July 27, 2015 | By Kira

Researchers from the Swinburne University of Technology in Australia have developed an ingenious foot prosthetic design that can be optimized according to the wearer’s individual gait and size, all for roughly $10 USD. The findings were presented this month at the 3rd European Conference on Design4Health and offer a very promising solution for amputees, and particularly for children who require regular re-fittings as they grow.

Currently, the typical foot prosthetic that is donated to those in developing countries is known as the Solid Ankle Cushioned Heel model  (SACH). While the SACH foot is cheap and reliable, it is a standard model and does not adjust to the wearer’s gait. Improper gait patterns can put strain on the amputee’s residual limb, and result in increased pain and alignment issues down the road. On the other end of the spectrum are high-end prosthetics that can cost up to $5,000 and are thus out of reach for much of the population.

Standard SACH prosthetic foot

“A demographic that may benefit from 3D printed assistive devices are those from developing countries; namely children who require regular fittings of new prostheses due to replacements usually being necessary every 6 months,” said the researchers. “Although donation-based services exist to provide them with free or low-cost prostheses, the ability to source appropriately sized prosthetic feet for everyone that requires assistance is not always possible.”

In a paper titled Low-cost 3D-printable Prosthetic Foot,” industrial designers Jonathan Yap and Gianni Renda present how they came up with, tested, and ultimately created a 3D printed prototype that is lighter and cheaper than the SACH, which comparable, if not better, performance. Their design is centered on the principle of ESR (energy-storing-and-return), which means that energy is stored upon ‘heel strike,’ transferred through the prosthesis, and released during the second and third phases of gait. In addition, they paid particular attention to overall stability and the concern of keel stiffness by exploring the potential of a modular design, and by incorporating a squash ball into the heel region that would allow for varying degrees of flexibility and compression.

Initial sketch concept ideation

Six CAD models were produced, out of which one was determined to provide the most stability, ESR, and natural gait. They also incorporated a mounting pyramid design that adjusts to users with various gait mechanics. Once happy with the CAD model, three 1:4 scale prototypes were printed at various orientations to observe how their 3D printer, a Makerbot Replicator 2, would handle the complex form as well as its supports and rafts. In the end, it was decided that the full-scale prototype would be printed on its side. “Like wood grain, the 3D printed component was much stronger across the layers than along, and therefore it was imperative that the layers ran along the length of the prosthesis in order to not only be able to withstand stress and impact loads, but to also allow for flex along the length of the form,” explained Yap and Renda.

Out of all this background work, two full-scale prototypes were brought to fruition using the Makerbot 2 and PLA filament. The first version took 24 hours and 27 minutes to complete, consuming 354g of PLA at a cost of roughly $6 USD. In order to ensure the best possible performance, the researchers didn’t just stop after printing: 2-part epoxy was applied around the mid-foot for added strength, a synthetic rubber coating was used to make up for PLA’s susceptibility to water, and a layer of pumice grit was added to the base to offer non-skid properties. With all the supports and rafts removed, the squash ball inserted, and final touches in place, the prosthetic weighed in at 340g, a full 22g lighter than the SACH.

Full-scale prototype V1

During initial testing of the V1 prototype, the results were highly promising. “Not only was the prototype able to support the subject’s weight (75kg), but drastic performance improvements over the SACH foot were experienced; such as improved comfort and energy return, as well as increased overall stability,” stated the researchers. However, there remained some serious flaws. The squash ball proved inadequate at moderating keel stiffness, and after repeated testing the mounting pyramid eventually broke.

The team went back to the drawing board and came up with the V2 prototype, which took only 21 hours to print, consumed 322g of PLA, and cost around $5 USD—talk about improvements. For this version, the squash ball was omitted and one-fourth inch threaded steel rods were embedded into the mounting pyramid for increased structural support. Lastly, a grip design was added to the base for increased non-skid properties.

After further testing, the researchers confirmed that the additional reinforcements were sufficient, and that the dynamic ESR capabilities ensure a higher level of comfort, a more natural gait, and superior stability over the SACH foot. As an added bonus, the prototype can be worn with various types of standard footwear, which would decrease the wear of the rubber coating and increase the device’s lifespan.

Full-scale prototype V2

In their conclusion, the designers call for additional evaluations with transtibial amputees and controlled fatigue tests, however from this initial research it is clear that desktop 3D printing offers huge benefits in terms of affordability and customization. “Home 3D printing technology is rapidly evolving from a means of creating low-fidelity trinkets, to becoming a robust and viable method of batch production,” said the researchers.  “The prosthesis’ ability to be modified and produced on-site, on- demand could potentially redefine the opportunities available to prosthetists for accommodating varying gait patterns when providing low-cost aid to developing countries.”



Posted in 3D Printing Applications



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Lana Waters wrote at 1/10/2017 3:26:23 PM:

I have a friend who has now lost three toes on one foot due to diabetes and she is worried about balance. Have you developed prosthetic toes that might aid her in walking. She is in her 70's and very active. She works with foster children and is hard to keep down. Any help in this matter would be greatly appreciated.

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