Although prosthetics do help amputees to get back some use of their missing limb, feeling is not among them. However, that may soon be changing now. Bionics prosthetics research from EPFL is promising enough to allow an amputee patient to perceive and distinguish between smooth and rough textures. An artificial finger connected surgically to nerves in the upper part of the patient’s arm does the trick. It is expected that this advance will expedite the development of the sense of touch in prosthetic limbs.

The EPFL research has also proven that the same prosthetic touch sensors meant for amputees can be easily tested on people who are able-bodied. For instance, non-amputee persons can feel roughness by stimulation of their nerves – without surgery.

Sylvestro Micera and his team at EPFL in Switzerland and SSSA in Italy have developed this technology in collaboration with Calogero Oddo and his team at SSSA – they have published the results in eLife. Their research is opening new windows on the development of bionic prostheses, and sensory perception is helping to improve the progress.

Dennis Aabo Sørensen, a hand amputee, is helping EPFL with its prosthetic research for some time. The team has implanted electrodes above the stump on his left forearm. The bionic finger connected to his stump allows him to feel sensations of texture at the tip of the index finger of his phantom hand. However, he still feels his missing hand as if he had a closed fist.

When EPFL connected a bionic hand to the electrodes in his left forearm, S⌀rensen could recognize both shape and softness. This time, the team wired the bionic finger to the electrodes meant for his fingertip. Rubbing the bionic finger against several pieces of plastic engraves with different patterns produced a sensation of texture at the tip of the index finger of his phantom hand. For 96 percent of the time, Sørensen was able to differentiate correctly between smooth and rough plastics using his bionic finger.

The group at SSSA in Italy tested the bionic finger on non-amputees while the subjects wore EEG caps. They noted the brain activity of the subjects while they were touching the plastic surfaces with their actual finger. They then compared these against the activity detected while they touched the same surfaces with the bionic fingertip. This was proof to the scientists that bionic fingers could activate the same parts of the brain, as did the real digits.

Therefore, the team is confident not only about leading to prosthetics that can feel, but also about offering the power of artificial touch to industrial, surgical and rescue robots as well.

The artificial fingertip was equipped with sensors that were wired to nerves in Sørensen’s arm. As the fingertip, assisted by a machine, moved over different pieces of plastic with smooth or rough patterns engraved on it, the sensors generated appropriate electrical signals. These signals were then translated into a series of electrical spikes to imitate the language of the nervous system. Once the spikes were delivered to the nerves, Sørensen was able to distinguish between rough and smooth surfaces with repeatable accuracy.