Abstract
Towards a distributed neural interface, consisting of multiple miniaturized implants, for interfacing with large-scale neuronal ensembles over large brain areas, this paper presents a mm-sized free-floating wirelessly-powered implantable opto-electro stimulation (FF-WIOS2) device equipped with 16-ch optical and 4-ch electrical stimulation for reconfigurable neuromodulation. The FF-WIOS2 is wirelessly powered and controlled through a 3-coil inductive link at 60 MHz. The FF-WIOS2 receives stimulation parameters via on-off keying (OOK) while sending its rectified voltage information to an external headstage for closed-loop power control (CLPC) via load-shift-keying (LSK). The FF-WIOS2 system-on-chip (SoC), fabricated in a 0.35-µm standard CMOS process, employs switched-capacitor-based stimulation (SCS) architecture to provide large instantaneous current needed for surpassing the optical stimulation threshold. The SCS charger charges an off-chip capacitor up to 5 V at 37% efficiency. At the onset of stimulation, the capacitor delivers charge with peak current in 1.7–12 mA range to a micro-LED (µLED) array for optical stimulation or 100–700 μA range to a micro-electrode array (MEA) for biphasic electrical stimulation. Active and passive charge balancing circuits are activated in electrical stimulation mode to ensure stimulation safety. In vivo experiments conducted on three anesthetized rats verified the efficacy of the two stimulation mechanisms. The proposed FF-WIOS2 is potentially a reconfigurable tool for performing untethered neuromodulation.
Highlights
Neurological disorders, such as Alzheimer’s disease, Epilepsy, Multiple sclerosis, Parkinson’s disease, and Stroke, are increasingly recognized as major causes of disability and death worldwide as societies grow older [1]
Optical stimulation is a much more recent approach with distinct advantages of cell-type specificity, high temporal precision, and rapid reversibility, which has become quite popular for neuromodulation in research settings [7,8]
The implant presented in [27] has both electrical and optical stimulation functions implemented in a mm-sized implant, but the number of channel-count for each type of stimulation is low
Summary
Neurological disorders, such as Alzheimer’s disease, Epilepsy, Multiple sclerosis, Parkinson’s disease, and Stroke, are increasingly recognized as major causes of disability and death worldwide as societies grow older [1]. A few tiny neural interface IMDs have been presented for neuromodulation with an impressive reduction in the device size [19,20,21,22,23,24,25,26,27]. In [26], an inductively-power device is equipped with electrical and optical stimulation capabilities, but its bulky volume makes it hard to be implanted. The implant presented in [27] has both electrical and optical stimulation functions implemented in a mm-sized implant, but the number of channel-count for each type of stimulation is low. We are demonstrating a new mm-sized free-floating wirelessly-powered implantable opto-electro stimulation (FF-WIOS2) device capable of 16-ch optical stimulation and 4-ch electrical stimulation.
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