Three-dimensional microelectrode arrays for in vitro neuronal network models: structural designs, manufacturing approaches, and future perspectives.

Three-dimensional (3D) microelectrode arrays (MEAs) have been actively developed to enable electrophysiological recording from in vitro 3D neuronal network models, which have attracted considerable research interest in recent years. These devices overcome the fundamental limitation of conventional planar MEAs, in which microelectrodes are confined to a single plane, by distributing microelectrodes throughout 3D space. This enables direct access to neurons throughout the tissue, allowing precise analysis of neural activity in 3D space across the neuronal network. Depending on the strategy used to position microelectrodes in 3D space, current 3D MEAs have been developed in a variety of structural configurations, including probe-, tip-, planar mesh-, 3D mesh-, curved surface-, stretchable mesh-, and wrapping-architectures. These structurally diverse devices have primarily been fabricated using photolithography-based microfabrication processes, while more recently, 3D printing technology has been adopted to improve structural design freedom for complex 3D structures. In this review, we discuss the structural diversity and fabrication strategies of 3D MEAs for in vitro 3D neuronal network models, examine recent advances and current limitations, and outline future directions for the field.