New artificial nerves could transform prosthetics

Prosthetics may soon take on a whole new feel. That’s because researchers have created a new type of artificial nerve that can sense touch, process information, and communicate with other nerves much like those in our own bodies do. Future versions could add sensors to track changes in texture, position, and different types of pressure, leading to potentially dramatic improvements in how people with artificial limbs—and someday robots—sense and interact with their environments.

“It’s a pretty nice advance,” says Robert Shepherd, an organic electronics expert at Cornell University. Not only are the soft, flexible, organic materials used to make the artificial nerve ideal for integrating with pliable human tissue, but they are also relatively cheap to manufacture in large arrays, Shepherd says.

Modern prosthetics are already impressive: Some allow amputees to control arm movement with just their thoughts; others have pressure sensors in the fingertips that help wearers control their grip without the need to constantly monitor progress with their eyes. But our natural sense of touch is far more complex, integrating thousands of sensors that track different types of pressure, such as soft and forceful touch, along with the ability to sense heat and changes in position. This vast amount of information is ferried by a network that passes signals through local clusters of nerves to the spinal cord and ultimately the brain. Only when the signals combine to become strong enough do they make it up the next link in the chain.

Now, researchers led by chemist Zhenan Bao at Stanford University in Palo Alto, California, have constructed an artificial sensory nerve that works in much the same way. Made of flexible organic components, the nerve consists of three parts. First, a series of dozens of sensors pick up on pressure cues. Pressing on one of these sensors causes an increase in voltage between two electrodes. This change is then picked up by a second device called a ring oscillator, which converts voltage changes into a string of electrical pulses. These pulses, and those from other pressure sensor/ring oscillator combos, are fed into a third device called a synaptic transistor, which sends out a series of electrical pulses in patterns that match those produced by biological neurons.

Bao and her colleagues used their setup to detect the motion of a small rod moving in different directions across their pressure sensors, as well as identify Braille characters. What’s more, they managed to connect their artificial neuron to a biological counterpart. The researchers detached a leg from a cockroach and inserted an electrode from the artificial neuron to a neuron in the roach leg; signals coming from the artificial neuron caused muscles in the leg to contract, they report today in Science.

Because organic electronics like this are inexpensive to make, the approach should allow scientists to integrate large numbers of artificial nerves that could pick up on multiple types of sensory information, Shepherd says. Such a system could provide far more sensory information to future prosthetics wearers, helping them better control their new appendages. It could also give future robots a greater ability to interact with their ever-changing environments—something vital for performing complex tasks, such as caring for the elderly.