This Skin-like Robot Can Heal Itself

IRA FLATOW: This is Science Friday. I’m Ira Flatow.

You’re familiar with robots, right? You’ve seen those big hulking bodies building cars, working in factories. They battle each other in the movies. Yeah. But there is now a growing field called softbotics. And these are thin, flexible materials closer to human skin than to a transformer. And there’s been a breakthrough in this field. Softbotics can not only conduct electricity, but can heal itself from damage.

Wow. So how could these materials be used? Joining me to talk about this is my guest, Dr. Carmel Majidi, professor of mechanical engineering at Carnegie Mellon University, in Pittsburgh, Pennsylvania.

Welcome to Science Friday.

CARMEL MAJIDI: Thank you very much. Glad to be here.

IRA FLATOW: Tell us what this material looks like. Describe it for us, please.

CARMEL MAJIDI: This material is a pretty soft and almost gel-like substance. It’s very stretchy. It has elastic properties. It’s kind of as soft as the softest natural biological tissue. So think even being softer than skin.

The material is electrically conductive. It has very high conductivity, enough to power digital circuits or even motors. And it also has this feature that it’s self-healing. So if it ever gets damage, if it gets torn, ruptured, punctured, the material can basically stick to itself and re-fuse, and restore its elasticity and also restore its electrical conductivity.

IRA FLATOW: We’re not talking about that liquid metal like the Terminator does in the movie and gets back together and heals itself?

CARMEL MAJIDI: Well, in a sense, there are elements of that in this material.

IRA FLATOW: Really?

CARMEL MAJIDI: Yeah. The material actually does incorporate a type of liquid metal alloy. This is a eutectic blend of gallium and indium. So gallium and indium, by themselves, are solid at room temperature. But when you mix the two together, they form this eutectic, where the alloy is liquid. And the liquid metal basically allows the conductive pathways within this material to quickly restore themselves, to heal themselves, if it ever gets damaged, and pressed back together.

So we mix in that gallium-indium liquid metal, along with silver flakes, and all that is suspended within this polyvinyl alcohol gel.

IRA FLATOW: That sounds really cool. What makes it different from other softbotics?

CARMEL MAJIDI: The key difference is the fact that it’s self-healing. So the material binds itself together through hydrogen bonds. So these are actually the same hydrogen bonds that produce forces between water molecules. And so these materials have a very high density of these hydrogen bonds. And when those bonds break, they can readily form themselves back together upon contact.

The other important novelty here is that we’re combining that mechanical or that elastic self-healing property with this electrical self-healing. So utilizing the liquid metal, we’re able to get the electrical pathways to also instantaneously re-form any time this material is ruptured.

IRA FLATOW: So just to be clear so I understand this, when you say self-healing, you don’t have to do anything to it– like put a Band-Aid on it or something and unite the parts together– it knows how to do that by itself?

CARMEL MAJIDI: Right. Yeah, just like if you apply a tape to a surface, it’ll just readily wet and stick. So this material has this self-adhering-type property. You don’t have to apply heat. You don’t have to do any special chemical treatment or stitch the material together. Just bringing it back in contact with itself is enough to re-form those bonds.

IRA FLATOW: And so how much can you beat it up and still have it fix itself? Not that I’m advocating violence here. I just wonder how much healing it can do.

CARMEL MAJIDI: Well, pretty much the same wear and tear that natural biological tissue would undergo. And so, definitely, if you were to really run this through the wringer and obliterate the material and remove material, you can permanently damage the robotic system or the soft electronics. The idea here more is to be able to create robots, machines, electronics, that can just withstand pretty much the same wear and tear that natural organisms have to encounter in their daily activities.

And so if you have your material rub up against a surface or just make some impact, if there’s a cut or a tear, or basically a bruise, with these materials, they’ll be able to restore their connectivity. They can stay functional. Anything beyond that, you would have to do more serious repairs to the robot or to the circuit.

IRA FLATOW: And so what would the best uses for this material be? What applications do you see?

CARMEL MAJIDI: There’s a couple of applications that motivated us to look at this. One of the primary motivations was actually to make electronics that are soft and stretchable and that can adhere to the body– basically, function as a second skin, or as an electronic sticker that could be used to, say, monitor physiological health. So the gel that we use is very similar to the gels that are used for medical devices that monitor cardiac activity or muscle activity.

The challenge with those, though, is that all those materials require being wired up to some external hardware. And so you can only perform those measurements within a clinical setting. With these materials, the idea is that you can stick these materials to your body and use them outside of a clinical setting. They can monitor your heart rate, your cardiac activity. They can monitor your muscle activity. And they can withstand the same wear and tear that you just encounter on a daily basis.

And so if these materials get torn or ruptured, they can re-fuse back together and they can provide those continuous electrical measurements. Another big application of these materials– or I should say another potential application of these materials– is to use them as artificial skin and artificial nervous tissue for a next generation of soft and biologically inspired robots. So imagine robots and machines that mimic, say, a snail or an octopus or, say, a lizard, in their ability to maneuver in environments, to form, squeeze through confined spaces.

When we shift from more conventional robotic systems to these softer, more biologically inspired robots, we no longer have the luxury of encasing or protecting all of the delicate electronics and soft materials within a hard case. So it’s important that we make those materials robust so that they can withstand the types of impacts and mechanical loading that, say, a natural organism would experience. And just like with natural organisms that can heal themselves and repair any kind of damage or cuts, we would want those same properties in these soft robotic materials as well.

IRA FLATOW: So the soft robotic material could squeeze itself into tight places, searching for people or something. And then, if it gets injured, it could heal itself at the same time?

CARMEL MAJIDI: That’s exactly it. I mean, one application of these soft robots would be to explore areas that it wouldn’t be practical or safe, say, for a human or for a more conventional, bulkier robotic system. You could imagine having these robots in aquatic environments or in dry environments, where they could do water quality testing or they could monitor air quality. You could use them to assist in, say, search and rescue operations.

So yeah, exactly. That’s the idea with these robotic systems.

IRA FLATOW: Wow. This whole field of softbotics, it’s just a game changer, it sounds.

CARMEL MAJIDI: There is that potential. This is something that’s exciting for us and a lot of other researchers out there. Because we do see a lot of transformative potential with softbotics. By virtue of taking the hard case off of robotic systems, engineering them out of materials that are soft and deformable and have these self-healing properties, that truly can really change how we use robotics in our everyday lives.

IRA FLATOW: Could it be used in the medical field, for example, in better prosthetics that have better sensory touch, and knowing where things are?

CARMEL MAJIDI: Definitely. One of the big motivators actually in this field of softbotics is to create robotic systems that are wearable, that can be used for human motor assistance, and could also potentially be used as prosthetics. And so there’s a lot of challenges there with engineering robotic systems that can match a lot of the same mechanical and functional properties of our biological tissue and our limbs and our organs. And so that remains one of the big challenges within the field.

This material that we worked on, combining soft and stretchable elasticity with electrical conductivity, with self-healing, this represents just one basic step. This material represents just one basic building block for those more complex systems that could eventually function as a soft prosthetic or some type of assistive device.

IRA FLATOW: I’m going to give you the Science Friday blank check question– not that I have one in my back pocket here. But if you could think about the future, and something that you would love to develop, but it would take some kind of real money and resources, where would that go? What’s something that you would really like to see happen or is something you could really use?

CARMEL MAJIDI: I mean, one dream in the field, one big grand challenge is if we could use these softbotic materials to engineer something like a robot hand that had the same degree of dexterity, the same degree of sensing capability that a natural human hand does. We could produce that using these materials that could be printable, that could seamlessly integrate together, a material that would be lightweight, that you could actually use as a prosthetic, or put on– say, mount to an arm of a robot. That would be one of the big dreams.

And that’s something, actually, that currently I’m looking to pursue with collaborators across multiple different universities. This does represent one of the big grand challenges in the field.

IRA FLATOW: It sounds great. Well, you’ll come back and tell us about it when you do, OK?

CARMEL MAJIDI: I hope to do so.

IRA FLATOW: Thank you for taking time to be with us today.

CARMEL MAJIDI: Thank you.

IRA FLATOW: Dr. Carmel Majidi, professor of mechanical engineering at Carnegie Mellon University, in Pittsburgh, Pennsylvania.

This is Science Friday, from WNYC Studios.

Copyright © 2023 Science Friday Initiative. All rights reserved. Science Friday transcripts are produced on a tight deadline by 3Play Media. Fidelity to the original aired/published audio or video file might vary, and text might be updated or amended in the future. For the authoritative record of Science Friday’s programming, please visit the original aired/published recording. For terms of use and more information, visit our policies pages at http://www.sciencefriday.com/about/policies/.