Developing 3D-Printed Prosthetics by Merging Robotics and Neuroscience

By Mike Koon

With Illinois, people around the world have access to state-of-the-art, printed prosthetics thousands less than more traditional models.

Tim Bretl, Associate Professor of Aerospace Engineering and a Research Associate Professor in the Coordinated Science Laboratory, works in two distinct areas of research to positively impact society: robotics and neuroscience.

“It has been wonderful to work in these two areas because although they sound different, all my projects overlap. A lot of the same tools can be applied to all my projects,” said Bretl. “I enjoy working with a diverse group of people who have expertise different from my own, and I’m lucky to have a great group of students who come to me with good ideas.”

One of Bretl’s four active projects involves developing upper-limb prosthetic devices. He and graduate student Aadeel Akhtar are building a prosthetic hand that connects to the user with electrodes that read muscle activity (called an electromyographic [EMG]-based interface) and incorporate sensory feedback.

“Developing prosthetics is all about building effective communication with the device.”

“Developing prosthetics is all about building effective communication with the device,” said Bretl. “There’s the EMG interface that translates muscle activity into commands for the device—so how the person tells the device what to do—and then there’s how the device tells the person what it’s doing—so that’s sensory feedback—and we do all of that.”

To research prosthetics in the field, Akhtar led a team of Illinois graduate students under Bretl's advisement to South America where they put their open-source dexterous artificial hand to the test on an Ecuadorian man. The group has created one of the first 3D-printed prosthetic hands with pattern recognition capability. A machine-learning algorithm allows it to do more than just open and close. It learns other positions of the hand for more functionality. In addition, it can be created for a mere $270 compared to the average myoelectric prosthetic, which retails for between $30,000-$40,000. Even taking in consideration mark-up, it still represents a significant cost decrease to the patient.

3-D printed prosthetic hand being tested in a lab setting. Electrical signals are taken from the muscles in the arm to move the hand and fingers.

The hand is trained to replicate several motions by taking the electrical signal from muscles in the arm and sending it to an EMG board, which is then sent to a microprocessor with a machine-learning algorithm on board. Based on those signals, it sends commands to motor drivers, which churn the motor and make the hand move. Although the EMG board that is being used for the current prototype is the size of a standard audio mixing board, it will eventually shrink to a size that can fit into the socket of a residual limb.

“Using the machine-learning algorithm based off the signals it picks up from the muscles, it can figure out which of these grips he is actually doing,” explained Akhtar. “The micro- controller with the machine-learning algorithm will then replicate the grip he’s trying to make.”

The hand itself takes about 30 hours to print, then another two hours to assemble. All the electronics that are necessary to convert the neural signals into movements are located within the hand. Through a mechanical connection from one of the artificial fingers directly to the skin, the patient will also be able to better feel the position of their hand without looking at it.

“No commercial prosthetic device has any sort of feedback,” Akhtar said. “We’re going to put sensors in the fingers. Based on the amount of force that the fingertips are detecting, we are going to send a proportional amount of electrical current across your skin to stimulate your sensory nerves. By stimulating your sensory nerves in different ways with different amounts of current, we can make it feel like vibration, tingling, pain, or pressure.”

“It’s really awesome to be able to help people,” Nguyen said. “I didn’t imagine doing something that has this direct impact on the world while still in college.”

“It’s really awesome to be able to help people,” Nguyen said. “I didn’t imagine doing something that has this direct impact on the world while still in college.”

“I mean, who doesn’t love robots? You figure out how to tell them what to do, and they do it—it’s a lot of fun,” Bretl said. “Even on the neuroscience side, a prosthetic hand is a robot that happens to be attached to a person. Robotics opens up a whole set of humanitarian applications and interesting science.”

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