A team of researchers at Washington University has developed a shoulder-controlled, externally powered 3-D printed prosthetic arm, according to data recently published in Prosthetics and Orthotics International.
The goal of the project was to address limitations of other 3-D printed devices and create an alternative to industry standard prostheses, Charles Goldfarb, MD, vice chairman and professor of Orthopedic Surgery at Washington University School of Medicine and medical director of the Orthopedic Center of St. Louis, Chesterfield, told O&P News.
“We wanted to share our thoughts and our early results with the scientific community [regarding] the process and how we approached a 3-D prosthesis with some elements of battery-powered control,” he said.
How it works
Using a 13-year-old female patient with traumatic transradial amputation, the team prototyped the device with five fingers, each having 2° of freedom.
The user can open and close each finger and control the thumb independently by moving his or her shoulder up and down. The inertial measurement unit assesses that movement and a microcontroller then activates motors in the hand. When the motors activate, cables that run through the lower parts of the fingers and hold the hand closed are put under tension, opening the hand.
The device also has a palm block, which imitates a human palm, helping users grasp objects. Based on measurements of the sound limb, the palm block can be customized to each patient before printing.
The arm’s socket is made of acrylonitrile butadiene styrene plastic, a low-cost, impact-resistant material that is easily machined and fabricated. It is attached to the residual limb using friction and is directly connected to the device’s electronics compartment.
That compartment holds the motors, microcontroller, a voltage regulator, wiring components and a rechargeable 9-volt lithium ion battery to power the device.
The top and bottom units of the electronics compartment are held together by Velcro, allowing it to be easily detached when the battery needs to be removed.
Benefits of the device
The prosthesis has many benefits, Goldfarb said. At less than a pound, it is lighter than most externally powered prostheses. He also noted customizable fit, individual thumb movement, ability to grasp objects with all five fingers and social experience as major advantages.
“I think, as others have experienced with standard 3-D printed prostheses, the kids and adults who like them, really like them,” he said. “They want to incorporate them in both functional and social situations.”
It also comes at an affordable price, he added, allowing users to print new devices to accommodate limb growth. The estimated cost of building is $300, whereas an industry standard, body-powered prosthesis could cost as much as $8,000 in total and an externally powered device could cost as much as $50,000 in total, according to the study.
Limitations ad future direction
The device does have some limitations. Although the device expands 3-D prosthetic capability to transradial amputees, it comes with a short battery life, noise from the motors, low grip strength and low durability compared with passive prostheses.
However, the team is working to improve that, Goldfarb said.
“We are trying to find a balance between providing enough power and avoiding a heavy battery or the need to recharge the battery [too often]. We have to find the right balance of function and practicality at a low cost,” Goldfarb said.
The researchers are currently testing the device with additional patients and taking steps to allow a more advanced generation to evolve.
“We are building upon the first prototype. The first 3-D printed prosthesis was a dramatic step forward in that it improved access to prostheses and dramatically decreased costs; our prosthetic is a further enhancement on the idea of practicality and usability for patients … and that is exciting.
“We know that as in the wider 3-D printed community, it is not necessarily medical experts that are doing this,” he said. “These are undergraduate students who head the project, come up with the ideas and make it functional. But I think when professionals in the prosthetic community get involved, this will become even more exciting.” – by Shawn M. Carter
- Goldfarb C. Prosthet Orthot Int. 2015;doi:10.1177/0309364615579317.
Disclosures: Goldfarb reports no relevant financial disclosures.