Planar microcoil arrays for in vitro cellular-level micromagnetic activation of neurons

In the treatment of neurodegenerative disorders, a potential cure at a single neuron cell resolution is still lacking. Micromagnetic neurostimulation, although in its infancy, is one of the most promising techniques that offer spatially selective activation of neurons through micrometer-sized coils or microcoils (μcoils). Time-varying current drives these μcoils and generates a time-varying magnetic field which in turn induces an electric field to activate the neural tissues. In this work, we report the design and fabrication of planar μcoil arrays, termed Magnetic Patch (MagPatch), for activating single neurons. Using numerical calculations on ANSYS-Maxwell and NEURON, we report an optimized MagPatch array design that exploits the directionality of the induced electric field from the μcoils to enhance spatial selectivity. Each μcoil has an outer dimension of 190 × 190 μm² and one MagPatch array contains 8 μcoils. For proof-of-concept design and development, the MagPatch array has been fabricated on Si-substrates using Ti, Au, and Si₃N₄ to ensure preliminary biocompatibility. They were then encapsulated in Parylene-C, a waterproof, anti-leakage current coating, thereby ensuring basic surface biocompatibility. Human neuroblastoma cells were cultured directly on the surface encapsulated MagPatch, and calcium fluorescence imaging was used to assess cell functionality. The impact of scaling the dimensions of the μcoil in the MagPatch array on electrical characteristics, Q-factor, and thermal effects on neural tissues from these μcoils have also been discussed.