3D printable prostheses to restore amputees’ finger mobility

An easy-to-use 3D printable finger prosthesis could offer amputees a low-cost solution to restore finger functionality. David Edquilang first designed Lunet, which doesn’t need metal fasteners, adhesives, or special tools to assemble, as an undergraduate student at the University of Houston (UH) Gerald D. Hines College of Architecture and Design. While standard prostheses can cost thousands of dollars, Edquilang aims to make his design open access on the Internet.

“Not every good idea needs to be turned into a business. Sometimes, the best ideas just need to be put out there,” says Edquilang, who graduated with a Bachelor of Science in Industrial Design. “Medical insurance often won’t cover the cost of a finger prosthesis since it’s not considered vital enough compared to an arm or leg. Making Lunet available online for free will allow it to help the greatest number of people.”

Edquilang’s mentor at UH was Associate Professor Jeff Feng, co-director of UH’s Industrial Design program. Through a partnership with Harris Health System, Feng learned of a patient whose fingers were amputated due to frostbite. Inspired by working on an upper limb prosthesis Edquilang previously developed with student Niell Gorman, working with Feng, Edquilang created prosthetic fingers that returned mobility to the patient, allowing her to pick up objects again.

Edquilang focused on making an even better product. Under Feng’s advisory, he designed and tested 60 prototypes before reaching a final design that was more durable, easier to configure and assemble, with improved functionality.

His breakthrough came from a literal break – he intentionally broke one of his prototypes to see where its structural weak point was. It buckled at the distal knuckle, the joint that connects the bones at the fingertips, so he added a linkage that replaced the previously rigid distal knuckle, and an award-winning version of Lunet was born.

Lunet’s geometry inspired its name

Lunet is made of two common types of 3D printed plastics: polylactic acid and thermoplastic polyurethane. Each finger is made of four parts held together by plastic pins. Edquilang describes arcs and circular orbits as the foundation for the motion of the finger mechanism. The geometric basis of the design evoked the idea that the prosthesis orbits around the user’s joints like a moon, or lunet.

Another element of Lunet’s uniqueness is it’s nearly impossible to break; other finger prosthetics can be complicated and require many parts.

“The problem with higher mechanical complexity is these designs are less durable,” Edquilang says. “The more parts you have, the more points of failure. You need to make prosthetic fingers robust and as strong as possible, so they don’t break under normal use, yet you want the design to be simple. This was one of the greatest challenges in making Lunet.” 

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