A fundamental challenge for bioelectronics is to deliver power to miniature devices inside the body. Wires are common failure points and limit device placement. On the other hand, wireless power by electromagnetic or ultrasound waves must overcome absorption by the body and impedance mismatches between air, bone, and tissue. In contrast, magnetic fields suffer little absorption by the body or differences in impedance at interfaces between air, bone, and tissue. These advantages have led to magneticallypowered stimulators based on induction or magnetothermal effects. However, fundamental limitations in these power transfer technologies have prevented miniature magnetically-powered stimulators from applications in many therapies and disease models because they do not operate in clinical "highfrequency" ranges above 50 Hz. Here we show that magnetoelectric materials -applied in bioelectronic devices -enable miniature magnetically-powered neural stimulators that can operate up to clinically-relevant high-frequencies.As an example, we show that ME neural stimulators can effectively treat the symptoms of a hemi-Parkinson's disease model in freely behaving rodents. We further demonstrate that ME-powered devices can be miniaturized to mmsized devices, fully implanted, and wirelessly powered in freely behaving rodents. These results suggest that ME materials are an excellent candidate for wireless power delivery that will enable miniature bioelectronics for both clinical and research applications.

Optocapacitance is a technique whereby flash illumination quickly changes membrane capacitance to elicit action potentials (APs) in unmodified (not genetically engineered) excitable cells. Spherical 20-nm gold nanoparticles (AuNPs) interfaced with the plasma membrane serve as light absorbers to induce AP generation in response to 1-ms, 100 mJ, 532-nm laser pulses. Light absorption by the AuNP produces localized heating that changes local temperature by <2C. This increases membrane capacitance, and a resulting depolarizing membrane current (VdC/dt; proportional to the rate of temperature change; Nat. Commun., 2012;3:736) induces opening of voltage-gated sodium channels and thus AP initiation in neurons (Neuron, 2015;86:207-17). Here we present new findings obtained from dorsal root ganglion (DRG) cells, by varying the flash wavelength, light-absorbing particle, and flash duration. Using cylindrical AuNPs (nanorods; 25x94 nm; plasmon absorbance peak at~780 nm), a 1-ms, 20 mJ, 785-nm laser pulse was sufficient to elicit APs. A single 1-2 mm graphite particle placed on the DRG cell induced AP generation upon delivery of a 532-nm laser flash of 4 ns duration and 47 nJ energy, representing 130-fold less energy than the 6.2 mJ needed with a 0.5-ms laser pulse. With AuNPs, reduction in flash duration similarly decreased the flash energy required for AP generation. Our data demonstrate the use of near-infrared flashes that penetrate deeper into tissue than green light to elicit APs with light. They also indicate that, in addition to gold and mesoporous silicon (Nat. Mater., 2016;15:1023-30), graphite can enable optocapacitive AP generation. The data furthermore show that, with~nanosecond flash durations, APs can be elicited by flashes of~nano-Joule energy, i.e., in the range of those used in optogenetic approaches. Support: NIH grants R21-EY023430, R01-GM030376, and the Beckman Initiative for Macular Research.