The glow of neon lights illuminates their translucent, bell-shaped bodies as they expand and contract rhythmically, their graceful tentacles flowing in wavelike patterns.
CU Boulder engineer Nicole Xu watches them with fondness. Xu, an assistant professor in the Paul M. Rady Department of Mechanical Engineering, first became fascinated with moon jellies more than a decade ago because of their extraordinary swimming abilities. Today, Xu has developed a way to harness their efficiency and ease at moving through the water in ways that could make some types of aquatic research much easier.
She fits the jellies with microelectronic devices that activate key swimming muscles, enabling researchers to steer them toward remote ocean areas that are hard to access in any other way. Eventually, she plans to add sensors to the devices that can gather critical data on temperature, pH and other environmental characteristics.
"Think of our device like a pacemaker on the heart," Xu said. "We're stimulating the swim muscle by causing contractions and turning the animals toward a certain direction."
Measuring changes in the ocean is essential to understanding how human activities are impacting all life on Earth. But because the ocean is so vast and deep, some parts are hard to study without prohibitively expensive equipment. The cyborg jellies could offer a way for humans to wade into these relatively uncharted waters.
Moon jellyfish are the most energy-efficient animals on the planet. They're prehistoric, with a simple body structure that has stayed the same for more than 500 million years. As invertebrates, they also lack a brain or spinal cord, though they do have basic organs and a pair of overlapping nerve nets. Importantly, the jellies do not have nociceptors, or sensory receptors that can detect potentially harmful stimuli.
Moon jellies can range from a centimeter to more than a foot in diameter. Their short, fine tentacles help them sting and catch prey like zooplankton, crustacean larvae and small fish. But thankfully for Xu, their sting cells can't penetrate human skin.
Though they're often found near coastlines, close to their favorite food sources, moon jellies live in diverse habitats worldwide and can swim to incredible depths: They've been found in some of the lowest places on Earth, including the Mariana Trench, which sits roughly 36,000 feet beneath the western Pacific Ocean's surface at its deepest point.
Xu co-created the biohybrid robotic jellyfish concept with her former academic advisor about five years ago, and she first tested them in the field in 2020, steering them around shallow ocean waters off the coast of Woods Hole, Mass.
On top of the implications for ocean and climate research, Xu believes we can draw inspiration from the jellyfish.
"There's really something special about the way moon jellies swim. We want to unlock that to create more energy-efficient, next-generation underwater vehicles," she said.
Xu, research associate Yunxing Su and graduate student Mija Jovchevska published a new study late last month that involved adding biodegradable particles to a jellyfish tank. The researchers then shone a laser through the tank to illuminate the suspended particles in the water and visualize how water flows when jellies swim.
In the past, researchers have used synthetic tracers such as silver-coated glass beads to look at underwater flow patterns, but the new study suggests biodegradable particles, such as corn starch, could be more sustainable, more affordable and less toxic alternatives.
She and graduate student Charlie Fraga are also working on making the jellyfish easier to steer in the wild. Going forward, Xu hopes to design other nature-inspired tools for studying the ocean.
There's more to learn about the ethics of studying invertebrates. In a paper published earlier this year, Xu and others pointed out the need for more investigation of how research affects invertebrates. It was once widely believed that invertebrates couldn't feel pain, but there is growing evidence that some do react to aversive stimuli.
Through all of her research, Xu says she strives to minimize harm to the animals she works with. When they're stressed, moon jellies may secrete extra mucus, and they often stop reproducing. But Xu's jellies have not shown increased mucus production, and small polyps-baby jellyfish the size of a pinhead whose tentacles are just beginning to form-line the inside of Xu's jellyfish tanks.
"It's our responsibility as researchers to think about these ethical considerations up front," Xu said. "But as far as we can tell, the jellyfish are doing well. They're thriving."
Research Report:Biodegradable tracer particles for underwater particle image velocimetry
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