In-vivo testing of a novel wireless intraspinal microstimulation interface for restoration of motor function following spinal cord injury.

Background: Spinal cord injury causes a drastic loss in motor and sensory function. Intraspinal microstimulation (ISMS) is an electrical stimulation method developed for restoring motor function by activating the spinal networks below the level of injury. Current ISMS technology uses fine penetrating microwires to stimulate the ventral horn of the lumbar enlargement.

Chronic stability of activated iridium oxide film voltage transients from wireless floating microelectrode arrays.

Successful monitoring of the condition of stimulation electrodes is critical for maintaining chronic device performance for neural stimulation. As part of pre-clinical safety testing in preparation for a visual prostheses clinical trial, we evaluated the stability of the implantable devices and stimulation electrodes using a combination of current pulsing in saline and in canine visual cortex. Specifically, in saline we monitored the stability and performance of 3000 μm geometric surface area activated iridium oxide film (AIROF) electrodes within a wireless floating microelectrode array (WFMA) by measuring the voltage transient (VT) response through reverse telemetry.

The use of digital image correlation for measurement of strain fields in a novel wireless intraspinal microstimulation interface.

Background: Intraspinal microstimulation (ISMS) has emerged as a promising neuromodulation technique for restoring standing and overground walking in individuals with spinal cord injury. Current and emerging ISMS implant designs connect the electrodes to the stimulator through lead wires that cross the dura mater. To reduce possible complications associated with transdural leads such as tethering and leakage of cerebrospinal fluid, we aim to develop a wireless, fully intradural ISMS implant based on our prior work in the cortex with the Wireless Floating Microelectrode Array (WFMA).

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

Consistent transmission of data from wireless neural devices is critical for monitoring the condition and performance of stimulation electrodes. To date, no wireless neural interface has demonstrated the ability to monitor the integrity of chronically implanted electrodes through wireless data transmission.In this work, we present a method for wirelessly recording the voltage transient (VT) response to constant-current, cathodic-first asymmetric pulsing from a microelectrode array.

Effects of Varying Pulse Width and Frequency of Wireless Stimulation in Rat Sciatic Nerve.

Peripheral nerve stimulation is a commonly used method for assisting movements after spinal cord injury, stroke, traumatic brain injury, and other types of neurological damage or dysfunction. There are many different patterns of electrical stimulation used to accomplish movement. And so, our study investigated stimulation with a wireless floating microelectrode array (WFMA) in comparison to previously reported data on functional electrical stimulation.

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

. 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.

Toward the development of a color visual prosthesis.

. All of the human prosthetic visual systems implanted so far have been achromatic. Schmidt(1996507-22) reported that at low stimulation intensities their subject reported that phosphenes usually had a specific hue, but when the stimulus intensity was increased, they desaturated to white.

Selective Wireless Stimulation of Rat Sciatic Nerve.

Chronic stability of functional performance is a significant challenge to the success of implantable devices for neural stimulation and recording. Integrating wireless technology with typical microelectrode array designs is one approach that may reduce instances of mechanical failure and improve the long-term performance of neural devices. We have investigated the long-term stability of Wireless Floating Microelectrode Arrays (WMFAs) implanted in rat sciatic nerve, and their ability to selectively recruit muscles in the hind limb via neural stimulation.

Activated iridium oxide film (AIROF) electrodes for neural tissue stimulation.

Objective: Iridium oxide films are commonly used as a high charge-injection electrode material in neural devices. Yet, few studies have performed in-depth assessments of material performance versus film thickness, especially for films grown on three-dimensional (instead of planar) metal surfaces in neutral pH electrolyte solutions. Further, few studies have investigated the driving voltage requirements for constant-current stimulation using activated iridium oxide (AIROF) electrodes, which will be a key constraint for future use in wirelessly powered neural devices.

Harmonization of Outcomes and Vision Endpoints in Vision Restoration Trials: Recommendations from the International HOVER Taskforce.

Translational research in vision prosthetics, gene therapy, optogenetics, stem cell and other forms of transplantation, and sensory substitution is creating new therapeutic options for patients with neural forms of blindness. The technical challenges faced by each of these disciplines differ considerably, but they all face the same challenge of how to assess vision in patients with ultra-low vision (ULV), who will be the earliest subjects to receive new therapies. Historically, there were few tests to assess vision in ULV patients.

Postmortem investigation of a human cortical visual prosthesis that was implanted for 36 years.

Objective: Postmortem analysis of the brain from a blind human subject who had a cortical visual prosthesis implanted for 36 years (Dobelle 2000 Asaio J. 46 3–9)

Approach: This provided insight into the design requirements for a successful human cortical visual prosthesis by revealing, (a) unexpected rotation of the electrode array 25 to 40 degrees away from the midsagittal plane, thought to be due to the torque of the connecting cable, (b) degradation of the platinum electrodes, and (c) only partial coverage of the primary visual cortex by the rectangular array. The electrode array only overlapped with the anterior 45% of primary visual cortex (identified by the line of Gennari), largely missing the posterior foveal representation of visual cortex.

Preparation of a neural electrode implantation device for in-vivo surgical use.

An instrument designed for the implantation of neural electrode array devices has been refined in preparation for use in cortical implantation procedures in non-human primates. This instrument has undergone extensive testing to ensure its successful first use in a live surgical setting. This work describes the modifications made to the instrument and the testing performed on it during that preparatory period as well as planned future modifications and augmentations.

Chronic in-vivo testing of a 16-channel implantable wireless neural stimulator.

Here, we report on chronic in-vivo testing of a 16-channel wireless floating microelectrode array (WFMA) in a rat sciatic nerve model. Muscle threshold currents, charge injection levels, and charge density were monitored for electrodes of two WFMA devices implanted into animal subjects over a five month period. This type of wireless stimulation device could eliminate problems associated with percutaneous connectors for a variety of neural prostheses and other medical devices.

Chronic and low charge injection wireless intraneural stimulation in vivo.

Functional stability and in-vivo reliability are significant factors determining the longevity of a neural interface. In this ongoing study, we test the performance of a wireless floating microelectrode array (WFMA) over a period of 143 days. The topography of the microelectrodes has allowed for selective stimulation of different fascicles of the rat sciatic nerve.

Web technology based microelectrode characterization instrument.

In order to track the on-going changes and ultimate reliability of neural recording and stimulation arrays, it is beneficial to regularly characterize electrode arrays within the use environment. Microelectrodes used for neural stimulation or recording research can have different behaviors in-vivo vs. in- vitro, and once implanted the success of the experiment often hinges upon knowing the stability, changes, or deterioration of the electrodes.

Multichannel wireless ECoG array ASIC devices.

Surgical resection of epileptogenic foci is often a beneficial treatment for patients suffering debilitating seizures arising from intractable epilepsy [1], [2], [3]. Electrodes placed subdurally on the surface of the brain in the form of an ECoG array is one of the multiple methods for localizing epileptogenic zones for the purpose of defining the region for surgical resection. Currently, transcutaneous wires from ECoG grids limit the duration of time that implanted grids can be used for diagnosis.

Low-power polling mode of the next-generation IMES2 implantable wireless EMG sensor.

The IMES1 Implantable MyoElectric Sensor device is currently in human clinical trials led by the Alfred Mann Foundation. The IMES is implanted in a residual limb and is powered wirelessly using a magnetic field. EMG signals resulting from the amputee's voluntary movement are amplified and transmitted wirelessly by the IMES to an external controller which controls movement of an external motorized prosthesis.

Accelerated-stress reliability evaluation for an encapsulated wireless cortical stimulator.

In preparing a wireless cortical stimulator for use in the Intracortical Visual Prosthesis (ICVP) project at the Illinois Institute of Technology (IIT), an accelerated environmental stress test is being performed on prototype stimulator modules. Stimulator devices, containing a custom application specific integrated circuit (ASIC), and encapsulated with PDMS, were soaked in an autoclave chamber at 121°C and 100% relative humidity for more than 2200 hours with and without power supplied to the ASIC. Experimental results showed no physical degradation of the stimulator devices after soaking.

Device for the implantation of neural electrode arrays.

Electrode arrays used in neural recording and stimulation applications must be implanted carefully to minimize damage to the underlying tissue. A device has been designed to improve a surgeon's control over implantation parameters including depth, insertion velocity, and insertion force. The device has been designed to operate without contacting tissue and to respond to tissue movements in real time during insertion.

Perspectives of optic nerve prostheses.

A number of projects exist that are investigating the ability to restore visual percepts for individuals who are blind through a visual prosthesis. While many projects have reported the results from a technical basis, very little exists in the professional literature on the human experience of visual implant technology. The current study uses an ethnographic methodological approach to document the experiences of the research participants and study personnel of a optic nerve vision prosthesis project in Brussels, Belgium.

A laboratory instrument for characterizing multiple microelectrodes.

The task of chronic monitoring and characterizing a large number of microelectrodes can be tedious and error prone, especially if needed to be done in vivo. This paper presents a lab instrument that automates the measurement and data processing, allowing for large numbers of electrodes to be characterized within a short time period. A version 1.

Identification and quantification of electrical leakage pathways in floating microelectrode arrays.

The long-term reliability of neural recording and stimulation electrode arrays is becoming the limiting factor for neural interfaces. For effective electrode design, electrical connection to the surrounding neural tissue and fluid should be limited to the electrode tips, with all other leakage currents minimized. It is the goal of this study to identify and quantify electrical leakage within commercially available floating microelectrode arrays (FMAs).

Electrical performance of penetrating microelectrodes chronically implanted in cat cortex.

Penetrating microelectrode arrays with 2000 μm (2) sputtered iridium oxide (SIROF) electrode sites were implanted in cat cerebral cortex, and their long-term electrochemical performance evaluated in vivo by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and current pulsing. Measurements were made from days 33 to 328 postimplantation. The CV-defined charge storage capacity, measured at 50 mV/s, increased linearly with time over the course of implantation for two arrays and was unchanged for one array.

Intrinsic activation of iridium electrodes over a wireless link.

Activated Iridium Oxide Film (AIROF) microelectrodes are regarded as advantage for stimulation of neural tissue owing to their superior charge injection capabilities, as compared to other noble-metal based electrodes. Including AIROF electrodes within an implantable neural stimulator can be challenging since the stimulator fabrication steps often involve elevated temperatures at which the AIROF can be damaged. In this work, a wireless neural stimulator application-specific-integrated-circuit (ASIC) was used to intrinsically activate iridium microelectrodes.

An implantable neural stimulator for intraspinal microstimulation.

This paper reports on a wireless stimulator device for use in animal experiments as part of an ongoing investigation into intraspinal stimulation (ISMS) for restoration of walking in humans with spinal cord injury. The principle behind using ISMS is the activation of residual motor-control neural networks within the spinal cord ventral horn below the level of lesion following a spinal cord injury. The attractiveness to this technique is that a small number of electrodes can be used to induce bilateral walking patterns in the lower limbs.