Neural electrodes for brain-computer interface system: From rigid to soft

Brain-computer interface (BCI) is an advanced technology that establishes a direct connection between the brain and external devices, enabling high-speed and real-time information exchange. In BCI systems, electrodes are key interface devices responsible for transmitting signals between the brain and external devices, including recording electrophysiological signals and electrically stimulating nerves. Early BCI electrodes were mainly composed of rigid materials. The mismatch in Young's modulus between rigid electrodes and soft biological tissue can lead to rejection reactions within the biological system, resulting in electrode failure. Furthermore, rigid electrodes are prone to damaging biological tissues during implantation and use. Recently, flexible electrodes have garnered attention in the field of brain science research due to their better adaptability to the softness and curvature of the brain. The design of flexible electrodes can effectively reduce mechanical damage to neural tissue and improve the accuracy and stability of signal transmission, providing new tools and methods for exploring brain function mechanisms and developing novel neural interface technologies. Here, we review the research advancements in neural electrodes for BCI systems. This paper emphasizes the importance of neural electrodes in BCI systems, discusses the limitations of traditional rigid neural electrodes, and introduces various types of flexible neural electrodes in detail. In addition, we also explore practical application scenarios and future development trends of BCI electrode technology, aiming to offer valuable insights for enhancing the performance and user experience of BCI systems.