Researchers Chen Tao and Xiao Peng from the Intelligent Polymer Materials Team at the Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, have designed a suspended double-layer sensing structure that achieves ultra-sensitive touch and adjustable pain perception. This innovation shows great potential in fields such as bionic electronics and human-machine interaction.
This intriguing development was recently published in the journal "Advanced Materials."
Efficient Coupling of Touch and Pain Perception
As a significant branch of electronic skin, flexible tactile sensors have been developed to mimic the tactile performance/function of human skin using various sensing mechanisms such as pressure resistance, capacitance, piezoelectricity, and friction electricity.
At the same time, pain perception, as another crucial sensation, can help humans effectively avoid potential dangers and achieve self-protection.
In recent years, researchers have developed artificial pain sensors using synaptic devices like transistors, memristors, or liquid metal composite materials to achieve harmless and harmful pain perception.
However, the human skin's sensory system is not limited to just touch or pain perception. Instead, it demonstrates efficient coupling of touch and pain perception functions. Therefore, integrating touch and pain perception in artificial sensory systems has attracted increasing attention from researchers.
One of the corresponding authors, Xiao Peng, told "Chinese Science Bulletin" that there are two strategies to achieve integrated touch and pain perception.
The most classic method involves combining force sensors with synaptic devices. By using the output of force sensors to control the activation of transistors or memristors, dynamic switching between touch and pain states can be achieved.
Another integration strategy is to build an integrated force sensor with unique electrical response behavior, such as responding to touch and pain through sensitivity differences or sensitivity mutation characteristics between sensing components.
However, both of these construction strategies have some limitations.
Graphene Double-Layer Sensing Structure
Xiao Peng mentioned that combining force sensors and synaptic devices in a dispersed form increases the complexity and manufacturing difficulty of the integrated system.
Although an integrated sensor structure can simplify the coupling process and achieve efficient integration, current artificial sensory systems mainly focus on integration strategies and coupling processes for touch and pain perception, neglecting the unique sensory performance and functions of human skin.
In the human skin sensory system, receptor activation induced by mechanical thresholds is the main reason for touch and pain perception.
Furthermore, human skin pursues the efficient integration of ultra-sensitive touch and pain perception functions, indicating dynamic switching between the two sensations through electrical signal mutation behavior.
Therefore, learning from the sensory behavior of human skin and achieving efficient coupling of sensitive touch and pain perception through rational material and structural design is of significant importance for artificial sensory systems.
Based on their research foundation in the construction of carbon-based/polymer composite thin films and flexible sensing, Chen Tao, Xiao Peng, and their team designed a suspended double-layer sensing structure composed of graphene conductive films. This structure achieves efficient integration of touch and pain perception mediated by mechanical thresholds, resulting in ultra-sensitive touch and adjustable pain perception.
Floating Double-Layer Electronic Skin with Tactile-Integrated Perception and Its Friendly Human-Machine Interaction Applications. Image provided by the interviewee.
Interesting Findings
In this work, the double-layer sensing structure is mainly composed of a floating elastic deformation layer and a mechanical contact sensing substrate.
Compared to a single floating configuration, the double-layer structure utilizes the three-dimensional deformation of the floating elastic film and mechanical contact behavior to trigger low-threshold and high-threshold sensing modes, respectively.
At the microscale, graphene nanosheets sequentially undergo a transition from tactile to pain perception through lateral electrical isolation and longitudinal electrical contact response, exhibiting a reverse current spike behavior.
The suspended structure can sensitively capture subtle deformations, distinguishing tiny dynamic displacements of 20 μm and detecting extremely weak tactile information as low as 0.02 Pa. By altering material and device structural parameters, the pain response range and pain threshold can be flexibly adjusted. Even under 5200 touch-separation cycles, stable and reliable tactile response performance can be maintained.
Furthermore, by constructing a miniaturized sensor array and integrating an optical feedback module, visual tactile perception and pain warning of sharp objects can be achieved. Finally, the floating double-layer sensor integrated into the hand of a commercial robot can serve as an efficient and safe human-machine interface, actively protecting humans from machine injuries while avoiding continuous damage to the robot's skin caused by mechanical forces.
Xiao Peng stated that the floating artificial sensory system based on three-dimensional deformation and mechanical contact mechanism efficiently mimics the tactile perception behavior of biological skin, demonstrating significant potential applications in bionic electronics and friendly human-machine interaction fields.
Regarding this achievement, reviewers from "Advanced Materials" believe: this type of sensor is intriguing as it offers new opportunities for closed-loop control and high-sensitivity tactile feedback.
For more information on the related paper: https://doi.org/10.1002/adma.202403447
