Tattoos are usually forever. A new kind of ink could make them optional from one day to the next.
Researchers at the University of Colorado Boulder have developed tattoo inks that stay nearly invisible in everyday light, appear when hit with ultraviolet light, and fade again on demand. The study, led by associate professor of biomedical engineering Carson Bruns, was published on October 9 in the journal Matter & Light.
How the ink works
The system uses three primary inks, blue, magenta and yellow, each made from photochromic dyes: compounds that change colour when they absorb particular wavelengths of light. The dyes are sealed inside nanoparticles of PMMA, a medical-grade plastic already used in implants and dermal fillers.
- A 365-nanometre UV LED switches the colours on in about two to three seconds.
- Different colours of visible light can switch individual channels off, so patterns and shades can be mixed.
- Under typical indoor lighting, activated colours last from hours to days. Bright sunlight erases them in seconds.
- The pigment stays in the skin throughout; only its appearance changes.
The inks can also be combined with ordinary black tattoo ink, so hidden parts of a design appear only when activated.
“PhotoTat is like a switch. You turn it on with UV light, but you can turn it off again when you go to grandma’s house,” Bruns said.
Tested on the inventor
Bruns tested each version of the ink on his own skin. In that single participant, all three colour channels could still be switched and rewritten 1.4 to 2.2 years after tattooing. The team also tested designs in silicone and in pig skin, and found the tattoos remained perceptible even in the darkest skin model tested.
What you can buy now
The technology is being commercialised as PhotoTat. So far only a purple ink, which third-party medical tests found safe, is on sale, at about $100 for a small bottle. The other colours need more research before they reach the market, and the formulations will need independent testing for toxicity, sterility and purity before wider use.
One practical catch: because sunlight contains UV, the inks can partly switch on outdoors unless protected with sunscreen.
Further reading
- Butterfield, Quigley & Bruns (2024), “Smart Tattoos of Intradermally Implanted Photochromic Nanosensors”, Advanced Functional Materials — earlier work from the same CU Boulder lab
- Photochromism — Wikipedia
- Tattoo ink — Wikipedia
Image: Italian-tattoo-artist-at-work by Technopop.tattoo, BY-SA 4.0 via Wikimedia Commons
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