Build Your Own Microfluidic Device

This project follows the Engineering Design Process. Confirm with your teacher if this is acceptable for your project, and review the steps before you begin.

Experimental Background

In this chemical engineering project, you will design and test your own microfluidic device and investigate how the channels' design and thickness impact the liquid's ability to flow through the microfluidic channels of the device. Microfluidic devices consist of multiple microscopic channels that allow fluid to go through them. Many different designs have been used to take advantage of different fluid dynamics and biochemical properties for many applications. In this project, you will test and compare two designs to a new design you create using polystyrene plastic sheets. 

Image Credit: Laura Ohl, Ph.D. / Science Buddies

Image showing 2-hole design, 3-hole design, and example design to test.

Experimental Protocol

Before you build your microfluidic device, develop a design you want to test. You can test multiple different designs, and we have provided a few examples in Figure 3 above. If you want a visual representation of these instructions, check out the video instructions at the top of this page. Polystyrene's shrinking process can be unequal, and bubbles can form in the microchannels. Therefore, to ensure reliable results, we recommend creating 6 microfluidic devices of each design to obtain 3 functional microfluidic devices to test.  

1. Cut the shrink plastic sheets into three similarly sized rectangles (minimum 5 by 7 inches).
2. Use a permanent marker to draw your design on one of the sheets; this will be the middle sheet. It should contain 2-3 holes at the top and bottom, connected by a channel that the fluid will travel through. See Figure 3 above for design examples and ideas, and Figure 4 below for how the 3 sheets should be created to align to allow fluid through them.
3. After you draw your design on the middle sheet, cut it out with a hole punch or scissors. 
4. Place the top sheet on the middle sheet and trace where the holes align. Hole punch the holes in the top sheet of shrink plastic.
5. Place the bottom sheet over the middle sheet and trace where the bottom holes align.
6. Hole punch the holes in the bottom sheet of the shrink plastic.
7. Use a permanent marker to trace the microchannels on the middle sheet and the holes on the middle, top, and bottom sheet. This will make the channels and holes easier to see and align while gluing.
8. Turn the middle sheet upside down or rough side up and trace the super glue around the channels, holes, and outer edges of the sheet, being careful not to get glue in the channels.
   1. Note: Gluing around the channels and the edges of the sheets will help ensure that the polymers crosslink and fuse together during the shrinking process.
9. Place the middle sheet glue side down onto the bottom sheet, carefully aligning the output or drainage holes.
10. Wait for the glue to dry before proceeding with the next steps.
11. Put glue on the top of the middle sheet by tracing the super glue around the channels, holes, and outer edges of the sheet, being careful not to get glue in the channels.
12. Place the top sheet onto the top of the exposed glue of the middle sheet, carefully aligning the input holes. 
13. Wait for the glue to dry before proceeding to shrink the plastic.

Image Credit: Laura Ohl, Ph.D. / Science Buddies

Image showing 2 holes in top sheet that align with 2 holes and inner channel design or middle sheet, and 2 holes at bottom of middle sheet aligning with 2 holes of bottom sheet.

Shrinking Your Microfluidic Devices

1. Preheat the oven to 330 degrees Fahrenheit with a metal baking tray inside to preheat it.
   1. Note: Preheating the baking tray will prevent uneven heating of the tray and plastic, aiding in more similar shrinking across the microfluidic device. 
2. While you wait, measure each channel's thickness and the dimensions (length, width, height) of the perimeter of your microfluidic device and record them in your data table like the one below (Table 1). 
3. Gently place the dry microfluidic device in the oven for 1-3 minutes or until the plastic polymer stops moving.
4. Record the time it took for the device to shrink in your data table (Table 1). 
5. With a hot pad, safely and carefully remove the baking tray and microfluidic device from the oven.
   1. CAUTION: Be careful! The baking tray and microfluidic device will be hot!
   2. Note: If your device is not laying flat, you can very gently press down the microfluidic device to the baking tray with a slotted spatula/turner or other flat kitchen utensil. Do not press hard! This can close the channels and prevent fluid from passing through them.
6. Carefully remove the microfluidic device from the baking tray by gently putting a slotted spatula/turner or other flat device under the device to remove it from the baking surface. 
7. Allow the device to cool before touching or observing the device fully. 
8. Measure the final dimensions of the microfluidic device after shrinking and record the measurements in your data table (Table 1). 
9. Before testing, note any imperfections in the design or during the shrinkage process in your data table (Table 1). 
10. Calculate the percent shrinkage of the microfluidic device with the equation below and record your calculation in your data table (Table 1):
    1. (( Final length - initial length ) / initial length ) * 100
    2. (( Final width - initial width ) / initial width ) * 100
    3. (( Final height - initial height ) / initial height ) * 100

Testing Your Microfluidic Device

1. Dilute 2 drops of dye into 1 cup of water to create a dye solution before using it. This will help prevent the dye from sticking to the plastic, allowing you to see it and remove it more easily for multiple trials. 
2. With a pipette, push the diluted dye through each input hole individually and watch which channel the fluid goes through and if it exits one or multiple of the output holes.
3. Measure the time it takes for the fluid to pass from the input holes through the channels and out the output holes. 
   1. Note: This test fails if the fluid does not go through the channels or exit one of the output holes. 
4. Give each channel a function score and write down your observations of how many channels are working. To give each trial a score, rate them as follows: 0 = all channels failed, 1 = some channels worked, 2 = all channels worked. 
   1. Note: Channels that work allow fluid to go through them. This can be impacted by bubbles, the thickness of the channels, or hydrodynamic forces through the channels from the micropipette. Note any of these observations in your data table below if they occur.
5. Record the number of working channels over the total number of channels for each design.
6. To ensure reliable results, test and score your microfluidic device multiple times and create a few of the same designs. We recommend creating at least 3 devices of each design and testing each device at least 3 times. Between each trial, flush out the dye with clear water and then air so each time the fluid flows through the channels, it is not impacted by previous experimental trials. 
7. Rank each design based on your results. Consider the time to go through each channel (the shorter the time, the better), the channel functional score, the number of working channels, and any dye mixing observations (backflow to input is bad, flow through channels is good, flow through to output is great). 
8. Record in your data table what worked and did not work well in the designs. Iteratively test any new designs with another round of experiments. Create a separate data table for each trial. We recommend doing 3 trials for each design.

Conclusion

• How big do the channels need to be (before shrinking) for fluid to be able to flow through them after shrinkage?
• How did the thickness and rigidity of the polystyrene change with heat? How much did your microfluidic device shrink? Which dimensions shrank and which didn't?
• Do the dyes mix in the microchannels? If so, where do they mix, and why do you think that is? Do different microfluidic device designs or devices have variations in mixing?
• Does the number of interconnected channels increase or decrease the functionality of each channel in the microfluidic device design?
• How long or short can you make a channel and still make the channels functional?
• Which designs work better than others? How many different designs can you test?