A Flexible Wireless System for Preclinical Evaluation of Retinal Prosthesis

Abstract

In this paper, we present a novel stimulation controller and monitoring system for evaluating the safety and efficacy of implantable neuroprosthetic devices in a preclinical setting. It features a programmable controller designed to be worn in a custom backpack by freely moving feline subjects. A custom controller powered two, modified, 22-channel clinical stimulators simultaneously. The controller and stimulators together weighed 140 g and measured 85 × 70 × 35 mm 3 . Power was supplied from a 3350 mAh lithium-ion battery. A Bluetooth-enabled laptop-PC base station managed up to six systems and allowed the remote adjustment of the stimulation amplitude and automated collection of stimulator telemetry data. The initial application was for the chronic safety testing of a 44-channel retinal prosthesis. Thirteen feline subjects were implanted with a suprachoroidal electrode array, which was then stimulated or monitored continuously for an average of 54.5 d. Batteries were changed twice weekly and electrode impedances were recorded hourly. This allowed broken electrodes and other issues to be quickly identified and addressed. The ability to remotely control the stimulation amplitude minimised the amount of subject handling that was required, likely reducing subject stress. Existing preclinical evaluation systems are either designed for short-term experiments and have many features but limited battery life, or for long-term static stimulation and are long-lived, but with restricted stimulation parameters and channel counts. Here, we have described a system designed to improve the chronic safety testing of electrode arrays. While it was used here with a suprachoroidal retinal implant, it could be readily adapted for other preclinical models requiring continuous, deterministic stimulation over a prolonged period.

Chronic electrical stimulation with a peripheral suprachoroidal retinal implant: a preclinical safety study of neuroprotective stimulation

“…Within the backpack stimulation system, there are hardware components comprising a battery cover, a battery and cable and a stimulation control system (Nimble) to control stimulation and measure and log impedances ( Thien et al, 2018 ), a Cochlear Implant CI-24RE stimulator to generate voltage controlled biphasic current pulses, connected to the cable wiring via a customized printed circuit board ( Figure 2 ). The backpack system itself is designed for strapping around the body and is secured with Velcro both around the body and around the pouch with the hardware components.…”

“…Although this measurement of ‘impedance’ does not include a phase angle, so could correctly be termed ‘mean of peak cathodic-phase instantaneous resistances’, the term ‘impedance’ has become commonly accepted in many clinical neuroprosthesis studies ( Nayagam et al, 2014 ). Individual electrode impedances were measured wirelessly using custom laboratory software (Nimble) running on a laptop computer ( Thien et al, 2018 ) for all eight subjects. Impedance measurements were calculated and averaged in response to trains of 25 µs phase-width rectangular biphasic current pulses of 75 µA amplitude.…”

“…From the orbital patch on the lateral orbital margin, the cable system traverses under the skin to the top of the skull and follows along the back of the skull to exit at a percutaneous extrusion at the neck, where the cable connects to the backpack stimulation system via a semi-customised mini-USB connector (Figure 2). Within the backpack stimulation system, there are hardware components comprising a battery cover, a battery and cable and a stimulation control system (Nimble) to control stimulation and measure and log impedances (Thien et al, 2018), a Cochlear Implant CI-24RE stimulator to generate voltage controlled biphasic current pulses, connected to the cable wiring via a customized printed circuit board (Figure 2). The backpack system itself is designed for strapping around the body and is secured with Velcro both around the body and around the pouch with the hardware components.…”

Safety Studies for a 44-Channel Suprachoroidal Retinal Prosthesis: A Chronic Passive Study

“…The remaining eight animals received electrical stimulation from 4 weeks postsurgery onward using the electrical stimulation system described previously. 31 These eight animals were also monitored longitudinally with clinical techniques, and the passive implantation outcomes pertaining to implantation safety, device stability, electrode array conformability, and electrode robustness are reported here. The electrical stimulation safety outcomes including retinal thickness and histopathology from the active stimulation subcohort will be presented in a companion publication.…”