Engineers at the Massachusetts Institute of Technology (MIT) have developed an exciting new smart material that responds to being stretched or pressured by changing color. It's even possible to encode secret messages on it and it’s all thanks its microscopic structure rather than to chemical additives or dyes. Oh, and the technology for this futuristic material actually comes from the year 1891.

This was the year Gabriel Lippmann invented this technique as a way to create color photography using a mirror and a special emulsion, where an image is imprinted after bouncing off the mirror. Despite being over 130 years old, for certain aspects, it remains unmatched. Lippmann won the Nobel Prize in Physics in 1908 for it.

MIT graduate researcher Benjamin Miller applied the Lippmann technique to modern holographic material. Similar to Lippmann’s emulsion, these materials respond to light but they can be prepared in a matter of minutes rather than days.

As reported in Nature Materials, Miller and colleagues first placed the material on aluminum sheets (a mirror-like surface) and projected images onto the sample. They then peeled it off and placed it on a black silicon backing for support. As the material was stretched, the nanoscale structures shifted so they began reflecting different wavelengths, some of them invisible to our eyes.  

The team has shown that the production of such material is perfectly scalable and is now investigating its properties. The film is sensitive enough to record impressions of coins, strawberries, and even fingerprints placed on it, which can be converted to maps of compressive stress. In fact, it has lots of potential applications.

“Scaling these materials is not trivial, because you need to control these structures at the nanoscale,” Miller explained. “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? It’s a big space we’re looking at now.”

Beyond robots, such a material could be employed in smart textiles like bandages that monitor pressure, something that wouldn’t have been possible with Lippmann’s original emulsion.

“Lippmann’s materials wouldn’t have allowed him to even produce a Speedo. Now we could make a full leotard,” Mathias Kolle, associate professor of mechanical engineering, added.

“The beauty of this work is the fact that they have developed a simple yet extremely effective way to produce large-area photonic structures,” said Sylvia Vignolini, professor of chemistry and bio-materials at the University of Cambridge, who was not involved in the study. “This technique could be game-changing for coatings and packaging, and also for wearables.”