“Monodispersed microfluidic droplet generation by shear focusing microfluidic device,” is from 2006. It’s a study on the design of the flow focusing droplet generator. It explores the role of flow rate and pinched geometry on the droplets. At the time, it wasn’t completely clear what these droplets could be used for. I was looking at them as little storage containers for cells.
In 2016, digital PCR was a clear application of this technology. A PCR reaction was segregated into lots of little droplets. Each droplet either has a DNA molecule or does not. As a consequence, the PCR reaction makes it go green or not. Instead of trying to interpret different levels of green fluorescence (which is relatively hard to quantify), the scientist can just count the bright droplets (much easier to quantify). “Centrifugal micro-channel array droplet generation for highly parallel digital PCR” presents an unconventional droplet generator to make lots of little droplets for that application.
The application I’m working toward is a little different. I want to make particles based on these droplets. The little particles will have a sensor on them so that we can detect what is happening near to the particle. The particle might then respond by glowing green or by releasing a drug. Similar particles have applications in cosmetics and lubricants. I think that we can make them smarter. We can apply them to research (reporting cell environments) diagnostics and maybe therapeutics (some day).
One of the reasons I am trying to develop these techniques for acrylic microfluidics is to shorten the design-build-test feedback loop. With the PDMS techniques I worked on and grad school the loop is about a week long. It takes a day to design, a few days to get the photomask, and a day or two to fabricate. If nothing goes wrong, I use to be able to get a design tested on day five.
With acrylic based microfluidics, the loop is much shorter. I can modify a design, cut it with the laser, fabricate the chip, and have it tested all within three hours. Three hours is a significant improvement over five days.
This morning I came in and cut a new chip with some new parameters. I was hoping to see a narrower width channel which would produce smaller droplets. I didn’t get that, but I can try again (tomorrow not next week). Plus, I learned something. I need to add a viewing area to the chip to see the droplets better.
I made a little video of some of the process. I skipped the bonding step in the video because it’s just 10 minutes of waiting while the hot press does its work.
Here are parts 1 2 3 4, 5 and 6.
I’m just going to do a brief update today on the microfluidics project. We set out to make acrylic plastic microfluidic chips that could generate tiny droplets of water in oil. Eventually, I hope to use these droplets to make polymer particles. We can make polymer particles from a water in oil emulsion. We usually just shake the mixture vigorously to make the emulsion. But that makes all kinds of different sizes and causes other problems as well. So now we’re going to use a much more complicated method: microfluidics.
I have some experience with droplet based microfluidics. I worked on it in graduate school. It’s a simple idea. Flow oil and water through tiny tubes that merge into a single tube. This forces them to mix and they break up into little droplets. In practice, it can be pretty hard. One of the practical challenges is that it takes a stable flow rate to make homogeneous droplets. It can be a big challenge to get a stable flow. That’s especially true if your microfluidic chip is made of a stretchy material (I’m looking at you PDMS). It makes sense to move to a chip that doesn’t stretch at all like acrylic plastic.
I had a great undergraduate come in and work with me this weekend on creating droplets with an acrylic plastic microfluidic chip. I had this working a few months ago but with much bigger channels. My first success was with channels that were more like 1 mm wide. The droplets were close to 1 mm wide as well.
We set about to optimize a fabrication technique that would make smaller channels and then uses channels to make droplets. After much difficulty, we have succeeded. We are now making channels that are approximately 100 µm wide and making droplets that are approximately 50 µm wide.
If you have an application that requires non-stretching microfluidic channels, please get in touch. We can send you one.
Here are parts 1 2 3 4, and 5.
I believe in public funding for science and especially revolutionary, high-risk/high-reward projects. Most of those projects will fail. That scares the funding agencies. It looks like a lot of wasted money. But I think that’s the price for innovation.
We need to fill the beginning of the pipeline with lots of good ideas. When something works, there will be plenty of motivation to move it down the pipe. There are big rewards at the end of the pipe. I think that’s great. I just want there to be more support at the beginning.
For projects that do have support (and not necessarily government support), I also see the little human weaknesses as a real problem holding back important projects. The two projects that come to mind are Open Source Ecology and Paul Wheaton’s Permaculture community.
This article (brilliantly titled The Post-Apocalypse Survival Machine Nerd Farm) reminded me of what it was like to live with roommates. Not everyone is equally motivated. Not everyone wants to volunteer their hours getting up early to build a DIY tractor. And not everyone knows that about themselves. It sounds amazing: sustainable agriculture, technical puzzles, building great things, sharing new technology with the world… Utopia! But the reality is pooping in a bucket and getting up at 6AM to troubleshoot a burst hydraulic line.
The Permies community ran into a similar issue. The Wheaton Labs Farm invited a bunch of people to come out and live and plant and experiment with sustainable agriculture. But people didn’t want to do dishes or do the hand towel laundry. A lot of the unsustainable parts of our culture are a direct result of our coping with these little irresponsible things. Why use paper plates and paper towels? Because nobody wants to take care of the dishes and laundry.
The bottom line is that there are natural resources and technology… but getting people to cooperate and do the unpleasant work is the hard part. That’s no surprise, I suppose. It’s just funny that the difference between utopia and dystopia… at the micro level… is doing the dishes.
I get the impression that there are not all that many people interested in Utopia (as a concept). Maybe we’re a bit more skeptical than folks were in the 1800s. Or maybe charismatic leaders just don’t gain so much traction in an era with electronic criminal records and background checks.
The good parts of living with room mates were really good. A built in social network and a always-on source of good conversation and affirmation? Yeah. Doing other peoples’ dishes… not so much.
I follow three projects with utopian visions:
Open Source Ecology
Paul Wheaton’s Permaculture community
I love that these folks are putting their experiences out there. It’s exciting to see folks trying to build something grand. It’s even interesting to watch the setbacks. I don’t know how much popular interest there is in this kind of thing.