Advancing prosthetics development with 3D printing

From makers to professional engineers, 3D printing has long been used to develop prosthetics because it can save time and money. It also helps stimulate innovative thinking, which led to this fully functional hydraulic prosthetic arm. Ben Ryan, founder of Ambionics, developed the prosthetic for his two-year-old son, Sol using a Stratasys multi-material, multi-color PolyJet 3D printer.

Researching infant development with prosthetics, Ryan developed this unique prosthetic for infants to wear, enabling a more natural acceptance of prosthetic arms for young children.

An unparalleled innovation within this sphere of the medical field, the custom design and production of the 3D printed hydraulic prosthetic has delivered cost savings of up to 76%, as well as time savings in design and production of 90%, compared to traditional methods of manufacture. This crucially permits prosthetics to be used at an earlier developmental stage.

When Ben’s son, Sol, was born in March 2015, complications resulted in the amputation of his lower left arm. Although able to keep approximately one inch of his lower arm, Sol would have to wait three years for a myoelectric prosthetic from the UK National Health Service (NHS), and one year before a cosmetic, non-functional prosthesis would be fitted. Ben saw his son losing responsiveness and acceptance of his left arm, and decided to act.

Based on his research into infant development, Ben saw that higher rejection rates occur when children are fit after the age of two years and that early fitting of functional devices correlates with continued prosthetic use throughout childhood. Another study* also found that children fitted before two years of age tend to accept their powered prosthesis more than those fitted after two years. With this in mind, Ben first designed a foam arm for his son, and later a hydraulic prosthetic, enabling Sol to move his thumb on his own.

Ben designed and created his 3D printed hydraulic prosthetic arm on the Stratasys Connex 3D Printer. First practicing with prototypes of his design, Ben 3D printed flexible actuators and a power-splitting unit (double acting helical bellow or DAHB) for the prosthetic. According to Ben, the DAHB unit enables the wearer to open and close the thumb in manual mode or with assistive power (using compressed air or a hydraulic pump and reservoir), but the grip continues to operate manually in the event of power interruption.

“The success of my patented DAHB mechanism draws on the advanced capabilities of the Stratasys Connex Printer – the ability to combine rigid and soft materials in a single print was vital to the success of the design,” explains Ben. “We were fortunate enough to have access to this technology, which enabled us to 3D print a prototype arm quickly and cost-effectively. In founding Ambionics, it’s now my goal to ensure that other limb deficient children like my son are not faced with the current constraints and delays of traditional prosthetic manufacture.”

To develop the design for the prosthetic, Ben relied on the use of Autodesk Fusion 360.

“This is a very innovative and ambitious project and it’s been inspiring to work with Ben on it,” says Paul Sohi, a product design expert at Autodesk. “It is amazing that despite Ben having no real background in product design, he’s effectively taught himself enough to create something that will not only help his own son Sol, but in Ambionics, potentially others facing the same challenges too.”

As well as its lightweight 3D printed design that weighs less than traditional myoelectric alternatives, the hydraulic prosthetic is body-powered and enables infants to grow accustomed to their “arm” earlier than traditional fittings. The ability to operate without the need for any electronic devices or batteries is unique to the Ambionics design and mitigates the risk of injury.

From scan to wearable prosthetic in five days

While the NHS takes 11 weeks to convert the plaster cast of the arm into a wearable prosthetic, Ben Ryan was able to produce the prosthetic in five days. With the flexibility to keep the scan on file, the digital copy allows replacement prosthetics to be easily produced through 3D printing.

“Essentially the entire prosthetic is 3D printed,” Ben adds. “Only Stratasys’ strong rubber-like and dissolvable support 3D printing materials make production and use of the DAHB units possible. The internal cavities are complex and it would be impossible to remove the support material using mechanical means. The materials must also be strong yet flexible as they transmit fluid pressure to operate the grip.”

Having patented its DAHB technology inside the prosthetic, Ambionics is aiming to offer the service to healthcare providers worldwide. Continuing its research and testing into infant development with prosthetics, the company is starting a Crowdfunding campaign on March 1st to enable medical device usability trials, which are required before seeking authorization to launch the product into the market.

“This case is indicative of 3D printing’s ability to improve lives by overcoming the traditional barriers of low-volume manufacturing,” says Scott Rader, General Manager, Healthcare Solutions, Stratasys. “We continue to support and enable innovators like Ben to bring customization to mainstream prosthetics manufacture,” he concludes.

Stratasys Ltd.
stratasys.com

*Toda M, Chin T, Shibata Y, Mizobe F (2015) Use of Powered Prosthesis for Children with Upper Limb Deficiency at Hyogo Rehabilitation Center. PLoS ONE 10(6): e0131746. doi:10.1371/journal.pone.0131746

Make Parts Fast