Characterization and Miniaturization of Silver-Nanoparticle Microcoil via Aerosol Jet Printing Techniques for Micromagnetic Cochlear Stimulation

Abstract

According to the National Institute of Deafness and other Communication Disorders 2012 report, the number of cochlear implant (CI) users is steadily increasing from 324,000 CI users worldwide. The cochlea, located in the inner ear, is a snail-like structure that exhibits a tonotopic geometry where acoustic waves are filtered spatially according to frequency. Throughout the cochlea, there exist hair cells that transduce sensed acoustic waves into an electrical signal that is carried by the auditory nerve to ultimately reach the auditory cortex of the brain. A cochlear implant bridges the gap if non-functional hair cells are present. Conventional CIs directly inject an electrical current into surrounding tissue via an implanted electrode array and exploit the frequency-to-place mapping of the cochlea. However, the current is dispersed in perilymph, a conductive bodily fluid within the cochlea, causing a spread of excitation. Magnetic fields are more impervious to the effects of the cochlear environment due to the material properties of perilymph and surrounding tissue, demonstrating potential to improve precision. As an alternative to conventional CI electrodes, the development and miniaturization of microcoils intended for micromagnetic stimulation of intracochlear neural elements is described. As a step toward realizing a microcoil array sized for cochlear implantation, human-sized coils were prototyped via aerosol jet printing. The batch reproducible aerosol jet printed microcoils have a diameter of 1800 μm, trace width and trace spacing of 112.5 μm, 12 μm thickness, and inductance values of approximately 15.5 nH. Modelling results indicate that the coils have a combined depolarization–hyperpolarization region that spans 1.5 mm and produce a more restrictive spread of activation when compared with conventional CI.

Development and Characterization of a Micromagnetic Alternative to Cochlear Implant Electrode Arrays

“…Though the strength of the magnetic fields generated by the solenoid microcoils alone are being actively evaluated to determine if an action potential will be fired, the magnitude of magnetic fields the can be increased through a microcoil stacking method. In previous work, planar microcoils were developed [16], and a future design may utilize planar microcoils wrapped by the microcoils reported here. Additionally, the electromagnetic response when activating several microcoils at once will be observed.…”

“…Present-day developments of this alternate CI design are in the proposal and early prototype stages [15]. The previous works of the Translational BioSystems Group at the Georgia Institute of Technology demonstrate that microcoils are capable of stimulating the cochlea, with the deduction of improved spatial resolution of the stimulation channels via theoretical FEM analysis, activating function calculation, as well as experimental functionality validation of fabricated microcoils [12], [16]. Additionally, experimental stimulation using microcoils in a feline cochlea has been observed by Blake et al where surface mount inductors were implanted into the feline cochlea.…”

Aerosol‐Jet Printed Sensors for Environmental, Safety, and Health Monitoring: A Review

“…Reproduced under the terms of the CC‐BY license. [ 90 ] Copyright 2020, The Authors, published by MDPI. b) A printed cochlear implant coil with 12 µm thickness connected to a two‐probe system for characterization.…”

Promising Applications of Nanoparticles in the Treatment of Hearing Loss

“…Some studies have investigated the silver NP microcoil with the micro size by aerosol jet printing. It has been demonstrated that the electromagnetic field generated by this material is not affected by cochlear environment (Sarreal and Bhatti, 2020). The eddy current generated by electromagnetic field can be used to stimulate the nearby tissues, and to improve the spatial resolution of cochlear tissues and CI function (Golestanirad et al, 2018).…”