Teaching Materials - Introduction to BioMEMS - page 424

he laser beam was focused through a 100× oil objective with a numerical aperture of 1.3 and
an 80% transmittance. Calculate the peak intensity at the focal point of the laser corresponding
to an average laser power of 30 mW. Assume a Gaussian laser beam proile, difraction-limited
optics, and a constant power during laser pulses.
Hint: Use the following equation to calculate the peak intensity, I 0 .

2

I = 2 P / ω π

0 0 0

Here P 0 is the peak power and ω 0 is the beam waist. he average laser power can be used to
calculate P 0 .

A.3 Suggested Exercises for Chapter 3
Exercise A.3.1. Describe ive properties of PDMS that have been important in its success in
microluidics.
Exercise A.3.2. Sketch three diferent designs of microluidic gradient generators.
Exercise A.3.3. Describe three diferent PDMS-to-PDMS or PDMS-to-glass bonding tech-
niques. Specify their chemistry principles as accurately as possible. State their advantages and
disadvantages.
Exercise A.3.4. Briely describe two diferent ways of fabricating microchannels in (a) silicon,
(b) glass, (c) PDMS, (d) PMMA, and (e) paper.
Exercise A.3.5. Describe two diferent platforms for creating and shuttling droplets within
microluidic channels. Explain their advantages and disadvantages.
Exercise A.3.6. Describe three PDMS microvalve designs and point to their comparative
strengths and limitations.
Exercise A.3.7. Compare three micropump designs of your choice.
Exercise A.3.8. Describe three low-based and three nonlow microluidic gradient genera-
tors and compare their advantages and shortcomings with respect to each other.
Exercise A.3.9. he Good-Girifalco-Fowkes equation describes the relationship between θ,
the contact angle, and γ sv and γ lv , the surface free energy values of the solid-vapor and liquid-
vapor interfaces, respectively:

cos θ = −1 + 2(γ sv /γ lv ) 0.5

Find γ lv given that θ = 70 degrees and γ sv = 22.1 ergs/cm 2 for methylene iodide on PDMS.
Exercise A.3.10. Consider a closed microluidic cell-culture chamber of dimensions 31 mm ×
1 mm × 120 μm ( l × w × h ). Neutrophils are attached to the loor of this chamber, and cell-
culture medium is lowed through the chamber at 0.20 mL/min. he density and viscosity values
of the cell-culture medium can be assumed to be the same as water.
(a) Calculate the Reynolds number and comment on the low conditions inside the
chamber.
(b) Calculate the maximum linear velocity ( v x ) experienced by the cells. For convenience,
assume that the velocity changes only as a function of the chamber height. Also,
assume that the cells are of a uniform height. Justify the selected height of cells and
any additional assumptions made.

Hint: Use equations describing pressure-driven low through a narrow rectangular
channel.