Stratasys’ PolyJet 3D printing technology has enabled Ben Ryan, founder of Ambionics, to create a fully-functioning 3D printed hydraulic prosthetic for his two year old son, Sol.
Stratasys' PolyJet
Researching infant development with prosthetics, Ryan has developed a prosthetic for infants to wear, enabling a more natural acceptance of prosthetic arms for young children. The customised 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 with traditional methods of manufacture. This crucially permits prosthetics to be used at an earlier developmental stage.
Sol was born with complications which 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 NHS in the UK, and one year before a cosmetic, non-functional prosthesis would be fitted. Ryan saw his son losing responsiveness and acceptance of his left arm, and decided to act.
Carrying out research into infant development, Ryan 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 designed a foam arm for his son and later a hydraulic prosthetic, enabling Sol to move his thumb on his own.
Ryan designed and created his 3D printed hydraulic prosthetic arm on the Stratasys Connex 3D printer. First practicing with prototypes of his design, he 3D-printed flexible actuators and a power-splitting unit (double acting helical bellow or DAHB) for the prosthetic. He says that 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 Ryan. “We were fortunate enough to have access to this technology, which enabled us to 3D print a prototype arm so 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, Ryan used Autodesk Fusion 360.
“This is a very innovative and ambitious project and it’s been inspiring to work on it,” says Paul Sohi, a product design expert at Autodesk. “It is amazing that despite Ryan 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 said to be unique to the Ambionics design and mitigates the risk of injury.
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, 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,” Ryan 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 are used to 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 and has started a Crowdfunding campaign to enable medical device usability trials.