Soft, algae-powered devices that glow in the dark when squished or stretched

The bioluminescent waves that may sometimes be seen at San Diego’s beaches during red tide events served as the researchers’ inspiration for these gadgets. The senior author of the research, Shengqiang Cai, a professor of mechanical and aerospace engineering at the UC San Diego Jacobs School of Engineering, was intrigued to find out more about what creates this stunning display while watching the glowing blue waves with his family one spring night.

Researchers at the University of California, San Diego have developed soft devices containing algae that glow in the dark when mechanically affected, such as squishing, stretching, twisting or bending. The devices don’t need electronics to produce light, making them ideal for building soft robots to explore deep seas and other dark environments. Credit: UC San Diego Jacobs School of Engineering

The source of the light is a type of single-celled algae called dinoflagellates. But what particularly fascinated Tsai was that dinoflagellates produce light when subjected to mechanical stress, such as the action of ocean waves. “It was very interesting to me because my research focuses on the mechanics of materials – everything related to how strain and stress affect the behavior of a material,” he said.

Tsai wanted to use this natural glow to develop devices for soft robots that can be used in the dark without electricity. He teamed up with Michael Lutz, a marine biologist at UC San Diego’s Scripps Institution of Oceanography who studies dinoflagellate bioluminescence and how it responds to different water flow conditions. The collaboration was a great opportunity to combine Latz’s basic bioluminescence research with Tsai’s materials science work for robotics.

To make the devices, the researchers inject a culture solution of the dinoflagellate Pyrocystis lunula into a cavity made of a soft, elastic, transparent material. The material can be of any shape – here the researchers tested a variety of shapes, including flat sheets, X-shaped structures and small pouches.

When the material is pressed, stretched, or deformed in any way, it causes the dinoflagellate solution inside to flow. The mechanical stress from this flow causes dinoflagellates to glow. A key design feature here is that the inner surface of the material is lined with small columns to give it a rough internal texture. This disrupts the fluid flow inside the material and makes it more durable. A stronger flow puts more stress on the dinoflagellate, which in turn causes a brighter glow.

The devices are so sensitive that even a gentle touch is enough to make them glow. The researchers also made the devices glow by vibrating them, drawing on their surfaces, and blowing air over them to make them bend and wobble — showing that they could potentially be used to collect airflow to produce light. The researchers also inserted small magnets inside the devices so they could be controlled by a magnet, glowing as they moved and twisted.

Devices can be charged with light. Dinoflagellates are photosynthesizing, which means they use sunlight to produce food and energy. The light on the devices during the day gives them the energy they need to glow at night.

The beauty of these devices, Tsai noted, is their simplicity. “They require almost no maintenance. When we inject the culture solution into the materials, everything. As long as they are charged by sunlight, they can be used again and again for at least a month. We don’t need to change the solution or anything. Each device is its own little ecosystem – engineered living material.”

The biggest challenge was figuring out how to keep the dinoflagellates alive and thriving inside the material structures. “When you put living organisms in a synthetic confined space, you have to think about how to make the space livable—for example, how it will let air in and out—while still maintaining the necessary properties of the material,” said the study’s first author, Chenghai Li. PhD in Mechanical and Aerospace Engineering. student in Tsai’s lab. The key, Lee noted, was to make the elastic polymer he was working with porous enough to allow gases such as oxygen to pass through it without leaking the culture solution. Dinoflagellates can survive in this material for over a month.

Researchers are now creating new glowing materials with dinoflagellates. In this study, dinoflagellates simply fill the cavity of pre-existing material. In the next stage of their work, the team uses them as a component of the material itself. “This can provide more versatility in sizes and shapes that we can experiment with moving forward,” Lee said.

The team is excited about the opportunities this work can bring to the fields of marine biology and materials science. “This is a good demonstration of the use of living organisms for engineering purposes,” Latz said. “This work continues to advance our basic research understanding of bioluminescent systems, laying the foundation for applications ranging from biological force sensors to electronics-free robotics and more.”

“High-Strength and Soft Biohybrid Mechanoluminescence for Optical Signaling and Illumination,” Chenghai Li, Qiguan He, Yang Wang, Zhijian Wang, Jijun Wang, Raja Annapuranan, Michael I. Latz, and Shenqiang Cai, July 7, 2022. Communications of nature.
DOI: 10.1038/s41467-022-31705-6

The research was funded by the Office of Naval Research and the Army Research Office