Bionic fingertip allows an amputee to feel textures for the first time - CNET

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An artificial fingertip that allows the wearer to distinguish textures in real-time could advance the development of bionic prostheses because it can be tested without the need for surgical installation.

The device interfaces directly with the nerves of the amputee, requiring surgical installation, but can be tested on non-amputees through needles that can be inserted through the skin into the individual's arm. It was developed by neuroengineer Silvestro Micera and his team at Ecole polytechnique fédérale de Lausanne and Scuola Superiore Sant'Anna, who published their research in the joual eLife on Tuesday.

The fingertip is the first to be able to detect not just pressure, but the difference between rough and smooth.

To test the fingertip's effectiveness, the team enlisted amputee Dennis Aabo Sørensen of Denmark, who lost his left hand 11 years ago handling fireworks. They connected the fingertip to nerves in his arm, using wires to integrate the sensors with his nerves. Because Sørensen had worked with the team previously on bionic prosthetic development, the interface with his ulnar and median nerves was already in place.

Then the fingertip was moved over pieces of plastic engraved with different pattes, some smooth, some rough. The sensors moved over the plastic and created an electrical signal and set it to a PC to be interpreted into tactile information about the surface. This final signal was sent up the wires and into Sørensen's nerves. A blindfolded Sørensen then reported what he felt.

He was able to tell the difference between rough and smooth with 96 percent accuracy.

"The stimulation felt almost like what I would feel with my hand," he said in a statement. "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."

Testing the fingertip on non-amputees means that development can be a lot faster. Instead of the surgical interface, needles are inserted into the skin and attached to the median nerve in the test subject's arm. The test subjects then touch the plastic surfaces with both their fingers and the artificial fingertip while wearing an EEG cap.

This allows the team to see how the test subject's brain responds to both kinds of touch. Whether using the artificial fingertip or their own hand, the test subjects' brains shows the same activity. Moreover, they were able to differentiate between rough and smooth with 77 percent accuracy. This is not as accurate as Sørensen, but it does demonstrate the feasibility of a temporary needle interface over surgery.

"This study merges fundamental sciences and applied engineering: it provides additional evidence that research in neuroprosthetics can contribute to the neuroscience debate, specifically about the neuronal mechanisms of the human sense of touch," said Calogero Oddo of the BioRobotics Institute of SSSA, who participated in the research.

"It will also be translated to other applications such as artificial touch in robotics for surgery, rescue, and manufacturing."