Stretchable organic optoelectronic sensorimotor synapse

Abstract

Emulation of human sensory and motor functions becomes a core technology in bioinspired electronics for next-generation electronic prosthetics and neurologically inspired robotics. An electronic synapse functionalized with an artificial sensory receptor and an artificial motor unit can be a fundamental element of bioinspired soft electronics. Here, we report an organic optoelectronic sensorimotor synapse that uses an organic optoelectronic synapse and a neuromuscular system based on a stretchable organic nanowire synaptic transistor (s-ONWST). The voltage pulses of a self-powered photodetector triggered by optical signals drive the s-ONWST, and resultant informative synaptic outputs are used not only for optical wireless communication of human-machine interfaces but also for light-interactive actuation of an artificial muscle actuator in the same way that a biological muscle fiber contracts. Our organic optoelectronic sensorimotor synapse suggests a promising strategy toward developing bioinspired soft electronics, neurologically inspired robotics, and electronic prostheses.

Fig. 1. Biological and organic optoelectronic synapse and neuromuscular electronic system.

(A to D) In a biological system, (A) light stimulates a biological motor neuron that has photosensitive protein expression, and an action potential is thus generated. (B and C) A chemical synapse of a neuromuscular junction transmits the potentials to a muscle fiber, (D) which causes the muscle to contract. Analogously, (E to I) in an organic artificial system, (E) light triggers a photodetector to generate output voltage spikes. (H and G) The voltage spikes produce electrical postsynaptic signals from an s-ONWST to activate an artificial muscle actuator, (I) which the artificial muscle then contracts. (F) Optical wireless communication via organic optoelectronic synapse with patterned light signals representing the International Morse code of “ABC.”

Fig. 2. Fabrication and electrical characteristics of s-ONWST.

(A) Fabrication procedure of s-ONWST based on a single ONW. An electrospun single ONW was first transferred onto prestretched rubbery SEBS substrate and subsequently buckled when the film contracted after the strain was released. (B) Optical microscopy image of a wavy NW stretched from 0 to 100% strain. (C) I-V characteristics of s-ONWST at 0, 50, and 100% strains. Blue arrows: clockwise hysteresis. (D) Maximum drain current and mobility as a function of various strains along the channel length and width directions.

Fig. 3. Synaptic characteristics of s-ONWST.

(A) Neural signal transmission from preneuron to postneuron through a biological synapse (top) and an artificial synapse (bottom). (B) EPSCs triggered by single and double spikes (each spike: −1 V, 120 ms). A₁ and A₂ are EPSCs of the first and second spikes, respectively, separated by Δt = 120 ms. (C to E) Postsynaptic characteristics of stretched artificial synapse from 0 to 100% strains; (C) PPF (A₂/A₁) as a function of 120 ≤ Δt ≤ 920 ms, (D) spike voltage–dependent plasticity (SVDP) with various gate voltages from −0.3 to −1 V, and (E) spike number–dependent plasticity (SNDP) with 1 to 50 spikes. (F and G) Spike frequency–dependent plasticity (SFDP) characteristics with spike frequency from 0.3 to 5 Hz; (F) maximum EPSCs and (G) EPSC gain (A₁₀/A₁) of stretched artificial synapse from 0 to 100% strains.

Fig. 4. Organic optoelectronic synapse and neuromuscular electronic system.

(A) Photograph of organic optoelectronic synapse on an internal human structure model. (B) Configuration of organic optoelectronic synapse (photodetector and artificial synapse) and neuromuscular electronic system (artificial synapse, transimpedance circuit, and artificial muscle actuator). (C) EPSCs triggered by single and double visible light spikes (each spike generated presynaptic voltage of −1.1 V for 120 ms). PPF (A₂/A₁) = 1.42. (D and E) Visible light–triggered EPSC amplitudes of s-ONWST from 0 to 100% strains; (D) SDDP from 120 to 960 ms and (E) SNDP with 1 to 30 spikes. (F) Visible light–triggered EPSC amplitudes of s-ONWST with the International Morse code of “SOS,” which is the most common distress signal. (G) Infrared (IR) and ultraviolet (UV) light–triggered EPSC amplitudes of s-ONWST with the International Morse code of “HELLO UNIVERSE.” (H) Maximum δ of polymer actuator and output voltage generated by s-ONWST according to 0 ≤ n_SPIKE ≤ 60 and (I) digital images of the polymer actuator according to 0 ≤ n_SPIKE ≤ 100 with 0 or 100% strain.