Over 60 million of citizens in the EU suffer from hearing loss with its associated restrictions. In severe cases, hearing can only be restored by surgically implanting a neuroprosthesis called cochlear implant, which directly stimulates the auditory nerve.
The bottleneck for optimal stimulation 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 (i) low frequency resolution, hence poor sound quality and (ii), strong signal amplification, hence high energy consumption responsible for significant battery costs and for impeding the development of fully implantable systems. Recent findings indicate that auditory nerve fibres can grow under neurotrophin stimulation towards the electrodes, which opens the door to address all issues simultaneously.
It is generally acknowledged that eliminating the gap between neurons and the electrode array and hence increasing the number of active channels should greatly improve the effectiveness of auditory nerve stimulation. The NANOCI project therefore aims to attract the peripheral processes of the auditory nerve towards the electrode array.
NANOCI aims at developing a neuroprosthesis with a gapless interface to auditory nerve fibres. The neurites will be attracted and guided by an innovative, nanomatrix containing diffusible and surface-bound neurotrophic compounds towards the functionalized, neurotrophic electrode array surface. A long-lasting operation without interface degradation, reduced biofouling and improved conductivity will be achieved by nanostructuring the array surface using (i) various functional nanomaterials, including carbon nanotubes, combined with (ii) structuration methodologies such as ion implantation and sacrificial nanoparticle embedding in parylene, SOLID (solid on liquid deposition) encapsulation, and sonochemistry. Components will be validated using appropriate bioassays including human auditory neurons in vitro. In parallel, software models will be developed to exploit the enhanced effectiveness of the bidirectional, gapless interface. By combining all these developments, an animal-grade, pilot nanoCI-device is manufactured and tested in vivo. This will allow to assess the feasibility of a future, cost-efficient, and fully implantable neuroprosthesis with substantially increased sound quality.
In summary, the current literature supports the assumption that mature auditory neurons are capable of sprouting towards a neurotrophin source located in the scala tympani, particularly in presence of electrical stimulation.
Novel solutions have to be developed to guide the neurons through the perilymph fluids of the scala tympani and to permanently lock them on the surface of the array.
For long-lasting restoration of the hearing function, biocompatibility, biosafety and antibiofouling activity of such an implant have to be guaranteed.
To optimally exploit the potential of a gapless interface through the associated increase in channel numbers and to capitalize on the simultaneous stimulation/recording of smaller neuronal populations, novel coding and signal shaping strategies will be required.