Biomedical Engineering Reference
In-Depth Information
especially difficult to mix as they have a tendency to remain in the laminar flow
regime. In this regime, flow-vector lines do not intersect, and mixing remains slow.
Several methods have been demonstrated to overcome this challenge for droplets in
the millimeter-size range. Such droplets were rapidly actuated between neighboring
pixels using electrowetting, inducing internal flow fields [ 37 ]. Dielectrophoresis-
induced flows can also be used. Another approach uses magneto-mechanical mixing
[ 47 ]. Superparamagnetic beads were inserted into unilamellar vesicles, and an
external magnetic field was applied, aligning the beads into chains. As the magnetic
field rotated, the vesicle contents were mixed by the spinning chains. The vesicles
were 10-20m in diameter - the same size-scale as droplets and cells used in hybrid
IC/microfluidic chips.
This chapter describes the development of a versatile platform for point-of-care
diagnostics using integrated circuit (IC) technology. This work is an important
step toward developing automated, portable, and inexpensive devices to perform
complex chemical and biological tasks. Such a device would revolutionize the
way that biological and chemical information is collected for medical diagnostics,
allowing doctors to make near real-time prognoses.
The hybrid IC/microfluidic chips developed thus far control living cells and
small volumes of fluid. Table 2.1 summarized the basic lab-on-a-chip functions
that the hybrid chips can perform. The chips can be programmed to transport,
deform, porate, and merge droplets and cells; they can control temperature, sense
temperature, sense capacitance, and sense color and fluorescence, and they can make
and mix droplets. These basic functions can be strung together to perform complex
chemical and biological tasks. The fast electronics and complex circuitry of ICs
enable thousands of living cells and droplets to be simultaneously controlled, allow-
ing many well-controlled biological and chemical operations to be performed in
parallel. With ICs becoming more powerful each year and microfluidics beginning
to enter the commercial arena, IC/microfluidic chips are poised to play an important
role in clinical diagnostics.
1. T.M. Squires, S.R. Quake, Microfluidics: Fluid physics at the nanoliter scale, Rev. Mod. Phys.
vol. 77 , pp. 977-1026, (2005)
2. D.J. Beebe, G.A. Mensing and G.M. Walker, Physics and applications of microfluidics in
biology, Annu. Rev. of Biomedical Eng. 4 , 261-286, (2002)
3. C. Hansen and S.R. Quake, Microfluidics in structural biology: smaller, faster . . . better,
Current Opinions in Structural Biol. 13 (5), 538-544 (2003)
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