A Wearable Thin-Film Hydrogel Laser for Functional Sensing on Skin.

Flexible photonics offers the possibility of realizing wearable sensors by bridging the advantages of flexible materials and photonic sensing elements. Recently, optical resonators have emerged as a tool to improve their oversensitivity by integrating with flexible photonic sensors. However, direct monitoring of multiple psychological information on human skin remains challenging due to the subtle biological signals and complex tissue interface. To tackle the current challenges, here, we developed a functional thin film laser formed by encapsulating liquid crystal droplet lasers in a flexible hydrogel for monitoring metabolites in human sweat (lactate, glucose, and urea). The three-dimensional cross-linked hydrophilic polymer serves as the adhesive layer to allow small molecules to penetrate from human tissue to generate strong light--matter interactions on the interface of whispering gallery modes resonators. Both the hydrogel and cholesteric liquid crystal microdroplets were modified specifically to achieve high sensitivity and selectivity. As a proof of concept, wavelength-multiplexed sensing and a prototype were demonstrated on human skin to detect human metabolites from perspiration. These results present a significant advance in the fabrication and potential guidance for wearable and functional microlasers in healthcare.

A zinc ion yarn battery with high capacity and fire retardancy based on a SiO2 nanoparticle doped ionogel electrolyte.

Ionogel electrolytes are proposed to be an excellent substitute for liquid electrolytes due to their superior portability, flexibility and safety without any leakage that may lead to the failure of batteries. Given these natural characteristics, ionogels can provide batteries with good flexibility and wearability. However, the instability under different extreme working conditions and low ionic conductivity limit the further applications of ionogels. In this research, an ionogel electrolyte is synthesized by polymerizing 1-vinyl-3-ethylimidazolium dicyanamide ([Veim][DCA]) and N,N-methylenebisacrylamide (NNMBA) in zinc acetate (Zn(CH3COO)2) and manganese sulfate (MnSO4) dissolved 1-ethyl-3-methylimidazolium dicyanamide ([Emim][DCA]). The fire retardancy of the ionogel electrolyte is improved by adding SiO2 nanoparticles into the electrolyte. The ionogel electrolyte with 40 wt% silicon dioxide (SiO2) nanoparticles possesses a high ionic conductivity of 0.013 S cm-1 and the zinc//manganese dioxide (Zn//MnO2) battery based on the ionogel electrolyte is able to deliver a high specific capacity of 277 mA h g-1 and a high energy density of 283 W h kg-1. Moreover, the SiO2 nanoparticles contained in the ionogel endow the battery with good fire retardancy. Put together, the yarn battery successfully meets the requirements of modern flexible and wearable electronics.

An intrinsically stretchable and compressible Zn-air battery.

An intrinsically highly stretchable and compressible Zn-air rechargeable battery with good electrochemical performance was fabricated for the first time. It exhibits the merits of 300% intrinsic stretchability and 85% intrinsic compressibility with excellently retained electrochemical performance, a decrease in catalyst cost of 40 times, the fewest number of components and facile fabrication.

Concentrated Hydrogel Electrolyte-Enabled Aqueous Rechargeable NiCo//Zn Battery Working from -20 to 50 °C.

Zn-based aqueous rechargeable batteries are promising in portable electronics because of their high voltage, low cost, etc. However, most conventional aqueous electrolytes are liable to freeze at low temperature and are incompatible with high ion concentrations, which hinders their application. Herein, we developed a sodium polyacrylate hydrogel (PANa) to superabsorb highly concentrated ions. Unprecedentedly, the hydrogel electrolyte can be stretched over ten times at -50 °C without any freezing. Therefore, the fabricated rechargeable NiCo//Zn battery worked well in a wide-temperature-range (-20 to 50 °C). This work creates many opportunities for the development and practical application of aqueous batteries.