Mechanical characterization of compliant neural probes, their insertion regimes and a rule of thumb design

Abstract

Investigates mechanical theory of buckling compliant neural probes, how this relates to insertion forces using normalized force data and discusses potential strategies to improve the insertion ability of neural probes. This report also provides a guide for mechanically testing compliant neural probes and demonstrates a design rule of thumb that insertion forces should be 1/3 lower than the buckling force to enable reliable insertion.

Double-Layer Flexible Neural Probe With Closely Spaced Electrodes for High-Density in vivo Brain Recordings

“…The mechanical tests performed show that the fabricated neural probe can be inserted into the brain without additional insertion aids to augment is buckling force threshold, since the compression force of the neural probe on a rigid base at 0.5 mm of displacement (1.5 mN) was greater than the insertion force of the neural probe in agar (1 mN). The forces involved in these experimental tests are in accordance with those reported for polymeric neural probes ( Haj Hosseini et al, 2007 ; Singh et al, 2016 ; Smith, 2019 ).…”

Recent Progress in Materials Chemistry to Advance Flexible Bioelectronics in Medicine

“…Considering the insertion of a cortical neural interface where forces up to ≈12-40 mN are needed to penetrate the dura mater of the brain, a material capable of undergoing a stiffsofttransition offers unique advantages with a rigid regime during insertion and soft regime during operation within the brain. [394][395][396][397][398] This problem has been tackled using several approaches, including hydrationinduced softening, rapidly dissolving stiffeners, shape memory polymer transitions, and stiff nanofiber and hydrogel composites. [399][400][401][402][403][404][405] A seminal breakthrough towards designing materials capable of significant change in mechanical modulus was reported by Capadona et al [406] Bioinspired nanocomposites of stiff cellulose nanofibers (1.43 GPa) in a soft poly(vinyl acetate) (PVAc) matrix undergo a chemically regulated transition from 4200 to 1.6 MPa upon hydration.…”

“…Considering the insertion of a cortical neural interface where forces up to ≈12–40 mN are needed to penetrate the dura mater of the brain, a material capable of undergoing a stiff‐soft‐transition offers unique advantages with a rigid regime during insertion and soft regime during operation within the brain. [ 394–398 ] This problem has been tackled using several approaches, including hydration‐induced softening, rapidly dissolving stiffeners, shape memory polymer transitions, and stiff nanofiber and hydrogel composites. [ 399–405 ]…”