Mad-scientist kind of moments happen fairly often for nanoengineer Carson Bruns. A few months ago in his lab at the University of Colorado-Boulder, he tested his latest invention on his own arm and asked a colleague for help.

"We were like: 'Okay, we're going to tattoo ourselves. Can you help us today?'" he said.

The tattoo is like a freckle, a little blue dot. But he can turn it on and off. Like the way a mood ring changes color with temperature, this tattoo changes with light: ultraviolet light to turn it on, daylight (or even a flashlight) to turn it off.

"You can go to court and turn it off, and then go to the party and turn it on. And then go to Grandma's house and turn it off," said Bruns.

Bruns started a company with tattoo-artist-to-the-stars Keith "Bang Bang" McCurdy, along with a former doctoral student.

Early next year, they plan to release their first product, Magic Ink, to a group of handpicked artists. The business partners have long-term hopes for smart tattoos that have a health value, but cosmetics are cheaper and simpler to get to consumers than medical devices.

So, that's where they're starting.

Bruns said Magic Ink is made of particles of dye, encased in beads of plexiglass - the same polymethyl methacrylate material in those dermal fillers people use to plump their lips.

John Swierk, a chemist at the State University of New York-Binghamton, said many of the tattoo pigments in use now have been around a long time, which gives some users a base comfort level about their safety. But a new material comes with new unknowns.

"If somebody is going to get tattooed with Magic Ink, they have to accept a degree of uncertainty about what the future is going to hold with that ink," he said.

Bruns recently received funding from the National Science Foundation, which he plans to use for probing which size and type of nanoparticles are less likely to irritate the immune system and more likely to stay put where they're placed. The immune system has been known to haul off bits of tattoo ink to the lymph nodes, dyeing them blue and green.

While Magic Ink is a cool party trick, Bruns and his colleagues have made other inks that align with their bigger goal: to make tattoos helpful.

Bruns and his colleagues have made one that changes color when exposed to gamma radiation - envisioning it might someday work as a built-in exposure meter.

Another ink shows up when it is time to put on sunscreen. He developed yet another ink intended to act as a permanent sunscreen. None of those are available to consumers, though the permanent sunscreen is furthest along. That ink has been tested in a small group of mice; the others have been tested on pigskin.

Bruns started a company, Hyprskn, a few years ago, when Bang Bang came across his work and suggested they team up.

The name might not ring a bell, but the tattoos he's done are very public: they're cascading down Rihanna, scattered across Miley Cyrus, and peering out from LeBron James, among others.

Turns out, Bang Bang loves tech.

"I would like to wave my hand and pay with my AmEx, or walk up to my car and it knows it's me," he said. Or maybe there could even be health applications - like alerting him if his blood sugar is high or low, just by looking at the color of his tattoos.

Scientifically, that is still way far off. If tattoo ink were to make the leap from cosmetics into the medical realm, it would require clearing all sorts of regulatory hoops.

"There's a lot of steps between where we are today and getting a functional tattoo that's going to tell you something about your health," Swierk said.

But Bang Bang thinks the product they're taking preorders for is step one toward building a consumer base that would be open to tattooable tech.

The first product they're offering to consumers is Magic Ink. It's a lot like that blue freckle on Bruns' arm, except it's red. For now, that's the only color available for purchase.

"That's how you can excite people," said Bang Bang. "It's almost a Trojan horse into that new goal of how do we bridge the gap between tattoo and technology."

It's US$100 (HK$780) for a half-ounce bottle. That's a lot more than regular ink costs. If the product takes off, the University of Colorado-Boulder will also benefit, as it owns the intellectual property.

Bang Bang is among a few dozen people who are already wearing the ink in their skin.

Tattoo artist Selina Medina has been in the business more than 20 years and used to work for an ink manufacturer. She spends a lot of time advocating for tattoo safety, volunteering with several national and international groups focused on the issue.

"I'd probably give it a year in the market before I would buy it. But it does look really interesting," said Medina, who is on the board of directors for the Alliance of Professional Tattooists.

Medina hopes this ink is different from the UV inks she saw pop up in the 2000s, which would glow under a black light.

"It seemed like an awesome idea, but then we noticed that it faded really fast," she said. "It would just disappear. We didn't know what it did. We didn't know where it went. And that was just kind of like: 'What the hell is this stuff?'"

She expects her customers will be clamoring for Magic Ink before she's ready to purchase it.

Further afield, some companies are already investing in technology embedded in the skin.

A European company called DSruptive makes injectable thermometers.

It said about 5,000 people - living primarily in Sweden, Japan, the United States and the United Kingdom - have had the devices installed.

Ali Yetisen, an engineer at Imperial College London, said for companies eyeing tech embedded in the skin, diabetes is a big focus.

"That's where the money is. Most companies invest in this area," said Yetisen. The dream is to create something like a tattoo that could measure blood sugar in real time, and be long-lasting, he said.

"That's the holy grail of all medical diagnostics,"

While Bruns' inventions sense external factors like light and radiation, for manufacturers looking to develop in-body tech that reacts to the blood, there are other scientific hurdles.

The immune system forms little shells around foreign bodies, effectively putting up a wall between a sensor and the blood.

No one has really figured a way around that yet, said Yetisen, but a lot of people are trying.

KFF Health News (TNS)

Nanotech gets under the skin