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A team of engineers led by a scientist at �鶹��ý have invented what could become one of the biggest tattoo innovations since the artform debuted more than 5,000 years ago.

PhotoTat, as they call it, is a color-changing tattoo pigment that can temporarily vanish with light exposure.��

These aren’t your parents' tattoos.��

To make PhotoTat, engineers have encased tiny color-changing pigments of dye inside a glass-like sphere of material commonly used in medical implants. They’re put into the skin the same way as a normal tattoo. But the tattoo can change shape and colors when exposed to different wavelengths of light.

The nano-sized pigments are invisible to the human eye until activated by ultraviolet light. It takes just seconds for the pigments to turn on. The tattoos stay visible for hours or days if they’re only exposed to ambient, indoor light. But they will rapidly disappear after they’re exposed to bright, visible light.

They have both cosmetic and medical applications. Doctors have expressed interest in using them to replace the permanent tattoos they sometimes have to give cancer patients during treatment.��

The science behind PhotoTat was��

“It opens up a new dimension to what your body art could do,” said Carson Bruns,��an associate professor in the Paul M. Rady Department of Mechanical Engineering and �鶹��ý’s ATLAS Institute. “ Every tattoo pigment has always been this static thing that you put in your skin and it stays the same for the rest of your life.”

Bruns, who has been getting tattoos since he was 19, is determined to change that.��

Dynamic ink

A synthetic arm sports several examples of PhotoTat pigments that change color and activate when exposed to light. (Credit: Mollie Stockton/�鶹��ý)��

With PhotoTat, a tattoo of a black stop light could magically reveal a green, yellow or red light when exposed to UV light.��

A tattoo of a tiger could fill in orange when exposed to the sun’s rays.��

A bright flashlight could also quickly erase a tattoo that might not be suitable for certain settings.

“It can be that tattoo that you turn off when you go to court and your grandma’s house, and turn on when you go to the club,” he said.����

The tattoo pigments can also become a sort of blank whiteboard on the skin. Shining a bright light onto a stencil placed on an arm filled with PhotoTat pigments can activate custom shapes.��

The pigments still need to undergo medical testing before they are deemed safe to put in humans. But Bruns, who thrives in the labs of the ATLAS Center at �鶹��ý, has already tested them on himself.��

Two years ago, he adorned his leg with a series of what look like color-changing fish scales. When he exposes them to visible light, the scales activate and turn red, orange and blue

“PhotoTat gives us a full palette of color by mixing blue, magenta and yellow pigments,” he said.��

Tattoo curious? These turn on and off��

Bruns previously led efforts to invent the ‘solar freckle,’ a small tattoo that only appears when someone is exposed to high levels of UV light, reminding them to apply sunscreen.��

Carson Bruns

His latest invention could appeal to many different kinds of people, including the “tattoo curious” who might have hesitated to get one because they didn’t want to commit to a lifetime of one image.

“This solves the problem, and you can turn it off if you want,” Bruns said.

Bruns said the pigments could also be used in permanent medical tattoos that are used for cancer treatments.��

“A lot of involuntary tattoos are given for dermatological biopsies and radiotherapy,” he said. “It’s a permanent reminder of a traumatic experience. PhotoTat makes it so it can be a tattoo that’s visible when you go to a doctor, and invisible the rest of the time.”

Bruns said the team is still working to enhance PhotoTat, and then the dyes will have to go through clinical and safety testing before they are cleared for use.��