An octopus’s adaptive camouflage has long inspired materials scientists looking to come up with new cloaking technologies. Now researchers have created a synthetic “skin” that independently shifts its surface patterns and colors like these intelligent invertebrates.
The ability to alter an object’s appearance on demand has a host of applications, from allowing machines to dynamically blend into their surroundings to creating adaptive displays and artwork. Octopuses are an obvious source of inspiration thanks to their unique ability to change the color and physical structure of their skin in just seconds.
So far, however, materials scientists have struggled to replicate this dual control. Materials that change color typically use nanostructures to reflect light in specific ways. But changing a surface’s shape interferes with these interactions, making it challenging to tune both properties simultaneously.
Now, in a paper published in Nature, Stanford University researchers cracked the problem by creating a synthetic skin made of two independently controlled polymer layers: One changes color and the other shape.
“For the first time, we can mimic key aspects of octopus, cuttlefish, and squid camouflage in different environments: namely, controlling complex, natural-looking textures and at the same time, changing independent patterns of color,” Siddharth Doshi, first author of the paper, told The Financial Times.
The new camouflage system took direct inspiration from cephalopods, which use tiny muscle-controlled structures called papillae to reshape their skin’s surface while separate pigment cells alter color.
To recreate these abilities, the researchers turned to a polymer called PEDOT:PSS, which swells when it absorbs water. The team used electron-beam lithography—a technology typically used to etch patterns into computer chips—to control how much different areas of the polymer swell when exposed to liquid.
The team covered one layer of the polymer in a single layer of gold to create textures that switch between a shiny and matte appearance. They then sandwiched another layer of the polymer between two layers of gold, creating an optical cavity that could be used to generate a wide variety of colors as the distance between the gold sheets changes.
The researchers can create four distinct visual states—texture combined with a color pattern, texture only, color only, and no texture or color pattern—by exposing each side of the skin to either water or isopropyl alcohol. The system switches between states in about 20 seconds, and the process is fully reversible.
“By dynamically controlling the thickness and topography of a polymer film, you can realize a very large variety of beautiful colors and textures,” Mark Brongersma, a senior author on the paper, said in a press release. “The introduction of soft materials that can expand, contract, and alter their shape opens up an entirely new toolbox in the world of optics to manipulate how things look.”
Applications could extend beyond camouflage the researchers say—for instance using texture changes to control whether small robots cling to or slide across surfaces or creating advanced displays for wearable devices or art projects.
The current need to apply water to control the appearance of the skin is “a huge limitation,” Debashis Chanda, a physicist at the University of Central Florida, told Nature. But the researchers told the Financial Times they plan to introduce digital control systems to future versions of the skin.
They also hope to add computer vision algorithms to provide information about the surrounding environment the skin needs to blend in with. “We want to be able to control this with neural networks—basically an AI-based system—that could compare the skin and its background, then automatically modulate it to match in real time, without human intervention,” Doshi said in the press release.
While the research faces a long road from the lab bench to commercial reality, sci-fi style cloaking technology has taken a tiny step closer to reality.
