Stretchy material can cause bandages to change color when they come off

A stretchable material developed for holograms and an outdated 19th century photography technique have been combined to create a material that changes color as its tension changes

Technology


August 1, 2022



An outdated photographic technique that won a Nobel Prize more than a century ago has been resurrected to create a new material that changes color when stretched. It could be used to make bandages that notify doctors if they’re wrapped too loosely, or mechanical sensors that don’t require any electronics.

Materials that change color under voltage have been made in the lab before, but scaling up the process has proven tricky and expensive. The accuracy with which different colors can be printed on these materials has also been generally poor.

Now, Benjamin Harvey Miller of the Massachusetts Institute of Technology (MIT) and his colleagues have revived a technique called Lippmann photography, named after physicist Gabriel Lippmann, to create a cheap method that could print even the most intricate patterns in multicolor onto a stretchy material. . When this material is strained, colors shift along the visible light spectrum, with red sections moving first to greens and then to blues.

Lippman never had commercial success with the color photography technique he developed in the 1890s – which involved coating a glass plate with a fine-grained emulsion – because the exposure times for photographs reached often hours and images could not be reproduced from negatives. But his work nevertheless earned him the Nobel Prize in Physics in 1908.

Harvey Miller realized that the technique could be used to print on a material called a photoelastomer – which can change in response to light shined on it – instead of glass slides, projecting the desired image onto it with a digital projector.

He says the material used by the team was created for holograms, where its elasticity is an undesirable property that means it’s normally attached to a rigid backing plate.

“On a whim, I bought one of those high school hologram kits that you might buy at a museum or something,” says Harvey Miller. “And it turned out that I had most of the things we needed. Now, after spending three years of my PhD trying other ways to do this, I was almost bored, actually.

This image changes color when the material it is printed on is stretched

Massachusetts Institute of Technology

It was a surprise that a combination of materials developed for holography and an outdated photography technique could be combined to create materials with new characteristics, he says. “That technique sat there for a very long time without really being affected,” says Harvey Miller. “When we realized that and started thinking about writing an article, for the first two months we were like ‘surely someone did this, it’s kind of there for all to see’, but they just didn’t.”

The team says one application for the material could be mechanical sensors that can visibly show strain and strain, without the need for electronics. It could also be used in medical bandages to show how applied or incorporated into clothing for fun.

Team member Mathias Kolle, also at MIT, says similar advances could be possible by combining old scientific techniques and materials that weren’t available at the time. “I think more scientists should look back to the 50s and 60s, or even two centuries back, and say ‘hey, what did people do that was way ahead of their time? What are the things that they had like designs, but the materials just weren’t there?”

Journal reference: Natural materialsDOI: 10.1038/s41563-022-01318-x

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