102 M. C. W. Chen and K. C. Cheung
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
For color reference, see page 263.
tumor cells, permitting tumor spheroid formation and anticancer drug testing.
67
5.4.2 Microfluidic Agarose Cell Culture
In an alternative configuration, the microfluidic channel itself can be made of
hydrogel in which the cells have been seeded. Ling et al. have molded microfluidic
channels made of agarose seeded with cells
68
(Fig. 5.12). The mold master was
made using SU-8 patterned on a silicon wafer. Low gel-temperature agarose was
mixed with phosphate buffered saline and cooled to 70
C, when it was loaded with
AML-12 hepatocytes. The mixture was poured onto the mold master and gelled.
A flat slab agarose was sealed onto the de-molded structure to created closed
microchannels. Culture medium was supplied using a syringe pump through the
microchannels. Although they were able to achieve uniform cell seeding, and good
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Hydrogel-Based Microfluidic Cell Culture 103
Figure 5.11. Microchannel layout for on-chip formation of alginate layers with embedded
cells using laminar flows of alginate and Ca
2+
.
63
Figure 5.12. Schematic of the fabrication of agarose microfluidic devices with (right) and
without (left) embedded cells.
68
For color reference, see page 263.
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