A rescued green sea turtle (Chelonia mydas) named Charlotte is getting the gift of better mobility this holiday season. Charlotte is one of many endangered turtles suffering from bubble butt syndrome, a serious injury which has partially paralyzed his back flippers and causes him to swim with his backside up instead of flat. Thanks to a team of volunteers, engineers, and 3D printing experts, the roughly 25 to 30 year-old reptile living at the Mystic Aquarium in Connecticut is the new recipient of a custom harness to help him regain some functionality and mobility.
What is ‘bubble butt syndrome’?
While the name may sound silly, bubble butt syndrome (or positive buoyancy syndrome) comes with some serious injuries to a turtle’s spine. It is typically caused by a strike from a boat that can lead to irreparable damage in the turtle. NOAA estimates that hundreds of thousands of sea turtles are struck by boats every year. Most rescued sea turtles with bubble butt syndrome cannot be released back into the wild due to their mobility issues.
“For turtles in general, their spine runs directly underneath the shell,” Claire Bolster, an aquarist at the Mystic Aquarium and Charlotte’s current handler, tells Popular Science. “So when turtles are hit by boats, most often the injuries go to their spines because it is directly connected. With the spine getting hit, the nerves to the gastrointestinal system also are impacted. They can also lose function of the rear flippers since those nerves are also damaged.”
Air then has a higher chance of getting trapped in the gastrointestinal system and causes the turtle to swim in a direction more perpendicular to the seafloor instead of straight ahead. Charlotte’s injury partially paralyzed his rear flippers and he struggles to control his buoyancy while swimming. This is why aquarium visitors will frequently see Charlotte swimming with his head down.
“You can kind of see where the air is trapped, depending on the day, based on which way his shell is tilted as he’s floating,” says Bolster.
Turtles like Charlotte with positive buoyancy syndrome (also called bubble butt syndrome) have difficulty maintaining their buoyancy when they swim. CREDIT: Formlabs.
According to Charlotte’s original intake form after he was stranded off the coast of Georgia, he was likely hit by a boat sometime around 2006 or 2007. He arrived at the Mystic Aquarium in 2008 as a juvenile who was not yet mature. It’s difficult to determine the sex of turtles, so the team assumed the still-young Charlotte was a female. As Charlotte has matured, it became apparent that he is male, which is why the team uses he/him pronouns.
While handlers like Bolster do not want to ascribe human traits to the animals in their care, she would describe Charlotte as “stubborn, but also very curious.”
“He’s definitely very engaged with turtle scratches,” says Boster. “They have so many nerves that run through that top shell and scratching serves as enrichment. He tends to stay put when we are doing that, so we take that as a sign that he’s enjoying it.”
Designing the turtle harness
To try to help Charlotte, there had been some attempts at making him a rehabilitation device or harness. However, Charlotte had some other ideas.
“The vet staff was joking around calling him ‘Charlotte Houdini’ because of all of the devices they’ve tried over the years,” Nick Gondek, an engineer and principal at 3D printing company Adia, tells Popular Science.
Eventually, the Mystic Aquarium sought the expertise from Adia. The company previously made custom orthotic boots for an African penguin at the aquarium, but had never worked on a project with a turtle. Adia also joined forces with the computational design team at New Balance Athletics. In addition to creating the athletic shoes, New Balance also has experience creating custom designs that can be printed with a widely available 3D printer from Formlabs.
[ Related: How does 3D printing work? ]
“The problem we’re trying to solve seems pretty simple,” says Gondek. “We have to weigh down the back end of the turtle and do so in a way which has adjustability for this air pocket that’s trapped in the GI tract.”
However, even a problem that sounds simple on a paper needs every bit of expertise it can get. Even if that knowledge comes from a budding scientist in high school. Gabriela Queiroz Miranda had been working on a weighted belt that could be used to help sea turtles with bubble butt syndrome while at Minnetonka High School in Minnesota. Her design even won her the prestigious 2019 Naval Science Award and she was a finalist for the Intel ISEF International Science Fair Award the same year.
“I am very passionate about creative problem solving and sea life, so I sought to combine the two in creating a solution for buoyancy that was better for the animals in captivity,” Queiroz Miranda, now a ride and safety engineer at Universal Orlando Resort in Florida, tells Popular Science.
She was brought onto the team at the start of the project in 2019, where she shared her award-winning design and knowledge with the team from New Balance and Adia.
“From there, we began setting parameters for Charlotte by identifying her key needs, including her specific shell geometry, buoyancy challenges, and viability of material implementation,” says Queiroz Miranda. “We scanned her shell and used the data to design a harness tailored to her unique requirements.”
Some early solutions lead to infections within the shell, so the team had to come up with a way to attach the weights without causing an infection. It also had to be comfortable, but not super easy for Charlotte to shimmy out of. The end result is the custom harness mechanism that Charlotte is using today. In all, it took five years and several tries to get the design right.
Charlotte seen getting used to swimming in his new weighted harness. CREDIT: Formlabs.
Charlotte’s new harness is made from Formlabs Nylon 11 CF Powder. This carbon fiber-filled material works when an object needs to be strong and stiff, yet also remain lightweight.
“Charlotte got like the Ferrari of turtle harnesses when he was fitted,” laughs Godnek.
The team used the Formlabs Fuse 3D printer, partially because of its track history with printing big things for animals. They were previously used by ZooTampa in Florida to create a prosthetic for a large hornbill. Charlotte currently weighs 138 pounds and he will keep growing, so the harness needed to fit his frame.
A better quality of life
The team at Mystic has already started seeing positive results from the harness. It is being used as a form of physical therapy, where Charlotte wears it for a few hours every day. As a result, his back flippers are starting to move a bit more and his tail is beginning to straighten out a bit.
“It is a common thing for an adult male green turtle to have a fully flat tail,” says Bolster. “His is currently curved underneath due to his injury and we’re seeing a little bit more of that tail straightening.”
The harness is also helping Charlotte equalize his buoyancy and no longer sleeps with his butt in the air. Sea turtles generally sleep at the surface of the water or underneath rocks or reefs in the wild.
“We’re also seeing him able to swim a little bit more neutrally buoyant, which is a very positive sign, because we can see him returning to a typical turtle behavior,” explains Bolster.
The final goal of this project is to help other turtles in need, by bringing this up to scale and creating a way that aquariums and rehabilitation centers can digitally create harnesses for the turtles they bring in.
“Engineering wise, I think it [this project] was a great reminder about usability,” says Queiroz Miranda. “The users here are sea turtles and veterinarians, so the device has to be easy for the veterinarians–who are not engineers–to adjust as needed, and comfortable to actually improve the quality of life for the sea turtles.”
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