NANOCI—Nanotechnology Based Cochlear Implant With Gapless Interface to Auditory Neurons

Abstract

Cochlear implants (CI) restore functional hearing in the majority of deaf patients. Despite the tremendous success of these devices, some limitations remain. The bottleneck for optimal electrical stimulation with CI is caused by the anatomical gap between the electrode array and the auditory neurons in the inner ear. As a consequence, current devices are limited through 1) low frequency resolution, hence sub-optimal sound quality and 2), large stimulation currents, hence high energy consumption (responsible for significant battery costs and for impeding the development of fully implantable systems). A recently completed, multinational and interdisciplinary project called NANOCI aimed at overcoming current limitations by creating a gapless interface between auditory nerve fibers and the cochlear implant electrode array. This ambitious goal was achieved in vivo by neurotrophin-induced attraction of neurites through an intracochlear gel-nanomatrix onto a modified nanoCI electrode array located in the scala tympani of deafened guinea pigs. Functionally, the gapless interface led to lower stimulation thresholds and a larger dynamic range in vivo, and to reduced stimulation energy requirement (up to fivefold) in an in vitro model using auditory neurons cultured on multi-electrode arrays. In conclusion, the NANOCI project yielded proof of concept that a gapless interface between auditory neurons and cochlear implant electrode arrays is feasible. These findings may be of relevance for the development of future CI systems with better sound quality and performance and lower energy consumption. The present overview/review paper summarizes the NANOCI project history and highlights achievements of the individual work packages.

Long-term delivery of brain-derived neurotrophic factor (BDNF) from nanoporous silica nanoparticles improves the survival of spiral ganglion neurons in vitro

“…Cochlear implants can replace the function of hair cells by direct electrical stimulation of primary auditory neurons (spiral ganglion neurons, SGNs) [ 5 , 6 ]. However, the efficacy of cochlear implants is limited by the anatomical gap between the electrode array inserted into the scala tympani and the SGNs situated in the Rosenthal´s canal leading to an unspecific stimulation of relatively large groups of neurons [ 7 , 8 ]. Moreover, the performance of cochlear implants strongly depends on the number of surviving neurons and their functionality, i.e., their excitability [ 3 , 9 ].…”

Alginate-encapsulated brain-derived neurotrophic factor–overexpressing mesenchymal stem cells are a promising drug delivery system for protection of auditory neurons

“…54 It may indicate a potential for BDNF-induced regeneration of dendrites, while protecting the axon against degeneration, what possibly improves the nerve electrode interface of the CI by neurite regeneration. 11,14 The detected doses of MSC-secreted BDNF were much lower than the previously tested exogenous 50 ng/mL but showed a similar effect on the neuronal morphology. This may indicate that a continuous production and availability of low doses of BDNF produced by the MSCs can support the SGN similar to NTF-producing cells in the organ of Corti.…”

“…But this regeneration was largely uncontrolled and rarely guided to the electrode. [9][10][11][12][13] In the presence of the alginate-embedded MSCs, the number of regenerated neurites was about six times higher and the length of the regenerated neurites was significantly increased. This effect was shown in several studies for exogenous, recombinant BDNF.…”

“…Another objective of current CI research for stimulation improvement is bridging the anatomical gap between electrode array and neurons by regeneration and guidance of the SGN peripheral processes. [9][10][11][12][13][14] For both goals, protection of SGN from degeneration and regeneration of their dendrites, local neurotrophic factor (NTF) therapy is a promising strategy. For example, for brain-derived neurotrophic factor (BDNF), several studies detected a potential to protect SGN from degeneration and also a neurite regeneration in vitro and in vivo.…”

Auditory Dysfunction in Aging: Prospects for Stem Cell Therapy

“…In a recent multinational study, named NANOCI, researchers tried to create a gapless interface between auditory nerve fibers and cochlear implant. They generated a modified nano-cochlear implant electrode array that was inserted into the scala tympani and resulted in a neurotrophin-induced attraction of neurites, which led to lower stimulation thresholds and reduction in required stimulation energy [100].…”