A flexible metal nano-mesh strain sensor with the characteristic of spontaneous functional recovery after fracture damage

One-step 3D shrinking method to prepare robust and multifunctional flexible strain sensor with brain cortex-like wrinkled structured

At the current stage of rapid development in flexible electronics technology, flexible strain sensors face the challenge of integrating multiple functions while maintaining high sensitivity, a wide strain response range, and stable sensing performance in complex and harsh environments. In response to this challenge, we propose a facile and transfer-free one-step 3D-shrinking approach inspired by the wrinkled structure of the brain cortex. This method involves spraying a uniform conductive layer onto a pre-inflated latex balloon and gradually releasing the air, which induces the formation of an intertwined, meandering conductive layer that resembles a brain cortex-like wrinkled structure. The conductive layer at the wrinkles is interlocked and engaged with the latex substrate, thus achieving a robust anchoring effect and effectively balancing the mechanical properties, surface wettability, and sensing performance of the sensor. The wrinkled conductive layer forms a hierarchical micro-nano structure, endowing the sensor with self-cleaning functionality and a water contact angle (WCA) of up to 168.4°. Meanwhile, the sensor exhibits a rapid response time of 100 ms, a gauge factor (GF) up to 2653.3, and a broad strain detection range of 0.1-191 %. More importantly, the sensor maintains excellent electrochemical stability and superhydrophobic durability even after being subjected to water scouring, finger wiping, ultrasonic cleaning, and exposure to humid or corrosive environments. In addition, after undergoing a stretch-release cyclic test lasting up to 30,000 s, the sensor demonstrates regular and repeatable resistance changes, and the wrinkled structure remains intact. Its compact and lightweight design allows it to be easily assembled for dynamically monitoring the full range of human body movements (from subtle pulse beats to large joint movements), air flow, liquid droplet falling height, and variable weather conditions. Consequently, this brain cortex-like wrinkled structure sensor offers a simple and universal fabrication method for high-performance strain sensors, providing valuable insights for advancing the next generation of flexible electronics.

Detection of Positive and Negative Pressure in a Double-Chamber Underwater Thruster

The aim of this paper is to develop a compact, rapid-response pressure sensor for underwater propulsion. Flexible pressure sensors are widely utilized in human-computer interactions and wearable electronic devices; however, manufacturing capacitive sensors that offer a broad pressure range and high sensitivity presents significant challenges. Inspired by the dermal papillary microstructure, a capacitive pressure sensor was prepared by infusing polydimethylsiloxane (PDMS) inside an anodic aluminum oxide (AAO) template and then demolding it. The resulting pressure sensor exhibits several key characteristics: high linearity in the range of -5.2 to 6.3 kPa, a comprehensive range for both positive and negative pressure sensing in air or water environments, a quick response time of 52 ms, a recovery time of 40 ms, and excellent stability. The sensor presented in this work is innovatively applied to detect underwater negative pressure, and it is employed for the swift detection of positive and negative pressure changes in underwater thrusters. This work highlights the promising potential of biomimetic flexible capacitive pressure sensors across various applications.

Muscle Fiber-Inspired High-Performance Strain Sensors for Motion Recognition and Control

The rapid development of wearable technology, flexible electronics, and human-machine interaction has brought about revolutionary changes to the fields of motion analysis and physiological monitoring. Sensors for detecting human motion and physiological signals have become a hot topic of current research. Inspired by the muscle fiber structure, this paper proposed a highly stable strain sensor that was composed of stretchable Spandex fibers (SPF), multiwalled carbon nanotubes (MWCNTs), and silicone rubber (Ecoflex). This sensor adopted an immersion coating process in which MWCNTs were conformally deposited on SPF, and Ecoflex was filled into the fiber interstices, completing the encapsulation and filling of the SPF to construct a stable three-dimensional conductive network. Thanks to the filling of Ecoflex, contact between conductive fibers during the stretching process was avoided, resulting in a significant change in the resistance. The sensitivity of the sensor reached 54.84, which is 10 times higher than before the Ecoflex filling with a stretchable strain range of up to 70%. The encapsulation of Ecoflex also prevented the detachment of MWCNTs on the fibers during stretching, improving the mechanical stability. The sensor can be easily attached to the surface of human skin to rapidly monitor various human motion signals. Furthermore, the sensor was related to the manipulator through wireless Bluetooth to realize the intelligent control of the manipulator. This work not only provided a more precise data monitoring method for medical and motion analysis fields but also offered an innovative solution for manipulator control.

A double-crack structure for bionic wearable strain sensors with ultra-high sensitivity and a wide sensing range

Flexible strain sensors are crucial in fully monitoring human motion, and they should have a wide sensing range and ultra-high sensitivity. Herein, inspired by lyriform organs, a flexible strain sensor based on the double-crack structure is designed. An MXene layer and an Au layer with cracks are constructed on both sides of the insulated polydimethylsiloxane (PDMS) film, forming an equivalent parallel circuit that guarantees the integrity of the conductive path under a large strain. The rapid disconnection of the crack junctions causes a significant change in the resistance value. Due to the effect of cracks on the conductive path, the sensitivity of the sensor is largely improved. Benefiting from the double-crack structure, the as-obtained sensor shows ultra-high sensitivity (maximum gauge factor of up to 14 373.6), a wide working range (up to 21%), a fast response time (183 ms) and excellent dynamical stability (almost no performance loss after 1000 stretching cycles and different frequency cycles). In practical applications, the sensor is applied to different parts of the human body to sense the deformation of the skin, demonstrating its great potential application value in human physiological detection and the human-machine interaction. This study can provide new ideas for preparing high-performance flexible strain sensors.

PDMS/Ag/Mxene/Polyurethane Conductive Yarn as a Highly Reliable and Stretchable Strain Sensor for Human Motion Monitoring

The conductivity and sensing stability of yarn-based strain sensors are still challenges when it comes to practical applications. To address these challenges, surface engineering of polyurethane (PU) yarn was introduced to improve its surface hydrophilicity for better deposition of MXene nanosheets in its dispersion. The introduction of Ag nanoparticles via magnetron sputtering greatly improved the surface conductivity; meanwhile, the encapsulation of the PDMS protective layer effectively enhanced the sensing stability over 15,000 cycling process, as well as the working range with a gauge factor value over 700 under a strain range of 150-300%. Moreover, the exploration of its applications in human motion monitoring indicate that the prepared strain-sensing yarn shows great potential in detecting both tiny motions or large-scale movements of the human body, which will be suitable for further development into multifunctional smart wearable sensors or metaverse applications in the future.