Microfluidics - Introduction to BioMEMS - page 205

AND THE WINNER IS …
In all fairness, when asking whether a given device gives “the best performance,”
we should irst agree on a set of benchmark tests that allow us to compare it to its contem-
porary devices. he problem is that this set of benchmark tests, for homogenizers, keeps
on changing in the BioMEMS ield. It seems reasonable to assume that the best homog-
enizer should be the one that homogenizes solutions in the shortest amount of length;
unfortunately, not all reports provide suicient data to compare devices because the com-
parison is dependent on Reynolds number. Also, there are many applications (e.g., where
cost is an issue) in which it is perfectly legitimate to sacriice length for simplicity of opera-
tion or of fabrication. But for now, with scattered data, and with good sportsmanship,
we can probably state that the brainchild of Tony Jun Huang, the “bubble micromixer”
( Figure 3.104 )—which achieves mixing practically instantly with minimal hardware, and
can even be turned on and of—probably deserves the title of he Micromixer Champion .
3.11 Summary
Microluidics is an enabling technology that allows for controlling luids on the micrometer
scale and in volumes down to the picoliter scale or lower. he laminar regime that governs the
low at these scales is a challenge for applications that require homogenization of an input mix-
ture, but it is possible to accelerate mixing by breaking the pattern of parallel laminar low—be
it by inducing helical low, by shearing the main low transversally (using a secondary pump), or
by using micropumps, among other strategies. On the other hand, laminar low can be advanta-
geous for mixing applications whose goal is to create a gradient and for keeping droplets (and
cells) on a steady stream. An important feature of microluidics is that for practically the same
price of fabricating the microchannel, one can also integrate low-control elements such as
microvalves, micropumps, microluidic resistors, and multiplexers, thus making its operation
amenable to automation . his feature has enormous implications for the efect of microluid-
ics in health care and diagnostics because the end user (who pays for devices) demands user-
friendly devices. Automation is also vital in cell biology and molecular biology research because
it enables large-scale (hands-free, unassisted) experimentation.
Further Reading
Atencia, J., and Beebe, D.J. “Controlled microluidic interfaces,” Nature 437 , 648-655 (2005).
Brody, J., Yager, P., Goldstein, R., and Austin, R. “Biotechnology at low Reynolds numbers,” Biophysical
Journal 71 , 3430-3441 (1996).
Dufy, D.C., McDonald, J.C., Schueller, O.J.A., and Whitesides, G.M. “Rapid prototyping of microluidic
systems in poly(dimethylsiloxane),” Analytical Chemistry 70 , 4974-4984 (1998).
Nguyen, N.-T., and Wereley, S.T. “ Fundamentals and Applications of Microluidics ,” Artech House (2002).
Purcell, E.M. “Life at low Reynolds number,” American Journal of Physics 45 , 3-11 (1977).
Santiago, J. G., Wereley, S., Meinhart, C.D., Beebe, D.J., and Adrian, R.J. “A particle image velocimetry system
for microluidics,” Experiments in Fluids 25 , 316-319 (1998).
Stewart, R.J., Ransom, T.C., and Hlady, V. “Natural underwater adhesives,” Polymer Physics 49 , 757-771
(2011).
Stone, H.A., Stroock, A.D., and Ajdari, A. “Engineering lows in small devices: microluidics toward a Lab-
on-a-chip,” Annual Review of Fluid Mechanics 36 , 381-411 (2004).
Teh, S.-Y., Lin, R., Hung, L.-H., and Lee, A.P. “Droplet microluidics,” Lab on a Chip 8 , 198-220 (2008).
White, F.M. Fluid Mechanics , McGraw-Hill (1979).