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Sun et al. Soft Sci. 2025, 5, 18 https://dx.doi.org/10.20517/ss.2024.77 Page 11 of 26

synaptic connections by adjusting the channel conductivity, thereby enabling the dynamic modulation of
signal transmission between simulated neurons similarly to biological synapses.

In a recent study, a single-electrode mode TENG and a MoS transistor were vertically coupled, allowing
2
[80]
MoS tribotronic to function as an interactive smart tactile switch with distinct on/off behavior . The
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system mimicked the natural arrangement of touch receptors and neurons by integrating TENG technology
with transistors for signal generation and processing. This self-powered system operated with event-driven
mechanisms, similar to biological nerve responses to tactile stimuli. A ring oscillator, combined with a
transistor, generated spike information, while an inverting amplifier circuit functioned as a synaptic
architecture, encompassing multiple synaptic connections of an artificial cuneate neuron [Figure 4A].
[81]
Each artificial tactile afferent is composed of a receptor (blue) and a leaky integrate-and-fire (LIF) neuron
(brown), with V denoting the drain voltage [Figure 4B]. The LIF neurons were implemented in hardware,
DD
while SNN algorithm was executed in software to extract tactile features from the encoded tactile
[82]
information ; finally, spike timing-based coding in neuromimetic tactile system achieved object
classification based on SNNs. Flexible pressure sensors are essential in e-skin applications, enabling
seamless interaction between biomedical prosthetics, robots, and their environments. These sensors are also
promising for long-term medical diagnostics and mobile biomonitoring. For example, flexible pressure-
-1
sensitive organic thin-film transistors with a peak sensitivity of 8.4 kPa and rapid response times under 10
milliseconds have been developed [Figure 4C]. As shown in Figure 4D, an active-matrix array for
[83]
reducing interconnect wiring is fabricated; however, it lacks circuits capable of generating spiking signals.
To construct a monolithic soft e-skin system, a monolithically integrated, low-voltage, and flexible e-skin
was designed to closely mimic the sensory feedback and mechanical properties of natural skin. This
advanced e-skin system was capable of multimodal perception, neuromorphic signal processing, and
closed-loop actuation. It was achieved with the high-permittivity elastomeric dielectric and stretchable
[84]
organic transistor [Figure 4E]. Besides this, other researchers have tried to integrate the sensors and
transistors vertically. The pressure-sensitive transistor was made by laminating two separate layers: the first
layer comprised the lower source and drain electrodes together with the semiconducting polymer, whereas
the second layer included the gate electrode and the microstructured dielectric . The integration of a
[85]
microstructured PDMS dielectric with the high-mobility semiconducting polyisoindigo-bithiophene-
siloxane in a monolithic transistor enabled its application in health monitoring. However, all existing
pressure sensors suffer from the interference between stretching and pressure sensing accuracy. Transistors
based on organic material undergo reversible redox reactions under an electric field, leading to changes in
conductivity . By using this characteristic, a highly stretchable and sensitive pressure sensor was achieved
[86]
through an ionic capacitive mechanism and a hierarchical microstructure has shown the ability to realize
the accurate sensation of physical interactions on soft robotic skin . A neuro-inspired monolithic artificial
[87]
tactile neuron (NeuroMAT) was fabricated by an ion trap and release dynamics (iTRD)-iongelgated-
synaptic transistor to emulate the tactile recognition and learning of human skin with low power
consumption [Figure 4F]. This tactile neuron could be attached to the robotic hand to grasp the object by
[88]
programming the required force [Figure 4G]. Transistors could also function as synapses to receive signals
from multiple sensors. The artificial system consists of multiple sensors and multi-gate synaptic transistors,
which are used to replicate the complex sensory and responsive functions of human skin. For example, a
pyramid pattern single-walled carbon nanotube (SWCNT) flexible tactile sensor array was integrated into
the artificial sensory system to sense stimuli . The artificial sensory system, which integrated multiple
[89]
tactile sensors, an oscillator, an I-V transimpedance amplifier (TIA), and multi-gate synaptic transistors,
was developed; it could sense, process the external tactile stimulus, and trigger the actuator [Figure 4H].
This comprehensive system effectively mimicked somatosensory feedback functions, demonstrating its
ability to imitate the biological somatosensory system.