New Flexible Electrode: Low Resistance, High Stability, Stretchable
How did fishing nets cross the border from the aquaculture industry to the field of wearable human-computer interaction?
Inspired by artificial fishing nets, Li Runwei’s team from Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, and Zhu Guang’s team from University of Nottingham Ningbo, designed an ultra-stable and stretchable electrode with a flexible and adaptive conductive interface. The electrode has undergone 330,000 100% tensile strain cycles, and its resistance only changes by 5%. Facing environmental changes such as cold and heat, acid and alkali, and water immersion, it still shows stable electrical performance, which solves the problem of electrical conductivity and tensile strength in the field of flexible electrodes. The problem is that the rate is incompatible and the electrical performance is unstable under cyclic deformation.
The electrode can be used in all-weather ECG monitoring, intelligent human-computer interaction system and human body hyperthermia, etc. It is expected to help the sustainable development of wearable health monitoring system and electronic skin human-computer interaction interface based on the Internet of Everything.
On April 7, the related paper “Ultradurable Stretchable Electrodes for Electronic Skin: Simulation of Water Film-Fishnet Structures with Nanofiber Scaffolds and Liquid Metal In-situ Self-Assembly” was published as the cover article of “Information Materials”.
The “water film” when fishing and pulling nets fascinates materials scientists
In the field of smart wearable electronics, stable and durable flexible and stretchable conductors are still a huge challenge. Especially in the process of collecting physiological signals of human epidermis, stable and stretchable electrodes can realize long-term and accurate signal collection. The current flexible electrodes are mainly divided into three types: surface structure design type, conductive material composite type and genuine stretchable type electrodes, but it is difficult to achieve stable electrical properties under dynamic deformation.
Cao Jinwei, the first author of the paper and Dr. Lianpei of the two teams, told the “Science China Journal” that in order to overcome this challenge, they initially considered the structure of simulating the window screen, but the flexibility of the window screen was insufficient. In the follow-up observation and search, they finally found an artificial fishing net It is a good simulation object – when the fisherman pulls the net out of the water, there will be a layer of water film attached to the net. This “water film-fishing net” structure can conform well and can follow the changes of the matrix without losing its own continuous shape. .
This is exactly the property needed to stabilize stretchable electrodes.
The team proposed that the use of polyurethane (TPU) electrospinning and liquid metal (LM) micro-nano particles, in-situ composite by electrospinning and electrostatic spraying, followed by mechanical activation to form a liquid metal TPU two-dimensional imitation “water film-” Fishnet” structure film, an ultra-stable stretchable electrode (NHSE) with flexible adaptive conductive interface was prepared.
Achieve low resistance, high stability, and stretchability
The electrode achieves a very low initial square resistance of 52mΩ/sq, and the external expansion of the liquid metal and the self-adaptive flow in the mesh are bound by the TPU mesh under strain, which solves the electrical conductivity and stretching that the stretchable electrode once faced. It has excellent dynamic cycle stability, and the resistance only changes by 5% after 330,000 100% tensile strain cycles.
“You can understand that we use liquid metal to replace water, and TPU electrospinning to replace fishing net wire. The TPU liquid metal composite material produced is not only thin, but also has excellent flexibility, stretchability, and industry-leading durability. Introduced by Cao Jinwei, the electrode still shows stable electrical properties in the face of changes in the service environment such as cold and heat, acid and alkali, and water immersion.
Applicable to many types of scenarios
In the paper, several application approaches are listed, such as local activation and laser cutting, TPU liquid metal composites can be prepared into multi-layer multi-functional human-computer interaction systems.
The upper-layer capacitive sensing array is connected to the integrated circuit and the Bluetooth module, which can realize wireless signal transmission, and can input wireless commands to the computer in the stretching and bending state, which can be used in smart wearable game control and other aspects. The lower layer serpentine heater exhibits good electrothermal stability, can achieve stable heating at 45°C to 90°C, and exhibits excellent heating cycle performance, which can be used for human body heating therapy.
The electrode has good biocompatibility and extremely low toxicity, and can also realize all-weather ECG signal detection in human epidermis. The research team designed three working scenarios for the electrode, including static, sports, and water flushing according to the human activity scene. The extremely low initial resistance enables the electrode to collect ECG signals with a signal-to-noise ratio of 0.43, especially in the water flushing scene. A stable and clear ECG signal can be collected.
The reviewers of “Information Materials” believe that for wearable electronic devices, the stability and durability of their electrical properties are crucial, and the authors of the paper have achieved the preparation of ultra-stable stretchable electrodes through careful design. In the service environment changes such as stretching, water immersion, acid-base, cold and heat, it is proved that NHSE has a good application prospect.