Researchers Turn to 3D Printing for a Low-Cost, Body-Powered Curling Prosthetic Finger

Researchers from the University of Arizona, Sampoerna University, and Politeknik Negeri Jakarta have developed a 3D-printable finger prosthesis powered by the wearer — with the aim of restoring natural grip functionality.

"High cost and ongoing maintenance requirements keep many finger amputees in underdeveloped nations from accessing prosthetic devices. The most prevalent upper-limb amputation, trans-phalangeal amputation (accounting for about 78% of cases), is addressed in this paper as requiring a low-cost, effective finger prosthesis. Using a single degree-of-freedom (1-DOF) connection mechanism and additive manufacturing, a body-powered prosthetic finger was designed and built," the researchers explain of the project. "Aiming to restore fundamental grip function, the device is customizable to the user's hand size."

The prosthetic has no power source of its own, and is simply printed from PLA using an unmodified commercial fused filament fabrication (FFF) 3D printer. It attaches to the body where the user's missing finger would be, adjusted for size and length to fit suitably — and then turns the movement of the remaining digit into a curling movement of its own, restoring the ability to grip items.

"It survived lifting items […] on the order of a few kilograms before mechanical slip occurred," the researchers note of the prototype, somewhat below the original target of 25kg (around 55lbs): testing showed "significant deformation of the plastic links" when curling and holding 1kg (around 2.2lbs) at the tip. "While this is far below the ambitious 25kg target," the team admits, "it is sufficient for many daily tasks like holding eating utensils, a toothbrush, or a TV remote. The minimum torque needed to actuate the finger (to overcome joint friction) was low — the tester reported it was easy to move, requiring only a gentle motion of the controlling finger."

The team's work has been published in the journal Sustainable Energy Science and Technology under open-access terms; a similar prosthesis design has, meanwhile, been showcased on Instructables by Pietro Vacchelli under the Creative Commons Attribution-NoCommercial-ShareAlike license, though at the time of writing STL files had not yet been uploaded.