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

Abstract

To stimulate the auditory nerve, cochlear implants directly inject electrical current into surrounding tissue via an implanted electrode array. While many cochlear implant users achieve strong speech perception scores, there remains significant variability. Since cochlear implant electrode arrays are surrounded by a conductive fluid, perilymph, a spread of excitation occurs. The functionality of the cochlea is spatially dependent, and a wider area of excitation negatively affects the hearing of the user. Importantly, magnetic fields are unaffected by the material properties of biological components. To utilize the electromagnetic properties of the human ear, a microcoil array was developed. The microcoils are 4-turn solenoids with a 250-µm turn radius and a 31.75-µm wire radius, coated with Parylene-C. The efficient design was implemented to accelerate testing. The obtained results describe stimulation capabilities. Functionality was validated using a frequency response analyzer to measure how the generated electromagnetic power radiates in space. 99.8% power loss was observed over a 100-µm separation between a pair of identical microcoils. Obtained through finite-element modeling, the microcoils can be driven by a 60 mA, 5 kHz, sinusoidal input for 10 minutes before predicted inflammation. Rattay's activating function was calculated to evaluate the magnetic stimulation effect of external fields on target neurons. Combined with the frequency response analysis, magnitude and spatial effects of the generated potential is established. As a result, each microcoil requires a 400-µmwide area for each independent stimulation channel, which is 84% narrower than a commercial cochlear array channel, thereby suggesting greater spatial selectivity.

Development of spiral square coils for magnetic labelling detection in microfluidic systems

“…Then, in the second step, the target (antigen) contained in the sample is recognized by the probe and adsorbs specifically on the surface of the microbeads (monocyte biomarkers) [29]. Finally, in the separation zone, the magnetic microbeads and labeled monocytes are trapped by a magnetic field generated by permanent magnets [30] or a specially designed microelectromagnet [31]. In the case of permanent magnets, it is possible to structure the magnets in the form of lines and it is also possible to use in the microelectromagnet the microcoils integrated in microfluidic systems [32] with vertical or horizontal separation [33].…”

Micromagnetic stimulation (µMS) dose-response of the rat sciatic nerve

“…Various µcoil shapes have been investigated in several different experimental settings. The optimized shape of the coil for neuromodulation is still under investigation, with several designs reported based on both computational modeling and experimental approaches [25][26][27][28][29][30]. Some of the notable experimental settings these µcoils have been tested in include in vivo intracortical µMS using V-shaped µcoils [28], in vitro focal control of pyramidal neurons with solenoidal µcoils [31], in vitro somatic and axonal inhibition of action potentials of ganglion cells in marine mollusk using solenoidal µcoils [32,33], and in vitro activation of the CA3-CA1 synaptic pathway in hippocampal tissue slices [25].…”