In December 2005, when winter the bottlenose dolphin was just a few months old, she was swimming with her mother in Mosquito Lagoon, along central Florida's Atlantic coast. Somehow she got herself tangled in a crab trap. An eagle-eyed fisherman spotted her struggling and called in a wildlife rescue team. The volunteers gently positioned the dolphin on a stretcher, carried her out of the water and drove her across the state to the Clearwater Marine Aquarium.
She was in bad shape when she arrived—exhausted, dehydrated, and sporting numerous cuts and abrasions. She could barely swim, and trainers stood in the tank with her, holding her little body up in the water. No one knew whether she would make it through the night. But she was a survivor, enduring that first night and the next one, too.
Slowly, with bottle-feeding and round-the-clock care, the team nursed the calf back to health. As Winter began to stabilize, though, other problems emerged. A line from the crab trap had been wrapped so tightly around her tail that it had cut off the circulation. The tissue was necrotic: the dolphin's skin started peeling off, and the tail itself began to decay. One day Winter's caretakers found two of her vertebrae at the bottom of her pool. Winter was getting her strength back, but her tail was clearly a goner.
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Although she didn't know it, in one way, Winter was lucky—she was born in the 21st century, and there has never been a better time for an animal to lose a body part. Materials ranging from carbon-fiber composites to flexible, shape-shifting plastics are making it possible for us to design artificial appendages for patients that fly, trot or swim, and prosthetists have succeeded in creating a new beak for an eagle, a replacement shell for a turtle and a false foot for a kangaroo.
Whereas sensors and tags affixed to animals' bodies could help save entire species, by informing conservation strategies, artificial tails and paws represent the other end of the spectrum: a way to provide a (sometimes literal) leg up to unlucky individuals. Prosthetic devices are not appropriate for every animal—indeed, one of the challenges prosthetists face is determining what is in the best interest of bodies that look nothing like our own—but when we get it right, our custom-designed and individually engineered devices are helping us aid animals one life and limb at a time.
Stumped
The Clearwater Marine Aquarium is located on an island just off Florida's Gulf coast. A few stairs lead from the main lobby to an open-air deck, where two dolphins frolic in a large tank. It is easy to pick out Winter—instead of a long full tail, she has a little curled stump that hangs off her torso like a comma.
Even with her abbreviated tail, Winter looks at home in the water, gliding and playing just like her fellow cetaceans. She has adapted to her unique body by adopting some unusual swimming techniques. Dolphins typically use their pectoral fins for balance, but Winter “cheats” and uses hers as little oars. And without the pair of flukes that typically adorn the end of a dolphin's tail, Winter lacks a dolphin's normal system of propulsion. So she taught herself to swim like a fish, moving her body from side to side, rather than up and down, as dolphins normally do. Unfortunately, this fishlike swimming posture puts unusual pressure on Winter's spine, causing it to curve unnaturally.
In the months after the dolphin's rescue, her caretakers began to worry that her strange method of swimming would cause permanent injury. In September 2006 an aquarium official mentioned this concern in an interview with National Public Radio, which was airing a segment about Winter. A prosthetist named Kevin Carroll happened to hear the broadcast while driving to his Orlando office. As he listened to Winter's saga, he thought: “I could put a tail on that dolphin.”
Carroll grew up near a hospital in a small Irish town, where seeing the ailing and injured children come and go inspired an interest in fixing the human body. Today Carroll is vice president of Hanger, based in Austin, Tex., and one of the world's leading prosthetists. Every once in a while, someone will walk into his clinic with a three-legged dog or a beakless bird and ask for his help. As an animal lover, Carroll finds himself unable to resist donating his weekends to the cause. Over the years he has worked with his Hanger colleagues to make prostheses for a veritable menagerie of animals: dogs, ducks, sea turtles, “whatever comes our way,” he says. “I've sort of become the Doctor Dolittle of prosthetics.”
When the aquarium agreed to let Carroll take a crack at a prosthetic dolphin tail, he began recruiting his team. He knew whom he wanted for a partner: Dan Strzempka, a prosthetist in Hanger's Sarasota, Fla., office. Strzempka, who has worn a prosthetic leg since he was run over by a lawn mower at age four, is a Florida native with a passion for the ocean and its creatures.
Carroll and Strzempka have agreed to meet me at the aquarium and walk me through how they tackled the task. They are an odd pair: Carroll is slight and cue-ball bald, with a white beard; Strzempka is tall, tanned and solidly built. When we get to the dolphin tank, Strzempka leans up against the railing and calls to Winter: “Hey, girl! What's up, buddy?” “Good marnin'!” Carroll shouts out to her in his Irish brogue.
Over the past five years the men have spent countless hours standing here beside this tank. Winter was unlike any other patient they had treated before, so the first task was understanding her body. Carroll and Strzempka began a crash course in dolphins, reading up on their anatomy and physiology and watching slow-motion videos of swimming cetaceans to understand their biomechanics. Although animal prosthetists can draw on human medicine, success often requires a degree of ingenuity; knowing how to build a leg for a human amputee won't get you far if you want to replace an elephant's missing foot or outfit a dog with a faux paw. So prosthetists often MacGyver each animal appendage, custom-designing and individually engineering it.
In Winter's case, the basic plan seemed easy enough—Carroll and Strzempka decided to create a plastic tail that would slip over what remained of Winter's peduncle, the muscular back half of a dolphin's body that normally runs from the dorsal fin to the tail flukes. The challenge, they realized, would be figuring out how to keep the prosthesis on. Winter would be putting an incredible amount of force on the tail while swimming, but she would not be pressing the entire weight of her body into it, as a human does with a prosthetic leg. “Water,” Strzempka reminds me, “is a totally different environment.” What is more, dolphin skin is slippery, sensitive and delicate—and very easily injured.
Human amputees commonly use soft liners to cushion their stumps and shield their skin, and Carroll and Strzempka decided that Winter would need something similar. The standard human liner would not do—for Winter, they would have to create a brand-new material, soft enough to protect her skin, sticky enough to stay put on a slick surface, and strong enough to withstand daily use and abuse in a tank full of saltwater.
They enlisted the help of a chemical engineer, who tinkered with the recipe for a gel liner common in human prosthetics, trying to create a version more suitable for a dolphin. The first few prototypes he made were promising, but their performance was inconsistent, and there were several dramatic failures, including a fire that burned a warehouse to the ground. (“It was a small warehouse,” Strzempka assures me.) Finally, the engineer nailed it.
“It's incredible material,” Carroll says, as we sit inside the trainers' office at the aquarium. He hands me a sheath of the rubbery gel, which is white, jiggly and slightly gummy to the touch. It resembles nothing so much as a supersized piece of calamari. Technically, the material is a thermoplastic elastomer—a mixture of plastics that begins as a liquid and can be molded into a variety of shapes when heated—but everyone just calls it the “dolphin gel.” Eager to show off its properties, Carroll takes a two-foot strip of the gel and hands the other end to Strzempka. He starts walking backward. Two, five, 10 feet—the material just keeps stretching. Finally, Carroll lets go. His end whips back across the room. Strzempka holds up the gel; it looks as good as new, neither distended nor deformed. The men beam, and I get the sense that this is a well-rehearsed stunt. The gel also provides serious cushioning, which Carroll demonstrates by wrapping his hand in the liner and beating it furiously with a heavy mallet, before breaking into a grin and pulling out his unharmed hand.
Keep Swimming
Winter is an old pro now, happily wearing a full-size, anatomically correct prosthetic tail. To put the device on, a trainer balances on a platform suspended in Winter's tank. With one swift command, Winter gets into position, pointing her head down toward the bottom of the pool and sticking her peduncle up out of the surface of the water. A trainer rolls a sleeve made of the dolphin gel onto Winter's stump. Then comes the prosthesis itself, which Carroll and Strzempka carefully constructed after taking a series of three-dimensional images and scans of Winter's body. The prosthesis has a flexible, rubberized plastic “socket” that slips on over the gel liner, hugging what remains of the dolphin's peduncle. The socket tapers into a thin carbon-fiber strip, which is bolted onto a pair of fake flukes. Suction keeps the entire apparatus on.
Although the device is modeled on a dolphin's natural tail, it is made of all sorts of unnatural materials, and Winter has to be supervised while she is wearing it. Winter's caretakers need to make sure that the tail does not suddenly start to slip off, for instance, or catch on something in the pool. So Winter does not wear the tail all the time. Instead it is reserved for her daily therapy sessions, when trainers lead the prosthesis-wearing dolphin through a series of drills designed to build up her muscles and reinforce proper swimming posture. The artificial tail helps keep Winter's spine in proper alignment, and with it on Winter does, indeed, flick her tail up and down rather than from side to side. “It's just beautiful to see her swim with it,” Carroll says. Winter's scoliosis has improved since she started wearing the device, and Carroll hopes the prosthesis, combined with regular therapy, will help the dolphin lead a long, healthy life.
Despite the progress she has made, Winter will spend the rest of that life in an aquarium; a dolphin without a tail, or with a human-fashioned one, is not a great candidate for survival in the wild. There is no telling how her prosthesis would hold up to years of constant use. And Winter will need continuing access to trainers to reinforce proper swimming posture and doctors to monitor her spinal alignment. Carroll and Strzempka are still making several new tails a year for Winter, who has not yet reached her full adult size, tweaking the design as her body changes. They also dream of making more dramatic improvements to the prosthesis. Strzempka would love to figure out how to incorporate a vacuum device that pumps air out of the tail whenever Winter moves it up and down. The result would be an even tighter seal and a self-adjusting prosthesis.
Winter's tail has earned her celebrity status. There are books, video games and documentaries about her, and in 2011 Warner Brothers released Dolphin Tale, a 3-D movie based on her story. (The prosthetist, or “mad scientist character,” as Carroll calls him, is portrayed by Morgan Freeman.) The aquarium's Web site and gift shop are chockablock with Winter gear: T-shirts, postcards, magnets and toy dolphins that are also missing their tails.
But Winter has become much more than a powerful marketing tool—she has also become an ambassador for prostheses. Children with prosthetic arms and legs regularly visit the aquarium, and many are invited into the tank with Winter. The encounter can do wonders for a kid's psyche, Carroll tells me.
Winter has helped human amputees in more concrete ways, too. As word spread about the so-called dolphin gel, prosthetists began ordering it for their human patients. The material, which grips the skin better than the liners commonly used with people, has proved especially useful for amputee athletes, whose replacement limbs start to slide off when they sweat. Strzempka, an avid golfer, became a convert the first time he tried the gel in his own artificial leg. “The stickiness is a huge benefit, especially in Florida,” he says. “If you're golfing 36 holes a day, your skin becomes like a dolphin's—slippery.” It did not take long for Hanger to start selling “WintersGel” liners to everyone from seasoned triathletes to 11-year-old girls. “Animals give back to us all so much,” Carroll says. “We learn so much from working with them.”