Engineers use modified 19th-century photography technique to make flexible films that change color

Engineers at MIT funded by the U.S. National Science Foundation have repurposed a photographic technique from the 1800s and detailed the outcome in a paper published in Nature Materials.

The experiment resulted in films that change shades when stretched. It’s the first scalable manufacturing technique for producing materials with "structural color" — color that arises as a consequence of a material's microscopic structure.

"Scaling these materials is not trivial, because you need to control these structures at the nanoscale," said Benjamin Miller, one of the authors of the paper. "Now that we've cleared this scaling hurdle, we can explore questions like: Can we use this material to make robotic skin that has a human-like sense of touch? And can we create touch-sensing devices for things like virtual augmented reality or medical training?"

The team worked to replicate the microscopic surface structures of iridescent organisms on a much larger scale. The researchers noted that "an approach that offers both microscale control and scalability remains elusive, despite several potential high-impact applications."

Using holography — a photographic technique that dates to the 1800s — as an inspiration, the scientists successfully modified and modernized the technique.

The team attached transparent holographic films to reflective surfaces, then used a projector several feet from the film to project images on the samples. The films produced the images in detail within several minutes. When the films were detached from the reflective surface and stretched, the microscopic structural changes reconfigured the films' wavelengths and changed the films' color.

The technique, the first to enable large-scale fabrication of structurally colored materials, could improve bandages, packaging, surface coatings, textiles and wearables.