Biomaterials for MEMS

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

SO13997_text.indd 116SO13997_text.indd 116 26/01/2011 3:50 PM26/01/2011 3:50 PM