Imagine you are a small crab in the Indian Ocean, making your way across a shallow coral reef, when you’re suddenly caught in the tight grasp of a soft-bodied creature. You struggle to get away, but your legs don’t move — you have become prey. 

An unlucky meeting with a certain blue-ringed octopus cuts your trip short as its beak pierces your shell, allowing its potent venom to paralyze you. The iridescent, flashing blue rings covering its skin quickly disappear as the octopus returns to its camouflaged state.

The greater blue-ringed octopus, or Hapalochlaena lunulata, is one of the ocean’s most toxic animals. This golf ball-sized sea-dweller is known, and named, for its sophisticated ability to change its appearance. This unique feature of the blue-ringed octopus, to signal warnings and camouflage according to its surroundings, has now guided chemists and engineers in creating technology that can modulate and reflect light and heat.

Chromatophores to conceal and protect

Like many cephalopods — members of a highly organized class of marine animals, notably squid and octopuses — the blue-ringed octopus has thousands of specialized cells called chromatophores under its skin. These cells contain sacs of pigment that widen when the octopus is threatened. 

Chromatophores work extremely fast. Both squid and octopuses have control over these sacs, allowing them to react to threats in milliseconds. When alarmed, the octopus tightens the muscles surrounding the chromatophores, drawing back the brown areas around them to reveal a vibrant ring of blue. These blue rings flash until the danger has passed.

The flashes of blue are not created by a pigment but by a class of light-reflecting chromatophores known as iridophores. These cells reflect blue light because of the way they are structured, and are actually colourless. When the brown-pigmented chromatophores draw back, the thin layer of iridophores on top of the skin reflects an almost glowing, vibrant blue. 

In an instant, the octopus can activate its distinct pattern of blue rings against its natural yellow-tan base, sending a clear message of “STAY BACK.” The sophisticated modulation of these chromatophores allows the blue-ringed octopus to rapidly adapt to its surroundings, whether by blending into the tan colour of the sand to hide, or flashing a warning signal to predators while it hunts for food.

Drawing engineering ideas from an octopus

In a 2023 study in Nature Communications, researchers at the University of California Irvine (UCI) drew inspiration from this remarkable ability. The team, composed of several chemists and biomolecular engineers, was fascinated by the signalling mechanism of the blue-ringed octopus. The senior co-author of the paper, Alon Gorodetsky, told The Varsity in an interview, “We were most inspired by this ability to signal [a warning] by changing the intensity of those blue rings.” 

The signalling system of the blue-ringed octopus offers a solution to issues that the creators of current camouflage technology are still dealing with regarding sustainability. The function of the chromatophores does not deplete a lot of resources, so they can continue signalling as long as the octopus remains unharmed. In other words, the octopuses’ deception is sustainable. The chromatophores’ ability to sense the environment of the octopus allows the iridophores to stay uncovered, reflecting light for the duration of a perceived threat. 

When the chromatophores are closed, the octopus is a brown-yellow, camouflaging it into the sand. When the chromatophores are open, the reflective iridophores are revealed, sending a rapid and clear signal to potential threats. If a lab could invent a structure that could modulate its colour indefinitely like this, but also respond to change quickly and with as much precision as a blue-ringed octopus, then they could have a highly capable camouflage system. 

The researchers at UCI developed a designer dye using acenes — chemical compounds of linearly fused rings of carbon atoms — that could be either blue or brown, similar in appearance to the colours found in the blue-ringed octopus. Acenes are easily synthesized and can be modified to respond to pulses of electricity and light, but are often unstable. The larger the ring is, the more likely it is to lose its structure in open air, leading most acenes to deteriorate quickly after synthesis.

Gorodetsky and colleagues developed an acene variant that was noticeably stable and responsive and could flash blue upon activation using light. This acene-like molecule could survive years in the air, while also maintaining its responsive properties. Using this material, the researchers developed a system consisting of electrodes to conduct the command that controls blue-ring intensity, and a film of blue rings surrounded by brown circles that could continuously be triggered by ultraviolet and near-infrared light to flash blue rings.

How can octopus-inspired signalling be used in the real world?

A molecule like this acene variant has tremendous potential in technological applications. The key feature of these molecules is their responsiveness to light, whether it’s infrared, visible, or ultraviolet. “You can use them for tunable colour in clothing, potentially, or even vehicles after more development,” said Gorodetsky in an interview with The Varsity. 

The bioinspired devices can also be extended to manipulating heat. According to Gorodetsky, “You can change how heat is reflected or transmitted, and you can change how visible light is reflected or transmitted using the principles from these animals.” If you apply the same concept of tuning a molecule like acenes to reflect a specific light source, you could tune a molecule to a specific heat source, meaning this technology could be used in thermal management. 

Gorodetsky mentioned the applications of adaptable molecules in sustainable buildings. He spoke about the possibility of bioinspired facades for buildings that could adapt to the environment and regulate the climate of a structure with a reduced amount of energy. 

If a group of chemists and computer engineers can draw inspiration from marine life, surely we can find a way to make sustainable technology by observing the world around us. The greater blue-ringed octopus is a fascinating creature that reminds us that we can still learn so much from nature.