Abstract

Micromotion-induced stress remains one of the main determinants of life of intracortical implants. This is due to high stress leading to tissue injury, which in turn leads to an immune response coupled with a significant reduction in the nearby neural population and subsequent isolation of the implant. In this work, we develop a finite element model of the intracortical probe-tissue interface to study the effect of implant micromotion, implant thickness, and material properties on the strain levels induced in brain tissue. Our results showed that for stiff implants, the strain magnitude is dependent on the magnitude of the motion, where a micromotion increase from 1 to 10 μm induced an increase in the strain by an order of magnitude. For higher displacement over 10 μm, the change in the strain was relatively smaller. We also showed that displacement magnitude has no impact on the location of maximum strain and addressed the conflicting results in the literature. Further, we explored the effect of different probe materials [i.e., silicon, polyimide (PI), and polyvinyl acetate nanocomposite (PVAc-NC)] on the magnitude, location, and distribution of strain. Finally, we showed that strain distribution across cortical implants was in line with published results on the size of the typical glial response to the neural probe, further reaffirming that strain can be a precursor to the glial response.

Highlights

  • High-fidelity from intracortical microelectrodes recordings are central for the efforts to understand the complexity of neural networks in awake patients or repair/bridge damaged pathways through open or potentially closed-loop prosthetic intervention (Chou et al, 2015; Lindner et al, 2019)

  • We focus on investigating the impact of the range of micromotion of the brain on the maximum strain for a stiff silicon-based microelectrode

  • A three-dimensional finite element model was used to simulate the probe-brain tissue interface and evaluate the strains formed in the tissue areas surrounding the probe as a function of different material properties and two probe sizes (Refer to Figures 2, 3)

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Summary

Introduction

High-fidelity from intracortical microelectrodes recordings are central for the efforts to understand the complexity of neural networks in awake patients or repair/bridge damaged pathways through open or potentially closed-loop prosthetic intervention (Chou et al, 2015; Lindner et al, 2019). The technology is used clinically in deep brain stimulation, auditory brainstem neuroprostheses, cortical stimulation, and brain-machine interface (Paralikar, 2009; Khraiche et al, 2013a; Kook et al, 2016) Despite these applications, chronic brain implants suffer many challenges including signal loss, reduced signal-to-noise ratio, and unstable recordings over time (Kook et al, 2016). One of the factors that can potentially contribute to limiting implant life for clinical applications of intracortical electrodes is the foreign body response at the implant-injury site (Campbell and Wu, 2018) This is characterized by a cascade of inflammatory events, which culminate in chronic inflammation, resulting in the failure of the implant over extended periods. In addition to immune response, recent evidence points to a direct role of mechanical forces in neural modulation, including heightened functional state and a high neural firing rate (Marin and Fernandez, 2010; Khraiche et al, 2017; Fomenko et al, 2018)

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