Histological evaluation of flexible neural implants; Flexibility limit for reducing the tissue response?

Research output: Contribution to journalArticle

Abstract

Objective. Flexible neural probes are hypothesized to reduce the chronic foreign body response (FBR) mainly by reducing the strain-stress caused by an interplay between the tethered probe and the brain's micromotion. However, a large discrepancy of Young's modulus still exists (3-6 orders of magnitude) between the flexible probes and the brain tissue. This raises the question of whether we need to bridge this gap; would increasing the probe flexibility proportionally reduce the FBR? Approach. Using novel off-stoichiometry thiol-enes-epoxy (OSTE+) polymer probes developed in our previous work, we quantitatively evaluated the FBR to four types of probes with different softness: silicon (∼150 GPa), polyimide (1.5 GPa), OSTE+Hard (300 MPa), and OSTE+Soft (6 MPa). Main results. We observed a significant reduction in the fluorescence intensity of biomarkers for activated microglia/macrophages and blood-brain barrier (BBB) leakiness around the three soft polymer probes compared to the silicon probe, both at 4 weeks and 8 weeks post-implantation. However, we did not observe any consistent differences in the biomarkers among the polymer probes. Significance. The results suggest that the mechanical compliance of neural probes can mediate the degree of FBR, but its impact diminishes after a hypothetical threshold level. This infers that resolving the mechanical mismatch alone has a limited effect on improving the lifetime of neural implants.

Details

Authors
Organisations
External organisations
  • Purdue University
  • University of Florida
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Other Medical Engineering

Keywords

  • chronic neural implant, flexible brain-computer interface (fBCI), foreign body response (FBR), neuroprosthetics, off-stoichiometry thiol-enes (OSTE)
Original languageEnglish
Article number036026
JournalJournal of Neural Engineering
Volume14
Issue number3
Publication statusPublished - 2017 May 4
Publication categoryResearch
Peer-reviewedYes