Hemdeep (00:10)
Welcome to Big Ideas in Microscale, the podcast where we explore groundbreaking research happening at the microscale where microinnovations makes a big impact. We're excited to showcase the incredible work being done by our users from around the world who are pushing the boundaries of microfluidics, lab on a chip, organ on a chip and beyond. Through these conversations, we hope to learn from their experiences, uncover their insight and bring their big ideas to a wider audience. So whether in a lab, On the go, we're just curious about the future of microtechnology. Join us as we dive into big ideas at Microscale.

Hemdeep (01:01)
Welcome back to Big Ideas at Microscale. I'm Hemdeep, your host and co-founder of Creative CADWorks, CADWorks 3D, and ResinWorks 3D.

Robin (01:10)
And I'm Robin, the co-host and technical writer on the marketing team. Previously in the last two episodes of Greg Norden and Adam Woolley from Brigham Young University, we dove into their fascinating journey of developing high resolution 3D printing solutions for microfluidics and explored their custom built 3D printer, which has reshaped how we think about microfluidic device fabrication.

Hemdeep (01:34)
If you missed those episodes, please be sure to go back and check them out. We'll be right here when you're ready to dive into this one. Today we hear about some exciting things, from new cutting edge ideas and techniques, and findings from surprising off-shoot experiments and research directions. You won't want to miss the exciting developments ahead.

Robin (01:53)
Let's jump right back into big ideas at microscale. do have a question though. Your 1600 valves, was that created for a specific purpose or were you really limit testing the abilities of the 3D printer?

Greg (02:08)
So it doesn't have a functional purpose in terms of an end application. This is simply a test design to allow us to evaluate the effects of turning some of these knobs we've been talking about. So for example, we have a new ⁓ uniformity correction method that we've developed. And so this design that's kind of uniformly placing these valves across the entire projected image area is something we're using to test the effectiveness of this uniformity correction. The results are, yeah, it works great. And then there are variety of other issues involved as well that this also is a good test design to evaluate what happens as we change various things and how effective it is in terms of getting a uniform result out.

Robin (03:00)
What other mecha-photic features have you sort of experimented with? suppose like droplet generators, regular channels.

Greg (03:08)
You name it, we've probably experimented with it. And a bunch of things that are probably on no one's radar. So for example, we have done things like 3D printed super hydrophobic surfaces out of hydrophilic materials. So you basically have this surface that's the native material is hydrophilic, but because of how we pattern it, it turns out to be super hydrophobic. So the contact angle for water is, know, 140 degrees or more.

We've done other things like created this little cone, little tiny thing. You can barely see it with your eye. And on the top of it, put this little ball. And then we have a channel that goes up through it. And because it's a hydrophilic material, if you wet the surrounding area, it draws liquid up through that cone. And it spills out over the ball and kind of uniformly coats the ball in a couple of microns thick of water. and then it flows down the side. And then as you get evaporative loss, it's self-replenishing. And so, you know, why would anyone want a little tiny micro fountain like that? Well, it turns out we have another group that we're collaborating with where they're looking at whispering gallery mode lasers. And so you can take that thin water film and bring this tapered fiber up close to it and couple light into that, that water. And it ends up being trapped. and going around and around in that water through total internal reflection off the surface, why would anyone want to do that? Well, they're looking at some different crazy laser ideas and materials issues and whatnot. But the point is, because we have this fabrication capability, we can make these kind of crazy shapes and they're effective and they work well. Or with the same group, another thing that we did and published on is they have these small chips, you know, maybe a square centimeter with silicon photonic devices on it, ring resonators, Machs zender interferometers, whatever. And then you want to be able to control the refractive index in the optical paths. And so we've created 3D printed microfluidic devices with integrated gaskets that you can just compression attach to these silicon photonic chips. And then just by changing the salinity of the water, you can change the refractive index that the light sees in the waveguides and do a bunch of tuning. It's almost a passive thing. It takes almost no energy to do that. And in the world where you need that sort of capability, the only other approach that's really been shown to be effective is to use heating, and that draws a lot of power. And so at any rate, just these off the wall kinds of things. So we've done tons of traditional microfluidic sorts of devices and components and integrations, but also kind of crazy way out there sorts of things as well.

Adam (06:00)
This is the part that I care a lot about because we use these things to do bioassays, detect molecules and things that are related to diseases. So, I mean, we've created a combination of pumps and valves and chambers that allows us to collect certain types of molecules and concentrate them. And that can be based on simple chemical interactions or affinity-based interactions, something like DNA base pairing. We've also designed 3D printed devices that can create chemical gradients. So the concentration of a given chemical varies as a function of position within the device. And that can be useful to study things that happen to cells, how they respond to chemical cues. We've used the pumps, valves, and a diffusive mixing chamber to do serial dilution, which is a really common process in a biochemistry lab where you want to study the effect of a compound as a function of concentration And so you have some poor student who does a bunch of pipetting to make different concentrations over several orders of magnitude range. And then you put them into some kind of a test system where you evaluate that. And with this combination of being able to create 3D printed pumps and valves and diffusive mixing, which only occurs at very small size scales, hence the need for truly microfluidic devices, we can bring in a concentrated solution and water and then flow those two together and in a controlled way, create 10 different concentrations that go over a factor of about a thousand range of concentration just by a design flow system. And we can create that and have it creating stable output outputs of the different fluids over the course of just like a minute to get it to stabilize. So, I mean, there are a lot of useful and interesting things that you can do. with the microfluidic devices and a lot of also off the wall things and probably some things we haven't yet even thought about that we still need to come up with some crazy ideas to address.

Hemdeep (08:00)
So now in terms of the material that you've been using to develop all these devices, is this just the exact same material that you've used right across all these unique platforms that you've developed?

Adam (08:12)
We have one that's sort of a go-to that is the common denominator, and this is polyethylene glycol diacrylate. And that was chosen for a number of reasons, one of them being that my lab had used that previously and done some photopolymerization using sort of conventional cleanering technologies to make devices. It's also a cross-linker, combined monomer and cross-linker because it has two reactive groups. And so that makes it useful as the polymerized material. And the fact that it has polyethylene glycol groups is also important because that particular chemical group, when it's formed into materials, it's known to resist nonspecific adsorption of things like proteins. So if you want to do bioassays, you want your device material not to have stuff stick to it. And so that particular base material, we are doing a lot of things now where we're substituting minor components, but That particular resin has really been our go-to for that. There's always exploration and trying some new add-ins, different materials. We've innovated probably more in the UV absorber space and also done some things with different photo initiators. But we do have our standard go-to one that just always works. If a student's coming in to try something, we recommend that one.

Greg (09:34)
first. We should also mention that these formulations for resins are all available in our papers. mean, anyone can pick up one of our papers and see what the components are and order them and mix them up and basically have the same materials to work with.

Robin (09:50)
I remember in a previous conversation when we first introduced the idea of doing a podcast, you mentioned some very interesting things like 3D printing in a vacuum that I'm wondering if you both can talk a little bit more about that because that concept alone sounds crazy. So like what is it that you're trying to do there and are you still pursuing this idea in the first place?

Adam (10:16)
I can maybe give some initial background and then I'll let Greg talk more in the details. I think part of the rationale is that when you 3D print things, you use a polymerization reaction. And that's initiated by the light from your projector, the optical engine that you use. And there are a lot of things that inhibit polymerization. One of them is oxygen. And so I think the initial thought experiment was, well, if we do it in a vacuum, there won't be any oxygen. And then it turns out if you do it in a vacuum, there'll be other things that happen too.

Greg (10:50)
So the vacuum thing, yeah, we're just putting together all the data to do a big paper to kind of reveal the whole thing. But the bottom line is this, when you 3D print at atmospheric pressure in a normal lab, the resin that you're photopormerizing has some dissolved gas in it, one component of which is the oxygen, which actually serves a useful function as an inhibitor. And in our paper, we'll go through all the details, why. But it turns out that dissolved gas also causes you problems because when you are polymerizing against whatever the bottom of your resin tray is, let's say a Teflon-like or FEP film, that's what we typically use, then your polymerized material is attached and adhered to that film. And then when you go to do your next layer, you need to pull it off of the film. and come up and then come back down to whatever your layer thickness is. And we often use 10 microns, although we do other things as well. But when you are pulling off, then you've got kind of this suction of you're creating space where resin needs to come in very rapidly. And so you're dramatically changing the pressure conditions locally within the resin. And it appears that what that causes is for some of that dissolved gas to come out of its dissolved state into a gas state in the form of little bubbles. And so now you've just generated these little bubbles in your resin and you've got little bubbles running around. They never do anything good. Usually they tend to be attracted to and get trapped at the exact features you're trying to create. And so now you just wiped yourself out. And so we've tried so many different things to avoid generating those little bubbles. and none of them were entirely successful or even maybe largely successful. And moreover, depending upon the time of year and atmospheric conditions, the generation of those little bubbles of berries. So there was one time of the year where it was just always, ⁓ no, our yield is just going to go way down because we're going to get more bubbles. And so kind of as a measure of desperation, because we didn't have anywhere else to go, a few years ago I said, well, let's just print and vacuum. Let's just completely degas the resin so that there is no gas to come out and cause this bubble problem. And so over a period of a couple of years, we got together some funding and we designed this monstrosity of a 3D printer with a vacuum system attached. It is a monstrosity. mean, it's just, but it's a beautiful monstrosity. And so now actually we can 3D print and vacuum. And so we have we've begun exploring kind of this space and we're far enough into it that we have a pretty good handle on what's going on and how to mitigate various issues. And in fact, the 1600 valve design was printed in vacuum. At any rate, that's kind of the overview of the story and we'll have tons of details in the paper that we hopefully send out here in the next couple of months.

Hemdeep (14:05)
I'm curious as to exactly what the scale and the scale of the bubbles are and what the scale of the features are that you're printing at that has caused you this much angst that you had to do something like this.

Greg (14:18)
Ha ha ha!

Adam (14:19)
I mean, think the problem is the bubbles are near the scale or larger than the scale of the features. And basically as they form, they tend to stick to surfaces. Our 3D printing occurs at the surface. The bubbles tend to stick to features. And so you end up with a bubble in lieu of a feature and the bubbles much larger. So you can imagine if you're trying to 1,600 valves and you have a bubble that's about the size of 10 of those and you can get a few of those and you're connecting them all together instead of. having all of them but two work, you have much less.

Greg (14:51)
Yeah, so the size of the bubbles varies widely. mean, they can be down around 20, 30 microns. When squished into a single 10 micron layer, they could be hundreds of microns. We've developed, again, not published yet, but we've developed various types of bubble traps because they like to get caught on edges and corners. We've developed bubble traps that are pretty effective at capturing bubbles if we locate those traps near features we care about. So we have some different tools that we... have developed to deal with this, and the vacuum is one of those tools. But it turns out if you take the oxygen out and the oxygen's an inhibitor, you cause yourselves all kinds of other problems. good. Yeah, spontaneous polymerization. mean, it's just... So we've solved all of that. All of that now, we can get that to work out really well. I mean, it's evidenced by the chip I was showing there.

Robin (15:32)
such as

Greg (15:46)
But maybe we should also say that 3D printing in vacuum has been one of our kind of offshoot to ⁓ 3D printer development directions. But we have another direction, which is multi-resolution, which is where we use two optical engines to print a device. And so those two optical engines are in an XY stage. So we can bring them to bear as needed within different regions of the entire 3D print. And so the lower resolution optical engine projects 15 micron pixels. And so the idea is you generate the bulk of your device at that lower resolution, which is still really high compared to what the commercial offerings are. And then we have this other optical engine that projects 0.75 micron pixels, so sub micron pixels. And then with that, you basically create super high resolution structures only where you need them. And they're fully embedded in the rest of the print. So we have then multi-resolution in X and Y because we have the two different projected pixel sizes. And then we also have multi-resolution in Z because we put two different optical absorbers in the resin and we shape the emission spectrum of the two different LEDs that we use, a 365 and a 405 nanometer LED. And we tune everything just right with those two absorbers so that the 365 nanometer light sees 10 times the absorption of the 405 nanometer light. And therefore we have multi-resolution in Z. So with the 405 nanometer light, with the 15 micron pixels, we'll print 15 micron layers. With the 0.75 micron pixels at 365 nanometers, we'll print at 1 and 1 micron layers. And with that, we have just gotten some stunning results where we can embed these super high resolution regions. One example, Adams has a student who is really moving forward on it is to embed very high surface area structures, high resolution inside of channels. And so now you can think about 3D printing a ⁓ chromatography column just directly. And that's looking very promising. And then another thing that we've done is created a little... little tiny mixer. mean, in microfluidics, mixing is always so problematic because you're at low Reynolds numbers, you have laminar flow. It's most likely diffusion unless you try to induce some the fructicity into the flow, which just generally needs long channels and different structures in the channel as well. So we have a different way of approaching that whole problem. And we have created this little tiny mixer that is maybe 500 microns long and maybe, I don't know, 300 microns wide. and maybe, I don't know, 300 or 400 microns tall. And within that super, super small volume, we can do a complete beautiful mixing of two flows, very fast and very tiny volume. And the key to that is the super high resolution 3D printing ability, because what we'll do is we'll take each of the two streams, and if you just bring them together, you just get diffusion across the interface. So what we do is we split them. into six different streams, make them really narrow, interleave them together. And so now you've got these streams that are maybe eight to 10 microns wide flowing side by side. And it just doesn't take very much time to diffuse across eight or 10 microns. And so then we route that into this very narrow channel that itself is maybe 10 microns wide. And we serpentine it a little bit, you know, in a few hundred microns. And then once you come out the other end, the fluid is just completely mixed. I mean, it's just beautiful. And so this is all done in a super tiny volume.

Hemdeep (19:30)
And it sounds like the scale of that mixer would be no more than what, maybe ⁓ a thousand microns long between the initial introduction and the serpentine and output.

Greg (19:42)
Yeah, less than that, know, maybe 600 microns, something like that.

Adam (19:46)
And with that, you can stack a whole bunch of those in an individual 3D print. And again, that's one of the powerful things about this. If you want to do this at scale, you could make dozens of them in a single 3D print.

Greg (19:57)
Yeah, so this multi-resolution I think is going to be an important innovation and again, we'd love to see it in the hands of everyone.

Robin (20:07)
What is the footprints of the 3D printer, the multi-resolution 3D printer? ⁓

Greg (20:13)
So that one, it's maybe, I don't know, three feet by three feet by maybe four or five feet tall, something like that. And this is actually our second iteration. We call this our MR1.1, multi-resolution 1.1. And the first one, the MR1, our first version of this we did in 2019, never published anything on it. And what we found is that the height of the thing, we used an aluminum strut. And the temperature excursions in our lab over the course of a day were enough to throw us out of focus. And so it just made it a bear to try to get results over any period of time. You could get one-offs, but it was just very difficult to keep it all in focus calibration. And so this MR1.1, we've replaced the aluminum strut with a welded in-var structure, so it's much more thermally stable. And then we've also put these Keyons confocal distance sensors on both of the lens barrels of the optical engine so that we can measure in real time what our actual distances are and compensate for any residual thermal drift. And that seems to work quite well.

Hemdeep (21:35)
So it sounds like the tech that you had to this new tech required another round of iterations of issues that you never would have imagined. When you mentioned the temperature control, I was like, yes, you would have a hell of a time trying to make sure that you're in focus at three quarters of micron, that you would be out of focus right away.

Adam (22:00)
These are really problems that you only run into when you really start pushing the edges and you know if again if you're making 200 micron features, it doesn't matter but if you're trying to make you know three-quarter micron pixels and getting the appropriate Z resolution for that, yeah focus matters a lot and so yeah temperature control, appropriate design of the materials for building the 3D printer all of a sudden that stuff starts to matter a lot.

Greg (22:27)
And even on our mainstream HR 3.3 series printers, of which we have two that we've built, we use Invar and strategic places on those just to reduce the thermal sensitivity of the prints.

Hemdeep (22:40)
So now that you've got these two projects, is there anything that you envision that's coming down the pipeline that you would love to share with us or at least give us a bit of a snippet so we can wait for those papers to come out?

Adam (22:57)
I don't know, great question. ⁓ Yeah, I'm trying to be careful because there's some IP associated with some of them, so I do have to be measured in what we're doing. we're doing a lot with, so taking advantage of this ability to make a combination of different sizes of 3D prints using this multi-resolution printer, and then again, the ability to create many valves that are functional. We are looking at things like improving the ability to carry out chemical separations. these are simple things like, I have a complex mixture that has, let's say it's blood or something like that, and we're looking for molecules. And in our case, we've studied molecules related to risk of a preterm birth, or we're looking at viral RNA from a mosquito-borne infection. And we've got this complex sample, and we want to just look at one molecule, one type of molecule, one class of molecule. within that. And so to do that, we need the ability to control fluid flow. We need the ability to pattern surfaces with high resolution and attach specific molecules to those surfaces. And all of that really becomes enabled with both the HR 3.33 printers, the MR1, and then the, I haven't yet figured out what we're gonna do with the vacuum one, but I'm sure once the workflow becomes, once he lets my chemistry students at. use that if ever. I'm sure we'll be putting it to good use because there's always things that you never knew you needed that 3D printer until somebody built it and you can make things. From my lab, some of the advances are going to be this automation of simple wet lab processes to improve the detection of molecules related to disease. And that uses a combination of the different 3D printers and then some other things that we do in post-processing of devices to... to make it so we can carry out those analyses.

Greg (24:55)
There's just so many things going on. mean, one thing I've wanted from the very early days, 2015, 2016, is to be able to simulate the photoclimatization process on a layer by layer basis to be able to predict what structures you're going to get as a function of how you tweak various operating parameters. And so for fun, for me, just to get away from administrative stuff, I don't like so well. The last year I ended up teaching myself the finite element method and found a paper that I really like from a group at Georgia Tech and implemented a solution of a set of four coupled partial differential equations with the finite element method to simulate layer by layer what happens in the photo polarization process. That's being very interesting. It's hamstrung a little bit by the fact that I don't have as much time as I would like to work on it. It's at the point where we're getting relatively close to where we can open source that as a tool. And so that's one thing going on. And then that gets combined with some fundamental studies we're doing about the relationship between resolution and the irradiance with which you hit the resin. And we're finding some very interesting effects there where we can get resolution enhancements and single pixel channels. And so I've got a PhD student working on that and hopefully she'll have a paper out sometime this year on that. And then we have some other, you know, just weird phenomena we've observed over the years and got some undergraduate students trying to figure that out. And then there's some really nice work out of the Memet Toners group at MIT and also followed up some with Albert Polk at University of Washington on fluidic logic, fluidic transistors. And the point there is not that... Fluidics is going to compete with electronics for doing computations. The point is rather that when you create a chip that does a particular assay, it'd be really nice to embed the operational sequencing of that chip into the chip itself so that in the end, all you have to do is take this little chip, have a completely untrained person put some sample into the chip, pipette on a couple of reagents. and then just hook it up to a vacuum source or pressure source. And then the chip itself generates a clock and then generates, goes through the entire sequence required to do a complete biomedical assay. And so that's really the point of developing fluidic logic. And so to go in that direction, then you need nonlinear fluidic structures to do the transistor-like operations that you need for the fluidic logic. And because we can print with such high resolution and do crazy things, I've got a number of students who are working on different paths towards realizing these fluidic logic types of ideas with three printed structures. So maybe that'll fail, but we'll see what happens. So far, it's looking pretty interesting.

Hemdeep (27:59)
It sounds a lot like the Eliza chip that's quite a bit larger than the chip that you're probably trying to develop, it seems to sort of fit that logic set, I guess.

Greg (28:11)
Yeah, right. Yeah, out of David Junker's group there, Miguel. Yeah, sure. And he's using the burst valve approach, which is a really nice way to go about things and I think has just tremendous potential. But yeah, so this is another avenue towards something kind of akin to that where the entire operation of the chip is embedded in the chip structure itself.

Hemdeep (28:34)
Well, we have come to an end of our conversation and it was extremely enlightening as always. I didn't expect anything other than that. Thank you again, Greg and Adam for taking time out and speaking to us and sharing your experiences to date and giving us some highlights into exactly what is coming around the corner as well.

Adam (28:58)
And thanks so much for hosting us. been a delight chatting with you.

Greg (29:01)
Yes, thank you. It really has been. We really appreciate you and all that you're doing in the 3D printing and microfluidic space and just love that you're making things available to people so they can pursue their dreams in terms of applications.

Hemdeep (29:16)
Thank you very much. And that ends this episode and we will see you next time around. Bye for now.

Robin (29:24)
And with that, we've reached the end of our series with Greg Norton and Anna Mouli from Brigham Young University. Over the past few episodes, we've explored their groundbreaking work in 3D printing for microfluidics, from building custom 3D printers and materials to pioneering applications in bioanalysis and diagnostics.

Hemdeep (29:43)
Their dedication to 3D printing innovation continues to push the limits of what's possible in micro-scale fabrication. A huge thank you to Greg and Adam for sharing their journey and insights. If you've enjoyed this series, be sure to explore their ongoing work and open source contribution and stay tuned for more fascinating conversations in upcoming episodes.

Robin (30:04)
You can join us next time on August 4th, where we'll be joined by Alexander LeBlond, a PhD student at McGill University. If you're curious, here's a clip from that conversation.

Alexandre (30:17)
So They developed this kind of supposed place, the chemical toilets made of mushroom. the very interesting part about this is that when he tried it, there was not. they saw that they found this Characteristics. smell of chemical, which was a very big surprise. it was. The macellum overall material is completely dead so the the remaining structure, it's chemical toilets. It was very interesting to see that as well. Even though the myself is just innings, they don't have the smell of the.

Robin (30:46)
So the entire toilet was made out of my ceilings? Like, I guess... Sorry, I'm just trying to wrap my head around that.

Alexandre (30:53)
What that looks like. Yeah, me too. It's a, it's interesting. Very interesting. thing to think about but yeah the whole toilet has been colonized by mycelium.

Robin (31:03)
Thanks for tuning in to Big Ideas in Microscale. If you enjoyed the episode, make sure to follow us and stay up to date. You can listen on Apple Podcasts and Spotify, or watch the full video on YouTube. You can also follow us for more updates and behind the scenes content on LinkedIn, Instagram, Blue Sky, and X. We're Cadworx3D across the board. That's spelled C-A-D-W-O-R-K-S-3D. For show notes, paper references, and bonus resources on today's topic, visit our website, catworks3d.com. That's spelled C-A-D-W-O-R-K-S 3D.com.

Hemdeep (31:44)
Thank you for tuning in and as always stay curious, keep exploring and never stop asking the big questions that are shaping our world. Whether you're in the lab, on the go or just curious about the future of technology, join us as we continue to dive into big ideas at Microscale.