Spiral nerve cuff electrodes for an upper extremity neuroprosthesis

Selective neural electrical stimulation restores hand and forearm movements in individuals with complete tetraplegia

Background

We hypothesized that a selective neural electrical stimulation of radial and median nerves enables the activation of functional movements in the paralyzed hand of individuals with tetraplegia. Compared to previous approaches for which up to 12 muscles were targeted through individual muscular stimulations, we focused on minimizing the number of implanted electrodes however providing almost all the needed and useful hand movements for subjects with complete tetraplegia.

Methods

We performed acute experiments during scheduled surgeries of the upper limb with eligible subjects. We scanned a set of multicontact neural stimulation cuff electrode configurations, pre-computed through modeling simulations. We reported the obtained isolated and functional movements that were considered useful for the subject (different grasping movements).

Results

In eight subjects, we demonstrated that selective stimulation based on multicontact cuff electrodes and optimized current spreading over the active contacts provided isolated, compound, functional and strong movements; most importantly 3 out of 4 had isolated fingers or thumb flexion, one patient performed a Key Grip, another one the Power and Hook Grips, and the 2 last all the 3 Grips. Several configurations were needed to target different areas within the nerve to obtain all the envisioned movements. We further confirmed that the upper limb nerves have muscle specific fascicles, which makes it possible to activate isolated movements.

Conclusions

The future goal is to provide patients with functional restoration of object grasping and releasing with a minimally invasive solution: only two cuff electrodes above the elbow.

Ethics Committee / ANSM clearance prior to the beginning of the study (inclusion period 2016–2018): CPP Sud Méditerranée, #ID-RCB:2014-A01752–45, first acceptance 10th of February 2015, amended 12th of January 2016.

Trial registration

(www.clinicaltrials.gov): #NCT03721861, Retrospectively registered on 26th of October 2018.

A rat model for assessing the long-term safety and performance of peripheral nerve electrode arrays

BACKGROUND

High-resolution peripheral nerve interfaces (PNIs) can provide amputees with intuitive motor control and sensory feedback. Current PNIs are limited by early device failure and suboptimal long-term stability. The present study aims to incorporate functional assessment into an in vivo test platform to assess the long-term safety and performance of PNIs for recording and stimulation.

NEW METHODS

Utah electrode arrays (EA) were implanted in the rat sciatic nerve along with electromyography wires in the gastrocnemius and tibialis anterior. Cranial EEG screws were implanted in the somatosensory cortex for 12 weeks. Spontaneous neural activity was recorded using the implanted EA and stimulation-induced activity was monitored throughout the experiment. The impedance of each electrode was measured, and nerve function tests were conducted throughout the EA lifetime. Post-hoc safety assessments included scanning electron microscopy (SEM) of the EA and nerve histomorphometric analysis.

RESULTS

EA recordings were stable, and stimulation with EA elicited somatosensory evoked potentials and muscle contractions. Motor and sensory function tests indicated minimal deficits. Histomorphometric analysis indicated changes in nerve microstructure. SEM indicated EA-tip fracture, while lead wire breakage primarily caused device failure.

COMPARISON WITH EXISTING METHODS

We improved our prior platform with the addition of functional assessments of sensory pathways, a robust EMG array design to increase device longevity, and quantitative analysis of nerve microstructure.

CONCLUSION

We present a test platform for long-term assessment of peripheral nerve interfaces for stimulation and recording. Using this platform, we demonstrate recording and stimulation with minimal impact on nerve function, while EA lead wire breakage and tip fracture could limit long-term device use.

The Evolution of Neuroprosthetic Interfaces

The ideal neuroprosthetic interface permits high-quality neural recording and stimulation of the nervous system while reliably providing clinical benefits over chronic periods. Although current technologies have made notable strides in this direction, significant improvements must be made to better achieve these design goals and satisfy clinical needs. This article provides an overview of the state of neuroprosthetic interfaces, starting with the design and placement of these interfaces before exploring the stimulation and recording platforms yielded from contemporary research. Finally, we outline emerging research trends in an effort to explore the potential next generation of neuroprosthetic interfaces.

Command of an upper extremity FES system using a simple set of commands

The purpose of this project is to develop a method of providing a complete set of movement commands to an upper extremity neuroprosthesis when the number of command signals available is fewer than required by the mechanical system. The functional relevance of the developed command interface will be tested in a virtual reality environment, where users-able bodied and paralyzed-will use a limited number of commands to control a simulated neuroprosthesis capable of executing a set of important daily activities that require coordinated motion of a larger number of mechanical degrees of freedom.