Assessing the Safety Margin for Micromotion-Induced Strain at Electrode–Tissue Interface: A Finite Element Analysis via COMSOL

Abstract

Brain movement significantly impacts the biocompatibility of neural probes, primarily due to continuous loading and strain on neural tissue. This study investigates the strain profile at the electrode–tissue interface under various brain displacements—vertical, lateral, diagonal, and torque—across different brain models (linear elastic, hyperelastic, and viscoelastic). The safety margin for tissue damage is assessed by evaluating a 5% strain threshold using two probe widths (30 µm and 100 µm) in tethered and floating configurations. The probe dimensions are informed by previously developed devices implanted in rats for 12 weeks, allowing to correlate the findings with existing immunohistochemical data. A comprehensive simulation studies accounting for various conditions, such as different brain displacements and physics, has not been reported elsewhere. These results challenge the conventional 5% strain threshold for tissue damage, revealing that strains below this critical limit may still pose risks depending on probe geometry and brain model. Furthermore, these simulations underscore the necessity of size-dependent micromotion models for accurate predictions in untethered conditions. This work highlights the feasibility of integrating immunohistological data into simulation studies, offering valuable insights for researchers while minimizing the need for extensive animal testing during initial probe design phases.