A seamlessly connected cochlear implant
CIs transform the lives of hearing impaired adults and children, allowing hearing and speech recognition. However, low specificity of neuronal stimulation results in sub-optimal sound quality and high electrical energy consumption. Furthermore, dependence of CIs on rechargeable batteries presents additional challenges for a fully implantable device. With EU funding, the project NANOCI (Nanotechnology based cochlear implant with gapless interface to auditory neurons) has worked on developing a gapless neuron: electrode interface for CIs. In an in vitro set up, response profiles of mice and human auditory neurons have been obtained on multi-electrode arrays. By modifying stimulus parameters in the gapless position in the arrays, there was up to a four-fold reduction of energy needed for a response. Screening of biomimetic growth factor analogues to stimulate axon growth resulted in three promising candidates. Most notably, a lead structure of a small-peptide mimetic of brain-derived neurotrophic factor (BDNF) has been identified, which is ready for patenting. The functionalised NANOCI gel-matrix containing laminin epitopes was successfully applied in vivo. For coatings of the electrode array, new nanoparticles have been developed with antibacterial activity at reduced toxicity. Other conducting hybrid polymer-nanomaterial phases have been produced for functional modifications to optimise electrode conductivity, reduce impedance and improve neuron-electrode coupling in the scenario of the gapless interface. An animal-grade NANOCI electrode was produced for successful multicomponent testing in vivo. Methods to dispense and visualise release of the growth factor/neurotrophin from the electrode surface and dispenser technologies have been investigated. An electrode location analyser in animal and human inner ears has also been optimised. NANOCI's in vitro model has enabled the study of responses of auditory neurons in detail. Researchers can now design optimum stimulation patterns suited to the gapless interface. Moreover, a patent-ready optical feedback sensor has been developed and tested in human temporal bones for monitoring insertion forces of the electrode array to minimise insertion trauma. Incorporation of a fraction of the energy reduction achieved by the NANOCI project into a clinical grade model could translate to a fully implantable CI device. Making hearing loss invisible would be a big boost to the hearing impaired psychologically. Furthermore the improved interface offers enhanced possibilities to improve sound quality through new coding strategies.
Keywords
Cochlear implant, brain-derived neurotrophic factor, laminin, gapless interface, fully implantable device
