Carmel Majidi

Self-healing Electronics


The power of technology cannot be understated, but neither can its vulnerability.

A team of mechanical engineers at Carnegie Mellon University in Pittsburgh, Pennsylvania, have developed a self-healing technology that would allow soft conductive material to maintain electrical function when mechanically damaged.

Here to discuss this technology is Dr. Carmel Majidi, associate professor of mechanical engineering at Carnegie Mellon.

So, how in the world is a material self-healing?

Well, first off, thanks for having me here.

It's a great pleasure.

So, a material is self-healing if it has the ability to maintain its properties -- in the case of a circuit, its electrical functionality -- as it undergoes mechanical damage.

If the circuit breaks, it's still gonna continue to pass current.



So, I mean, I think we're all familiar with electronics that, at some point or another, does fail.

The circuitry breaks or a connection gets loose, and to restore the properties of the circuit, we have to go and pop open the hard case and either replace the circuit board or we have to go and solder the connections.

In the case of a self-healing circuit, the circuit wiring is able to just automatically, on its own, re-route itself, form new electrical connections, and maintain the functionality of the circuit.

So, I brought a few examples here.

Hopefully this can better demonstrate the principle.

I mean, this just looks like kind of a rubbery...



And, so, in a sense, it is kind of a rubbery, soft circuit.

And what you see here is -- there is kind of two components to it.

One is this darker part, and that's these -- These are conductive traces.

They have electrically conductive pathways that can carry electrical current.

And then this lighter area here -- this is electrically insulating.


And it's made up of these microscopic droplets of a metal that's liquid at room temperature.

And in the case of the insulating part, these droplets are isolated from each other, so they can't carry electrical current.

But in these darkened regions here, those droplets are in contact.

They are connected with each other and they can pass electrical current.


And in a self-healing circuit, we can engineer this so that when we mechanically damage the circuit, say by tearing it, scratching it, puncturing it, or, in some extreme cases, removing material, those droplets can form new networks of connected pathways around that damaged area.


So, you've got an example here.

So, I've got an example here, yeah.

So, this is a pretty simple circuit.

It's just one of these conductive traces of these liquid-metal droplets.


All right, so, right now, the circuit is complete, and that's why we're seeing a tiny red light.



And, so, as I start to tear at the material, typically, what you would expect in a circuit is that when I break through this conductive pathway, the light should turn off.

That's the dark gray line is the pathway.



But, in this case, you can see, as I cut through it...


...the light stays on, right?

Even as I've completely severed that conductive area.

So, what has happened here is that all those microscopic droplets of liquid metal inside the rubber that are near the damaged area -- those spontaneously rupture, they form connections with their neighbors, and they form new electrically conductive pathways around that damaged area, and so the circuit can remain intact and current can continue to flow through the light.

So, basically, what is the bare minimum that they have to have in contact with each other?

So, I mean, you've ripped that thing all the way through that pathway, but do you need 20% more of the -- You know, how much do you need for that circuit to kind of self-heal?

So, for a circuit like this, we do need to maintain a lot of the same connectivity that we originally had in our circuit, and so it was very important to us, when we engineered these materials, that we could configure the droplets in a way that when the material did get damaged, a lot of that same connectivity could be preserved.

And, now, when you put that back flat, does it heal in a different way?

Does it see the existing pathways?

'Oh, hey, let's just go back and use that.'


So, with this current type of material or current technology, we get the electrical self-healing, but we don't get mechanical self-healing, and so we can't actually restore the mechanical integrity.

Once when we have that cut, that cut remains.

And that's actually something that my research lab at Carnegie Mellon is currently working on -- developing conductive materials that are not just electrically self-healing but also mechanically self-healing.

So, give me examples of how this is applied.

So, we're really interested in applying these materials in cases where you want electronics to be soft and stretchable and, in particular, outside of the hard case.

I mean, we're all familiar with electronics that are encased in, you know, hard plastic and metal casing.

Our cellphones.



Cellphones and laptops.

But when we talk about incorporating electronics into textiles, into clothing, say stickers or Band-Aids that adhere to our skin, we have to take those electronics outside of the hard case.

It's not enough for the circuits to be soft and stretchable.

They also have to be durable and resistant to just everyday wear and tear.

And so we're interested in wearable computing, applications in virtual reality, augmented reality, human-machine interaction.

Also, there is healthcare applications.

In fact, my research lab recently launched a spin-off company that's developing electronic stickers that can do continuous healthcare monitoring.

It would do what?

A sticker would do what?

So, a sticker would go on your skin.

These are wireless electronic circuits.

And they would monitor your health vitals, like cardiac activity, heart rate, blood oxygenation, respiration.

Kind of another area where we see these materials as potentially useful is not just in managing electrical current, but also managing heat.

And so we're also making versions of this material that are thermally conductive.


So you could be wearing some sort of a V.R.

skin suit, and the gloves could be giving feedback, or at least it would say, 'The heart rate is elevated.

This person's blood pressure is -- They're really enjoying this game' or whatever.

They're excited by this.



And in current virtual reality, A.R.

applications, I mean, a lot of this is done with headsets or, say, data gloves or joysticks, but there's only so much you can learn by just from gesture monitoring or having something on your wrist or on your hand.

The idea with these circuits is that you could incorporate them in a clothing, put them in more parts of your body --

And if it scratches against something, that's fine, 'cause it will self-heal.



The same thing if a hospital or a doctor is putting one of those patches on you.

Now that's gonna monitor all of your vitals, regardless of whether there's a cord attached to a wall.



What are examples of thermal connectivity?

I mean, how would you apply those?

One application of this material is to incorporate it into these electronics to help better dissipate the heat or transfer it to some type of, say, fan-cooled heat sink or heat exchange.

Down the road, when we start thinking about wearable computing, electronic skins that complement, say, our virtual reality or A.R., we need these thermoconductive materials to not just be efficient with managing heat, but they also have to be soft and stretchable and compatible with our clothing and our skin.

All right, Carmel Majidi, of Carnegie Mellon University, thanks so much.

Hey, thanks a lot.