Buckling-Resistant and Trace-Stacked (BRATS) Design Enables Aid-Free Implantation of Flexible Multielectrode Array with Minimized Inflammatory Tissue Response.

Intracortical microelectrode arrays (MEAs) are vital tools for brain-machine interface applications and basic neuroscience research, with the potential to advance treatments for neurological disorders and enhance the understanding of the nervous system. However, implanting intracortical electrodes can damage native tissue along the insertion path and trigger inflammatory responses characterized by neuronal loss and glial activation. While flexible electrodes reduce some of these adverse effects compared to rigid counterparts, their mechanical compliance often leads to buckling during insertion, necessitating the use of insertion aids such as stiff shuttles or dissolvable coatings. These aids, however, introduce additional complexity and can cause further tissue damage. In this work, microfabricated polyimide MEAs featuring a buckling-resistant, trace-stacked (BRATS) design are presented. It is demonstrated that BRATS MEAs can penetrate agarose brain phantoms and the rat cerebral cortex without the need for insertion aids. Once implanted, BRATS MEAs established a stable and functional electrical interface with the brain, enabling high-fidelity, single-unit electrophysiological recordings. Compared to conventional flexible MEAs inserted with a stiff shuttle, BRATS MEAs elicited significantly lower inflammatory responses and preserved a higher density of neurons near the implant site one week post-implantation.