ReStore: A wireless peripheral nerve stimulation system

Abstract

Background: The growing use of neuromodulation techniques to treat neurological disorders has motivated efforts to improve on the safety and reliability of implantable nerve stimulators.

New method: The present study describes the ReStore system, a miniature, implantable wireless nerve stimulator system that has no battery or leads and is constructed using commercial components and processes. The implant can be programmed wirelessly to deliver charge-balanced, biphasic current pulses of varying amplitudes, pulse widths, frequencies, and train durations. Here, we describe bench and in vivo testing to evaluate the operational performance and efficacy of nerve recruitment. Additionally, we also provide results from a large-animal chronic active stimulation study assessing the long-term biocompatibility of the device.

Results: The results show that the system can reliably deliver accurate stimulation pulses through a range of different loads. Tests of nerve recruitment demonstrate that the implant can effectively activate peripheral nerves, even after accelerated aging and post-chronic implantation. Biocompatibility and hermeticity tests provide an initial indication that the implant will be safe for use in humans.

Comparison with existing method(s): Most commercially available nerve stimulators include a battery and wire leads which often require subsequent surgeries to address failures in these components. Though miniaturized battery-less stimulators have been prototyped in academic labs, they are often constructed using custom components and processes that hinder clinical translation.

Conclusions: The results from testing the performance and safety of the ReStore system establish its potential to advance the field of peripheral neuromodulation.

Keywords: Implantable pulse generator; Integrated electrodes; Nerve stimulator; Neuromodulation; Telemetry; Wireless.

Figure 1:

Key components of the ReStore nerve stimulator system.

Figure 2:

Implantable Pulse Generator. (A) Block diagram of the implantable pulse generator. View of the front (B) and back side (C) of the IPG. The electrodes are visible in C. (D) The silicone cuff with the IPG inserted. (E) IPG wafer

Figure 3:

Circuit schematic of the IPG

Figure 4:

Relay module (A) Block diagram of the relay module (B) Relay module PCB with the flex coil that is used to power the IPG (C) Relay module housed in a plastic enclosure (D) Relay module in a collar

Figure 5:

Results of benchtop testing. (A) Current waveforms of a 100 μs biphasic pulse at 8 different amplitudes. (B) Corresponding voltage waveforms for the 8 amplitudes. (C) Current waveforms of a 1200 μA pulse through different loads

Figure 6:

Results of range testing (A) Percentage of successful stimulations delivered by the IPG at different distances and angles from the relay module (B) Illustration of range measurement

Figure 7:

Results of chronic biocompatibility testing (A) Voltage that was required to deliver 1.2 mA of current in the five animals (B) IPG communication success rate for the five animals

Figure 8:

ReStore devices demonstrate reliable nerve recruitment. (A) Force measurements using normal devices (16 trials) shows the low amplitudes required to activate the sciatic nerve (B) Comparison of nerve recruitment of an aged device with a normal device shows a slight increase in activation threshold, but still well within the range of the device (C) Comparison of nerve recruitment of an explanted device from chronic safety study with a normal device shows similar activation thresholds (D) Comparison of activation thresholds of normal, aged and explanted devices

Figure 9:

IPG temperature at the electrode surface during maximum stimulation