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.NANOCI aims at developing a neuroprosthesis with a gapless interface to auditory nerve fibres. The neurites will be attracted and guided by an innovative, nanostructured gel matrix containing diffusible and surface-bound neurotrophic compounds towards the functionalized, neurotrophic electrode array surface. The 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 bidirectional, gapless interface. Fusing all 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.