Regenerating spiral ganglion neurons employing the cochlear implant

Sensorineural hearing loss is treated using cochlear implants. The electrodes in the implants directly stimulate spiral ganglion neurons (SGNs). However, SGNs continually degenerate and are difficult to access behind the bony modiolar wall of the cochlea. The electrode-tissue interface needs to be improved to enhance hearing for users. Implanting the electrode closer to the SGNs, requires a greater insertion depth and increases the amount of scar tissue that forms around the electrode. The introduction of neurotrophic factors has the potential to improve neural regeneration. However, currently there are a lack of methods to deliver neurotrophic factors locally and sustainably into the cochlea. We propose a neural electrode system utilising electrical stimulation (ES) to increase the expression of brain-derived neurotrophic factor (BDNF) and guide SGNs and their neurites towards the electrode. Additionally, the electrode system would utilise an electrospun nanofiber scaffold surrounding the electrode to act as a mechanical support to the cells and their projections.Nanofiber scaffolds were electrospun onto wires and glass coverslips and cultured with human SH-SY5Y neuroblastoma and rat Schwann cells. Immunohistochemistry and scanning electron microscopy were used to characterise the scaffolds and biocompatibility. Platinum electrodes were used to stimulate both rat Schwann cells and SH-SY5Y cells for 3 hours using a 100mV/mm DC electric field. Following 20 hours of incubation, the cells were immunostained to measure changes in BDNF expression.We discovered that not only were the scaffolds biocompatible, but the cells aligned along the nanofibers, forming networks on the scaffolds. We observed statistically significant increases in BDNF expression in Schwann cells, as well as a limited BDNF increase in SH-SY5Y cells that may be a result of the incubation period used in our experiment and is currently under investigation.These results suggest the feasibility of the system and have the potential to improve cochlear implants.