Tag Archives: microfluidics

Droplet microfluidics with acrylic part 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.

2017-03-27 06_35_38-Presentation1 - PowerPoint

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.

Modular designs, microfluidics, fab lab and rep-rap

I saw today that in the journal “Lab on A Chip,” Rhee and Burns published a new design for modular microfluidics. Microfluidics has been my life for the last 5 years. I think I’ve mentioned it at some point. It’s been an interesting way to go about science and I’m glad to have been doing it. I can see how lots of projects would be easier if people knew how to use these techniques.

It’s a lot like programming, actually. If you have a problem in the digital world, and you solve it with a clever program, then you’re good to go. It’s easy to repeat it, and you can share the design easily, and the next person who uses it doesn’t have to learn the same level of skill. That’s key: once a programmer gets something to work, it’s a program. The next person just has to run it.

I don’t know if the magic of that is clear to people. Imagine if you were a blacksmith. You train for ten years, build your shoulders, learn the dark luminous secrets of molten iron. Then you can make amazing things like the gate to the winter palace in St. Petersburg. Now let’s say you want to be able to share that ability. You can’t just post it on the ‘net. You can share some ideas, maybe a 10 year curriculum that would help develop the skills… but the skills are not transferrable.

These days, if you have an idea and you write it into code, and you post it on the net, anyone can do what you did. With a click. No practice is required. But what about other, more physical things? In the next while, if Gershenfeld is to be believed, we are going to see material things produced by open source software. The RepRap project is gaining some momentum already. But in the microfluidics arena, a certain kind of open source physical goods is already there.

People publish designs and those designs can be reproduced by people who have only limited training in things like fluid mechanics, lithography, and cell culture. Once produced, they open whole avenues toward the data that was once only obtainable by people with years of skill and training. And it will only get better.

How does modular microfluidics fit into this? That’s another step toward anyone being able to build these devices. A number of user facilities will generate the master for replication molding. Once generated, that master can be used to produce hundreds of the modules that the paper describes. Once produced, these modules are like toy bricks: they can be used to produce anything, from automated, computer controlled chromatographs to microeractors.

I suspect that in 10-20 years, the complex synthesis for all kinds of substances will be reduced to a set of a few of these blocks (or something like them). I can imagine that, in principle, anybody could take a simple instruction set, have their RepRap print it, hook it up to their computer and have it produce LSD from a few household chemicals.

How will that play out, legally and socially?

-Peter

destroying glass, slow progress, testing to destruction

Todays activities were… marginally productive. I saw more-or-less what I need to see in the model system. Even better, I saw it at slightly less intense conditions than I had originally suspected would be necessary. Then, when I went to repeat the experiment and get the data that will make or break my thesis, my chip died. Of course.

So I did what anyone would do. I troubleshot it to destruction. It turns out that my chips literally explode at about 10-15 kilovolts. I figure that’s good information to have. Here’s an image of the glass surface that blew up. It was a small explosion, but satisfying. Now I need it to work again without blowing up.

That means it’s back to fabrication hell. More hydrofluoric acid will be used. I’m not going to lie: I hate hydrofluoric acid. Not only is it corrosive, but it is also highly toxic. And, even better, it tends to have a numbing effect. So if you get it on you, it will burn and poison you and you won’t know it until it’s too late to get the antidote. Delightful.

I love science!

-Peter

spider silk proteins, microfluidics, and cool stuff that is small

A pair of German groups collaborated to produce an artificial spinarette. They made very small tubes (called Microfluidics by those in the business) into which they injected engineered spider silk proteins produced in bacteria. The obvious cool tings aside (e.g. arachnoweave armor) there are several interesting scientific oddities. The first is in the aggregation of protein eADF3. According to the article, at low concentrations it forms aggregates. But if you add shear flow (like forcing it through a small channel or a spinarette) it makes fibers instead of particles. That’s pretty strange.
Here’s something else. The protein aggregates in salt water under static conditions into tiny particles. These particles unfold and dissolve in pure water. The the fibers made of the same stuff in the same conditions stable in pure water. Something pretty drastic has changed about how those proteins are structured when they assemble under the shear conditions in the flow of that microfluidically confined stream. Indeed, spectroscopy shows a high beta-sheet content of the fibers, although I didn’t see anything about the beta-sheet content of the particles.
But these authors go one step further. A two part mixture of two silk proteins, both found in spiders (the above mentioned eADF3 and another, eADF4) produce a twisted fiber of higher strength and similarity to the natural product of a spider. If you’ve ever watched a nature show and seen a spider at work, you’ll know that they have to pull the silk tightly when they are spinning in order to make it strong; this explains why. The shear forces of the fluid moving through the spider’s little orifice are really important. Maybe that’s another step toward that arachnoweave armor. That and that d3o stuff (like a d3o Hat to protect your head) would make a product fit for Batman.

It’s not recombinant spider silk, but the D3O videos are worth looking at, if you have not already.

-Peter