similarly conceived laminar low switching system that features a piece of tubing that ends in
an open reservoir has been used in ion channel research for a long time, but it requires much
larger low rates.)
Rustem Ismagilov's group at the University of Chicago has interfaced a droplet generator with
Telon tubing and a piece of PDMS (termed a “chemistrode”) that allows for a brief exit of the
droplets from the system (
Figure 6.82
)—for example, to expose cells to the droplets' contents. It
is crucial that the outlow rate be very well balanced with the droplet production rate, especially
Input matrix: I
NS
a
b
Microfluidic chip
Sample reservoirs
Probe
N
1
N
2
N
3
N
4
N
5
Probe
S
1
S
2
S
3
Channel outlet
z
P
1
P
2
y
Scanning stage
X
S
1
S
2
S
3
S
1
+ S
2
+ S
3
Y
1
0
0
2
200
0
3
0
25
4
200
50
5
0
100
6
200
250
7
0
350
8
200
500
9
0
350
10
200
250
11
0
100
12
200
50
13
0
25
14
200
0
15
0
0
16
0
0
Channel number
[β-alanine] (mM)
[Bicuculline] (µM)
Antagonist
Agonist
c
Output
landscape:
P
4
P
3
Scanning trajectory
S
1
+ S
2
S
2
+ S
3
S
2
+ S
3
S
3
S
1
+ S
2
+ S
3
S
1
+ S
2
+ S
3
S
1
+ S
2
+ S
3
40.0 pA
1.00 s
WSS-1 cell
GABAA receptor
FIGURE 6.81
A.chemical.waveform.synthesizer..(From.Jessica.Olofsson,.Helen.Bridle,.Jon.Sinclair,.
Daniel. Granfeldt,. Eskil. Sahlin,. and. Owe. Orwar,. “A. chemical. waveform. synthesizer,”.
Proc. Natl.
Acad. Sci. U. S. A.
. 102,. 8097-8102,. 2005.. Copyright. (2005). National. Academy. of. Sciences,.
U. S. A..Figure.contributed.by.Owe.Orwar.)
