Materials for neural interfaces

The treatment of disorders of the nervous system poses a major clinical challenge. Development of neuromodulation (i.e., interfacing electronics to nervous tissue to modulate its function) has provided patients with neuronal-related deficits a new tool to regain lost function. Even though, in principle, electrical stimulation and recording by interfacing technology is simple and straightforward, each presents different challenges. In stimulation, the challenge lies in targeting the effects of stimulation on precise brain regions, as each region specializes for particular functions on a millimeter scale. In practice, our experience with deep brain stimulation for treating Parkinson's disease reveals that stimulation of larger regions of the brain can be relatively well tolerated. However, the task of fabricating an ideal electrode that performs reliably for long periods of time has been daunting. The primary obstacle in successful interfacing comes from integration of electrodes ("foreign" material) into the nervous system (biological material). The second tier of complexity is added by the need for the electrodes to "sense" signals emanating from individual neurons, an estimated microenvironment of 10 to 20 microns in diameter. Materials design and technology impact electrode design-with their size, shape, mechanical properties, and composition all being actively optimized to enable chronic, stable recordings of neural activity. The articles in this issue discuss designing interfacing technology to "listen to the nervous system" from a materials perspective. These include identification of materials with a potential for in vivo development, electrodes with various material types, including natural nanocomposites, and optical neural interfacing.