Advances in flexible high-density microelectrode arrays for brain-computer interfaces

Recent advances in flexible high-density microelectrode arrays (FHD-MEA) have revolutionized brain-computer interfaces (BCIs) by providing high spatial resolution, mechanical compliance, and long-term biocompatibility. This technology enables stable neural recording and precise stimulation, addressing the shortcomings of conventional rigid BCI arrays. In this review, we outline the challenges of signal acquisition and stimulation of conventional low-density, rigid BCI systems. These include poor spatial resolution, micro-motor-induced instability, electrochemical degradation, wiring bottlenecks, off-target activation, and charge injection hazards. We then describe how these barriers are addressed through advanced materials, device designs, and system-level integration. We summarize representative applications of clinical therapy for sensory enhancement, human-machine interfaces, and neurological diseases, highlighting translational potential. Collectively, this review article presents recent progress and emerging trends in establishing FHD-MEAs as a crucial foundation for next-generation, clinically viable BCIs.