New Insights into Squid Coloration: The Role of Bragg Reflectors

In a groundbreaking study published on July 25, 2025, researchers at the University of California, Irvine (UCI) unveiled the intricate mechanisms behind the remarkable color-changing abilities of squid. Utilizing advanced holotomography, the team revealed that the optical properties of squid skin are derived from winding columns of platelets in specialized cells known as iridophores, which function as Bragg reflectors. This discovery not only enhances our understanding of cephalopod coloration but also holds potential applications in various fields, including materials science and adaptive camouflage.

The study, co-led by Alon Gorodetsky, a professor at UCI, and Georgii Bogdanov, a former PhD student under Gorodetsky, builds upon decades of research into cephalopod biology. According to Gorodetsky, “Our new result not only helps advance our understanding of structural coloration in cephalopods’ skin cells, it also provides new insights into how such gradient refractive index distributions can be leveraged to manipulate light in both biological and engineered systems.” This research offers a clearer picture of the complex three-dimensional structures within squid skin that allow them to transition between nearly transparent and vividly colored states.

In their experiments, the researchers focused on the longfin inshore squid (Doryteuthis pealeii), examining how iridophores, which are responsible for producing color, consist of stacked, winding columns of platelets made from a protein called reflectin. The unique arrangement of these platelets, alternating between high and low refractive indices, enables the squid to selectively reflect and transmit light at specific wavelengths, effectively acting as a natural Bragg reflector. This mechanism is akin to the structural coloration observed in other species, such as Morpho butterflies and panther chameleons, which also employ similar optical structures to achieve their distinctive appearances.

The significance of this research extends beyond biological curiosity. The study illustrates how the principles of structural coloration can be applied to the development of advanced materials. The team at UCI has begun exploring the creation of artificial nanomaterials inspired by the squid’s iridophores, which could have diverse applications ranging from adaptive camouflage technologies to enhanced optical devices such as sensors, displays, and lasers. Gorodetsky adds, “Composite materials like the ones we developed could revolutionize how we approach multispectral displays and photovoltaics, utilizing multilayered Bragg reflectors with sinusoidal-wave refractive index profiles.”

As the team continues to investigate the optical properties of these iridophores, they aim to refine their engineered materials to maximize performance for specific applications, including wearable technologies that respond to environmental stimuli. This innovative research not only sheds light on the biological marvels of cephalopods but also paves the way for future advancements in optics and materials science, highlighting the intersection of biology and engineering.

In conclusion, the findings from UCI underscore the intricate relationship between biological systems and optical engineering. The ability of squids to manipulate light through their skin serves as a reminder of nature's ingenuity and opens new avenues for research that could lead to transformative technologies. As the field of bio-inspired engineering evolves, the lessons learned from these marine creatures may prove invaluable in addressing complex challenges in science and industry.