Imagine a paint that can change colours in response to light exposure. Researchers at Northeastern University’s Kostas Research Institute (KRI) are exploring the possibility of replicating the natural ability of an octopus to change colours rapidly in response to threats or even just changes in light.

Cephalopods such as octopi and squid can change the colour of their skin due to the presence of a naturally occurring dye called xanthommatin in their bodies. KRI researchers are now experimenting with a synthesised version of this dye to create colourants that change in response to different stimuli, and using their findings to create natural paints that can change colours when exposed to light.

Cephalopods have been a starting point due to the unique nature of their skin, says Cassandra Martin, a research scientist at the institute. “Their colour change is so rapid and it’s so vibrant and it’s so intense. There’s not a lot of natural systems out there that change that fast and there’s not a lot of colour-changing materials that are that fast without requiring a lot of external (changes).”

The lab has previously created wearable patches that change colour when the wearer gets too much sun. Dan Wilson, senior research scientist at the institute, says the team wanted to try to find a way to make a material where this change could be reversed to return the material back to its original colour.

Last summer, Kaitlyn Flynn, then an intern/visiting student, was working on a project using this colourant. On researching further, she and the team found that titanium dioxide served as a conductor for the colour change – mixing different amounts with xanthommatin could speed up the change or add to the intensity of the colour shift.

The changes can happen in as quickly as five minutes and can last as long as 24 hours, depending on how long the paint is exposed to light. The colourant can easily be made in as little as two hours and added to water or oil-based paints.

The research was published recently in Advanced Science.

“We’ve imagined a scenario where if you want to have art that changes from day to day on an interior wall, like maybe in a coffee shop or something you could use a regular projector to project a pattern onto the wall, temporarily paint in this colour and this pattern or this art, and then over time that fades away and you can redo it again, ideally as many times as you want,” Wilson said.

“We can create temporary artwork or art or paint that could potentially track the weather or track the environment that it’s in.”

Going beyond temporary art, this discovery has environmental implications too as it can serve as an eco-friendly alternative to paints currently on the market.

“Paints that are commercially used nowadays can have harmful chemicals in them, so they can have things that can be harmful to the people that are painting them,” says Flynn who is now getting her PhD. in chemistry at Northeastern. “The fumes can be super harmful. They can be harmful long term if you’re exposed to them for a long time. They can also leach out into the environment. Searching for a more natural way to make these paints creates a safer environment for the people using it and for the people that are going to be exposed to it.”

The research team is now looking to apply this system to other materials and expand beyond the yellow-red colour palette. Eventually, users should be able to decide how quickly they want the colours to change on the paint.

Image: Researchers at the Kostas Research Institute found a component in squids and octopi can be used to create paints that change colours in different lights. Photo by Alyssa Stone/Northeastern University

Source: https://news.northeastern.edu/2023/10/12/colour-changing-paint-octopus-skin/