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Prosthetic Prototyping

Although hand prosthetics on the market today are rapidly approaching levels of functionality that rival their human counterparts, these devices are prohibitively expensive for most adults, let alone children as they may either outgrow them or break them in less than a year. To meet this need for functional, low cost hand prosthetics many families are turning to 3D printing, where a large community has formed around designing, iteratively improving, and sharing free and open source hand prosthetic designs for small children.

While groups like UNC’s own Helping Hands Club do great work fabricating and assembling these hands for many children of need in the community, unfortunately not everyone is a good candidate for the current models. This semester the club tasked the Junior Design and Manufacturing class, BMME 310, to help in finding innovative solutions for their toughest cases. Rather than adapting current open source designs to a wider audience, one group, consisting of Andrew Conley, Kaylee Clary, Logan Frederick, and Jonathan Alvarez, took a different approach borrowing from the subfield of soft robotics.

As opposed to the often bulky and complex system of intricate 3D printed parts, elastic, and wires that comprise the current rigid hand prosthetic models, soft robotic grippers use rubbery “fingers” that bend downward as air is forced inside and distends their specially designed inner channels. Ultimately, the group decided to use motor-driven syringes to generate this air pressure, separating their prosthetic into a pressure generation component and the hand itself. With the equipment and expertise at BeAM the students were able to create custom 3D printed molds for their fingers and cast them out of a special silicone. They also used the uPrint and its soluble support material to make precisely routed tubing channels in the hand component and a very sturdy pressure generator housing.

Although their pressure generation device was far too heavy and bulky to be worn by an actual child, the fact that the group were able to get it working reliably enough to consistently pick up a full water bottle, warrants further study into soft robotics prosthetics. This unique approach has many advantages including increased durability, higher cost effectiveness, a wider range of graspable objects, lower manufacturing times, no choking hazards, and easier cleaning. These devices can also be used in mixed-media situations like showering or finger painting. The group members are eager to refine this technology with the help of their professor, Dr. Donnelly, and the helpful staff at BeAM. Stay tuned for next semester’s progress!

The team that researched and created a soft hand Prosthetic prototype. From left to right: Andrew Conley, Kaylee Clary, Logan Frederick, Jonathan Alvarez