Between wars, accidents, birth defects and diseases like diabetes, there are more than 1.6 million people in the U.S. who suffer from some kind of limb loss. Advances in technology have allowed doctors to fit prosthetics that are comfortable and function well, but there are no artificial limbs that allow patients to regain sensation.
However, researchers recently created a prosthetic that has the potential for users to regain a sense of touch.
A team at Case Western Reserve University (CWRU) has developed a prosthetic that not only allows sensations for more than a year but also conveys different textures to the user.
“[The system] provided [the patients] with confidence in using the hand and the ability to perform fine manipulations that are not otherwise possible,” Dustin Tyler, an associate professor of biomedical engineering at CWRU and director of the research, said.
Numerous scientists have attempted to restore patients’ sense of touch. Most experiments have produced sensations that lasted for months and only allowed patients to discern simple senses such as changes in pressure.
Many prosthetics that attempt to reproduce the effect of touch rely on electrodes that are inserted into nerve membranes. The electrodes produce an electric shock to the nerve, causing the nerve to transmit information to the brain. Though they can convey simple information such as pressure, these pulses are not sophisticated enough for textures.
Furthermore, the electrodes soon lose their ability to stimulate the nerves and convey information regarding pressure. Most of the patients report loss of sensation within months of implantation.
The researchers at CWRU modified the approach of electrode insertion. Instead of inserting electrodes directly into nerve membranes, scientists create cuffs that circle nerve bundles responsible for sensation. Each cuff contains independent channels capable of creating electrical impulses to the nerve bundles. Individual cuffs are then responsible for either sensations within a certain area or a type of sensation. With three cuffs individuals are able to perceive 19 different areas of the prosthetic.
“[The prosthetic interface] has been on the nerve for over two and a half years without changes in nerve response, stimulation threshold or subject sensation,” Tyler said.
After implanting the electrodes, the scientists stimulated the sensors within the prosthetics. Patients described these first stimulations as tingles down their arms. With more tuning they soon were able to perceive different sensations.
“[The stimulations] represent a new ‘language’ for interacting with neural tissue,” Tyler said.
The researchers discovered that touch sensations depend on the intensity and frequency of the electrical pulses. With a larger pulse intensity patients reported a sense of greater pressure applied to their prosthetics. A faster frequency produced a pulsing sensation as though they were squeezing and relaxing their hands.
Intensity of sensation depends on the frequency with which the cuff stimulates the nerve bundles with faster frequencies corresponding to stronger sensations. The variations in sensation offer a more natural feel to patients. “[An] unexpected benefit has been the reduction or elimination of debilitating phantom pain,” Tyler added.
The system demonstrates that sensation can be reproduced with electrical signals.
“With support a commercial system is plausible in the next five to 10 years,” Tyler said.
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