Wireless Implantable Microwave Neural Device for Neural Inhibition

Neuromodulation using electromagnetic wave allows manipulation of brain circuits in a minimally invasive manner. To date, researchers have explored a broad spectrum of electromagnetic wave and developed wireless neuromodulation methods. Microwave (MW), with frequencies between 300 MHz and 300 GHz, fills the gap between optical wave and magnetic wave, yet has rarely been explored for neuromodulation. Microwave has much longer wavelength than photons, which have been known to provide >50 mm penetration depth into the human brain noninvasively, while maintaining more than 50% of its energy, Yet, its wavelength is much shorter than that of magnetic wave, promising higher spatial resolution to specifically modulate subcortical regions. Here we will discuss a miniaturized millimeter size microwave antenna as a wireless implantable neural interface to inhibit neural activities in vitro, ex vivo and in vivo. The developed split-ring resonator (SRR) generates a localized and enhanced microwave field at the gap site of the ring with submillimeter spatial precision. The SRR breaks the microwave diffraction limit and greatly enhances the efficiency of microwave inhibition. With the SRR, microwaves at dosages below the safe exposure limit are shown to inhibit neurons within 1 mm from the gap site. Importantly, we measured the temperature at the neurons under microwave modulation using mCherry as a temperature reporter and found the temperature increase to be less than 1 degree, confirming a non-thermal effect for microwave inhibition. The inhibition effect was also confirmed in a crayfish nerve model using electrophysiology recording. Application of the microwave SRR to suppress seizures in an in vivo model of epilepsy is demonstrated. These results suggested that the millimeter microwave resonator is a novel platform for wireless, battery-free neuromodulation in the deep brain with high spatial precision. The device operates within safety limits and occupies a volume < 2 mm³. This approach opens up a broad potential of wireless deep neural inhibition through miniaturized microwave implants treating neural disorders as well as managing pain.