Micro- and nanotechnology for neural electrode-tissue interfaces

Implantable neural electrodes can record and regulate neural activities with high spatial resolution of single neuron and high time resolution of sub-millisecond, which are the most extensive window in neuroscience research. However, the mechanical mismatch between conventional stiff electrodes and soft neural tissue can lead to inflammatory responses and degradation of signals in chronic recordings. Although remarkable breakthroughs have been made in sensing and regulation of neural signals, the long-term stability and chronic inflammatory response of the neural electrode-tissue interfaces still needs further development. In this review, we focus on the latest developments for the optimization of neural electrode-tissue interfaces, including electrode materials (graphene fiber-based and CNT fiber-based), electrode structures (flexible electrodes), nano-coatings and hydrogel-based neural interfaces. The parameters of impedance, charge injection limit, signal-to-noise ratio and neuron lost zone are used to evaluate the electrochemical performance of the devices, the recording performance of biosignals and the stability of the neural interfaces, respectively. These optimization methods can effectively improve the long-term stability and the chronic inflammatory response of neural interfaces during the recording and modulation of biosignals.