Bionic fingertip lets amputee feel texture

"Yeah. That was amazing."

These are words from amputee Dennis Aabo Sørensen, the first person to feel texture using a bionic fingertip connected to electrodes surgically implanted in his arm above his stump.

The bionic fingertip, developed by scientists at the Swiss Federal Institute of Technology in Lausanne and Sant'Anna School of Advanced Studies in Pisa, Italy, was published in the journal eLife today.

Sørensen's implanted electrodes had been used before. In a previous study, they were connected to a sensory-enhanced prosthetic hand that allowed him to recognise shape and softness. But this is the first time he – or any other amputee – has been able to perceive roughness via a bionic limb.

Nerves in Sørensen's arm were wired to an artificial fingertip fitted out with sensors. A machine controlled the movement of the fingertip over different pieces of plastic engraved with smooth or rough patterns. 

As the fingertip moved across the textured plastic, the sensors generated an electrical signal. This signal was translated into a series of electrical spikes, imitating the language of the nervous system, which was delivered to the nerves. 

Sørensen could distinguish between rough and smooth surfaces 96% of the time.

"The touch sensation is quite close to when you feel it with your normal finger," he says. "You can feel the coarseness of the plates and the different gaps and ribs.

"I still feel my missing hand, it is always clenched in a fist. I felt the texture sensations at the tip of the index finger of my phantom hand."

The same experiment was conducted on non-amputees, but instead of surgically implanting electrodes, signals from the bionic fingertip were transmitted through fine needles temporarily latched onto the arm's median nerve, which runs all the way from the neck down to the fingers.

Non-amputees were able to pick up roughness 77% of the time. And when the scientists measured their brain activity as they touched a rough surface with their finger, and compared them to brain waves generated when they "felt" through the bionic fingertip, the same parts of the brain lit up. 

In other words, texture felt via the bionic fingertip resembled real touch.

Hear more from Sørensen and the research team behind the bionic fingertip here:

Further reading:
Artificial skin returns a sense of touch