Tunicates Help Researchers Create Super-Resistant Building Material That Can Be Used For Just About Anything

NIST researchers have used dried-up tunicate bodies to develop a flexible and UV-reflective construction material.

Yellow and blue tunicates on a coral reef.
Agata Marianna / Shutterstock

NIST researchers have used dried-up tunicate bodies to develop a flexible and UV-reflective construction material.

When you think of tunicates, you most likely picture either flavorful Asian cuisine or your favorite fishing and diving spots gradually being taken over by these exotic pests. But these marine invertebrates, commonly known as “sea squirts,” have found a new usefulness in the field of science, ScienceDaily reports.

These water-filtering creatures are built like a barrel and get their name from the firm but flexible tunics covering their bodies, notes the University of Washington in Seattle.

Their morphology inspired researchers at the National Institute of Standards and Technology (NIST) to develop a new composite material, made up of two unusual components: dried tunicate carcasses and wood pulp, usually discarded after the processing of paper and commercial lumber.

This new material, described in a study that was featured in Advanced Functional Materials on Friday, is a builder’s dream come true — it’s flexible, sustainable, nontoxic, and it’s particularly resistant to cracking. It’s also UV-reflective and could be used as a protective coating for a number of things.

According to the NIST, the new material that came to life from a mixture of dried-up tunicates and wood pulp “could soon be used in a wide variety of applications, including food packaging, biomedical devices, building construction and the design of cars, trucks and boats.”

“The right product, if developed, could be used in everything from aerospace composites to packaging that would keep food fresh,” said Jeff Gilman, who led the NIST project.

The secret of its unprecedented adaptability lies in the method of combining the two raw materials, reveals a NIST news release. “This unlikely marriage of wood and pests,” as the researchers call it, is the first successful use of wood pulp in what is known as the “Bouligand structure.”

This structure offers the material a unique kind of resilience to cracking, because its molecules are stacked up in a twisted shape, which deflects the force of impact through a tortuous path of staircase-like twists and turns. This allows the overall material to remain intact and functional, making it impervious to cracking up to a certain degree.

Since this type of structure doesn’t naturally occur in wood products, the NIST team resorted to washing the wood pulp with acid and turning it into a milky solution filled with tiny crystalline rods of cellulose.

Known as cellulose nanocrystals or nanocellulose, these microscopic rods do possess a Bouligand structure but are too brittle to support any type of weight on their own. So, the team turned to tunicates for their unique physical properties and had the brilliant idea of combining the nanocellulose with dried tunicates.

As study lead author Bharath Natarajan explains, adding tunicates to the wood pulp composite made it stronger and more flexible.

“If your mixture is 30 percent tunicate and 70 percent wood pulp, the resulting composite is 15-20 times tougher.”

His team tested various mixtures with different tunicate-to-wood ratios and discovered that this was the optimum combination. Natarajan points out that adding more that 30 percent tunicate to the wood pulp composite ends up reducing the material’s toughness.