Photo of a stretchable microneedle adhesive patch (SNAP) device. (Image: Jae-Woong Jeong/KAIST)

In a new study, engineers from Korea and the United States have developed a wearable, stretchy patch that could help to bridge the divide between people and machines — and with benefits for the health of humans around the world.

The patch, about the size of a BandAid, sticks to your 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.

“We get these natural signals from muscles and send them to outside equipment to give people more control,” said study co-lead and Associate Professor Jianliang Xiao.

The team described its design, known as the stretchable microneedle adhesive patch (SNAP), 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 your body may sound scary, but the team’s microneedles only enter the top layer of your 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,” said study co-lead Jae-Woong Jeong said.

Xiao noted that the human body, just like many machines, is pulsing with electricity on a near constant basis. Every time you bend your arm, twist your back, or even twitch a finger, currents run along your 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.

The team 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. 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 percent less muscle power while lifting than subjects who were using the robotic exoskeleton on its own.

Xiao noted that 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.

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