Research ArticleNEUROTECHNOLOGY

Microstructured thin-film electrode technology enables proof of concept of scalable, soft auditory brainstem implants

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Science Translational Medicine  16 Oct 2019:
Vol. 11, Issue 514, eaax9487
DOI: 10.1126/scitranslmed.aax9487

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Beneficial bending

Some people with deafness receive auditory brainstem implants (ABIs), neurotechnology that directly stimulates the cochlear nucleus (CN). Unfortunately, auditory outcomes after implantation are limited, possibly due to mismatch between the stiffness of the implant and the CN. Vachicouras et al. developed ABIs that conform to the curvature of the CN. The soft arrays could be easily handled during surgery and functioned over 1 month when implanted in mice. A scaled-up version of the conformable ABIs inserted in human cadavers showed good electromechanical and electrochemical stability and a potentially larger dynamic range compared to the clinical ABIs. These proof-of-concept results support further testing in models of deafness.

Abstract

Auditory brainstem implants (ABIs) provide sound awareness to deaf individuals who are not candidates for the cochlear implant. The ABI electrode array rests on the surface of the cochlear nucleus (CN) in the brainstem and delivers multichannel electrical stimulation. The complex anatomy and physiology of the CN, together with poor spatial selectivity of electrical stimulation and inherent stiffness of contemporary multichannel arrays, leads to only modest auditory outcomes among ABI users. Here, we hypothesized that a soft ABI could enhance biomechanical compatibility with the curved CN surface. We developed implantable ABIs that are compatible with surgical handling, conform to the curvature of the CN after placement, and deliver efficient electrical stimulation. The soft ABI array design relies on precise microstructuring of plastic-metal-plastic multilayers to enable mechanical compliance, patterning, and electrical function. We fabricated soft ABIs to the scale of mouse and human CN and validated them in vitro. Experiments in mice demonstrated that these implants reliably evoked auditory neural activity over 1 month in vivo. Evaluation in human cadaveric models confirmed compatibility after insertion using an endoscopic-assisted craniotomy surgery, ease of array positioning, and robustness and reliability of the soft electrodes. This neurotechnology offers an opportunity to treat deafness in patients who are not candidates for the cochlear implant, and the design and manufacturing principles are broadly applicable to implantable soft bioelectronics throughout the central and peripheral nervous system.

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