Lunet is a low-cost, fully 3D printable, modular finger prosthesis designed to provide millions of finger amputees around the world with an accessible prosthesis solution, as opposed to the few, very expensive commercially available finger prostheses today.

Two years ago, another student and I were designing a prosthetic arm for an amputee. After that project concluded, I designed finger mechanisms for a prosthetic hand in my free time. My professor and I were then given an opportunity to work with another amputee—a woman who lost 3 fingers on her right hand due to frostbite. I applied my explorations in prosthetic finger mechanisms for her use case and designed a functional prosthesis for her. I later realized the magnitude of the issue: how many finger amputations occur in the world annually and the unaffordability of prostheses. I revisited the design and refined it into what Lunet is today.

The fingers function through a novel, modified crossed four-bar linkage mechanism that differs in the addition of a fifth linkage in the distal knuckle that makes the finger function as a semi-compliant (flexible) mechanism. This allows the fingers to partially bend backwards (hyperextend) like real fingers, increasing their durability and flexibility. Rings worn on the user’s finger stumps drives the motion of the finger mechanism. Sections of 3D printer filament are used to assemble the fingers and act as pivot points for articulation. The fingers snap into the hand plate through interference-fit conical pegs and holes. This creates a stable point of attachment which also serves as a pivot point for the fingers, allowing them to individually splay, providing even greater range of motion. The fingers, hand plate, and wristband can be easily modified in parametric CAD to suit the user’s anatomical dimensions and then 3D printed.

Lunet began when I decided to design and 3D print prototype finger mechanisms for a prosthetic hand for fun in my free time. 2 weeks and 18 prototypes later, I created a mechanism and finger structure that closely replicated the range of motion of real fingers. My professor and I were then referred to a finger amputee who lost 3 of her fingers. I applied the mechanism I created to design a finger prosthesis for her. Nearly 40 design iterations and multiple rounds of patient testing were performed to ultimately create a functional prosthesis that fit her. After we finished working with this amputee patient, I continued to tinker with my finger designs. I intentionally broke one of my finger prototypes to see where its structural weakpoint is. It broke at the distal knuckle. This led to me having a breakthrough in the design. I added a linkage that replaces the previously rigid distal knuckle, and I stumbled upon inventing a novel finger mechanism that was more flexible and nearly unbreakable. I then set on refining the design to be more functional, easily 3D printable, and more visually appealing. Inspiration from cyberpunk art and fighter jets influenced the design. 28 design iterations and a myriad of prototypes later resulted in Lunet.

Lunet is an entirely 3D printable finger prosthesis, making it vastly more affordable, quicker, and thus more accessible to produce and obtain compared to currently commercially available finger prostheses which cost thousands of dollars. Lunet takes advantage of the ever-growing accessibility of affordable consumer 3D printers in the world today to allow people to 3D print their own prosthesis. Lunet requires no metal fasteners, no adhesives, and no tools to assemble; making it suitable for low-cost production and assembly in poorer areas of the world and by people with limited use of their hands. Lunet features a novel mechanism that I invented to actuate the fingers, consisting of only 5 main moving parts, and closely replicates the range of motion of real fingers. The modular and configurable design of Lunet can be easily modified in parametric CAD to suit the dimensions of the user, and then personalized in CMF when 3D printed.

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