An electrochemical method that stimulates nerves locally and blocks the propagation of electrical signals along nerve fibres, thus minimizing undesirable side effects, is reported online this week in Nature Materials. The proof-of-concept demonstration, shown in frogs, may one day pave the way to low-power, flexible neuroprosthetic devices that can be wrapped around nerves.
Patients affected by paralysis from stroke, spinal cord injury or other neurological disorders can undergo functional electrical stimulation to activate affected motor nerves and perform physical therapy. However, conventional stimulation of motor nerves often causes pain, as the electric currents used can also affect neighbouring sensory nerves. Jongyoon Han and colleagues modulated the excitability of a frog\\\'s sciatic nerve in vitro by using microfabricated electrodes with membranes that are selective to calcium, potassium and sodium ions — the ions involved in nerve impulses. Electrical modulation of the ions’ local concentration allowed the researchers to control nerve activation at the site of stimulation, and to suppress signal propagation on demand. In addition, the method reduces the electrical threshold to induce nerve twitching by up to 40%. Although the approach could eventually be applied to implantable neuroprosthetic devices, the authors point out that further work to validate the method in vivo and to extend it to mammalian nerves is needed.