108 M. C. W. Chen and K. C. Cheung
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
For color reference, see page 264.
λ
c
< 2λ
K
,whereλ
c
is the interchannel distance. By adjusting the flow rate through
the microchannels, they can ensure high Peclet number (Pe = u
c
h
c
/D
s,c
>> L/h
c
,
where D
s,c
is the diffusivity of a solute in the solution in the microchannels), to
avoid depletion of solutes along the length of the microfluidic channels, and high
Biot number (Bi = k
c
λ
K
/D
s,g
for reactive solutes and Bi = k
c
H/D
s,g
for non-
reactive solutes), to avoid having higher convective mass transfer than diffusive
mass transfer in the gel. Here, λ
K
is the Krogh length, λ
c
is the interchannel
distance, w
c
and h
c
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.
Using primary bovine chondrocytes embedded in calcium alginate structures,
they have demonstrated the ability to control the spatial and temporal distribution
of solutes within the alginate bulk.
5.5 APPLICATIONS
Currently, the majority of characterization techniques give information averaged
over large cell populations. Although a large population of cells may be required to
ensure statistically relevant data, the ability to measure each cell individually with
high throughput analysis would provide both information over the cell population
as well as the distribution or variability. For example, while flow cytometry does
analyze each cell individually, the resulting data still reflects the aggregation of
the cell population. Another example of single cell analysis is high-throughput
screening using patch clamp. Highly integrated systems, which incorporate cell
culture and characterization onto a single platform, will permit characterization
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