Podcast: 3D Printing Robot Muscles

In this episode, we discuss how Harvard researchers cracked the code of 3D printing “shapeshifting” materials and why their efforts lay the groundwork for other innovations in the material science field.

This podcast is sponsored by Mouser Electronics. 

Episode Notes

(2:22) - Encoding many properties in one material via 3D printing

This episode was brought to you by Mouser, our favorite place to get electronics parts for any project, whether it be a hobby at home or a prototype for work. Click HERE to learn more about the history of soft robotics and its current/future applications!

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Transcript

What's up folks in today's episode, we're talking about programmable materials using 3D printing. We're talking about a team that basically cracked the code on how to print liquid crystal elastomers that change shape when heated. They can be used like muscles for soft robotics, which is super awesome. Let's jump into it.   

What's up friends, this is The Next Byte Podcast where one gentleman and one scholar explore the secret sauce behind cool tech and make it easy to understand.

Daniel: Hey everyone. Welcome back to the Next Byte. We're coming at you live, wearing some fresh new Next Byte merch. So, if you're looking at us and it looks better, this is why, if you're listening to us and we sound happier, that's also why.

Farbod: This is why.

Daniel: But today's episode I'm pretty excited about. We're talking about 3d printing, but kind of in a unique sense, it's programming materials with properties. And in this case, learning to 3d print soft materials that you can essentially program the geometry of soft material and program the way that it shifts under different stimuli, which is pretty interesting. And it has direct applications in the realm of soft robotics. So, before we jump too deep into the topic around 3D printing soft robotics, let's talk about the evolution and potential of soft robotics, this field as a whole. So, we're talking about an episode from today's sponsor, Mauser Electronics.  They're one of the largest electronics distributors in the world. They are one of our favorite places to order components for a hobby project at home. They've also saved my tail at work a couple of times, which is pretty interesting. But in addition to them being an awesome electronics distributor, they also have a ton of knowledge and a ton of relationships with folks who are working at the cutting edge. And they write awesome technical resources, which can help you understand what's going on. What's the new next big thing in technology, which is kind of what we're trying to communicate to you guys as well. So that's why we partner so well. We've got a link in the show notes to an article that they wrote on the evolution and potential of soft robotics. It's kind of a technical primer on what the entire field of soft robotics looks like, what the potential opportunities for growth are, and what the key enablers are to make soft robotics basically come to fruition, to make it in the real world, which links really well to today's topic because we're talking about one of the ways that you can help make soft robotics real, right? One of the key enablers to making soft robotics actually effective in the real world.

Farbod: Yeah. And this class of materials that we're talking about, liquid crystal elastomers, they're not really new either. They've been around for a while, right? Like materials that react to heat. I think we've even talked about it at some point over last two years or so, right? But what's interesting here, these folks at Harvard, in collaboration with the Department of Energy, they're trying to bring it into 3D manufacturing or additive manufacturing, as 3D printing. And it looks like the previous attempts at this have been mostly trial and error because the building blocks that allow you to have this incredible mechanical property or even electrical property, depending on what you want to do, is based all on alignment, like how these little building blocks called mesogens aligned as they're being manufactured.  No one's really cracked it. Everyone's been just like, let's tune this, tune that, figure something out. We got what we want, let's move on. So, these folks took on the challenge of figuring out what's the fundamental science behind how it's coming out of the nozzle.

Daniel: And a little bit of background here on liquid crystals in general, right? So, there was a generation of screen technology called LCDs. Probably the vast majority of folks listening to this either had at one point or may still have an LCD screen in their house and the way that an LCD screen works is you've got a bunch of liquid crystals, or crystals suspended in liquid and they're aligned perfectly when the screen is off. But as electricity is applied to each crystal, it changes the alignment of the crystal, modulating how much light is let through and in what color is let through. So, each of these crystals essentially is like a pixel on the screen and electricity is programmed to change the shape and the alignment of the pixels to give you a picture on your screen that you can see. When we're talking about liquid crystal elastomers, it's a very similar principle where you want to have a bunch of crystals suspended in a liquid that are aligned perfectly and then you apply a stimulus to them. They change their alignment and they change their shape. In the elastomer realm, they're trying to basically 3D print the equivalent of muscles, right? So, you align a bunch of these crystals in here and then as you apply a stimulus, the change of shape to either contract or relax. But the challenge here is to be able to use this to make soft robotics artificial limbs cool new types of clothing, etc, etc, right? The applications or something that we can talk about later, but to get this to work you need to have a way of really programmatically and reliably being able to align the crystals so that when you apply a stimulus you know exactly what the response is going to be. If the crystals are all randomly scattered throughout this artificial muscle that you're making, if you apply heat to it, which is the stimulus they're using here, the muscle is not going to contract in unison or relax in unison the way that you would expect a muscle to. It's actually just going to like spasm all over the place. And it's not actually going to create any macro reaction, right? The entire structure isn't going to change in unison because they weren't aligned when they were placed into that muscle. So, I think in this case, they're not necessarily using 3d printing because they think it's cool or because they want to. They're using 3D printing because they found 3D printing as a way that they can actually reliably align the shape and alignment of the crystals when they deposit them. And then that gives, that unlocks the use of these liquid crystal elastomers as an actuator type thing for soft robotics. It's not just that they're using 3D printing because it's a buzzword and it's cool and they want to get like create an article that gets a bunch of clicks. They're using 3D printing because this is probably the only way at scale to deposit these crystals in a way that's predictable, that's repeatable, and that when you apply a known stimulus, you get a known response.

Farbod: Yeah. And for the purpose that they were shooting for here, which is actuation and contraction in response to heat, the ideal alignment is for all of these LCEs to be pretty much parallel to each other. That's the most desirable output. And like you're saying, they chose the 3D printing approach because that allows a lot of control over how these structures are going to come out.  And they had this hypothesis that some configuration of the nozzles geometry where the ink is coming out or the filament is coming out and control over temperature and speed would result in them being able to tune these properties. And what they came up with was kind of two different types of filaments. One, where the walls are in full alignment and the core is scattered, and the other one is uniform throughout. What I thought was interesting is they had this hypothesis, they did the experiment to kind of prove that through changing some of these properties, they were able to modify the alignment. And then they took that to the Department of Energy, that's where the folks at the Brookhaven National Lab come in, and then they set up an X-Ray machine with the printer itself to understand what's going on at the nozzle level.   That's the part of the article that really got me excited. I don't know about you.

Daniel: No, I'm with you, man. Obviously, the title of the article is pretty cool, which is Encoding Properties in Material Using 3D Printing. That's awesome, right? Basically, being able to program things in 3D space as opposed to just programming things on a computer, which is awesome.  But my favorite part was looking at their visualization, they used an X-ray microbeam during printing, not after, to analyze what the material looked like. They were able to use an x-ray microbeam during printing to locally measure the way that all these liquid crystals were aligned and then what direction they were in. That allowed them to optimize all the different parameters, right? You can change the material. You can change the speed at which you're depositing that material. You can change the speed at which the nozzle is moving. You can change the ambient temperature, the heat.  You can also change the geometry of the nozzle, which they tried a number of different geometries of the nozzle. They basically, the way I think about it, and it's an analogy we use a lot in the podcast because we like to say we're looking for the secret sauce. But in this case, they like went through the exploratory phase of creating a recipe and a cookbook to be like, hey, if you want to create these repeatable structures using liquid crystal elastomers, here's the recipe. Here's what temperature you need to set the oven to. Here's how long you need to bake it. Here's how exactly you need to mix it. Like they created a recipe similar to baking a cake, but in this case for making like soft robotic actuators using liquid crystal elastomers.

Farbod: I think you hit the nail right on the head there. It's obviously cool that they came up with their own filaments that matched the properties that they were looking for. But the real impact here is again, that fundamental understanding of how this different aspect of the manufacturing process, whether it's the nozzle geometry, the flow speed, the temperature impacts the properties of the end product. Like what you're saying, if you want to design for this, then tune this. And they said it in the article, it opens up the avenue for creating all sorts of program materials within this material family. And then, earlier you were talking about applications. You named that a couple, but imagine the kind of impact this can have outside of robotics within the medical realm, or even like selfishly on the consumer side. Consumer plastic goods that can self-heal when heat is applied. Or shoes, I love shoes. Shoes that can conform to your feet when a certain amount of heat is applied. The opportunities are pretty exciting.

Daniel: Yeah, exactly. And I think one thing that's awesome here is they said a lot of the previous research, even from their group has been focused on tuning the material properties of like the filament, right?  Of the mix of liquid crystals and all the other additives that go into the 3D printer. A lot of research has been focused on material choice to make sure that these things work properly. They found that basically by changing the printer nozzle shape and the printer parameters, they were able to get as much or more improvement in performance as changing material choice. So, they're basically saying, you know, it's not just what ingredients you put in the cake. It's also how you cook it that matter a lot on the final product, which I think is intuitive and it makes sense, but there's not always as much focus. I think it's maybe not always as shiny or as sexy to be like, hey, I found the exact printing parameters to do this, to make it work effectively. A lot of people want to be at the forefront of like finding, unlocking a new material, right? That, sounds a lot more buzzy than being like, Oh, I helped industrialize it. But in this case, it matters a ton toward the actual outcome as being like, hey, I take your cool materials and I raise you by finding the actual production method that makes it work.  

Farbod: I totally agree with you. And I'll add one more thing, I think they called this out in the article, but within the 3D printing community, they were like, look, the type of nozzle you use is pretty much an afterthought. Like there might be like two or three options that we all pick from, but we don't really give it a second thought. This is a good reminder that when you're facing a challenge within the material realm and FDM printing. First principles thinking could actually be pretty helpful, like analyzing every bit of this process and being like, okay, what could actually impact the end result here? And, you know, the geometry of the nozzle ended up being one that most people were kind of brushing aside.

Daniel: Yeah, and I think one of the interesting things to mention there specifically to the nozzle was a lot, the standard I would say for nozzles. And when we're talking about nozzles, think about like the tip in a piping bag to go back to our cake analogy. Like the tip in a…

Farbod: You're loving this cake analogy. You've just been going back to it. Are you cake?

Daniel: I'm baking it up today. I don't know why.  

Farbod: Oh my gosh. This guy's funny today.

Daniel: Think about like the nozzle or the tip on a piping bag. Typically, a lot of those are just tapered, right? They look like a cone. And that's also similarly the standard assumption in 3D printing is you've got a tapered nozzle that helps take a wide flow of material and condense it to a very, very controlled size bead that you're able to deposit. And that's the end of that, the narrow end of the cone is where the material actually comes out and is deposited onto the build platform. But they said when you're trying to align these crystals inside the nozzle before they get deposited onto the build platform, the taper, the narrowing, just like a normal cone, isn't actually the best geometry through their tests with the x-ray, shooting an x-ray through the nozzle while they're printing to see what the liquid crystal alignment looks like, they're actually able to find that hyperbolic.  So, using two curves as opposed to a straight line as a part of the narrowed part of the cone actually helped improve the alignment of the molecules, not just on the outside, but also all the way throughout the deposit of filament, which is pretty interesting for me to think. Obviously in terms of liquid crystal elastomers, but I also think about folks that are trying to do 3D printing with other types of additives. There's a lot of people 3D printed plastics are awesome, but you can make plastics even stronger with additives. That's the vast majority of how plastics are actually used in the real world is they're filled with glass or they're filled with other types of additives. Some of them are filled with carbon fiber to make them stronger, but specifically carbon fiber is a lot stronger and also glass fibers are a lot stronger when you can predictably tune the alignment. It'd be awesome to see if people can use this narrowing versus hyperbolic nozzle shape approach to be able to tune the alignment of other additives inside 3D printed filament, not just liquid crystal elastomers.

Farbod: Shout out to Dr. Eric Knutson from our materials class. This just brought me back to sophomore year of college when we were going over the orientation of additives in a composite material. And you're right, you look at the value of carbon composites right now within the high-end hypercar world. You love F1. It's all over F1 because of how lightweight and strong it is. You look at aerospace, Boeing's and Airbus planes went from being what, 80 to 90 % aluminum to being only 10 to 20 % aluminum because composites to cover, you're absolutely right. The value of additives here is huge.

Daniel: Interesting sidebar on the use of aluminum versus composites in aerospace. Have you been following with our friend of the podcast, not boom, Ed Mehr, Machina Labs?

Farbod: Oh yes, they've been leveraging their technology for composite molds, right?

Daniel: No, no, no, no, even better. He just robo-formed a scale model aircraft win completely out of aluminum. And he says it has a higher strength to weight ratio than a composite contemporary.

Farbod: You're kidding.

Daniel: Yeah.

Farbod: I didn't see this.

Daniel: Pretty interesting. So, friend of the pod, Ed Mehr, hopefully we'll have you back on the podcast and you can talk about what the cool stuff you're doing at Machina Labs.

Farbod: Dude, we gotta fly out. That's what we gotta do. I wanna see this thing in person.

Daniel: But pretty sweet. He's basically saying like, aluminum is a lost art, right?  We've essentially forgotten how to process aluminum at scale for aerospace. And he's saying, you know, with this roboforming, you don't need lots of tooling. You can just have two robots get the exact geometry you want. And maybe just maybe it'll perform better than composites because, we kind of, or let's say, give composites a run for their money because while they do have a really high strength to weight ratio, they are also ridiculously expensive to produce.

Farbod: Dang, I'm looking at the post right now. This is crazy. Well, that's good tangent. I'm glad you brought it up.

Daniel: Sorry, it's like largely unrelated to liquid crystal elastomers.

Farbod: I feel like if you're into the LCEs, you'll appreciate this.

Daniel: Yeah, man. All right. Well, I'll give us a quick wrap up just to summarize what we talked about today. Essentially, we're talking about a team of scientists that found a way to 3D print liquid crystal elastomers or LCEs. These are special soft materials that move when heated and they can basically be treated like muscles for soft robotics. They discovered that they can change the printer tip shape, the speed and temperature. And this controls how the tiny crystals line up inside the material, which determines how the material moves when a stimulus is applied like heat. So, they used x-rays shot at through the printer nozzle during printing and they created a simple guide. I liken it to a recipe for baking a cake. They made a simple recipe for making these materials behave exactly as needed for robots, artificial muscles, and for special clothing moving forward. I think it's really interesting.

Farbod: Boom! I love it.

Daniel: All right. That's the pod?

Farbod: That's the pod.

Daniel: Thanks everyone. See you.

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The Next Byte: We're two engineers on a mission to simplify complex science & technology, making it easy to understand. In each episode of our show, we dive into world-changing tech (such as AI, robotics, 3D printing, IoT, & much more), all while keeping it entertaining & engaging along the way.