Colorado chemist updates tattoo chemistry with an eye toward medical diagnostics

Tattoos might be the ultimate form of bodily self-expression. But Carson Bruns envisions a future in which people’s body art also monitors their health.

His team at the University of Colorado Boulder is developing permanent “chameleon tattoos” that change color in response to signals such as heat and ultraviolet light and could someday help people take an active role in their health by watching out for a fever or excessive sun exposure, respectively. Carmen Drahl spoke with Bruns about the science—and art—underlying the project.

What inspired you to develop functional tattoos?

I’ve been interested in art since I was a little kid, but I have this background in nanotechnology. When I took a job as a professor, I had an opportunity to start something totally new. I sat down and thought, “What’s something I’m passionate about that I might be able to work on as a nanotechnologist?” It dawned on me that we haven’t updated tattoos as a technology in thousands of years. We’ve invented machines that make tattooing slightly more efficient, and we have more colors. But that’s kind of it.

How does nanotechnology come into play in your tattoo inks?

A tattoo is just a bunch of pigment particles in the dermis, that layer of tissue underneath the surface of the skin. Those particles are nanoparticles. They range in size from 20 to 900 nm in diameter. Instead of using solid pigment particles, like in standard tattoos, we use hollow microcapsules as our particles. They range in size from about 100 to 2,000 nm. We can fill the microcapsules with practically whatever we want, which is where we get the function of the tattoo.

The dyes that we put inside the microcapsules differ from tattoo pigments. Pigments are solid particles, whereas dyes are dissolved in a carrier liquid. If you tried to tattoo only the dye, it would disappear within a day or two. There’s some critical size below which your body’s macrophages will just carry stuff away. The microcapsules are what allow us to make those dyes big enough to act as a permanent tattoo.

What’s the chemistry of your microcapsules and dyes?

We’ve been using a melamine formaldehyde resin to make the microcapsules because we partnered with a local company that makes microencapsulated dyes using melamine formaldehyde as the shell material. This partnership allowed us to focus immediately on making tattoo inks and tattoos rather than fabricating the microcapsules, but there are health concerns about formaldehyde because it’s a carcinogen. We’ll probably move to a more biofriendly acrylic-based polymer for the capsule in the future.

In the case of our ultraviolet-light-sensitive tattoo for tracking sun exposure, we fill the inside of the microcapsules with a commercially available UV-sensitive dye. The one we use the most turns from colorless to blue under UV light, but we could easily swap out the dye to get any color we want.

The temperature-sensitive tattoos are made from the same microcapsules but filled with a thermochromic dye. Different thermochromic dyes transition at different temperatures. We’re interested in having people be able to check their body temperature for fever by glancing at their tattoo.

Multiple companies are developing temporary tattoos for those two applications. Why would people want to permanently ink themselves instead?

It’s inconvenient to have to reapply a temporary tattoo to your skin. Another consideration is that temporary tattoos can be a little uncomfortable. You can feel them on the surface of your skin. A permanent tattoo, because it’s actually implanted in your skin, is imperceptible.

What other applications are you thinking about?

We’re thinking about things like blood alcohol content, blood oxygenation, or maybe blood glucose levels. We might not be able to make a tattoo that detects your blood glucose levels with the sensitivity of machines that people with diabetes are using today. But maybe it can at least let you know if you’re really in a dangerous zone.

Can I get a tech tattoo now?

No, you cannot have one right now. I’m sad to keep turning people down. We definitely have to do a lot of work to make sure these are safe, and we are not biologists, so we need help.

We’ve applied tattoos to pieces of pig skin but haven’t started any animal studies yet. We’re at the stage now where we’ve got our initial results and we’re looking for funding so that we can do more comprehensive animal studies. I think it will take us a pretty long time. If they are safe, I would guess it would still be years before they’re in your local tattoo parlor.

But you’ve given yourself a tech tattoo.

I get a lot of reactions to that. It was probably a little bit risky to tattoo myself not knowing much about the safety of the microcapsules. But it was a very, very small tattoo. It was photoactive, and it changed colors in sunlight for about 6 months. It faded after that. We’re still trying to figure out if the reason it faded was because the microcapsules degraded or because the dye inside the microcapsules degraded. I went to the dermatologist. They didn’t find anything wrong with my skin. Hopefully we’ll get results from the histologist soon, also showing that there’s nothing unusual going on and that the tattoo is normal.

Do you consider your tattoo project chemistry or art?

I consider it chemistry for sure because we are using our ability to organize matter in a new way to create new functions.

Carmen Drahl is a freelance writer. A version of this story appeared in ACS Central Science: cenm.ag/bruns. This interview was edited for length and clarity.