Micro-magnetic Stimulation of Auditory Neurons: a New Paradigm in Overcoming Hearing Loss

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As estimated by the World Health Organization, over 5% of the world's population (360 million individuals: 32 million children) experience disabling hearing loss. Unattended hearing loss results in feelings of isolation, loneliness, and extreme frustration. This is especially prevalent in older individuals. Not only does hearing loss severely impair communication, it often leads to delays in spoken language abilities in children. A host of strategies, with varying degrees of success, can be used to reduce the detrimental effects of hearing disability: these range from screening, protection, captioning, sign language, to assistive devices such as hearing aids and cochlear implants (CI). CI devices function by coding sound waves as electrical pulses. In turn, these pulses determine the amount of electrical charge applied to neurons in the inner ear (cochlea) thereby conveying a lost or diminished sensation of sound. Approximately 324,000 CI have been implanted worldwide enabling some individuals to perceive speech very well. However, outcomes are highly variable and unpredictable. Everyday situations, such as understanding speech in noisy settings, and appreciating music, present users with significant challenges. A major contributor is the inability of CIs to precisely control the path of electrical charge in the highly conductive intracochlear fluid. This work pursues a promising and novel alternative to direct electrical stimulation - micro-magnetic stimulation via electrically pulsed coils housed on a flexible substrate and implanted in the cochlea. An intracochlear micro-coil array can activate auditory neurons with greater specificity while also enabling longer-term safety since the micro-coils are fully encapsulated. The applicability of micro-magnetic coils can naturally be extended to overcome loss in balance, sight, as well as to improve deep brain stimulation. To further enhance the societal impact of the research, partnerships with the Centers for Disease Control and Prevention, and Fernbank Science Center will enable and promote hearing health awareness and education in Atlanta, GA.The proposed work is a necessary first-step toward advancing an understanding of how locally induced fields may serve to excite neurons. In contrast with transcranial magnetic stimulation requiring a bulky coil and consuming considerable power, micro-coils implanted proximal to target neural tissue may engage the nervous system more effectively. To pursue this research, direct metal inkjet printing methods to build micro-coils on polymeric substrates will be developed. The devices will be fully encapsulated with a medical grade polymer and tested in solution to examine for impedance shifts and leakage current. Ex-vivo testing will also be accomplished with organotypic spiral ganglion neurons cultured on a 2D multichannel electrode array (MEA). The 2D-MEA and associated software system will enable the unprecedented possibility of non-invasive, closed-loop micro-magnetic stimulation and neural response recording. From this, neural threshold and specificity will be assessed and compared with conventional CI electrode-based stimulation. In a parallel and highly collaborative fashion, array insertion studies in human cadaver cochleae to assess insertion trauma, depth of insertion, and scalar wall distances will be pursued. More broadly, the application of novel printing and additive manufacturing, combined with flexible electronics, has the potential to transform fabrication of neural interface technologies to processes outside of the cleanroom, while enabling seamless integration with supporting drive electronics and packaging.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.