An Ultra-Flexible Neural Electrode with Bioelectromechanical Compatibility and Brain Micromotion Detection.

Neural electrodes, as core components of brain-computer interfaces(BCIs), face critical challenges in achieving stable mechanical coupling with brain tissue to ensure high-quality signal acquisition. Current flexible electrodes, including semi-invasive meningeal-attached types and implantable cantilever designs, exhibit significant mechanical mismatches (elastic modulus 5-6 orders higher than brain tissue) due to material/structural limitations, leading to interfacial slippage. While thread-like implants (e.g., Neuralink's electrodes) improve compliance via elongated structures, quantitative characterization of mechano-bioelectric interactions remains unexplored. This study proposes a bioelectromechanical coupling strategy, emphasizing synchronized motion between the electrode and the brain tissue through exposed-end deformation. A 4-channel ultra-flexible electrode (40 mm in length, 164 µm in width, and 3 µm in thickness) is optimized using finite-element simulations and zero relative-motion criteria, achieving an equivalent stiffness of 0.023 N m^-1-matching brain tissue micromotion stiffness. A nanorobotic manipulator installed inside a scanning electron microscope(SEM) with an atomic force microscope(AFM) cantilever enabled precision characterization under the simulated displacement of 25 µm, revealing interfacial forces of 575 nN and piezoresistive sensitivities of 6.4 pA mm^-1 (length) and 10.2 pA µm^-1 (displacement). The dual-functionality (signal acquisition and micromotion sensing) electrodes demonstrate breakthrough potential, establishing quantitative design standards for next-generation bioelectronic implants.