Once the hallmark of bikers, sailors, and general riff-raff, tattoos have become far more mainstream, decorating the bodies of everyone from teachers to lawyers to world-class surgeons.
Nonetheless, being a 24-7 art gallery may not be to everybody’s taste. But new inks could add a degree of transience to tattoos, making them more like summer fashion than permanent features.
Called PhotoTat, the inks can be switched between almost invisible and brightly coloured states using different kinds of light. In the future, that could mean hiding a tattoo at a business meeting, revealing it later, or even rewriting what's on your skin.
A team of researchers led by University of Colorado Boulder chemist Carson Bruns developed three light-sensitive dyes that are encapsulated in tiny particles of polymethyl methacrylate (PMMA), a transparent plastic better known as plexiglass.
Under ordinary visible light, the dyes are almost invisible. Shine 365-nanometre ultraviolet light on them, however, and they rapidly switch on, producing vivid blue, magenta, and yellow colours.
The three colours can be combined to produce different shades and patterns. Once the UV light is removed, the colours gradually fade over hours, although bright visible light can make them disappear faster.
In other words, the same tattooed skin could display different images at different times.
“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,” says Bruns.
The researchers demonstrated this by using patterned UV light, stencils, and projected images to write designs into PhotoTat. In tests using silicone and excised pig skin, they produced multicoloured images, as well as tattoos that were almost invisible under ordinary light but appeared when illuminated with UV.
The technology could have applications beyond simply giving tattooed people a more flexible wardrobe.
One possibility is radiotherapy. Patients can receive small permanent tattoos to help clinicians align radiation beams with the correct part of the body. PhotoTat could potentially allow those marks to remain hidden until they are needed in a clinic, reducing the psychological burden of having a permanent reminder of treatment.
“They’re not beautiful, and they become a permanent reminder of a traumatic experience,” says Bruns.
“With PhotoTat, we could turn an involuntary medical tattoo into something that's only visible to the doctor when you go in the clinic, and then it can be invisible the rest of the time.”
The researchers also demonstrated a similar approach for marking biopsy sites, with the marks becoming visible when activated.
There is some evidence that the basic technology can persist in living human skin. In a single human participant, the three PhotoTat colour channels continued to respond to light and could be rewritten for between 1.4 and 2.2 years after tattooing.
But that is still a long way from programmable tattoos becoming available at your local parlour.
The human experiment involved just one participant, while the full patterned, multicoloured tattoos were demonstrated in silicone and pig skin. The researchers also found that the tattoos became less visible as skin pigmentation increased, although they remained perceptible in the darkest skin model tested.
And while PMMA and related photochromic materials have a history of medical use, the specific PhotoTat formulations still need independent testing for toxicity, sterility, and purity before they would be considered for widespread use.
There is another practical problem: sunlight contains UV. Outdoors, the inks can gradually shift towards an intermediate state, meaning keeping them fully hidden would require UV protection such as sunscreen.
Still, the idea changes the nature of a tattoo in a pretty fundamental way.
Instead of choosing an image you're prepared to carry for the rest of your life, you could eventually choose what you want your skin to display today.
This research was published in the journal Matter and Light.
Source: SciMex
