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Development of a neural electrode scaffold system to enhance cochlear implant function

Quy-Susan Huynh (1, 2), Philip Boughton (3), Norbert Dommel (4), Paul Carter (4) and R. M. Damian Holsinger (1, 2)

  1. Laboratory of Molecular Neuroscience and Dementia, Brain and Mind Centre, School of Medical Sciences, Faculty of Medicine and Health, The University of Sydney, New South Wales, Australia

  2. Discipline of Pathology, School of Medical Sciences, Faculty of Medicine and Health, The University of Sydney, New South Wales, Australia

  3. Sydney Spine Institute, Burwood, New South Wales, Australia

  4. Cochlear Ltd, Macquarie University, New South Wales, Australia

The cochlear implant (CI) is the gold standard for sensorineural hearing loss (SHL). The electrode of the CI targets spiral ganglion neurons (SGNs). However, SHL is characterized by the degeneration of SGNs and although not all SGNs atrophy, surviving SGNs are difficult to access as they are located behind the cochlea’s bony modiolar wall. Consequently, charge spreads from the electrode towards the surrounding tissue rather than solely to the target tissue, leading to suboptimal hearing. Inserting the electrode deeper into the cochlea leads to an increase in scar tissue formation and the use of trophic factors for the regeneration of neural tissue in the cochlea requires a sustainable delivery method.

Our solution is to design a neural electrode scaffold system that utilises electrical stimulation (ES) to upregulate brain-derived neurotrophic factor (BDNF) expression, a potent trophic factor in the brain. ES can facilitate neuronal survival and extension of SGN neurites, directing them towards the electrodes. The electrospinning of a nanofibre scaffold onto the electrode will provide structural support for the cells and their neurites.

In our test system, a nanofibre scaffold was electrospun onto wires and glass coverslip and tested in vitro using SH-SY5Y neuroblastoma and Schwann cells. Scanning electron microscopy and tubulin immunostaining were used to characterise the scaffold and visualize cell attachment. Not only did cells attach to the scaffold but also used the nanofibres to form networks. There was evidence of neurite extension aligning along the electrospun fibres and cell filopodia extending and interacting with the nanotopography.