A wireless millimetre-scale implantable neural stimulator with ultrasonically powered bidirectional communication

Magnetoelectric materials for miniature, wireless neural stimulation at therapeutic frequencies

“…One potential challenge with future free-floating devices for clinical applications is that they could migrate over time from the target tissue. Indeed future work should address this issue and explore methods to anchor or tether the devices using biocompatible adhesives (Mahdavi et al 2008), or mechanical anchors like nerve cuffs (Piech et al 2020).…”

“…Approximately 100 μA biphasic stimulation is applied only when then the magnetic field frequency matches the resonance condition. (d) Angular velocity of the hemi-Parkinsonian rat over a 40 minute DBS trial with intervals of resonant and non-resonant stimulation shows that rotations are reduced only when the stimulator is activated by a resonant magnetic field (e) Typical trajectories show the location of the animal's head over two 30-second intervals denoted in c (scale bar = 5cm) (f) Average angular velocity of the rat during the 30 seconds before stimulation and the first 30 seconds of stimulation for each interval during the 40-min experiment shows a clear reduction in angular velocity only when the ME film is activated on resonance (**** P = 4x10 -7 , n.s.=not significant P=0.70, paired t-test) (g) Average angular velocities for n=3 rats shows repeatable results across multiple animals (**** P = 2.8x10 -18 , n.s.=not significant P=0.11, paired t-test) Figure 5 |Fully implanted ME device stimulates place preference in freely moving rats (a) Schematic of the device implanted under the skin of a rat with stereotrode implanted into the MFB (b) Photo of inner circuit and ME films used in the implant scale bar=5 mm (c) Representative voltage and current waveforms used for stimulation (d) Experimental setup showing the linear track and coil 1 and 2 and representative heat maps for two individual trials showing a location preference for the ON resonance coil demonstrating that we could change the preference by altering the magnetic field frequencies in each coil (scale bar=10 cm) (e) side view of the experimental setup showing a rat in the coil with the skin sutured up over the implant scale bar=3cm(f) Preference results from one rat over six trials (***P = 9x10 -4 , *P = 0.038) and (g) Average results for n=3 rats shows repeatability across subjects (***P = 2.7x10 -4 , ****P = 3.6x10 -5 ) (Ho et al 2015)[e] (Piech et al 2020) [f] (Park et al 2016) [g] (Chen et al 2015)[h] (Munshi et al 2017)…”

“…However this approach requires transgenesis, which adds regulatory complexity and has yet to show high-frequency operation due the requirement for the tissue to cool between stimulation pulses. Ultrasound provides a promising and efficient method to power bioelectronic implants because ultrasound wavelengths are 10 5 times smaller than electromagnetic waves at the same frequency allowing sub-millimeter-sized devices to have wavelength-scale piezoelectric antennas (Johnson et al 2018;Seo et al 2016;Piech et al 2020). However, implementation of these "StimDust" motes can be challenging in freely moving animals because the impedance mismatch between air, bone, and tissue requires contact between soft tissue and the ultrasound transducer for efficient power transfer.…”

Injectable Nanoelectrodes Enable Wireless Deep Brain Stimulation of Native Tissue in Freely Moving Mice

“…A key challenge of such devices is powering, and wired-in powering can require that patients undergo surgical battery changes, every 3-5 years in the case of DBS devices (4). Instead, neural devices that are remotely powered have emerged using magnetic induction (5), opto-electric signaling (6)(7)(8), acoustic powering of piezoelectric materials (9)(10)(11)(12)(13)(14), magnetic heating (15), piezoelectric powering of LEDs (16,17), or magnetoelectric materials (18), instead of a wired-in battery.…”

“…Ultrasound-powered piezoelectric devices are perhaps the most promising of these technologies, recently showing recording at multiple sites through 5 cm of tissue phantom material with a submm 3 device (10). Modulation with piezoelectric devices, however, has currently only been demonstrated in the peripheral nervous system using millimeter-scale devices, or in vitro (12)(13)(14). As power transmission is typically done at the mechanical resonance frequency of such devices, this creates a fundamental tradeoff where an increasingly smaller device with a higher resonance frequency can be powered at increasingly shallower tissue depths (20,21).…”