Commercial prostheses can mimic the range of movements of natural limbs, but even the latest experimental models have limited ability to ‘feel’ objects being manipulated. Researchers from Switzerland and Italy say they have improved the capacity by which different textures can be felt and identified by combining an artificial fingertip and electrode implants.

Bionic fingertip electronics and plastic gratings with rough and smooth textures. Image source: Hillary Sanctuary / EPFLThe technology developed in collaboration between Ecole Polytechnique Fédérale de Lausanne (EPFL) and Scuola Superiore Sant’Anna allowed an amputee to distinguish between rough and smooth surfaces 96 percent of the time (see video). Nerves in the patient’s arm were wired to the sensor-equipped artificial fingertip. A machine controlled its movement over plastic pieces engraved with different patterns, smooth or rough. As the fingertip moved across the textured plastic, the sensors generated an electrical signal which was translated into a series of electrical spikes, imitating the language of the nervous system, and then delivered to the nerves.

The same experiment testing coarseness was performed on non-amputees, without the need of surgery. The tactile information was delivered through fine needles temporarily attached to the arm's median nerve through the skin. These subjects were able to distinguish roughness in textures 77 percent of the time.

The scientists tested whether this information about touch from the bionic fingertip really resembles the feeling of touch from a real finger. They did so 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 similar.

The researchers say their work demonstrates that the needles relay the information about texture in much the same way as the implanted electrodes, giving new protocols to accelerate for improving touch resolution in prosthetics.