A mm-Sized Free-Floating Wireless Implantable Opto-Electro Stimulation Device

Area of Science:

• Neuroscience
• Biomedical Engineering
• Electrical Engineering

Background:

• Developing distributed neural interfaces for large-scale brain area modulation requires miniaturized, untethered implants.
• Existing systems often face limitations in power delivery, control, and stimulation flexibility.

Purpose of the Study:

• To present a novel, mm-sized, free-floating, wirelessly-powered implantable opto-electro stimulation (FF-WIOS2) device.
• To demonstrate its capability for reconfigurable neuromodulation using both optical and electrical stimulation.
• To validate the device's performance in in vivo experiments.

Main Methods:

• The FF-WIOS2 device utilizes a 3-coil inductive link for wireless power and control (60 MHz) with on-off keying (OOK) and load-shift-keying (LSK).
• A switched-capacitor-based stimulation (SCS) architecture delivers high peak currents for micro-LED (µLED) optical stimulation and micro-electrode array (MEA) electrical stimulation.
• The system-on-chip (SoC) is fabricated using a 0.35-µm standard CMOS process, incorporating charge balancing for electrical stimulation safety.

Main Results:

• The SCS charger achieves 37% efficiency in charging an off-chip capacitor to 5 V.
• Stimulation currents range from 1.7-12 mA for optical and 100-700 μA for electrical stimulation.
• In vivo experiments in anesthetized rats confirmed the efficacy of both optical and electrical stimulation mechanisms.

Conclusions:

• The FF-WIOS2 device represents a significant advancement in miniaturized, untethered neural interfaces.
• Its reconfigurable opto-electrical stimulation capabilities offer a versatile tool for neuromodulation.
• The successful in vivo validation supports its potential for large-scale, long-term brain interfacing.