Color Inserts 261
Figure 5.3 Overview of hydrogels used for 3-D cell entrapment.
14
D E
F G
H I
Figure 5.7 Microfabrication of PDMS structures. (a–b) Photoresist is spin-coated on a
silicon wafer. (c) A mask is placed in contact with the layer of photoresist. (d) The
photoresist is illuminated with ultraviolet (UV) light through the mask. An organic
solvent dissolves and removes photoresist that is not crosslinked. The master consists of
a silicon wafer with features of photoresist in bas-relief. An expanded view of one of the
microfabricated structures with its characteristic critical dimensions is shown. (e) PDMS is
poured on the master, cured thermally and peeled away. (f) The resulting layer of PDMS
has microstructures embossed in its surface.
47
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262 Color Inserts
(b)
(c)
(d)
(a)
Figure 5.8 For color reference, see page 100.
Figure 5.9 (a) A two-layer polydimethylsiloxane (PDMS) push-down microfluidic valve.
An elastomeric membrane is formed where the flow channel is positioned orthogonal to the
control channel directly above. Fluid flow is out of the page. (b) A two-layer PDMS push-up
microfluidic valve where a control channel lies orthogonal to and below the flow channel.
(c) A three-layer device with both push-up and push-down valves. (d) Schematic of a linear
peristaltic pump using three membrane valves in a series.
53
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Color Inserts 263
Figure 5.10 (A) Optical micrograph showing six microchemostats that operate in parallel
on a single chip. Various inputs have been loaded with food dyes to visualize channels
and sub-elements of the microchemostats. The coin is 18 mm in diameter. (B) Optical
micrograph showing a single microchemostat and its main components. Scale bar, 2 mm.
(C) Schematic diagram of a microchemostat in continuous circulation mode. Elements such
as the growth loop with individually addressable connected segments, the peristaltic pump,
supply channels, and input/output ports are labeled. (D) Isolation of a segment from the
rest of the growth chamber during cleaning and dilution mode. A lysis buffer (indicated in
red) is introduced into the chip through the lysis buffer port. Integrated microvalves direct
the buffer through the segment, flushing out cells, including those adhering to chamber
walls. The segment is then rinsed with fresh sterile medium and reunited with the rest of
the growth chamber.
46
Figure 5.12 Schematic of the fabrication of agarose microfluidic devices with (right) and
without (left) embedded cells.
68
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264 Color Inserts
Figure 5.15 Schematic cross-sectional view of a cell-seeded microfluidic scaffold. The
dispersed cells (circles) surround the microchannels (squares). The pink shading represents
steady-state distributions of solutes. Here, a reactive solute is delivered via the channels
and is consumed by the cells as it diffuses into the matrix. λ
K
is the Krogh length, λ
c
is
the interchannel distance, w
c
and hc are the microchannel width and height, k
c
is the mass
transfer coefficient of the flow in the microchannels, and u
c
is the speed of the flow in the
microchannels.
94
Figure 5.16 Tissue organization, culture and analysis in microsystems. Microsystems can
incorporate 3D scaffolds to guide cell growth, microfluidic systems for nutrient transport,
different techniques for biochemical analysis (such as image-based analysis), to give multi-
ple functionalities on a single chip.
96
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Color Inserts 265
ŵƉĞƌĂƚƵƌĞ΀Σ΁
sŝƐĐŽƐŝƚLJ΀WĂ Ɛ΁
Figure 6.1 Viscosity as a function of temperature for different concentrations of Pluronic
F127 in water from cone and plate viscometry at controlled shear stress (0.6 Pa s).
26
0.01
0.1
1
10
100
10 15 20 25 30
0
0.15
0.18
0.243
0.253
Na
3
PO
4
Concentration[mol/L]
Temperat ure(°C)
Viscosity(Pa s)
Figure 6.2 Viscosity as a function of temperature for different concentrations of sodium
phosphate in a 15 wt% Pluronic F127 solution in water from cone and plate viscometry at
controlled shear stress (0.6 Pa s).
110
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