How scientists learn from the masters of invisibility: octopuses
Octopus and other cephalopods are good at hiding themselves—and are inspiring cutting-edge technologies that may help us do the same.
When it comes to near-invisibility, the world champions may be the octopus and other cephalopods, which can shift their color and texture on cue to become virtually indistinguishable from their surroundings. As an octopus glides across sand, tucks itself between rocks, and wriggles into a clump of seaweed, its color and texture shift continuously, transforming from grainy beige to mottled grey to iridescent green to match different backgrounds. Squid, too, have an uncanny ability to trick the eye, turning shiny, iridescent, and even transparent against the flickering background of underwater light.
How cephalopods achieve this instantaneous camouflage is a mystery that has tantalized humans since at least 350 BCE, when Aristotle made observational notes on the subject, says Leila Deravi, associate professor at Northeastern University, whose BioMaterials Design Group specializes in biomimicry.
“Cephalopods have so many different optical organs in their skin with a lot of different functions,” Deravi says. “They also have really complicated neuromuscular controls that elevate their ability to create dynamic displays in a way that no other animal in nature can do.”
We humans may be able to learn from these creatures. Scientists have recently demonstrated a crop of innovative materials that mimic these biological processes—stretchable, reflective skins, light-refracting color-changing membranes, light-scattering films and fibers, and texture-changing silicon-mesh fabrics with the potential to trick the eye, avoid detection, and seemingly disappear.
Most research is still in the testing and prototype phase as scientists collaborate with engineers and manufacturers to improve scalability and overcome production challenges. But Gorodetsky, an associate professor at the University of California at Irvine, who has pioneered numerous cephalopod-inspired camouflage materials, says interest from manufacturers is high and products could begin to reach consumers within the next decade.
"It feels very slow, but we've made some very significant advances,” he says. “And when you introduce a really exciting technology into the wild, then people will do all sorts of interesting things with it, things we couldn't possibly have imagined.”
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(These are the weird and wonderful reasons octopuses change shape and color)
Playing with pigments
Cephalopods have tiny sacs under their skin called chromatophores that contract to release a color-changing pigment called xanthommatin. For some researchers, this pigment is the key to bringing undersea magic to the human realm.
Recently, Deravi and colleagues at the University of California San Diego’s Scripps Institution of Oceanography announced they had developed an efficient, nature-based method for producing the rare pigment in unlimited quantity. In contrast to previously existing methods that required expensive precursor chemicals and produced only tiny amounts of the pigment, lead researcher Leah Bushin, now an assistant professor at Stanford University, genetically modified a bacterium such that it needed to produce xanthommatin to survive.
“Usually when we try to engineer microbes to make a compound that we want, the microbe has no incentive to make it,” Bushin says. “So we wanted to rethink this and say, ‘is there a way that we can make it beneficial for the organism to actually want to make the compound?’”
This study produced the compound on a small scale. But researchers say the simplicity and affordability of the process means that the sky’s the limit in terms of how much xanthommatin could be produced, the researchers say.
“Being able to do fermentation of an organism and grow it on simple sugar and water and get an expensive material out of that is really the holy grail of the chemical engineering community,” says study co-author Brad Moore, also of U.C. San Diego. “We’re training or engineering these bacteria to become super-efficient little chemical factories living in a cell.”
In fact, the lab is producing xanthommatin so inexpensively that Moore has high school volunteers experimenting with making paints from the pigment and using them in art projects. “We’re very much amateurs right now but we’re having a lot of fun with it,” he says.
Color-changing paints may be the first application that comes to mind, but the pigment could have many other uses in coatings, electronics and cosmetics. Deravi’s lab has patented a cosmetic version of the pigment under the name Xanthochrome for use in sunscreens and skin care. And together with Camille Martin, formerly a graduate student researcher in her lab, Deravi launched the skin care company Seaspire to market Xanthochrome and products containing the pigment.
“What our research showed was that the inclusion of xanthommatin can boost the critical wavelength of sunscreen made with zinc oxide, so it doesn’t just protect against UV light but has visible light protection as well, which is important for protecting against photoaging.” The effects of photoaging on skin include skin darkening or “age spots,” wrinkles, and spider veins. Another benefit: Xanthochrome has proven entirely reef-safe, showing no ill effects when tested on coral cuttings, according to Deravi’s research.
(The deeper this purple octopus lives, the bumpier its skin)
Meanwhile, the simple process of genetically engineering microbes to become pigment factories has wide-reaching possibilities for producing other compounds, particularly those used in antibiotics and other pharmaceuticals.
“Making materials to support 8 billion people on planet Earth really is a costly thing, so being able to simplify that is paramount to being economically viable,” Moore says. “And we can do this process anywhere—every small town in the U.S. that has a brewpub has a fermenter.”
How cephalopods reflect, refract, and redirect
In addition to chromatophores, a lot of biological camouflage research focuses on two other components in cephalopod skin: iridiphores, which reflect light at different wavelengths to create more opalescent colors, and leukophores, which scatter light to appear white.
In June, researchers at the University of Chicago’s Marine Biological Laboratory (MBL) at Woods Hole and the University of California at Irvine identified the mechanism in squid skin that allows the elusive creatures to switch between transparency and various opalescent hues on demand.
“Very few animals can change their iridescence, and the squid does it in milliseconds,” says Roger Hanlon, senior scientist at the MBL, whose Hanlon Lab focuses on animal-inspired camouflage. “So that dynamic change of structural coloration, that's what the human world wants in terms of engineering.”
Using advanced 3D imaging technology, the researchers mapped the structure of iridophores, identifying closely stacked columns of reflectin proteins that work like the miniscule multi-layered mirrors to dynamically manipulate light.
“Squid have a remarkable ability to transition from colored to transparent and in this study we found that cells containing these specialized columnar structures allowed them to accomplish this,” says Alon Gorodetsky, associate professor at the University of California at Irvine and researcher on numerous squid-inspired bioengineering studies, including the one that came out in June.
The researchers then went a step further, engineering a flexible camouflage skin that mimics the action of the reflectin structures.
The findings build on a fast-growing body of research going back to a 2017 study that demonstrated a programmable texture-shifting skin capable of morphing from 2D to 3D, just as an octopus might turn bumpy to match jagged rocks. In 2018, Gorodetsky and fellow researchers published another headline-grabbing study in which they demonstrated an elastic squid-inspired skin that when pulled from wrinkled to smooth could evade infrared detection by changing the way it reflected light.
In a related study published in December 2023, Gorodetsky and fellow researchers created a signaling device inspired by the blue-ringed octopus with the ability to change both color and pattern across the electromagnetic spectrum, making it possible to trick detection systems. The device also has the ability to repair itself when damaged, an advantage in inaccessible conditions such as outer space.
("Bizarre" Octopuses Carry Coconuts as Instant Shelters)
Incognito advantages
All of these developments are relatively early stage, and have challenges associated with mass-production, but experts say that solid groundwork has been laid for some of these camouflage innovations to eventually come into real-world use.
So will cephalopod-inspired camouflage make a Harry-Potter-style invisibility cloak a reality? Not quite, but camouflage innovations still offer tantalizing possibilities.
“I don’t think it’s physically or scientifically possible to turn invisible, basically because you’d have to break too many laws of physics,” says Gorodetsky. “But while I can’t be invisible, I can look so similar to my background that you can't tell I'm there. And if that happens, then the question of visible or invisible becomes semantics.”
Another way to describe this type of pseudo-invisibility is hiding in plain sight, says Hanlon. “If you’re an octopus or any other animal, you have two choices in the visual world not to get eaten, and one is not to get detected, and the second is to put on a pattern that can't be recognized. And those in a nutshell are the two basic ways that animals play this very key evolutionary game.”
The materials Hanlon and colleagues engineered have military defense applications, such as hiding equipment and soldiers from thermal drones. “I personally have a lot of military background and I've been in a place where I wish I'd had better camouflage in the real world,” says Hanlon, adding that hunters could also benefit from the technology.
There are also plenty of other everyday uses for these experimental materials, from reflective layers in building materials that could self-adapt to changes in environment to coatings that could keep electronics from overheating, Gorodetsky says.
“I would really love to have a technology that people use on an everyday basis, whether it is something as simple as camping gear or some sort of clothing that's slightly more colorful and comfortable,” he says. “That’s a major dream and goal of mine that I hope will happen in the next decade.”
