Integration of Soft Materials in Microfabrication for Auditory Neuroprostheses

Implantable neuromodulation systems often rely on macroscopic electrodes to deliver streams of electrical pulses to a small targeted region of the nervous system. Miniaturisation and design of electrode materials can help improving on the spatial selectivity and electrode reliability over time. In the context of auditory neuroprostheses, we are designing, scaling and implementing soft microelectrode arrays to generate resolutive sound percept with minimal off-target effects in a pre-clinical model of auditory brainstem implants (ABI).<br/>Using microfabrication, we manufactured a macaque sized multichannel, MRI compatible, soft auditory brainstem implant (150µm thick silicone carrier, 11 platinum-silicone composite electrodes of 300µm diameter) that delivers selective electrical stimulation. We engineered customised biodegradable implant holder to ease handling and implantable without compromising the ABI compliance, as well as connectors to reliably interface mechanically and electrically the soft implant with flexible cables and a head-mounted pedestal. The ABI is surgically implanted through a retro-sigmoid craniotomy under endoscopic visualisation at the surface of the cochlear nucleus (&lt;5 mm² surface area).<br/>We evaluated the efficacy of the soft ABI by monitoring the animal’s performance in a behavioural task. Using burst of electrical pulses (ranging from 50-100 pulses per second at 0.1-2 mA) applied through the ABI electrodes, we confirmed the resolutive capability of the implant: the animal was able to differentiate percept generated from different electrode pairs, with distinct activation threshold for each electrode, indicating good spatial resolution.<br/>Systematic characterisation of the materials and processes at each step of the manufacturing of the implant enabled the successful deployment of the soft auditory neuroprosthesis.