Wildcard Week: Lo-Fi Microfluidics
- Design and produce something with a digital process not covered in another assignment, documenting the requirements that your assignment meets, and including everything necessary to reproduce it. Possibilities include but are not limited to wildcard week examples.
This week gave me a choice paralysis. I didn’t know what I wanted to do and I have many interests.... but so little time. I thought maybe I should use this week as a chance to create something that is more on the biological end. Food Printer, Soft Robotics, or Fluidics - those were the top three choices I considered. Montse happened to be in town; so I had her taught me how to make a lo-fi microfluidics.
Materials
There are so many ways you can approach this. There is one open-source resource that will tell you the different methods you can try to fabricate microfluidics. Montse taught me how to make her lo-fi microfluidic in a manual way. Ideally the materials that you will need would be:
- Mylar or Clear Stencil Paper
- Double Tape with wide surface area
- Food Dye
These material are optional but depending on your design you may need it
- Syringe
- Silicon tubes
- Glue gun
- Thin Hypodermic Needle
The great thing about mylar or clear stencil paper is that they are safe to be used in the Laser Cutter. Unfortunately I couldn’t find such material and we ended up getting a clear plastic transparent sheet. The clear plastic transparent sheet looks like PVC and I know PVC is not recommended to be cut with Laser Cutter because of health risk as the fumes produced when cutting with laser is toxic. So the only way to work around this is to use a Vinyl Cutter.
What Elaine ended up using
- PVC Sheet (DO NOT USE THIS MATERIAL IN THE LASER CUTTER)
- Vinyl Transparent Sticker
- 4.8mm Wide Double Tape
- Food Dye
Paper Tape Microluidic Design Logic
Basically what to understand about Paper Tape Fluidic Design is that it needs at least 3 layers
-
Top Layer with Inlet & Outlet Holes.
Inlet channel: This is the designated entry point for the liquid samples into the microfluidics.
Outlet Channel: This is the designated exit point for the processed liquid or waste product to leave the device.
-
Adhesive layer cut in the form of channels
- Clear mylar sheet that covers the adhesive and the inlet/outlet hole.
Why do we need a hole for the outlet channel? If we don’t create a tiny hole - the inlet wouldn’t be able to pass through the outlet channel properly because there is no release of air pressure. We need to score a tiny hole in the outlet channel to let the droplet of liquid sample move.
Manual Fabrication
Montse demonstrated quickly to me how to make the paper-tape microfluidics using the manual method.
- Firstly stick a double tape on top of the PVC Sheet (ideally Mylar).
- Draw inlet, channel track, and outlet.
- Cut the the parts and get rid off it from the tape (massive hassle to keep the tracks clean because the tape is very sticky - however a mounting tape is easier for this operation)
- Stick the upper PVC sheet layer (ideally Mylar)
- Create a hole on the inlet channel big enough so you can put your fluids in
- Poke a hole in the outlet channel to allow air pressure to pass - so the fluid can travel from inlet channel to outlet channel.
Digital Fabrication
Design
Firstly I designed the file in Fusion and export it as .dxf
I opened the file in Illustrator to make several edits
And using the same protocol from the Vinyl Cutting exercise in Week 3, I exported the file in png so that it can be processed in our vinyl cutter’s proprietary software.
Preparing
I had two types of clear PVC sheet. The difference is just the thickness. However we still have to prepare the material the same way. Cover the sheet with double tape all over, with no gaps because you want to make sure that the liquid will only flow inside the channel that we have designed. Ideally we want one big double tape. Unfortunately the widest I had was at 4.8mm. To leave no gaps, I layered the tape on top of each other, however this proved to be a problem later.
Cut
Setting
Make sure that we run a test cut to configure your ideal cutting setting. I followed the same protocol with Week 3. Both of the PVC Sheets are way thicker than the vinyl paper. I went with the second strongest and second slowest setting at 250 gsm, 2m/s. With that speed, it is enough to cut the double tape and the vinyl clear sticker but not both type of PVC Sheets.
Making Channels
This part was a chore. Remember how I mentioned that ideally it’s better to use a big double tape as an adhesive? The problem is if we layered the double tapes on one another - there is a chance for us to not get a clean cut when we’re removing the tapes from the cut tracks.
Inlet Outlet Layer
This part is the trickiest and could definitely make the whole process we did a failure if you make a fatal mistake. We want to make sure that the top layer is in the right position because the specific holes will allow the droplet liquid to flow through the channel. The only way is to cut in a seperate space and hope that as we try to stick it onto the adhesive layer it will be in the right position.
I tried to put the top layer on top the adhesive layer that has formed the shape of the channel. However, there is a risk that the machine will cut the vinyl in a wrong position. Case and point.
At the time of writing this… I realised that maybe I should have done the order of the layer in reverse… instead of bottom to top, top to bottom is better - Which is to cut through the inlet outlet layer first, then the adhesive layer.... then all I had to do is stick onto the clear sheet.
Assembly
Make sure that as we stick all the layers together - leave no gaps or air inside when sticking. Sandwich it between two hardcovers!
Test
Put a droplet onto the inlet channels and let the fluid flow through till it reached the outlet. My results are not perfect - but hey at least the fluids went through some of the channels.
Key Takeaways
I asked Montse what went wrong and she told me that:
- My design was too complicated for the medium. This design would worked better on cellulose/paper based microfluidics
- For this material it requires less amount of inlets and longer channel tracks
I also think that I may have put too much fluid. Ideally we would want to have a control which is the volume of the fluid in microLitres - unfortunately I didn’t have a micropipette that day to test it out. Another control to be considered is the composition of the food colouring. Because I was using different colours - maybe the chemical composition of each food colouring were different and hence why some food colours were able to travel better into the tracks. The food colouring I was using is an oil-based food colouring - this could be also be a factor to the failure… possibly.
Overall I still want to explore more ways to fabricate microfluidics with the tools we have in the lab.
