Sep 5, 2017 | By Benedict

LimbForge, an offshoot of 3D printed prosthetics community e-NABLE, has developed a 3D printed prosthetic elbow that incorporates features suggested by both patients and prosthetists. The nonprofit will now test the device on patients.

Most regular readers of 3Ders will have heard of e-NABLE, the simple 3D printed prosthesis project that became a global movement for affordable assistive devices. But with so many people from all across the world involved with the movement, it can be hard to keep track of all its separate branches and sub-communities.

One of those offshoots is LimbForge, a nonprofit organization dedicated to the development and testing of prosthetic devices. The organization has its origins in the e-NABLE movement, having originally been founded as the Enable Community Foundation, but has gone through a number of changes.

LimbForge is now its own independent entity, and its new name reflects that. It’s also exploring some pretty cutting-edge solutions that seem a world away from e-NABLE’s classic 3D printed hand design.

Its latest project involved designing, producing, and testing a 3D printed elbow prosthetic, made with the input of patients and prosthetists.

According to a recent blog post, LimbForge has just put its new 3D printed prosthesis through rigorous testing, paving the way for its first human wearers.

But getting the device to its current stage has taken some time.

Early versions of the 3D printed elbow were passable, but testers didn’t like how the friction between parts caused the elbow to make noise.

“The first version of the elbow we presented made loud clicking noises as the teeth of the clutch plates indexed past each other and the elbow could not swing freely due to this friction,” LimbForge explains.

The solution was to create an elbow that “swings” more like a human arm, rather than one that locks in an inorganic-looking position. This swinging feature also comes with an added benefit, as it allows the user to quickly flip the prosthetic into a bent position without using their other arm to position it.

This prototyping phase also allowed LimbForge staff to choose the right couplings, and also gave them time to make small fitting adjustments.

Eventually, the team made two different elbow couplings, one a quarter-turn coupling, the other using a threaded stud with counter-tightened nuts. After testing, LimbForge decided to go for threaded studs with counter-tightening nuts, to allow for better pronation and supination (turning the hand downwards and upwards).

Other features of the 3D printed elbow include complete “reversibility,” so it can be disassembled, repaired, or resized, while engineers also had to ensure a “mechanically sound union” between the elbow and the rest of the prosthetic device.

To get a second opinion on all these features, the LimbForge team then took several prototypes to the University of California, San Francisco, where they got the green light from Richard Nguyen and Alex Hetherington, two certified prosthetists and orthotists.

While all aspects of the design stage suggested that the 3D printed elbow would perform well, the real test would come over a longer period of time.

“To investigate durability and longevity, [LimbForge designer James Wang] designed and built a cycle testing rig that can be used both for testing prototype elbows as well as terminal devices with moving parts,” the organization explains.

With this testing rig, the elbow has been subjected to over 20,000 cycles (equivalent to 6–12 months of human use) of locking, unlocking, and motion.

And following this rig testing, LimbForge is now ready to try out its 3D printed elbow on real patients “so that they can try them outside of the clinic in a more diverse set of environments and use cases.”

But while that human testing goes on, LimbForge won’t be sitting around waiting.

“We’ll begin work on a new elbow with more than one degree of freedom, as one of the most important shortcomings of this design is a lack of internal-external rotation,” the organization says.

We can’t wait to see how that model turns out.



Posted in 3D Printing Application



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