The ability to feel texture allows us to interact with the world in remarkable ways. Indeed, our extraordinary dexterity is at least partially a function of our ability to gauge what an object feels like, which yields information about how to best manipulate it.
But building a sensor that can feel texture is extremely complicated.
So it's big news that an amputee was able to feel smoothness and roughness in real-time with an artificial fingertip that was surgically connected to nerves in his upper arm.
The technology was developed by Silvestro Micera and his team at EPFL (Ecole polytechnique fédérale de Lausanne), NCCR Robotics, and SSSA (Scuola Superiore Sant'Anna) together with Calogero Oddo and his team at SSSA. The results, published yesterday in eLife, provide new and accelerated avenues for developing bionic prostheses, enhanced with sensory feedback.
"The stimulation felt almost like what I would feel with my hand," says amputee Dennis Aabo Sørensen about the artificial fingertip connected to his stump. He continues, "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."
Sørensen is the first person in the world to recognise texture using a bionic fingertip connected to electrodes that were surgically implanted above his stump.
Nerves in Sørensen's arm were wired to an artificial fingertip equipped with sensors. A machine controlled the movement of the fingertip over different pieces of plastic engraved with different patterns, smooth or rough. 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, then delivered to the nerves.
Sørensen could distinguish between rough and smooth surfaces 96% of the time.
In a previous study, Sorensen's implants were connected to a sensory-enhanced prosthetic hand that allowed him to recognise shape and softness. In this new publication about texture in the journal eLife, the bionic fingertip attains a superior level of touch resolution.
This same experiment testing coarseness was performed on non-amputees, without the need of surgery. The tactile information was delivered through fine needles that were temporarily attached to the arm's median nerve through the skin. The non-amputees were able to distinguish roughness in textures 77% of the time.
The research demonstrates that the needles relay the information about texture in much the same way as the implanted electrodes, giving scientists new protocols to accelerate for improving touch resolution in prosthetics.