Engineering news
An artificial fingertip surgically connected to the nerves in an amputee’s upper arm has successfully stimulated the sensation of touch, allowing him to feel smoothness and roughness in real-time.
In addition, the research found that nerves of non-amputees can also be stimulated to feel roughness, without the need for surgery, meaning that prosthetic touch for amputees can now be developed and safely tested on intact individuals. Further applications of artificial touch in robotics could be applied to surgery, rescue, and manufacturing.
The technology to deliver this tactile information was developed by Silvestro Micera and his team at Ecole polytechnique fédérale de Lausanne (EPFL) together with Calogero Oddo and his team at the BioRobotics at Institute Scuola Superiore Sant'Anna (SSSA). The results, published in eLife, provide hope to accelerate the development of bionic prostheses, enhanced with sensory feedback.
"The stimulation felt almost like what I would feel with my hand," said amputee Dennis Aabo Sørensen. "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 research team said that 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 recognize shape and softness. The bionic fingertip has attained a superior level of touch resolution.
Simulating touch in non-amputees
This same experiment testing coarseness was performed on non-amputees, without the need for 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 scientists tested how realistic this prosthetic touch sensation was to real touch by comparing brain-wave activity of the non-amputees, once with the artificial fingertip and then with their own finger. The brain scans collected by an EEG cap on the subject's head revealed that activated regions in the brain were comparable.
The fact they could demonstrate that the needles relay the information about texture in much the same way as the implanted electrodes gives scientists hope they can use the technique to accelerate improvements for touch resolution in prosthetics.
"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. "It will also be translated to other applications such as artificial touch in robotics for surgery, rescue, and manufacturing."