Patch developed to help control robotic exoskeletons

Robotics insights

• Engineers have developed a stretchy, wearable patch, SNAP, with microneedles that pick up muscle signals, enhancing control of robotic exoskeletons.
• SNAP, a comfortable and resilient device, may one day assist in moving robotic limbs and aiding doctors in diagnosing neurological illnesses.

Engineers from Korea and the University of Colorado have developed a wearable, stretchy patch that could help to bridge the divide between people and machines. The patch, about the size of a BandAid, sticks to human skin and picks up tiny signals coming from human muscles. In lab experiments, the researchers showed that humans could use these devices to operate robotic exoskeletons more efficiently—machines that try to mimic, and even enhance, the power of human muscles and bones.

The team hopes that one day, similar patches may help people move robotic arms or legs, or even assist doctors in diagnosing neurological illnesses.

“We get these natural signals from muscles and send them to outside equipment to give people more control,” said Jianliang Xiao, associate professor in Paul M. Rady Department of Mechanical Engineering at CU Boulder.

Xiao led the study alongside Jaewoong Jeong, associate professor in the School of Electrical Engineering at the Korea Advanced Institute of Science and Technology (KAIST). The team described its design, known as the stretchable microneedle adhesive patch (SNAP), this month in the journal Science Advances.

The secret to SNAP comes down to what the researchers call “microneedles.” The patches are integrated with an array of about 144 needles. They are made of silicon coated with gold and are less than a hundredth of an inch long, making them hard to see with the naked eye.

The idea of small needles poking the body may sound scary, but the team’s microneedles only enter the top layer of the skin and aren’t long enough to reach the body’s pain sensors. That makes the patches surprisingly comfortable to wear, even for long periods.

“People can wear these patches for a week, and we see hardly any skin irritation,” Jeong said.

Like your own skin

Xiao noted that the human body, just like many machines, is pulsing with electricity on a near constant basis.

Every time you bend an arm, twist your back or even twitch a finger, currents run along the muscle fibers. Doctors typically monitor these electromyography (EMG) signals using gel electrodes that stick onto your skin, but the task can get tricky—gel dries up over time, and when people jump or run, the electrodes often slide around, resulting in poor data.

In the new study, Xiao, Jeong and their colleagues set out to design an EMG sensor that could function almost like a part of your body.

The team’s SNAP devices are self-contained machines made of a stretchy, polymer base. They incorporate stretchable serpentine wires fabricated out of ultrathin metal. They also come with their own batteries and are remarkably resilient: In lab experiments, the group found that the patches collected accurate EMG data, even when human subjects were running on treadmills or doing squats.

“The patch deforms in a way very similar to your own skin,” Xiao said.

Subject in a lab wears a robotic device to help him lift heavy objects. Courtesy: Jaewoong Jeong, KAIST, University of Colorado

Human and machine movements coming together

They could also help people do some very non-human things.

To test out those possibilities, researchers from KAIST ran a series of experiments in their lab in which they asked real people to take on an everyday task—lifting a heavy weight from the floor. In this case, the humans had a little help. They strapped on a machine that looks a bit like a knapsack and provides a robotic boost for the lower back.

Some of the subjects also wore SNAP devices just above their glute muscles. When the patches detected that the subjects were flexing their muscles during lifting, the devices called for help. They sent a wireless signal to the robotic backpacks to begin moving—all in a fraction of a second. Humans wearing the patches, the team reported, used an average of 18% less muscle power while lifting than subjects who were using the robotic exoskeleton on its own.

“These devices can reduce the muscles you need to accomplish certain tasks,” Xiao said.

He added the researchers still have a lot of work to do before their patches make it into the real world. For a start, they need to test the tools with other kinds of exoskeleton machines.

“We hope that our work in the lab will eventually help to make life better for a lot of people,” Xiao said.

– Edited by Chris Vavra, web content manager, CFE Media and Technology, cvavra@cfemedia.com.

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