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Student start-up makes 3D printed prostheses more accessible for amputees

30 May 2022

Engineers from UC San Diego are taking smartphone scans of amputees’ limbs to provide free, custom-made 3D printed prostheses.

Every quarter, UC San Diego engineers Joshua Pelz and Luca De Vivo, as well as prosthetics specialist Herb Barrack, travel to Ensenada, Mexico, where they work with amputees to provide 3D printed prostheses.

The team takes scans of the amputees’ residual limbs with smartphones, which they then bring back to the UC San Diego campus. They use the scans to build a digital model of the amputated limb and a compatible prosthesis. Then, using a 3D printer the team developed, the prosthesis is printed in just 12 hours.

After the prosthesis is 3D printed, the team returns to Mexico, where they fine-tune the fit. The project is supported by the Rotary Foundation and is looking for other funding sources as well. 

The World Health Organization estimates that there are 40 million amputees in developing countries, 95 percent of whom have to make do without a prosthetic limb. This is because prosthetic limbs are expensive and time-consuming to manufacture. Patients have to undergo repeated visits to doctor’s offices and need to have access to specialists.

Using this combination of personalised scans as well as digital designs and 3D printing on a large scale could reduce the cost of a prosthesis by anywhere from 50 percent to 90 percent – and deliver prosthetics much faster to those who need them. Pelz, De Vivo and Barrack have formed a start-up, LIMBER Prosthetics & Orthotics, Inc., to commercialise the technology.

LIMBER’s business plan is two-fold. The company plans to sell its personalised prostheses in developed countries while providing its services for developing countries at discounted prices or for free.

The company will revolutionise access to prostheses for amputees, said Diana Zambrano, a San Diego resident who is herself an amputee and has helped the team test the devices.

“Mobility is a necessity,” Zambrano said. “LIMBER can print out a leg in a day, and right away, you have a leg to walk on. It’s amazing.”

LIMBER’s methods will also make prostheses much more affordable – costs currently can run upwards of $20,000, Zambrano said. “It’s going to be wonderful to have prosthetics that are affordable for everyone,” she added.

The LIMBER devices are comfortable, she said. They are also made from water-proof materials, in contrast to traditional prosthetics made of carbon fibre and metal. Materials for prosthetics have improved dramatically over the last 35 years, from wood all the way to space-age materials and materials that can be 3D printed, said Barrack, who is a certified prosthetist and orthotist.

LIMBER has conducted many tests to see what kinds of loads 3D materials could bear and design their prosthetics accordingly, Barrack said. They also are conducting testing to make sure the prosthetics are safe. “Patient safety comes first,” he said.

Democratising prosthesis

Traditionally, a model of the residual limb is carved by hand by a specialist; a time-consuming process that is expensive and can’t be replicated. “They are like sculptors,” De Vivo said. “And there are not enough of them.” Specialists then build the prosthesis to fit around this model.

Instead, LIMBER uses digital tools to democratise access. The team is using an off-the-shelf app on their phones to scan the amputated limb. They upload the data to a computer-aided design program to build a digital twin of the patient’s residual limb. They then build a model of the prosthesis to complement the digital twin. This allows the researchers to save a lot of time, as they don’t have to do several fittings to get the shape of the prosthetic right.

Researchers also decreased the weight of the prosthetic by using cutting-edge 3D printing materials. Most of their new prosthetics are made from a combination of nylon and nylon filled with chopped carbon fibre. By 3D printing with the two materials, the team can vary the stiffness of the limb, making the foot more flexible, for example. Researchers also built a custom 3D printer from the ground up.

Bioinspiration and next steps

The design of the prosthesis is inspired by the structure of the Cholla cactus, which De Vivo studied both as an undergraduate and graduate student. The cacti’s wooden skeleton needs to withstand difficult desert conditions and hurricane force winds. It does this thanks to its skeleton: a cylinder of wooden fibres that crisscross at a 45-degree angle, with oval empty spaces in between them, a little like a chain link fence. This open space allows the cacti skeleton to bend or rotate in windy conditions.

Pelz and De Vivo are still working to perfect their process. They are now conducting materials testing. This summer, they will start a human subject study to evaluate the prosthetics’ performance. They also plan to incorporate sensors within the prosthesis for better performance. Their work will be documented in several scientific articles set to appear this year.

“Digital twin technology combined with 3D printing holds tremendous promise to change the way prosthetics are manufactured – and made accessible,” Kuester, the Structural Engineering Professor, said.

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