Wireless microelectrode arrays for selective and chronically stable peripheral nerve stimulation for hindlimb movement

Abstract

Objective. Maximizing the stability of implanted neural interfaces will be critical to developing effective treatments for neurological and neuromuscular disorders. Our research aims to develop a stable neural interface using wireless communication and intrafascicular microelectrodes to provide highly selective stimulation of neural tissue. Approach. We implanted a wireless floating microelectrode array into the left sciatic nerve of six rats. Over a 38 week implantation period, we recorded stimulation thresholds and movements evoked at each implanted electrode. We also tracked each animal’s response to sensory stimuli and performance on two different walking tasks. Main results. Presence of the microelectrode array inside the sciatic nerve did not cause any obvious motor or sensory deficits in the hindlimb. Visible movement in the hindlimb was evoked by stimulating the sciatic nerve with currents as low as 4.1 µA. Thresholds for most of the 96 electrodes we implanted were below 20 µA, and predictable recruitment of plantar flexion and dorsiflexion was achieved by stimulating rat sciatic nerve with the intrafascicular microelectrode array. Further, motor recruitment patterns for each electrode did not change significantly throughout the study. Significance. Incorporating wireless communication and a low-profile neural interface facilitated highly stable motor recruitment thresholds and fine motor control in the hindlimb throughout an extensive 9.5 month assessment in rodent peripheral nerve. Results of this study indicate that use of the wireless device tested here could be extended to other applications requiring selective neural stimulation and chronic implantation.

Wireless transmission of voltage transients from a chronically implanted neural stimulation device

“…Interestingly, we did not observe any obvious trend or relationship between motor recruitment thresholds (I th reported in [12]) and either E mc or V acc for the electrodes. Suggesting that the changes in stimulation-evoked limb movement over time that were recorded in parallel to this study were not directly caused by changes in the electrodes.…”

“…Increasing electrode surface area from 2000 µm 2 to 3000 µm 2 would mean additional exposure (removal of insulation) of approximately 30 µm along the length of the iridium wire tip, and we expect this increase would not notably decrease selectivity of neural stimulation with the penetrating microelectrode array. Additional information on selectivity of stimulation within this study can be found in [12].…”

“…For each voltage transient, we determined the maximum cathodic potential excursion (E mc ), driving voltage (V drive ), and access voltage (V acc ) at each applied current level for each electrode. VT data were then used to assess the state of each implanted electrode and correlate changes over time to separate observations investigating hindlimb movements evoked by sciatic nerve stimulation [12]. All animal procedures were performed in accordance with the guidelines of the Institutional Animal Care and Use Committee of The University of Texas at Dallas.…”

“…First, the VT response was recorded for each of the 16 implanted electrodes with 200.2 µs, 4.7 µA pulses applied at 50 Hz. Movement of the implanted limb was then assessed during a separate nerve stimulation study (reported in [12]), where varying levels of current were applied to the sciatic nerve one electrode at a time using 200.2 µs pulses at 1 Hz. The nerve stimulation study was used to find the threshold current value causing visible motor recruitment (I th , defined as the lowest current value at which visible motion of the limb or digits occurred) for each individual electrode.…”

A narrative review of cortical visual prosthesis systems: the latest progress and significance of nanotechnology for the future

“…Over a 9.5-month period, the researchers implanted a WFMA into each of 6 rats' left sciatic nerves and observed that a combination of wireless communication and a lowprofile neural interface permitted very steady motor recruitment thresholds and fine motor control in the hind limb. The groundwork has been laid for the development of a visual brain prosthesis in the future (78). Clinical trials in humans are now ongoing (ClinicalTrials.gov Identifier: NCT04634383).…”