Engineering smart tattoos

From smartwatches to Bluetooth shoes, electronic wearable devices have exploded in popularity. Now engineers are working to create lighter, thinner, and more efficient electronics. A team at Carnegie Mellon University has even created a printable smart tattoo that can monitor body functions.


From smart watches to Bluetooth shoes, electronic wearable devices have exploded in popularity.

Now engineers are working to create lighter, thinner, and more efficient electronics.

One team at Carnegie Mellon University has even created a printable smart tattoo that can monitor body functions.

Carmel Majidi, an associate professor of mechanical engineering at Carnegie Mellon University, joins me now to talk about this breakthrough.

So first of all, what is a soft machine?

Because what you're describing in electronics that are kind of bendable and wearable, how do you do that?

So, number one, thanks for having me over.

And so the work I'm going to show, this is from my research group, the Integrated Soft Materials Lab, and there's a few different approaches to engineering machines and electronics that are soft, stretchable, bendable, compatible with the body.

Just brought a few examples here just so you have a sense of the types of materials that we work with.

So this is based more on a conventional flex circuit technology, and so this circuit is actually designed from measuring muscle activity.


And so on the bottom side here you see these electrodes that make contact with the skin.

As your muscle contracts, it generates electrical signals.

That gets picked up by the electrodes, and then the signals are processed by these electronics on the other side.

So this is just one approach.

I mean, you can tell it's pretty thin.

It's flexible.

It conforms nicely to the skin.

But, I mean, you asked about, you know, soft and, you know, stretchable electronics.

Effectively what we would really like to have is something more like a second skin.

And for that there's a few different approaches that my group has been looking at.

One approach incorporates insulating and conductive rubbers.

So here's an example of the same muscle-monitoring circuit, but now instead of these thin copper traces, we have these conductive rubber composites.

Another approach uses liquid metal.

This is a nontoxic mixture of gallium and indium.

The alloy has similar conductivity than what you get with conventional wiring.

But it's liquid, so it deforms with the surrounding rubber.

The circuit remains intact as we stretch.

So there's been a lot of progress in the space of manufacturing and materials for these soft stretchable electronics and machines.

So what's it going to, you know, when you get, you get kind of thinner and thinner.

When you get down to liquid metal, and we talked about this idea of almost a tattoo, I mean, you're putting that tattoo into that rubber, right?




And so the idea is that the, you know, the rubber film and the electronics are just so soft and thin that they can just stick to your skin, you know, almost like a Band-Aid, or if you will, like a smart tattoo, or at least that's the, that's the vision.

And, you know, eventually where we'd like to go with this, I mean, not just talking about electronics on your skin but potentially also in implants.

And how would that work?

So the thinking, so, I mean, you know, already, I mean, we have, say, pacemakers and defibrillators.

I mean, these go in the body.

I mean, they play a, you know, a vital role for example in preventing cardiac arrest.

The, one of the challenges, though, with these are they typically depend on fairly rigid and then bulky electronics.

And so the thinking is if we can take some of these same soft and stretchable electronics and incorporate that into these medical implantables, then we can have implants that are more compatible with the surrounding tissue and organs.

And they could probably send you more information back.


I mean, so --

Because right now, sometimes people think of implantables as almost dumb objects.

They're pumps to do one specific thing over and over again until they run down.


And they're in limited parts of the body or just even, you know, wearables in general.

I mean, when we think about, say, sensors in your smart phone or an activity tracker in a smart watch, I mean, there's only so much, right, that you can learn from having a sensor, say, in your pocket or on your wrist.

By having electronics that are kind of soft, have this kind of second skin type functionality, we can place them on different parts of the body.

We can put them, implant them in various locations so we can get a much richer picture of your physiological state.

So when you go work out, this could just be a sensor that's embedded in your shirt that's monitoring your heart rate?



So it could be embedded in the clothing.

It could stick to your skin.

It could monitor heart rate, muscle activity, oxygen in your blood.

I mean, all sorts of different types of vitals that would otherwise be very difficult to access with existing wearables.

In this process, have you had to design how you actually print these things into existence?

Because probably not too many printers can do what you're talking about.


So a lot of the manufacturing techniques with these conductive rubbers and these metals are going to be different than what we use for traditional flex and rigid circuit.

So a lot of the research, a lot of the work in my group and others at Carnegie Mellon and elsewhere, I mean, has focused on novel printing techniques for patterning these circuits.

Another challenge is also interfacing these soft, stretchable circuits with the pins of these rigid microchips, so --

This isn't something that a 3D printer at home is ever going to be able to do?

Or maybe...?

Well, you know, potentially maybe.

I mean, we're actually, you know, looking right now at ways of retrofitting 3D printers so they can print conductive rubber composites or this liquid metal alloys.

And so, no, it could be possible in a few years.

So best-case scenario, ten years from now, if there are applications of this sort of soft, wearable electronics in the marketplace, how would life be different?

How do you see somebody interacting with this?


Well, like I said, I mean, you know, one is in the space of wearable computing and biomonitoring.

And another potential application and, you know, something that, you know, we're very excited about is the potential for using these in robotics.

I mean, you an almost think about these materials as being artificial skin, artificial nervous tissue that could be used to make robots safer for physical interaction, a little bit more natural to the touch.

I mean, when we think about, you know, robots and the robot revolution, I mean, oftentimes you picture a humanoid that's working in close proximity with humans, and so physical contact is going to be inevitable.

And so we do have to be mindful of the types of materials that we use that construct these machines.

I mean, better to be in contact with kind of a soft, rubbery robot as opposed to a machine built from hard plastics and metals.


Carmel Majidi, associate professor of mechanical engineering at Carnegie Mellon.

Thanks for joining us.

All right.

Thank you.

It was a pleasure.