Conductive hydrogels are attracting tremendous interest in the field of flexible and wearable soft strain sensors because of their great potential in electronic skins, and personalized healthcare monitoring. However, conventional conductive hydrogels using pure water as the dispersion medium will inevitably freeze at subzero temperatures, resulting in the diminishment of their conductivity and mechanical properties; meanwhile, even at room temperature, such hydrogels suffer from the inevitable loss of water due to evaporation, which leads to a poor shelf-life. Herein, an antifreezing, self-healing, and conductive MXene nanocomposite organohydrogel (MNOH) is developed by immersing MXene nanocomposite hydrogel (MNH) in ethylene glycol (EG) solution to replace a portion of the water molecules. The MNH is prepared from the incorporation of the conductive MXene nanosheet networks into hydrogel polymer networks. The as-prepared MNOH exhibits an outstanding antifreezing property (−40 °C), long-lasting moisture retention (8 d), excellent self-healing capability, and superior mechanical properties. Furthermore, this MNOH can be assembled as a wearable strain sensor to detect human biologic activities with a relatively broad strain range (up to 350% strain) and a high gauge factor of 44.85 under extremely low temperatures. This work paves the way for potential applications in electronic skins, human−machine interactions, and personalized healthcare monitoring.

Wearable epidermal sensors are attracting growing interests in human activity monitoring and flexible touch display, but they are still limited by the poor self-healing property and the difficult dissolvable feature. Herein, we report polyvinyl alcohol (PVA)-stabilized liquid metal particles (LMPs) (PVA-LMPs) hydrogels with excellent self-healing performance and the dissolvable feature for wearable epidermal sensors, constructed by dispersing LMPs of eutectic gallium and indium into the borate-modified PVA polymer networks. Interestingly, the PVA-LMPs hydrogels exhibited excellent electrically and mechanically self-healing ability. Moreover, the PVA-LMPs hydrogel can be fabricated as epidermal sensors, which can accurately monitor the human activities. Additionally, the epidermal sensors are dissolvable, showing an attractive feature for on demand transient electronics. It is demonstrated that the hydroxyl groups of PVA can stabilize LMPs via hydrogen-bonding interactions. Furthermore, the dynamic cross-linking bonds between hydrogels and LMPs can rupture and coalesce reversibly in the hydrogel network, which endow the hydrogels with both electrically and mechanically self-healing ability. This work shows the potential of constructing next-generation multifunctional hydrogel-based epidermal sensors for human activity monitoring, wearable healthcare diagnosis, portable electronics, and robot tactile systems.

MXene nanocomposites exhibit self-healing capability, self-adhesive performance and long-lasting moisture, and can be assembled as epidermal sensors to wirelessly detect human motion.

Flexible wearable soft epidermal sensors assembled from conductive hydrogels have recently attracted tremendous research attention because of their extensive and significant applications in body-attachable healthcare monitoring, ultrasensitive electronic skins, and personal healthcare diagnosis. However, traditional conductive hydrogels inevitably face the challenge of long-term usage under room temperature and cold conditions, due to the lost water, elasticity, and conductivity at room temperature, and freezing at the water icing temperatures. It severely limits the applications in flexible electronics at room temperature or cold environment. Herein, we report a flexible, wearable, antifreezing, and healable epidermal sensor assembled from an antifreezing, long-lasting moist, and conductive organohydrogel. The nanocomposite organohydrogel is prepared from the conformal coating of functionalized reduced graphene oxide network by the hydrogel polymer networks consisting of poly­(vinyl alcohol), phenylboronic acid grafted alginate, and polyacrylamide in the binary ethylene glycol (EG)/H2O solvent system. The obtained organohydrogel exhibits excellent temperature tolerance (−40 °C), long-lasting moisture (20 days), reliable self-healing ability, and can be assembled as wearable sensor for an accurate detection of both large and tiny human activities under extreme environment. Thus, it paves the way for the design of highly sensitive wearable epidermal sensors with reliable long-lasting moisture and excellent temperature tolerance for potential versatile applications in electronic skins, wearable healthcare monitoring, and human–machine interaction.

Electrically conductive asphalt concrete has the potential to satisfy multifunctional applications. Designing such asphalt concrete needs to balance the electrical and mechanical performance of asphalt concrete. The objective of this study is to design electrically conductive asphalt concrete without compromising on the mechanical properties of asphalt concrete. In order to achieve this goal, various tests have been conducted to investigate the effects of electrically conductive additives (steel fiber and graphite) on the laboratory-measured electrical and mechanical properties of asphalt concrete. The results from this study indicate that the critical embedded steel fiber length is 9.6 mm to maximize the fiber's potential to bridge across the crack from single fiber tensile test. Both steel fiber and graphite can produce conductive asphalt concrete with sufficiently low resistivity, but steel fiber is much more effective than graphite to improve the conductivity of asphalt concrete. A combination of steel fiber and graphite can precisely control the resistivity of asphalt concrete over a wider range. Besides, asphalt concrete containing an optimized amount of steel fibers has a significant improvement in Marshall Stability, rutting resistance, indirect tensile strength, and low temperature cracking resistance compared to the plain concrete. The addition of graphite could increase the permanent deformation resistance with compromised stability and low temperature performance. Asphalt concrete containing steel fibers and graphite weakens the steel fiber reinforcing and toughening effect, but still has a significant improvement in mechanical performance compared to the plain concrete.