Hands-on Microfluidic Hacking

 The goal of our first day of hacking was to find the materials that were accessible and cheap to make a microfluidic device. There are a couple of commonly used methods out there and we were playing around to see which methods worked in our hands. We focused on making the devices directly, rather than making molds to cast the devices out of PDMS...that will be next time. Stay posted.

Materials

1. Glass Slides
2. Shrinky- dinks
3. Armour etch
4. Vinyl sheets for masking
5. double-sided tape
6. tape
7. Exacto-knifes
8. gloves
9. Food Coloring
10. Lab toaster oven

To test the materials we used several common designs used in microfluidic with the goal of observing capillary flow. Descriptions of the designs from left to right. The Y-channel is good for showing off laminar flow. Water with and without dye can be dropped at each inlet. When the fluids meet they will flow adjacent to each other without mixing. In the H-membraneless filter. Here your two fluids are dropped at either inlet, and exhibit laminar flow to a point. Depending on the diffusion coefficient of the solutes in your dye water and the length of the vertical channel, filtering of the dye from one flow to the adjacent flow will occur. Lastly, the serpentine channel is supposed to overcome the properties of microfluidics to induce turbulence and mixing. Here you would drop water followed by dye then by water. If no turbulence is induced the dye droplet will not mix with the water. Mixing is expected at the sharp turns. For more information about the properties of microfluidics, check out the blog on Dimensionless numbers on this site.

So, we made some microfluidics. We first used Shrinky-dinks, which is a hobbyist polystyrene material that shrinks symmetrically and can be used a mold or a device. When the material shrunk in the toaster oven at 275 F, it was wavy and had a rough texture, so this is what happened. 

Typically, devices are smooth and hydrophobic. Channels were taped on either side to make an enclosure.
Next we tried etching glass slides and covering the channel with tape. First we masked a glass slide with the sticky vinyl material, then cut out a negative of the region to be etched. Armour Etch was allowed to act on the slide for 30 minutes, although, we think an hour would do better, and an automatic decal cutter to cut our mask would have given smaller channels. If we had had borosilicate glass or pyrex glass, our channels would have been smooth, but we did get flow. This method will be explored more since glass is easily sterilized and is inert to most materials. Here is the video.

Since we are next to a hackerspace, we have some tools that not everyone else has, like a laser cutter. So we used some extra acrylic lying around and made a suite of channels to try, also covered with tape. We will play with this tech more, but we are aiming for accessibility. Here is the video.

The most low tech method seemed to work the best, but there will be issues down the road for our final application of growing bacterial cultures, but it demonstrates the principles of microfluidics and is great to try for the viewers at home. For this last method we used double sided tape and left space between the pieces of tape for the dye to flow through. We then stuck a slide on top to seal the channels, making sure to keep the inlets and outlets open.