Transparent and Conformal Microcoil Arrays for Spatially Selective Neuronal Activation

Abstract

Micromagnetic stimulation (MS) using small, implantable microcoils is a promising modality for achieving neuronal activation with high spatial resolution and low toxicity. Microcoils can be designed to achieve localized, spatially asymmetric fields that target neurons of a particular orientation. Insulation of the coil avoids the direct contact between metal and tissue and the use of specialized biopolymers may help to further reduce chronic inflammation and glial scarring. Studies to date have largely focused on single channel devices; herein, we report the design and development of a microcoil array for localized activation of cortical neurons and retinal ganglion cells. We utilized a computational model that related the activation function to the geometry and arrangement of coils and selected a coil design that maintained a region of activation <50 {micro}m wide. The device was composed of an SU8/Cu/SU8 tri-layer structure, which was flexible, transparent and conformal and featured four individually-addressable microcoil stimulation elements. Interfaced with ex vivo cortex or retina slices from GCaMP6-transfected mice, we observed that individual neurons localized within 40 {micro}m of the element tip could be activated repeatedly and in a dose (power) dependent fashion. Taken together, these results highlight the potential of magnetic stimulation devices for brain-machine interfaces and could open new routes toward bioelectronic therapies including prosthetic vision devices.