ABSTRACT
We introduce a single channel neuro-stimulator consisting of a reflector-coupled microscale light emitting diode (µLED) with an integrated mm-sized wireless receiver (Rx) coil for free-floating, battery-free, untethered optogenetics neuromodulation. The system utilizes a two-coil inductive link to deliver instantaneous power at a low operating frequency (<100 MHz) for continuous optical stimulation with minimized invasiveness and tissue exposure to electromagnetic radiation. Coupling a microscale reflector to the µLED provides significant light intensity enhancement compared to a bare µLED. Our activated stimulators have an operational temperature increase of <1 °C, well below the safety limit of biomedical implants. In vivo experiment and histological analysis verify the efficacy of wireless optical stimulation in the primary visual cortex of rats, using c-Fos biomarker as a reporter of light-evoked neuronal activity.
ABSTRACT
This paper presents a mm-sized, free-floating, wirelessly powered, implantable optical stimulation (FF-WIOS) device for untethered optogenetic neuromodulation. A resonator-based three-coil inductive link creates a homogeneous magnetic field that continuously delivers sufficient power (>2.7 mW) at an optimal carrier frequency of 60 MHz to the FF-WIOS in the near field without surpassing the specific absorption rate limit, regardless of the position of the FF-WIOS in a large brain area. Forward data telemetry carries stimulation parameters by on-off-keying the power carrier at a data rate of 50 kb/s to selectively activate a 4 × 4 µLED array. Load-shift-keying back telemetry controls the wireless power transmission by reporting the FF-WIOS received power level in a closed-loop power control mechanism. LEDs typically require high instantaneous power to emit sufficient light for optical stimulation. Thus, a switched-capacitor-based stimulation architecture is used as an energy storage buffer with one off-chip capacitor to receive charge directly from the inductive link and deliver it to the selected µLED at the onset of stimulation. The FF-WIOS system-on-a-chip prototype, fabricated in a 0.35-µm standard CMOS process, charges a 10-µF capacitor up to 5 V with 37% efficiency and passes instantaneous current spikes up to 10 mA in the selected µLED, creating a bright exponentially decaying flash with minimal wasted power. An in vivo experiment was conducted to verify the efficacy of the FF-WIOS by observing light-evoked local field potentials and immunostained tissue response from the primary visual cortex (V1) of two anesthetized rats.
Subject(s)
Electric Power Supplies , Optical Devices , Photic Stimulation/instrumentation , Prostheses and Implants , Wireless Technology , Action Potentials , Algorithms , Animals , Computer Simulation , Electrodes , Female , Microtechnology , Models, Theoretical , Optogenetics , Proto-Oncogene Proteins c-fos/metabolism , Rats, Sprague-Dawley , SheepABSTRACT
This paper reports the design, fabrication and characterization of a head-mounted, flexible, and ultralight optogenetic system that enables wireless delivery of light into the brains of awake and freely behaving animals. The project is focused on miniaturized design, light weight (2.7g), small volume, low cost (< 25 USD) and simple fabrication. The chip, the substrate material, the battery, and the micro light emitting diode (µLED) are commercially available. The device implementation consists of one step photolithography, soldering, and packaging along with Arduino programming. In vivo study is carried out where the battery-powered µLED stimulates the visual cortex of a rat with parameters that can be controlled wirelessly via a smart-phone user interface application. The efficacy of optical stimulation is validated using c-Fos as a report of light-evoked neuronal activity.
Subject(s)
Smartphone , Wireless Technology , Animals , Brain , Optogenetics , Photic Stimulation , RatsABSTRACT
OBJECTIVE: We have developed a wireless opto-electro interface (WOENI) device, which combines electrocorticogram (ECoG) recording and optical stimulation for bi-directional neuromodulation on small, freely behaving animals, such as rodents. APPROACH: The device is comprised of two components, a detachable headstage and an implantable polyimide-based substrate. The headstage establishes a bluetooth low energy (BLE) bi-directional data communication with an external custom-designed USB dongle for receiving user commands and optogenetic stimulation patterns, and sending digitalized ECoG data. MAIN RESULTS: The functionality and stability of the device were evaluated in vivo on freely behaving rats. When the animal received optical stimulation on the primary visual cortex (V1) and visual stimulation via eyes, spontaneous changes in ECoG signals were recorded from both left and right V1 during four consecutive experiments with 7 d intervals over a time span of 21 d following device implantation. Immunostained tissue analyses showed results consistent with ECoG analyses, validating the efficacy of optical stimulation to upregulate the activity of cortical neurons expressing ChR2. SIGNIFICANCE: The proposed WOENI device is potentially a versatile tool in the studies that involve long-term optogenetic neuromodulation.
