UC Irvine-led team uncovers cell structures that squids use to change their appearance

(Press-News.org) Irvine, Calif., June 26, 2025 – By examining squid skin cells three-dimensionally, a University of California, Irvine-led team has unveiled the structures responsible for the creatures’ ability to dynamically change their appearance from transparent to arbitrarily colored states.

The group of scientists, which included collaborators from the Marine Biological Laboratory at Woods Hole, Massachusetts, found that in vibrantly colored squid mantle tissues, light-manipulating cells called iridophores or iridocytes contain stacked and winding columns of platelets from a protein called reflectin, with the columns functioning as Bragg reflectors that selectively transmit and reflect light at specific wavelengths.

In a paper published today in Science, the researchers discussed how they took inspiration from the cells and their internal columnar structures to develop a multispectral composite material with adjustable visible and infrared properties.

“In nature, many animals use Bragg reflectors for structural coloration,” said co-author Alon Gorodetsky, UC Irvine associate professor of chemical and biomolecular engineering. “A squid’s ability to rapidly and reversibly transition from transparent to colored is remarkable, and we found that cells containing specialized subcellular columnar structures with sinusoidal refractive index distributions enable the squid to achieve such feats.”  

Co-author Roger Hanlon, a senior scientist with the Marine Biological Laboratory, provided Gorodetsky’s UC Irvine team with access to squids, and his laboratory helped unravel the coloration and anatomy of the iridophore-containing tissues.

“These are longfin inshore squids – Doryteuthis pealeii – that are native to the Atlantic Ocean,” said Gorodetsky. “Marine Biological Laboratory has been famous for studying this squid and other cephalopods for more than a century, so we were fortunate to be able to leverage their world-class expertise with properly collecting, handling and studying these biological specimens.”

The team used holotomography, a microscopy technique that combines low-intensity light with quantitative phase imaging to create 3D images of clustered and individual cells. The instrument directly measures subtle shifts in light as it passes through the tissue and constructs a refractive index map of the sample, revealing structural and biochemical features.

“Holotomography used the high refractive index of reflectin proteins to reveal the presence of sinusoidal refractive index distributions within squid iridophore cells,” said co-lead author Georgii Bogdanov, a UC Irvine postdoctoral researcher in chemical and biomolecular engineering. “Platelets composed of the protein reflectin form winding platelet columns that fill the interiors of the iridophores. This complex system drives cephalopod mantle optics, with the cells and their internal structures regulating light transmission and reflection.”

Gorodetsky said the process of exploring and discovering the mechanisms underpinning the squids’ color-manipulation abilities inspired his team to develop flexible and stretchable visible appearance-changing composite materials from nanocolumnar sinusoidal Bragg reflectors and to then further augment these materials with infrared appearance-modifying capabilities by incorporating nanostructured metal films.

Using a suite of microscopy and spectroscopy instruments, the team verified that the modular and multifunctional composites could perform a variety of multispectral functions, including as camouflage, signaling, and sensing.

“These bioinspired materials go beyond simple static color control, as they can dynamically adjust both their appearances in the visible and infrared wavelengths in response to environmental or mechanical stimuli,” said co-lead author Aleksandra Strzelecka, Ph.D. candidate in chemical and biomolecular engineering. “Part of what makes this technology truly exciting is its inherent scalability. We have demonstrated large-area and arrayed composites that mimic and even go beyond the squid’s natural optical capabilities, opening the door to many applications ranging from adaptive camouflage to responsive fabrics to multispectral displays to advanced sensors.”

Gorodetsky said that the underlying fundamental insights gained from studying squid skin can be potentially broadly leveraged for improving a wide range of other optical technologies, such as lasers, fiber optics, photovoltaics, and sensors.

“This study is an exciting demonstration of the power of coupling basic and applied research,” he said. “We have likely just started to scratch the surface of what is possible for cephalopod-inspired tunable optical materials in our laboratory.”

Other team members were Sanghoon Lee, a UC Irvine postdoctoral scholar in chemical and biomolecular engineering; Nikhil Kaimal, a UC Irvine Ph.D. candidate in chemical and biomolecular engineering; and Stephen Senft, a research associate at the Marine Biological Laboratory.

The research was funded by the Defense Advanced Research Projects Agency and the Air Force Office of Scientific Research.

About the University of California, Irvine: Founded in 1965, UC Irvine is a member of the prestigious Association of American Universities and is ranked among the nation’s top 10 public universities by U.S. News & World Report. The campus has produced five Nobel laureates and is known for its academic achievement, premier research, innovation and anteater mascot. Led by Chancellor Howard Gillman, UC Irvine has more than 36,000 students and offers 224 degree programs. It’s located in one of the world’s safest and most economically vibrant communities and is Orange County’s second-largest employer, contributing $7 billion annually to the local economy and $8 billion statewide. For more on UC Irvine, visit www.uci.edu.

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