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uFluid chip experiment

by merlinjim, published

uFluid chip experiment by merlinjim Mar 10, 2011

Description

This is for a prototype microFluidic digital mixer.

For details about how these devices operate:

http://en.wikipedia.org/wiki/Digital_microfluidics http://microfluidics.ee.duke.edu/ http://www.liquid-logic.com/technology.html

No clue if this is going to work yet. ABS is hydrophillic, this might change the implementation or require a catalyst to convert to hydrophobic. The included .scad let's you specify different PCB and dielectric thicknesses.

Ideas for bottom electrode: PCB Unicorn-drawn on holder with conductive pen

Ideas for dielectric:

Acrylic sheet PCB printed dielectric (thickness will be an issue here)

Ideas for top electrode: Al foil Sn foil un-etched PCB Unicorn-drawn on spacer with conductive pen

Recent Comments

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This version of the things has a couple minor issues - I had to drill out some holes, cut some new slots, they didn't bolt together so hot (holder section not deep enough) plus the nuts on the bolts were making contact with some of the pins.

I've redesigned it to be a bit wider. I finished printing all the pieces out yesterday; I'll likely etch, assemble, and test later. I'll be updating this object with the new pieces when done.

For materials, I'm leaning more towards kapton now. I just don't think the pcb I got is thin enough to
form a good capacitor. If I had the wide roll of kapton makergear sells I'd be almost done, I'm still debating how to put the tape on so the effect of gaps is minimized.

Maybe in v.3 I'll put the ports and electrodes in a line lol
good notes!

I've been planning on using RAINX!!! Who knows if it'll work... I've got two chips printed and etched so far and plan on doing another 1-2 tonight, so I've got some room for experimentation. Of course, it could also be totally unnecessary, the device could in theory be working right now and I ju
st need to try it out lol!

Anyone have any thoughts on whether EWOD happens on Kapton (polyimide) surfaces? How thick of a dielectric layer is necessary here? I'm using .14" PCB but I wonder if I should switch over to using the top surface with a kapton dielectric... or even go for a more exotic
setup...
Also if you found that interesting there are several more you may like here:

chem.utoronto.ca/staff/WHEELER/html/Publications.htm

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Instructions

Use .scad to customize to the materials you're using and their thicknesses.

Print a holder and spacer. The spacer and electrodes are 2-symmetric, meaning you can rotate them 180 degrees but not 90 degrees and end up with the same mechanical construction. The boards are slightly taller than they are wide to assist in assembly.

Create bottom and top electrodes using your method of choice. UFDMixer.gcode should work for a unicorn based etch-resist pen. uFluidChip-Laser.gcode should work for a Laser-Unicorn resist etch.

Assemble.

Connect to arduino and program (open source driver coming soon!)

This version of the things has a couple minor issues - I had to drill out some holes, cut some new slots, they didn't bolt together so hot (holder section not deep enough) plus the nuts on the bolts were making contact with some of the pins.

I've redesigned it to be a bit wider. I finished printing all the pieces out yesterday; I'll likely etch, assemble, and test later. I'll be updating this object with the new pieces when done.

For materials, I'm leaning more towards kapton now. I just don't think the pcb I got is thin enough to
form a good capacitor. If I had the wide roll of kapton makergear sells I'd be almost done, I'm still debating how to put the tape on so the effect of gaps is minimized.

Maybe in v.3 I'll put the ports and electrodes in a line lol
For another way to make this you might be interested in this paper:

chem.utoronto.ca/staff/WHEELER/Papers/OnDemand.pdf

That work was done on a standard colour printer.

Once we get this sort of thing working routinely it would be useful to have an integrated design / operation software platform. E.g. draw the desired electrode locations, have the softw
are work out the leads to a set of standardized pads around the periphery, and print the board. Then plug in to standardized test bed, and using the same software (since it knows which leads / pads go to which electrode), it allows you to click on an electrode to turn it on or off. After that the co
mmunity takes over and you get macros, per-droplet parallel agent-based navigation ("you - go here by cycle 15" etc). I think a lot of the problems in this area need large numbers of interested amateurs more than they need perfect expertise - clearly not true of all the issues, but there's a lot to
be said for just trying a bunch of stuff and seeing who gets inspired.

Just watch the voltages... :-D
Thanks for the link! I never saw it before, but heard of work like it in the past. I made the electrode on my makerbot this weekend, so I know my makerbot could duplicate that work!

I would like to point out that link is for continuous flow microfluidics, which is a different area of research than digital microfluidics - but I was going to look into continuous flow next, so useful link nonetheless...
Also if you found that interesting there are several more you may like here:

chem.utoronto.ca/staff/WHEELER/html/Publications.htm
The original application for that approach was intended to be "open" DMF (no upper electrode) but droplet transition between pads was a bit tricky - figuring out the ideal geometry (interdigitated etc) for that is an example of where I see the "army of talented amateurs" coming in.

RE the hydrophobic / hydrophilic thing, typically spin-coating of e.g. Sylgard-184 from Dow is used to make that layer, you could whip up a Dremel-fuge-ish spinner fairly quickly. Not sure if bathtub sealant silicone would work, probably have to thin it a bit. I have also wondered if spray-on sili
cone lubricant might do the trick...
good notes!

I've been planning on using RAINX!!! Who knows if it'll work... I've got two chips printed and etched so far and plan on doing another 1-2 tonight, so I've got some room for experimentation. Of course, it could also be totally unnecessary, the device could in theory be working right now and I ju
st need to try it out lol!

Anyone have any thoughts on whether EWOD happens on Kapton (polyimide) surfaces? How thick of a dielectric layer is necessary here? I'm using .14" PCB but I wonder if I should switch over to using the top surface with a kapton dielectric... or even go for a more exotic
setup...
Fascinating. I'm going to keep watching this space for more developments.
mifga - in reply to mifga
Speaking of which -- I know people have taken those Pigma Micron pens and modified them for conductive inks. It would be great to have details about how to do that up in Thingiverse and elsewhere so the various teams working with the unicorn to print electronics can build on each other's experiences.
I don't know about that - my conductive pen was a rat shack purchase.

radioshack.com/product/index.jsp?productId=3964901

P.S. Reading the comments at that page, maybe scotch tape is my dielectric of choice now!
This is very cool.

I think Mifga might have been referring to the Pigma Micron pen modified with silver ink-jet ink to print a similar capacitive surface:

thingiverse.com/thing:5141

The MG Chemical pen is more like a small toothpaste tube. The "ink" is metal flake suspended in relatively thick acrylic and solvent. You could screen print it maybe. I couldn't get it to do much as a pen.

Maybe isolation routing could do it without using chemicals.

It would be totally awesome i
f you got any part of this to work.
Thanks for the kind words mrkim!

I went and got some more materials at lunch, assuming the rain stops as advertised I'll be trying this out tonight...

I also picked up some RainX - I'm hoping it'll convert the ABS from hydrophillic to hydrophobic properly.

I'll post the successes AND failures here when I get it etched.
All my tests at laser-etching a resist failed.

So did my tests at using a unicorn. At first.

Then I figured it out. The key is to use inkscape and inset the design 0.5 pixel or so at a time. I'll upload the fixed path when I get a moment tonight.
This is mind-blowing, never heard of digital microfluids before. Found this gem though:

youtube.com/watch?v=k9YE4jf-wzo

Could you briefly elaborate what you think is possible with digital microfluids in 3D printing? Are we talking about manufacturing our own filaments? Our are we talking about an alternative form of electronics?

Thanks
I think basic mixing, incubating, and pumping operations should be possible with this device. This is a generic "Lab on a Chip" design that would allow the automated handling of protocols, limited only by the number of ports in the device, since one port is taken up for each input/output fluid. With a bigger microcontroller or a serial shift register, you could easily get into the hundreds of electrodes.

I also think we can create traditional microfluidic devices like electroosmotic pumps, t-filters, h-filters, biological and dna assays, and so on. The trick there will be laser etching the microfluidic channels as well as the electrodes to drive them.
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