A self-insertable 5-μm-diameter flexible microneedle for minimally invasive and stable in vivo neural recording

Implantable intracortical microelectrodes are essential tools for neuroscience research, clinical applications, and brain–computer interfaces. Achieving stable chronic recording of neuronal activity, however, remains challenging due to tissue damage—including neuronal loss, foreign body responses, and disruption of neuronal networks—induced by electrode implantation. Although flexible device strategies can reduce chronic damage, insertion using mechanical supports still creates a large footprint and causes substantial acute tissue damage, leading to neuronal network disruption. Overcoming these electrode issues, here we report a 5-μm-tip-diameter parylene microneedle electrode that offers advantages of ultrasmall size, mechanical flexibility, and insertion capability without additional support. The parylene microneedle was fabricated via silicon microneedle growth, parylene encapsulation, and subsequent core‑silicon removal. In vivo experiments in mice demonstrated that the flexible microneedle reduced tissue disruption compared with rigid needles, preserving neuronal populations comparable to unimplanted tissue. Notably, recording quality recovered over the implantation period, reflecting superior chronic recording stability arising from minimal invasiveness compared with conventional microelectrode technologies. This study represents a promising step toward chronic, high-quality neural interface device technology that maintain the native brain tissue state. • Developed a self-insertable 5-μm-diameter flexible intracortical microneedle electrode using silicon growth technology. • Flexible microneedle minimized tissue damage and preserved neuronal populations in vivo. • Demonstrated superior chronic recording stability compared with conventional microelectrodes.