Investigation of critical buckling load enhancements via ultrasonic vibration assisted implantation of microwire-based brain electrodes

OBJECTIVE: Ultrasonic vibration assisted insertion has shown promising results on large and rigid brain electrodes but had limited benefits towards small and flexible electrodes like thin microwires. This study aims to quantitatively investigate the vibration's impact on the electrode's critical buckling load and optimal vibration parameter choice for effective vibration transmission to microwire tips. APPROACH: A custom ultrasonic insertion platform was developed to deliver controlled longitudinal vibrations to tungsten microwires under a fixedpinned boundary condition. Experiments varied four factors: wire diameter (50.8 -101.6 µm), preload mass (0 -112.35 g), vibration frequency (33 -42 kHz), and drive voltage amplitude (106 and 212 VRMS). Vibration characteristics were quantified using Photonic Doppler Velocimetry, and buckling outcomes were assessed by enhancement percentage of the critical buckling load against static theoretical values. Analysis of variance was conducted to investigate vibration parameters' impacts on the critical buckling load enhancement. MAIN RESULTS: Ultrasonic vibration assistance not only reduces membrane rupture force but also significantly increased the effective critical buckling load, with enhancements exceeding 60% in some cases. ANOVA revealed that all four factors-frequency, voltage, preload mass, and wire diameter-had statistically significant effects (p < 0.05). Higher vibration frequency (38-42 kHz) and smaller wire size (50.8 µm) generally yields higher critical buckling load enhancement while an intermediate level of pre-load mass (54.51 g) would be beneficial for high efficiency vibration transduction to the tip of small lightweight wire electrodes. Vibration amplitude and corresponding drive voltage should be carefully chosen to mitigate imperfections during the acceleration and deceleration periods. SIGNIFICANCE: This study, for the first time, quantitatively demonstrates the enhancement of electrode critical buckling load under ultrasonic vibration assistance. The experimental investigations provided valuable insights and guidelines for vibration assistance parameter selection to ease the brain electrode implantation process.