Magnetoelectric Materials for Miniature, Wireless Neural Stimulation at Therapeutic Frequencies

Abstract

A fundamental challenge for bioelectronics is to deliver power to miniature devices inside the body. Wires are common failure points and limit device placement. Wireless power by electromagnetic or ultrasound waves must overcome absorption by the body and impedance mismatches between air, bone, and tissue. Magnetic fields, on the other hand, suffer little absorption by the body or differences in impedance at interfaces between air, bone, and tissue. These advantages have led to magnetically-powered stimulators based on induction or magnetothermal effects. However, fundamental limitations in these power transfer technologies have prevented miniature magneticallypowered stimulators from applications in many therapies and disease models because they do not operate in clinical "high-frequency" ranges above 20 Hz. Here we show that magnetoelectric materials -applied for the first time in bioelectronics devices -enable miniature magnetically-powered neural stimulators that operate at clinically relevant high-frequencies. As an example, we show that ME neural stimulators can effectively treat the symptoms of a Parkinson's disease model in a freely behaving rodent. We also show that ME-powered devices can be miniaturized to sizes smaller than a grain of rice while maintaining effective stimulation voltages. These results suggest that ME materials are an excellent candidate for wireless power delivery that will enable miniature neural stimulators in both clinical and research applications. Wireless neural stimulators have the potential to provide less invasive, longer lasting interfaces to brain regions and peripheral nerves compared to batterypowered devices or wired stimulators. Indeed, wires are a common failure point for bioelectronic devices. Percutaneous wires present a pathway for infection 1 and implanted wires can also limit the ability of the stimulators to move with the tissue, leading to a foreign body response or loss of contact with the target tissue 2,3 . Additionally, chronic stress and strain on wires, particularly for devices in the periphery, can lead to failure in the wire itself or its connection to the stimulator 4 . In small animals like rats and mice, wires used to power neural stimulators can interfere with natural behavior, particularly when studying social interaction between multiple animals 5 .

Ultra-compact dual-band smart NEMS magnetoelectric antennas for simultaneous wireless energy harvesting and magnetic field sensing

“…Current technology for doing so exists, but is limited in the number of sites and spatial extent coverable. To address the need for a distributed neural interfacing tool, a new generation of wirelessly powered standalone implantable medical devices (IMDs) have emerged in the last few years [1][2][3][4] . Wirelessly powered IMDs eliminate the invasiveness and discomfort caused by batteries and wires in most conventional implants.…”

“…(2) thanks to its physical characteristics, magnetic neural sensing is more localized than electrical sensing, which consequently enables better spatial resolution of neuronal activities; (3) it is practical to create safe and contact-less implants coated with biocompatible polymer films such as parylene, unlike in conventional devices where the necessary direct contact between electrode and tissue degrades over time due to electrochemical fouling and tissue reactions; (4) the same technology can be used for animals and human, allowing for direct comparisons and easier translation of animal to human information; and (5) compact size allows for distributed, addressable, high channel count use in the parenchyma, pial surface, extra dural, and in both central and peripheral nervous tissue 18 . In the following sections, we will discuss the design and characteristics of the proposed smart ME antenna, its wireless energy harvesting performance, its magnetic field sensing capability, and the device's performance for simultaneous energy harvesting and magnetic field sensing.…”

Energy-Efficient Integrated Circuit Solutions Toward Miniaturized Closed-Loop Neural Interface Systems

“…MS converts magnetic to mechanical, and PE converts mechanical to electrical and vice versa (Nan, 1994;Fiebig, 2005). Such a set of conversions resolves the reflection issue of ultrasound and alleviates the miniaturization difficulty of inductive (Singer et al, 2020;Yu et al, 2020b). Nevertheless, ME composite is hard to fabricate, and the composite's low energy conversion ratio is a hurdle to overcome (Truong, 2020;Yu et al, 2020a).…”

Encapsulated Magnetoelectric Composites for Wirelessly Powered Brain Implantable Devices

“…This allowed the magnetostrictive layer to deform within the flexible polymer. As suggested in [14], in which an ME device was coated with parylene-C, the polymer introduces "increased mechanical coupling." Voltage outputs from the model parameterised polymer are shown in Fig.…”