Touching moments
Engineers around the world developing bionic prosthetic limbs that can ‘feel’
Phantom pain was all that Keven Walgamott had left of the limb he lost in an accident more than a decade ago — until he tried on a LUKE Arm for the first time in 2017, and told researchers he could “feel” again.
The arm is a motorized and sensorized prosthetic that has been in development for more than 15 years at the University of Utah.
Researchers around the world have been developing prosthetics that closely mimic the part of the human body they would replace. This goes beyond the cosmetic and even the functional. These are bionic body parts that can touch and feel, and even learn new things.
“Touch isn’t a single sense,” said Gregory Clark, associate professor of biomedical engineering at the University of Utah and lead researcher of the study. “When you first touch objects with a natural hand, there’s an extra burst of neural impulses.”
The brain “translates” these into characteristics such as firmness, texture and temperature, all of which are crucial in deciding how to interact with the object, he said. In other words, by using the LUKE Arm (named after the Star Wars hero Luke Skywalker, and manufactured by Deka), Walgamott, of West Valley City, Utah, was able to “feel” the fragility of a mechanical egg, just as he would have with a natural limb. He could pick it up and transfer it without damaging it.
As he performed everyday activities — such as holding his wife’s hand, sending a text message and plucking grapes from a bunch — Walgamott told researchers it felt like he had his arm back. Even his phantom pain was reduced.
“When the prosthetic hand starts to feel like the user’s real hand, the brain is tricked into thinking that it actually is real,” Clark said. “Hence, the phantom limb doesn’t have a place to live in the brain anymore. So it goes away — and with it goes the phantom pain.”
Clark’s team was able to achieve these results by stimulating the sensory nerve fibres in a “biologically realistic” manner. Using a computer algorithm as a go-between, they were able to provide a more biologically realistic digital pulse similar to what the brain normally receives from a native arm.
“Participants can feel over 100 different locations and types of sensation coming from their missing hand,” Clark said. “They can also feel the location and the contraction force of their muscles — even when muscles aren’t there. That’s because we can send electrical signals up the sensory fibres from the muscles, so the brain interprets them as real.”
The critical component of a prosthetic powered by thought would be the communication between the brain and a robotic body part — the brain-computer interface (BCI).
The LUKE Arm uses a neural interface, but in other mind-controlled prosthetics, brain implants are used to send instructions to a robotic limb, much like how neurons transmit messages from the brain to a muscle. But this means the risks, cost and recovery time of precision brain surgery.
This might be about to change. Bin He, professor and head of biomedical engineering at Carnegie Mellon University, and his colleagues have been working on a non-invasive high-precision BCI, and reported a breakthrough in June: a “mind-controlled robotic arm ... that demonstrates for the first time, to our knowledge, the capability for humans to continuously control a robotic device using non-invasive EEG signals.”
The term non-invasive is key. Non-invasive BCIS have shown promising results but only in performing distinct actions — for example, pushing a button. For sustained, continuous action such as tracking a cursor on a computer screen, non-invasive BCIS have resulted in jerky, disjointed movements of the robotic prosthesis. In He’s demonstration, the subject controlled with their mind a robotic arm to track a cursor on a computer screen, and the prosthetic finger was able to follow the cursor in a smooth, continuous path — just as a real finger would. While they used a computer-wired EEG cap on the subject in the lab, He said it’s not necessary.
A smartphone app programmed with EEG recordings and wireless electrodes could streamline the process for everyday use, He said.
This could pave the way for thought-controlled robotic devices by decoding “intention signals” from the brain without needing invasive and risky brain surgery.
Just as our limbs are trained to perform various actions — basic ones such as grasping or walking, to precision ones such as neurosurgery or ballet — prosthetics, too, have to be calibrated for specific uses. Engineers at the lab of Joseph Francis, associate professor of biomedical engineering at the University of Houston, have been working on a BCI that can autonomously update using implicit feedback from the user.
“We are moving toward an autonomous system that will learn to perform new actions as per the user’s intentions with the least supervision from outside, and enable the user to control the prosthetic more independently,” said Taruna Yadav, a PHD student who is part of Francis’s team.
In 2018, a bionic hand developed in a collaboration between the Imperial College London and the University of Göttingen used a human-machine interface that interpreted the wearer’s intentions and sent commands to the artificial limb.
The team used machine learning-based techniques to interpret neural signals from the brain to improve the performance of prosthetic hands.
“Our main goal is to let patients control the prosthetic as though they were their biological limbs,” said Dario Farina, lead author of the paper about their findings. “This new technology takes us a step closer to achieving this.”
Would there be a difference in the way that bionic body parts would work for an amputee versus a paralyzed person? No, Yadav said.
“In both cases, it will still read the user’s neural activity and generate a command to control a prosthetic limb,” she said. “However, the time and effort required to learn to control the BCI output may differ.”
For The Washington Post