Invisible, light-activated tattoo ink could appeal to both body‑art fans and medical professionals.
Image credit:©iStock.com, bobakphoto
Tattoos are inherently permanent. Yet what if they could be made temporary? While many people choose tattoos for self‑expression, others receive them for medical purposes—such as guides for radiation therapy in cancer treatment or markers for skin‑biopsy sites.
“They aren’t attractive, and they serve as a lasting reminder of a painful experience,” said Carson Bruns, a bioengineer at the University of Colorado Boulder, in a press release.
In a recent study published in the journal Matter & Light, Bruns and his team described a new tattoo ink that can make these reminders vanish when they are no longer needed.¹ The engineered ink, dubbed PhotoTat, remains invisible until exposed to UV light or specific visible wavelengths and is available in several colors.
A few seconds of UV exposure brings the invisible ink to life, revealing the colored tattoo; white light erases it again.
Matter & Light, Bruns et al.
“With PhotoTat, an involuntary medical tattoo could become visible only to a clinician during a visit and invisible the rest of the time,” Bruns added.
Light Activates Invisible Tattoos
To formulate the ink, Bruns and his team began with three photochromic molecules—blue, magenta, and yellow—that change color when struck by particular light wavelengths. They encapsulated these molecules in poly(methyl methacrylate) (PMMA) nanoparticles, choosing PMMA for its established safety and biocompatibility; it is already used in bone cement, intraocular lenses, and dermal fillers.² Indeed, a small safety trial of another PMMA‑based tattoo ink conducted by Bruns’s group showed no adverse reactions among the 11 participants.³
The team then evaluated PhotoTat on silicone and pig‑skin models. After a two‑ to three‑second UV pulse, the colored tattoos appeared; illumination with white light from an LED flashlight made them disappear again. By blending the three base colors in various ratios, they produced 16 distinct inks, allowing multicolored designs. Selective exposure to red, green, or blue laser light can deactivate individual photochromes, enabling tattoos that shift hue on demand.
PhotoTat Gets a Human Test
Carson Bruns tried PhotoTat on his own skin, injecting the light‑activated ink into his existing black fish‑scale tattoos.
Matter & Light, Bruns et al.
Bruns then tested the ink on himself. “I love body art because it’s deeply personal,” he remarked. He inserted the PhotoTat into several of his black fish‑scale tattoos on his legs; the sites healed normally. Roughly two years later, the tattoos remain functional, appearing and shifting color according to the light he applies.
Although rendering PhotoTat visible requires some UV exposure, the dose equals about six to ten seconds of ordinary sunlight. Nevertheless, the ink is still far from clinical use; it must first pass tests for toxicity, sterility, and purity.
In the interim, Bruns is enthusiastic about its prospects. “There is a stigma attached to body art in both scientific circles and many cultures,” he said. “I’m proud to be challenging that perception.”
