Biomedical Engineering Reference
In-Depth Information
Stimulus
1
Stimulus
2
Stimulus
N
a
b
Gene 1
Gene 2
Gene M
Microscope
objective
d
c
+ Pressure
- Pressure
Stimulation
inlets
Seeding
valve
control
Closed valve
Open valve
LPS TNF-α
IL-1
IL-6
IFNγ Dex
Cyts Cyts/Dex
e
Cell
seeding
outlet
NFκB
AP-1
STAT3
ISRE
GRE
HSE
D4G
Stimulation
valve
control
Reporter cell
seeding inlets
2 mm
Stimulation
outlets
0
36 hrs
0
1
FIGURE 5.39
Microluidic.gene-expression.cell.array..(From.Kevin.R..King,.Sihong.Wang,.Daniel.
Irimia,. Arul. Jayaraman,. Mehmet. Toner,. and. Martin. L.. Yarmush,. “A. high-throughput. microluidic.
real-time.gene.expression.living.cell.array,”.
Lab Chip
.7,.77-85,.2007..Reproduced.with.permission.
from.The.Royal.Society.of.Chemistry.)
hese gene expression microarrays are limited in that all the cells, which form a monolayer cul-
ture, share the same cell culture medium. A Massachusetts General Hospital team led by Maish
Yarmush has accomplished a gene expression platform in which cells are cultured in a square 16 ×
16 array of circular microchambers (50 μm height and 420 μm diameter), connected to each other by
microvalves; the cells are transfected with diferent genes by rows and exposed to diferent stimuli
by columns, thus allowing for a rich combinatorial matrix of conditions of genes and stimuli that
can be monitored noninvasively by time-lapse luorescence microscopy (
Figure 5.39
). As a demon-
stration, hepatocyte inlammatory gene expression dynamics were proiled [see heat map in
Figure
5.39e
; each reporter was stimulated with bacterial endotoxin (LPS), inlammatory cytokines (TNF-
α, IL-1, IL-6, and IFNγ), a synthetic glucocorticoid hormone (dexamethasone), and combinations
thereof (Cyts ≡ TNF-α/IL-1/IL-6 or Cyts+Dex ≡ TNF-α/IL-1/IL-6/Dex), cellular luorescence was
measured from three cell chambers for each of the 64 stimulus-response pairs every 90 minutes for
36 hours to create the 192 time series composed of 4608 single time point measurements].
5.6 Micro-Bioreactors
Living systems are far from homogeneous. In fact, they are full of microscale (substrate-bound
and soluble) gradients of small ions and a rich variety of growth factors, which require energy
expenditure to create and maintain. It is not an exaggeration to say that, deep inside, our physi-
ological systems are all microluidic (
Figure 5.40
). If these microluidic systems stop working,
we develop a disease and eventually die.
Biologists and doctors have attempted to recreate “organ-like” conditions in petri dishes.
In these conditions, cells dissociated from the organ are seeded on a homogeneous plastic sur-
face (usually coated with protein) and homogeneously bathed in cell culture medium. hese
conditions do not reproduce the microscale gradients present in vivo, which can afect critical
