Interdisciplinary Applied Mathematics

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Another application area is microdevices that involve particulate flows for sorting, analysis, and removal of particles or cells from a sample, with both liquid and gas microflows (Ho, 2001; Green and Morgan, 1998; Telleman et al., 1998; Wolff et al., 1998; Yager et al., 1998). Examples of two different devices for    cell    sorting are    shown    in    Figure    1.5    (Telleman    et    al., 1998).

The device    on    the    left    is based    on    microfluorescent    activated    cell    sorting

(p,FACS), while the device on the right is based on micromagnetic activated cell sorting    (p,MACS).    In    the    former,    the    targeted    cells    are labeled    with

fluorescent antibodies, and as they pass through an optical sensor a valve is activated, letting the desired cells collected at one outlet. However, there is

Collected Waste

FIGURE 1.5. Diagrams of particle separators in microflows based on microfluorescent activated cell sorting (pFACS; left) and micromagnetic activated cell sorting (pMACS; right). (Courtesy of S. Lomholt.)

always a residual amount of undesired cells, and thus the process should be repeated using multiple pFACS devices. In the second device, the targeted cells are labeled with paramagnetic antibodies, and only the desired cells reach the collection outlet. The typical size of the channels is 100 pm, and the cells are about 5 to 10 pm (Lomholt, 2000). The carrying fluid and the buffers are neutral liquids for living cells. Similar devices exist for removing particles from gases, e.g., an airstream for environmental applications. In a device presented in (Yager et al., 1998), multisized particles of up to 10 pm were removed at various stages. Such particulate microflows require special numerical modeling to deal efficiently with the multiple moving surfaces, i.e., cells or particles present in the domain (see Section 14.3.2).

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