Have you ever had to wear a heart monitor, even for a day? If so, you know it SUCKS. You have lots of wires stuck to you, and they’re all attached to a hard box the size of a BLT that you have to tuck … somewhere. They stick a bunch of electrodes all over your torso with Nuclear Gorilla Glue, and you end up resigned to leaving them there for 2 weeks after they unsnap the wires because you don’t want to even try to pull them off. This is what you look like (if you’re a professional athlete):
I had to wear this when I was in the hospital back in 2014, and also another time at home for 24 hours. I hated it. My mother had to wear this when she was in the hospital in the last 2 weeks of her life. She kept rolling over onto it and trying to move the wires, and it drove her crazy.
But the days of this monstrosity are numbered, thanks to researchers at Rice University. They’ve developed wearable carbon nanotube threads that not only allow replacement of the unwieldy wires and electrodes with a comfy shirt, but actually give better EKG monitoring! Soon-to-be Ph.D. Lauren Taylor, Professor Matteo Pasquali, and others report their cool invention in the August 30 edition of Nano Letters.
So now, instead of having electrodes superglued to you and tangled wires everywhere, you’ll soon be able to wear a flexible shirt under your normal clothes that provides the electrical contacts that snap onto leads in a very unobtrusive way. The nanotube wires run right through the shirt:
And those same carbon nanotube threads also serve as the electrodes that contact the skin. Unlike wires, these feel like fabric, and stretch along with it, too:
NOW our professional athlete is going to feel a lot more comfortable having his heart monitored. Check this out:
The other nice advance here is that the signals can be Bluetoothed from a small snapped-on device to a Holter monitor, computer, or even smartphone, so no more rolling over onto that plastic BLT. Set that thing aside. The shirt can be washed 100 times without any loss of performance.
Soon-to-be-Ph.D. Oliver Dewey, who also worked for the Pasquali lab on the project, said:
You just don’t find soft, flexible, threadlike materials that are comfortable to the touch, that you can work with, that are … you can build a bridge out of it, or you can build a power line out of it, but you can also run it through a sewing machine. Nothing else behaves like this. What’s really gratifying is being able to go to the lab and make that.
The EKG signal this system can produce is quite good. They generated EKGs from a walking, running user with their athletic shirt setup versus sticky electrodes. Three cardiologists took a look at the signals, not knowing anything about them, and each of them said the athletic-shirt EKG signal was a bit better than the sticky-electrode version.
Here’s a sample of what they saw:
After spinning very thin carbon nanotube wires out of a solution, they wove them into sewable threads with a device custom-made by a model shipbuilder! It wove three thin fibers together, then seven of these triple fibers into a 21-fiber sewable thread. Ahoy, mateys!
OK, now wait a second. How can plain old carbon conduct electricity, anyway? Carbon is just soot, or a diamond. How can it behave like a metal?
It is indeed true that a diamond won’t conduct electricity. The reason is that carbon atoms in diamonds bond to each other in such a way that all the electrons are part of those bonds and thus can’t move around. All carbon atoms have four electrons, and each electron can be part of a covalent bond (pair of electrons shared by two atoms). In diamond, every carbon atom is bound to four other carbon atoms, so all the electrons are held in place by these bonds:
But this isn’t the only way carbon can bind to itself to make a huge molecule. In a sheet of graphene, each carbon atom is only covalently bound to three others:
In this case, only three of each carbon atom’s electrons are bound, and that leaves one of them free to move around, so now we have a conductor. You might notice that graphene looks a lot like chicken wire, so let’s roll some up into a tube:
That’s exactly how it works with carbon nanotubes. You can cut the chicken wire at different angles before you roll it up, and some of those configurations will conduct electricity better than others.
“Armchair” is a full-on conductor, just like a metal, while “zigzag” and “chiral” are semiconductors. Our researchers rolled graphene into “armchair” tubes this way and got an average of 1.5 tube-wall layers for an average fiber thickness of 1.8 nanometers. For comparison, a sheet of paper is about 100,000 nanometers thick.
Another great thing about carbon nanotubes is that they’re single molecules with strong bonds — large by molecular standards — that don’t have faults between different crystal regions like a metal, so they’re about 100 times stronger than steel.
If you’re wondering about cost, carbon nanotubes can be had for $100 a kilogram or so. That’s no problem at all for small applications like this. But of course there are people out there working to make them cheaper so you’ll start to see them in more macro applications.
I was able to read this paper even though it’s behind a paywall because Prof. Matteo Pasquali was kind enough to send me a reprint of it. He told me that now they are working on long-term studies to tune the shirt up for overnight wear. That means sayonara, auf Wiedersehen, and до свидания to the stinkin’ heart monitor. I can’t wait!
And for all the workers who’ll be sewing these together someday soon, here’s to you….