Wax Paper Microfluidics

Microfluidics and lab on a chip technology have been an emerging field in the biomedical field since the 80's and continues to show promising applications in just about every industry you can think of.

In the following instructable, I will show the procedure I have found most efficient in creating paper microfluidic devices based on Whiteside original paper on the subject:

http://gmwgroup.harvard.edu/pubs/pdf/1060.pdf

Instead of using fancy science lab equipment I have reduced the procedure to use cheaper and easily obtainable items that produce more repeatable and reliable results than those discussed in the Whitesides paper.

Bellow are the materials, the specific models and products we used are in parenthesis but are not the only options.

1. Wax Based Printer(Xerox ColorQube 8570)
   
   • This is the main restriction of this procedure as wax printers while available are not as common as other printers and do tend to cost a bit.
2. Chromatography Paper(Whatman 3mm)
   • Here is a good table of some and their capabilities
3. Laminator(AmazonBasics Thermal Laminator)
4. Some sort of CAD or vector graphics software(Inkscape, Fusion360)
5. Syringe(3 ml with a blunt needle tip)
6. Parchment Paper

You can use any vector drawing or CAD software to design the channels and patterns, although using cad makes it a bit easier to get exactly one to one dimensions from screen to paper. We used both Inkscape and Fusion 360 what will work best depends on your pattern.

Here are a few guidelines that we found produced the best results:

• 0.9 mm walls with 1 mm channels tend to give pretty consistent results, I recommend starting here and adjusting based on your results (If it leaks make the walls thicker, if it doesn't seem to flow try increasing the channel width).

• In order to get full penetration through the paper with the wax we printed a solid black fill on the reverse side of the paper, this effectively halves the thickness that the wax on the pattern side has to penetrate.

• In general, the reservoir walls should be a bit thicker than the channel walls since they will need to hold a greater amount of fluid.

As with many steps in this process I recommend playing around and finding what works best for your specific setup.

Take your freshly printed microfluidic device and place it inside a folded piece of parchment paper making sure the entirety of the pattern is covered. Feed this through the laminator twice on the 3mm setting(We found this to work best for us but recommend playing with laminator settings and the number of passes to find what works best for you).

When it comes out the lines should have spread and faded in color. If you are unsure it has been baked properly cut through the pattern with an exact and look at the cross section, you should see the ink through the full thickness of the paper.

Use a pipette or syringe to test your results!

You can get creative with food coloring to make it look cooler or even additives like fluorescein.