Three-legged dog to get 3-D-printed limb from UC Davis students

Andrea Bledsoe has recruited a few of her fellow UC Davis graduate students to design and create a fourth leg for her dog, Hobbes.
Andrea Bledsoe has recruited a few of her fellow UC Davis graduate students to design and create a fourth leg for her dog, Hobbes.

Hobbes the terrier mix can do a lot, for a dog with three legs. He can climb stairs, graze the backyard and jump roughly 4 feet in the air – more than high enough to clamber onto the bed with his owner, Andrea Bledsoe.

Even so, Bledsoe and a few of her fellow UC Davis graduate students are determined to give him a fourth leg. They’ve cast him in a plaster mold, fitted him for harnesses and tried a few materials in an effort to come up with a design for a prosthetic limb, which they plan to produce with a 3-D printer.

The project took root after Bledsoe, a veterinary student, adopted Hobbes from a pet clinic, where he was taken about two years ago with a badly broken front left leg. The break had healed incorrectly, and the veterinary surgeons were forced to amputate, she said.

Fortunately for Hobbes, his owner’s friends Randy Carney and Holly Abney have a knack for materials science and animal anatomy, respectively. The two put their heads together to find a way to help their furry friend and started on what’s turned out to be a challenging extracurricular project.

“When he goes on long walks, he starts to get fatigued, and it seems that it’s because he has this weird hop he has to do to move forward,” said Carney, a postdoctoral fellow in biochemistry and molecular medicine. “And he’s so young and full of energy that it seemed like a waste if he couldn’t get moving like he wanted to.”

Carney, who has a master’s and doctorate in materials science, initially thought he could mold a leg from carbon fiber but later decided it could be done more cheaply and safely using a 3-D printer. When he found out there was a public-use machine at Arcade Library in Sacramento County, the choice was clear.

Put simply, the library’s 3-D printer creates an object by putting down layers and layers of melted material. First the operator sends a design, either pre-existing or created using computer software, to the printer, which is loaded with a spool of hard plastic. A small motor feeds the filament through a metal extruder, which heats up to melt the material. The machine lays out the melted plastic in the shape demanded by the design – a process Carney likens to a “hot glue gun that moves in three directions.”

Once a novel and futuristic concept, 3-D printing has become increasingly accessible to Sacramentans in recent months, through schools, co-working spaces and, perhaps most notably, the Sacramento Public Library system.

Since spring 2013, the Arcade library has provided a 3-D printer in its “Design Spot” free of charge, and it’s been immensely popular. The small room set aside from the books gets 15 to 20 visitors each of the three days of the week that it’s open. People make everything from holiday gifts to miniature artworks – but Hobbes’ leg will be the first medical device, said Design Spot volunteer Tom Sanderson.

Just a few weeks ago, the Fair Oaks library purchased its own 3-D printer with money raised by selling used books. Library officials there haven’t yet decided whether they’ll make it available for general use or for classes only, but word got out and people are already calling, according to library services assistant Sabrina Hill. Robbie Waters Pocket-Greenhaven Library bought a printer in the fall and uses it to teach monthly 3-D printing classes for adults.

“They’re fascinating machines,” Sanderson said. “It gives some of our clients a new way to think about the world. Maybe we don’t have to run to the dollar store to get something anymore. We can print it if we have a 3-D printer at home. Or we can come here!”

Jim Carroll, a retired Roseville resident, takes classes at Hacker Lab in midtown – the only other spot offering 3-D printers and education to everyday folks. Carroll recently purchased his own 3-D printer – consumer models sell for anywhere from $300 to $2,000 – and has been making knickknacks such as screw caps and coffee cup holders.

Though sales of consumer-friendly 3-D printers so far have been limited to tech-savvy hobbyists, industry analyst Gartner Inc. projects the market will grow 97 percent annually over the next five years, with 826,000 printers being sold per year by 2017.

Those looking to explore the third dimension have an important choice to make: they can take a pre-existing digital design from a massive free archive called Thingiverse, or come up with their own using computer-assisted design software, a far more intensive process.

“It’s something that’s not mainstream quite yet, but it should be,” he said. “Every home should have one of these. But the barrier to entry is not cost, it’s knowing the software. It’s a steep learning curve.”

While the 3-D printing trend has been a hotbed for business ideas (two Placerville designers launched a profitable multi-tool after experimenting at the library last year), the real promise for its future lies in the medical possibilities, said Alan Ware, maker space manager at Hacker Lab.

In recent months, the Internet has been swarmed by heartwarming stories of children getting customized 3-D-printed prostheses, some made to look like a stormtrooper’s arm or the mighty Thor’s hand. Hearts, livers, exoskeletons and even cells printed from biomaterials might soon be a reality.

“Some of the coolest stuff you’ll see with 3-D printing is in the medical field,” Ware said. “Creating solutions tailored for individual people is a very powerful thing ... If you think about the World War II stump, we’ve come a long way.”

Printed prostheses are still rare for animals, though, Carney said. Buttercup the duck got national attention when he received a 3-D-printed webbed foot last year. A December video of Derby the dog running for the first time on 3-D-printed prostheses has nearly 8 million views on YouTube. If Hobbes’ leg works out, he too could become famous.

But fitting a pet with a peg leg is no easy stunt. Carney and Abney, both busy with graduate studies, spend as much time as they can spare brainstorming for Hobbes and redesigning prototypes.

His case is especially challenging because his leg was amputated so high up, leaving no stump to attach to, Abney said. To solve the problem, they came up with a harness design that wraps around Hobbes’ chest with the leg protruding out. Carney printed the harness in a flat form on the Arcade printers, and then heated the material so it would bend around Hobbes for fitting. Carney is now experimenting with the leg itself and whether he can give it any spring-back capabilities by using a special printing filament called NinjaFlex.

Most three-legged dogs can function just fine without a fourth limb, said Abney, a second-year veterinary student, but the team figured they’d give it a shot anyway. Even if Hobbes doesn’t take to the limb, their design could have implications for animal prostheses in the future.

“It’s extremely exciting to me, and much more exciting than studying at this point,” she said. “It’s nice to get hands-on and try to help an animal, instead of sitting home learning about helping an animal all the time.”

Call The Bee’s Sammy Caiola, (916) 321-1636.

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