Experts at the American John Hopkins University has developed a specialized coating for bionic prostheses. This coating is called "electric skin" (e-dermis). It's like real skin reacts to external factors. When providing physical pressure to cover the skin sends a signal of pain initially in the elbow and the median nerve and then to the somatosensory cortex.
As can be understood, the prosthesis connects to the rest of the limb, particularly to the nervous system. Thanks to this prosthesis is able to form pain to which the person responds. It is clear that this was not intended to cause a person to feel pain, and with the intention that the bearer of the prosthesis can respond to potentially dangerous artificial limb situation. The results of a study published in the online edition of Science Robotics.
In a typical situation for the formation and transmission of the signal, which ultimately allow a person to feel pain, respond so-called nociceptors. They are sometimes called pain receptors. They are located in the outer layer of the skin. The appearance of an external factor (chemical, thermal or mechanical) of cocktail recipes. aktiviziruyutsya, generates a signal which is transmitted to the spinal cord and then to the head. The trip signal long enough, it passes directly through the three types of nerve fibers: Aß-, Aδ - and CThe first type of receptor is responsible for ensuring that person as quickly as possible responded to the emerging danger. Appears almost instantly the pain signal that triggers a reflex reaction and people, for example, pulls his hand from the hot pan.
Interestingly, the receptors able to distinguish the signal "danger" from the usual warnings. If this were not so, the human body would react exactly the same to cut with a knife or the pressure exerted by the edge of a wooden ruler. But in the first case we sharply react, the second may not pay attention to an external stimulus.
In General, pain is useful for humans and animals, since it gives to understand that something is going wrong and allows you to avoid danger or at least try to do it. Realizing this, scientists and developers of bionic prosthetics has long been looking for a way to learn to form a sense of touch and pain in different parts of the artificial limb. This, in particular, allows to avoid the destruction of the prosthesis in case of excessive load on it.
It seems that furthest in this direction has progressed experts from the Medical school of Johns Hopkins University. The team leader is Luke Osborne. As a volunteer for the "test-pain" was made by 29-year-old man with both hands amputated. Scientists used the remains of the nerve endings for skin electrical myostimulation ulnar and median nerves. The experiment was successful because the team was able to form a certain pain in the body of the volunteer.
He talks about it as a tingling in the places where once were fingers (remember that both hands amputated). The intensity of the feeling, as it turned out, depended upon such pulse characteristics as length and frequency. The most efficient and painful was the signal with frequency 10 to 20 Hz. In order to verify the results of the study, the scientists not only based on the words of men, but also checked the reaction of his organism with the help of electro-encephalograph.
Regarding the coating, it is not homogeneous, but is composed of several layers of fabric, rubber, conductive layer and the layer that reacts to pressure change. This coating was applied to the prosthesis, but only on fingers, thumb and index. As it turned out, at a pressure of a certain intensity signal reaches the threshold, which already perceives the human body (approximately 250 kPa).
The maximum pressure per unit area exerted sharp objects. With a strong compression of the volunteer subject to feel the pain of a brush, that is, the prosthesis automatically relaxed. In the case that the brush and squeezing objects with rounded edges, the volunteer felt no pain.
While that faux leather responds only to the mechanical factor, but in the near future, experts hope to create more advanced systems that can sense chemical and thermal effects. As far as can be judged, the future is near.