The Science Behind Cephalopods

The cephalopod family includes squid, cuttlefish, and the octopus – a group of exclusively marine animals with a prominent head and a set of arms. These intelligent and complex creatures have fascinated biologists for years, but now they are coming to the attention of the tech industry, thanks to some of their remarkable abilities – most notably the ability to change color.

Color changes are achieved by a combination of leucophores, iridophores, and chromatophores on the skin;1,2 the first two bodies act to scatter and reflect light, and the third can contract or expand to expose or cover pigment on the skin’s surface. Uniquely, cephalopods can also alter the physical form and shape of their skin,1 resulting in a sophisticated three-dimensional display of camouflage or courtship rituals. Also, some types of squid possess a structure on their underside called the light organ that houses luminous bacteria and a stack of tiny reflecting plates that control the luminescence, allowing the squid to manipulate the intensity to match any light coming from above, thus masking the creature from potential predators. Any of one of these adaptations alone would be a marvel, but deployed together; they allow the cephalopods to be shape-shifters – able to blend almost perfectly into their environment – both physically and temporally.

Octopuses have an amazing ability to blend with their environment. This octopus (Octopus cyanea) can change from blue to brown in a coral garden. It can also change the pattern and texture of its skin.
Wearable color- and shape-changing technology have clear applications for the military, but it could also be used in the leisure industry, and may even provide health benefits by allowing the wearer to regulate their thermal comfort or by giving direct continuous monitoring of vital signs.1 Many cephalopods also can squirt ink, a form of almost pure melanin (composed of polymerized networks of 5,6-dihydroxyindole).2 For many years, it was assumed that melanin was also involved in skin pigmentation, but recent research in cuttlefish has discovered that the pigments in the chromatophore are reflectin and crystallin proteins, and ongoing research in squid suggests there may also be ommochromes involved – a set of redox-active substituted phenoxazinones derived from tryptophan.3,4

We know that coloration changes in cephalopods are controlled by both chemical and mechanical stimuli,1 and this helps to guide how we approach our cephalopod-inspired tech. By using reflectin on a graphene sheet, researchers have been able to create color-changing films that respond to pH and artificial elastomers that respond to electrical stimuli. These pave the way for true camouflage fabrics, especially when different films are stacked to give different optical functionality, with clusters of pixels able to generate a range of colors.1 The three-dimensional plasticity of cephalopod skin is a source of inspiration for designers of systems that need reconfigurable shapes and textures.1,5 Research is ongoing to develop these futuristic materials. Reflectin has also been investigated in the field of bioelectronics, where a project is underway to develop devices and materials that are compatible with biological systems – an idea that could revolutionize medicine.6

Besides their unique skin properties, cephalopods also offer up new worlds in pharmaceutical research. In particular, the venom from some species represents a largely unexplored source of novel proteins, some of which may be derived from endosymbiotic bacteria.7 This is the case with tetrodotoxin, a potent neurotoxin found in the saliva of the southern blue-ringed octopus.7 This sodium channel blocker is currently undergoing clinical trials for cancer-associated pain treatment.8

Given that octopus and squid are a traditional part of the human diet in many parts of the world, looking at these creatures for new technological and medical advancements may mean a new lease of life for by-products from the food industry.

1. Phan, L.; et al. Dynamic Materials Inspired by Cephalopods. Mater. 2016, 28, 6804–6816.
2. Dinneen, S. R.; et al. Color Richness in Cephalopod Chromatophores Originating from High Refractive Index Biomolecules. Phys. Chem. Lett. 2017, 8, 313−317.
3. Deravi, L. F.; et al. The structure–function relationships of a natural nanoscale photonic device in cuttlefish chromatophores. R. Soc., Interface 2014. DOI: 10.1098/rsif.2013.0942.
4. Dissecting Cephalopod Camouflage. Eng. News 2015, 93, 32.
5. Halford, B. Octopus inspires electroluminescent skin. Eng. News 2016, 94, 7.
6. Ordinario, D. D.; et al. Photochemical Doping of Protonic Transistors from a Cephalopod Protein. Mater. 2016, 28, 3703−3710.
7. Whitelaw, B. L.; et al. Combined Transcriptomic and Proteomic Analysis of the Posterior Salivary Gland from the Southern Blue-Ringed Octopus and the Southern Sand Octopus. Proteome. Res. 2016, 15, 3284−3297.
8. Hagen et al. Tetrodotoxin for Moderate to Severe Cancer-Related Pain: A Multicentre, Randomized, Double-Blind, Placebo-Controlled, Parallel-Design Trial. Pain Res. Manage. 2017, 7212713.