An integrated monolithic synaptic device for C-tactile afferent perception and robot emotional interaction

Human emotional interaction relies heavily on CT afferents—unmyelinated nerves in hairy skin that convert gentle tactile stimuli into affective states. For robots to engage in similar empathetic communication, existing tactile sensing technologies fall short: most rely on segregated "sensation-transmission-processing" modules, which cause latency accumulation and high energy consumption due to repeated analog-to-digital conversion. "Current neuromorphic devices for touch either lack low-threshold sensitivity or separate sensing from computation," explained Yue Li, first author of the study. "We aimed to create a single device that both feels gentle touch like human skin and processes that touch into emotional signals—just as CT afferents do."

Pressure-Electronic-Gated (PEG) synaptic device that integrates tactile perception and neuromorphic computing in one monolithic structure. Its design draws direct inspiration from biological systems: (1) A proton-conductive chitosan hydrogel (derived from crustacean exoskeletons or fungi) acts as the gate dielectric, enabling neurotransmitter-like ionic transport and ensuring biocompatibility for potential epidermal integration; (2) A solution-processed poly(3-hexylthiophene) (P3HT) semiconductor channel mimics postsynaptic receptor activation via ionic trapping/detrapping; (3) Gold (Au) source/drain/top-gate electrodes complete the 3-terminal architecture.

The device operates via the synergistic effect of dynamic ionic migration (triggered by voltage) and injection (enhanced by pressure). Key performance metrics set it apart: (1) Ultralow threshold: Responds to pressures as low as 80 Pa—comparable to the gentle touch detected by human CT afferents. (2) Energy efficiency: Operates at just -0.2 V, with a current range of 0.039–24.872 μA (nearly 3 orders of magnitude). (3) Stability: Maintains <1% signal deviation during 2,000 seconds of continuous use and over 1,000 cycles. "Unlike previous devices that require large forces to drive computation, our PEG device processes gentle touch in real time," Prof. Xu noted. "It’s chitosan layer also solves the biocompatibility issue that has blocked epidermal or implantable tactile systems."

To translate tactile input into emotional states, the team leveraged the device’s ability to encode spatiotemporal tactile parameters (pressure, frequency, duration) into distinct Excitatory Postsynaptic Currents (EPSCs)—electrical signals analogous to neural activity. When connected to a microcomputer, the device automatically classifies these EPSC signals into discrete emotions—achieving reliable emotional recognition without separate processing modules.

"We’re now working to scale the device into flexible arrays for full-body robot 'skin,'" Prof. Xu added. "This technology does not just make robots 'touch-sensitive'—it makes them capable of understanding the emotional meaning behind touch."

Authors of the paper include Yue Li, Lu Yang, Qianbo Yu, Yi Du, Ning Wu, Wentao Xu.

This work was supported by the National Key R&D Program of China (2022YFA1204500, 2022YFA1204504, and 2022YFE0198200); the National Science Fund for Distinguished Young Scholars of China (T2125005); the Fundamental Research Funds for the Central Universities, Nankai University (BEG124901 and BEG124401); the China Postdoctoral Science Foundation (2024M761520); the Postdoctoral Fellowship Program of CPSF (GZC20250388); and the Shenzhen Science and Technology Project (JCYJ20240813165508012).

The paper, “An Integrated Monolithic Synaptic Device for C-Tactile Afferent Perception and Robot Emotional Interaction” was published in the journal Cyborg and Bionic Systems on Aug 19, 2025, at DOI: 10.34133/cbsystems.0367.

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