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. 2020 Jun 25;11(6):621.
doi: 10.3390/mi11060621.

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

Yaoyao Jia  1 , Yan Gong  2 , Arthur Weber  3 , Wen Li  2 , Maysam Ghovanloo  4
Affiliations

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

Yaoyao Jia et al. Micromachines (Basel). .

Abstract

Towards a distributed neural interface, consisting of multiple miniaturized implants, for interfacing with large-scale neuronal ensembles over large brain areas, this paper presents a mm-sized free-floating wirelessly-powered implantable opto-electro stimulation (FF-WIOS2) device equipped with 16-ch optical and 4-ch electrical stimulation for reconfigurable neuromodulation. The FF-WIOS2 is wirelessly powered and controlled through a 3-coil inductive link at 60 MHz. The FF-WIOS2 receives stimulation parameters via on-off keying (OOK) while sending its rectified voltage information to an external headstage for closed-loop power control (CLPC) via load-shift-keying (LSK). The FF-WIOS2 system-on-chip (SoC), fabricated in a 0.35-µm standard CMOS process, employs switched-capacitor-based stimulation (SCS) architecture to provide large instantaneous current needed for surpassing the optical stimulation threshold. The SCS charger charges an off-chip capacitor up to 5 V at 37% efficiency. At the onset of stimulation, the capacitor delivers charge with peak current in 1.7-12 mA range to a micro-LED (µLED) array for optical stimulation or 100-700 μA range to a micro-electrode array (MEA) for biphasic electrical stimulation. Active and passive charge balancing circuits are activated in electrical stimulation mode to ensure stimulation safety. In vivo experiments conducted on three anesthetized rats verified the efficacy of the two stimulation mechanisms. The proposed FF-WIOS2 is potentially a reconfigurable tool for performing untethered neuromodulation.

Keywords: charge balancing; free-floating implants; inductive link; switched-capacitor-based optical/electrical stimulation.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Conceptual view of the system setup for operating multiple mm-sized free-floating wirelessly-powered implantable opto-electro stimulation (FF-WIOS2) devices, distributed on a freely moving rat brain.
Figure 2
Figure 2
Block diagram of the FF-WIOS2 system-on-chip (SoC) architecture.
Figure 3
Figure 3
Schematic diagram of (a) the voltage doubler with built-in charger and the cap-less LDO, (b) the clock generator for the timing of stimulation and charging functions, (c) the OOK demodulator and PPM-CDR in forward data telemetry, (d) the LSK back telemetry, (e) the stimulation driver in H-bridge configuration, and (f) the active charge balancing (CB) circuit.
Figure 4
Figure 4
(a) In vitro system setup with a close-up view of the FF-WIOS2 device. (b) The fabricated FF-WIOS2 SoC micrograph.
Figure 5
Figure 5
Block diagram of the headstage.
Figure 6
Figure 6
(a) In vivo experimental setup with its (b) block diagram.
Figure 7
Figure 7
Transient waveforms of the power management block at starting up.
Figure 8
Figure 8
Measured results of forward data telemetry.
Figure 9
Figure 9
(a) Measured optical stimulation waveforms. (b) Measured µLED current at different stimulation current settings. (c) Measured light intensity as a function of the μLED current.
Figure 10
Figure 10
Measured electrical stimulation waveforms with active charge balancing.
Figure 11
Figure 11
Measured waveforms under CLPC operation, when moving the headstage to change the distance between LTx and LRes, D.
Figure 12
Figure 12
Power consumption of each block in the FF-WIOS2 device when applying (a) electrical stimulation and (b) optical stimulation.
Figure 13
Figure 13
LFP analysis in terms of (a) amplitude variation and (b) normalized PSD with maximum and minimum optical stimulation.
Figure 14
Figure 14
C-Fos expression in the left (stimulated) vs. right (control) V1 lobes.
Figure 15
Figure 15
LFP analysis in terms of (a) amplitude variation and (b) normalized PSD with maximum and minimum electrical stimulation.
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