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How Sea Stars Build Materials That Can See

In the News, Research + Innovation, Research and Innovation / July 6, 2026

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Melissa Pappas

When engineers think about protective materials, like those used in packaging and support, they usually think about strength, stiffness and durability. But what if those same materials could also sense their external environment?

That question emerged unexpectedly for Ling Li, Associate Professor in Materials Science and Engineering, when his lab and colleagues were investigating how sea stars build lightweight yet resilient skeletons.

“We were looking at sea stars to understand how nature creates porous skeletal materials that are both strong and lightweight,” says Li. “Then we discovered lens-like structures embedded in the tips of the sea stars’ arms.”

That surprise became the focus of a study published in Proceedings of the National Academy of Sciences (PNAS), where Li, Ph.D. student and first author Liuni Chen and their collaborators from Penn Engineering, Virginia Tech, MIT, Bowdoin College, the University of South Carolina and the Zuse Institute Berlin, revealed that the skeleton of the sea star Protoreaster nodosus contains specialized mineral structures capable of guiding and concentrating light. The finding suggests that nature may have evolved a way to combine mechanical support and optical sensing within the same material system.

The sea star, Protoreaster nodosus, is commonly known as the horned sea star or the chocolate chip sea star and is found in the shallow waters of the Indo-Pacific region (© Liuni Chen).

Multifunctional Materials Found in Nature

Li recognizes that the discovery was accidental, but that the multifunctionality of the sea star skeleton is indeed intentional and expected.

“Natural materials often have to do many things at once,” Li says. “They provide structural support, protection, sensing and other functions. We study how these systems are designed and then extract the underlying principles that can inspire future engineering materials, such as lightweight, impact-resistant structures, self-monitoring materials that can sense damage and architected materials for aerospace, transportation and protective applications.”

Like other echinoderms — including sea urchins and brittle stars — sea stars build their skeletons from calcium carbonate, a mineral that engineers know well. Although lightweight and abundant, calcium carbonate is inherently brittle. Making it porous, a common strategy for reducing weight, typically makes it even more fragile.

Yet sea stars somehow achieve the opposite outcome. Their skeletons are highly porous but remain strong, resilient and capable of withstanding the demands of life in the ocean.

Li’s group originally set out to understand how this remarkable skeletal architecture works, which led to the discovery of a unique dual-scale architected microlattice published as a cover story in Science. But when they examined the tips of the sea star’s arms, they noticed something unusual: dozens of smooth, lens-like protrusions embedded within the mineral skeleton.

Li holds the skeletons of two differently sized sea stars, both showing the calcium carbonate skeleton.

Collaborating Across Fields to Understand the Sea Star

Using high-resolution imaging and optical experiments, the researchers found that these structures — called light-guiding structures — extend deep into the skeleton like tiny mineral cones. Rather than serving only a mechanical purpose, they can transmit and focus incoming light into an internal cavity within the skeletal element. Optical simulations showed that individual structures can guide roughly 70 percent of incident light while concentrating it at their base. Working together as an array, the structures collect light across a wide field of view and produce a signal several times stronger than any single structure alone.

The finding helped solve a longstanding mystery. Similar lens-like features had been observed decades ago in sea stars and brittle stars, but their function remained unclear.

“A different group had already identified related lens structures in brittle stars,” says Li. “When we found similar features in sea stars, we were able to connect the dots and investigate them systematically.”

Combining expertise in materials science, optics, biology, crystallography and computational modeling, the research team aimed to understand not only what the structures looked like, but also how they might function in the animal’s daily life.

Light sensing can help marine organisms detect predators, find shelter, locate food and navigate their environment. Although the exact biological role of the structures remains under investigation, the work demonstrates that the sea star skeleton is doing more than providing support and protection.

For engineers, that multifunctionality may be the most exciting...