Tiny Electrodes Monitor Neurons

Composite microelectrodes that can record electrical activity from individual neurons are suitable for chronic neural interfaces, a team led by researchers from the University of Michigan reports (Nat. Mater., DOI: 10.1038/nmat3468). Such electrodes could eventually be used to interface neurons with brain-controlled prosthetic devices such as artificial limbs. Daryl R. Kipke, Nicholas A. Kotov, Joerg Lahann, and coworkers coated micrometer-sized carbon fibers with four polymers to give the electrodes the properties they wanted. The first coat is an insulating layer of poly(p-xylylene). That layer is covered with a functionalized xylylene block copolymer, followed by a layer of poly(ethylene glycol) methacrylate. The latter polymer makes the device biocompatible and lessens tissue immune response. Finally, a polythiophene-based cap on the end of the fiber creates a site for recording electrical activity. The resulting probe is significantly smaller—about 9 μm in diameter versus 50 to 100 μm—than others typically used for measuring neuronal electrical activity, allowing it to get right next to individual neurons. The researchers implanted the electrodes in the motor cortex of rats for more than five weeks with minimal immune response.