DOT magnetoelectric epidural stimulator, 2024
Applications
DOT epidural cortical stimulator
The April 2024 Science Advances paper reports a Digitally programmable Over-brain Therapeutic (DOT) for externally powered cortical stimulation. The primary affiliations include Rice, Motif Neurotech, UTHealth and Baylor. It links to the Rice magnetoelectric laboratory brief.
This entry describes the published research device, not a specification for a later commercial product. It is separate from endovascular ME-BIT and the 2025 distributed spinal IPGs. Its acute human tests and chronic pig study are separate applications.
Published hardware
| Component | Specification in this paper |
|---|---|
| Packaged device | 9 × 9 × 11 mm; rounded-square borosilicate glass tube and two caps |
| ME antennas | Two 7.5 × 3-mm Metglas/PZT/Metglas laminates, connected in parallel; 218 kHz |
| Bias magnet | 1 × 2 × 3.5-mm neodymium magnet |
| Stimulation contacts | One on each cap, 1.5-mm diameter; Ti/Pt/Ti/IrOx sputtered stack |
| Electrode stack | 10/100/10/300 nm for Ti/Pt/Ti/IrOx |
| Feedthroughs and seals | Tungsten through-glass vias; medical-grade epoxy seals, not a fully hermetic enclosure |
| Electronics | Off-the-shelf PCB components, including KL15 microcontroller, LTC3129 boost converter, INA186 current monitor and DG636 output switch |
| Programmed output | Voltage controlled; ±6.75 to ±14.5 V in 250-mV steps; 250/500-µs pulse widths in these studies |
| External transmitter | 6-cm, three-layer pancake coil with H-bridge driver; separate paired receiver coils |
The implant sits above intact dura in a 14-mm skull burr hole, with a silicone sleeve, PEEK cover and conductive return mesh in the chronic configuration. The top and bottom contacts form a pseudo-monopolar path. Earlier feasibility cohorts used a different, bottom-only bipolar arrangement.
Power and diagnostic communication
The transmitter supplies a 218-kHz alternating field, tested at 7 mT at its surface. The bench alignment test used 10 biphasic pulses at 500 Hz across a 1-kΩ resistor. At 7.5 mm from the coil, the operating diameter was 1.8 cm for 9-V output and 1 cm for 14.5-V output. These are configuration-specific bench results, not a universal implant depth or all-orientation guarantee.
The transmitter consumes 18 W peak to generate that field; roughly 500 ms at this state was needed for a maximum-amplitude pulse train. A battery-free implant still needs an external energy source. The paper’s field-limit assessment uses IEEE limits, not a blanket approval under every exposure standard.
The ME films carry digital downlink commands and 8-bit diagnostic uplink packets through ringdown backscatter. Uplink reports status and approximate electrode impedance, not recorded neural signals. The paper calls a message 3.4 ms while giving a 1.8-3.0-ms downlink plus a 1.6-ms uplink; those timing descriptions are retained rather than converted into one unqualified throughput claim.
Limits and unresolved qualification
Methods describes sequential stimulation of the two contacts as maintaining charge-balanced output. Discussion still calls for future current-controlled, charge-balanced therapeutic stimulation. The proof of concept is voltage controlled; neither statement is treated as chronic human safety qualification.
The authors explicitly did not use fully hermetic encapsulation. Multi-year packaging, biocompatibility, durability, electrode optimization and higher-bandwidth authenticated/error-checked communication remain future work. The paper expects MRI artifacts from the bias magnet and expects MRI safety, but does not supply completed MRI qualification here. IrOx would need further testing for a commercial human device.
No full model is supplied. Figure 1 establishes the assembly and scale, but exact cap outline, wall thickness, PCB geometry, internal routing and fixation details are not fully specified. A model built from the outer box alone would not be the manufactured implant.
Primary source
- Woods, Singer and colleagues, Miniature battery-free epidural cortical stimulators, Science Advances, 2024, DOI 10.1126/sciadv.adn0858. Results, assembly, characterization and Discussion support this entry.