Microfluidics and Laminar Flow

In this lab, students will make a simple microfluidic device. They will use this device to investigate the behavior of fluids at this small scale and discover that fluids exhibit laminar flow instead of the more familiar turbulent flow. They will learn what factors causes this different flow behavior and how mcrofluidics in holds great promise for transforming medicine.

If you have any questions about this lab, please contact Joe Muskin at (217) 265-6481 or by email at jmuskin@uiuc.edu.

Purpose:

Chemistry done in test tubes or microtubes use relatively large amounts of liquid in an open environment. If the chemicals are expensive or hard to make, smaller volumes are often desired. Microfluidics allows small scale chemistry so these substances can be created and tested more readily. However, fluids can behave differently in small volumes compared to our experiences with the same fluids in large volumes. If a liquid dyed red and blue are poured side by side, we might expect that it would mix and a purple liquid immerges from the bottom. This activity allows you to test how these fluids behave at the small scale.

Materials:

  • PDMS
  • Disposable cup
  • Petri dish
  • Puffy Paint
  • Pre-drilled 2 x 3 inch Plexiglas plates
  • Large binder clips
  • Pie tin
  • Food coloring
  • Isopropyl (rubbing) alcohol
  • Plastic knife
  • Writing utensil
Various laboratory equipment for use within the lab.

Click on the image above to open a full sized version.

Experimental Procedure

  1. Make microchannel master.
    1. Trace around a Petri dish on a piece of paper and mark the inlets and outlet using the Plexiglas as a guide.
    2. Draw the pattern to test.
    1. Trace pattern with Puffy Paint and allow to dry overnight.
  2. Make microchannels
    1. Add 15 – 25 grams of PDMS elastomer base to a drinking cup (for 1 Petri dish)
    2. Add 1/10 mass (1.5 – 2.5grams) of curing agent crosslinker to the cup and stir with plastic knife.
    1. Carefully pour the PDMS mixture into the Petri dish and gently tap and blow to remove air.
    1. Place the Petri dish into an oven at 65ΒΊ C to cure the PDMS in about 30 minutes. PDMS can also be cured at room temperature for 2 – 3 days.
  3. Assemble Microchannel Device
    1. Remove PDMS from Petri dish when it has cured (firm to the touch).
    2. Add a backing plate of Plexiglas to the bottom (flat side) of the microchannel device.
    3. Add an inlet plate of Plexiglas to the top (channel side) of the microchannel device.
    4. Add binder clips to hold the Plexiglas plates in place.
  4. Determine Device Flow Results
    1. Fill pipettes with fluid.
    2. Carefully add liquids to microfluidic device being sure to add liquid to both channels at about the same rate.

Downloadable Materials:

  • Activity Guide

    Instructors guide containing all relevant information to conduct the lab.

    PDMS versions - requires longer curing time and is more expensive, but closely resembles modern techniques to create lab-on-a-chip devices:

    Spray version - much quicker, easier, and less expensive method to demonstrate laminar flow and basic lab-on-a-chip ideas:

  • Presentation

    Presentation for teacher to introduce the activity to students.

Safety:

As with all labs, it is a good idea to use eye protection. However, the supplies used in this lab are very safe, consisting of only water to ethanol colored with food coloring, and PDMS, a polymer that has been tested and found to be safe.

Acknowledgements:

Thanks to Josh Tice, Sarah Perry and Dr. Paul Kenis for all their expertise and assistance.

Developers:

Joe Muskin, Bridget Mueller-Brennan, and Mathew Ragusa