2020, Han, L., Wang, M., Prieto-López, L.O., Deng, X., Cui, J.

Adhesive hydrogels are widely applied for biological and medical purposes; however, they are generally unable to adhere to tissues under wet/underwater conditions. Herein, described is a class of novel dynamic hydrogels that shows repeatable and long-term stable underwater adhesion to various substrates including wet biological tissues. The hydrogels have Fe3+-induced hydrophobic surfaces, which are dynamic and can undergo a self-hydrophobization process to achieve strong underwater adhesion to a diverse range of dried/wet substrates without the need for additional processes or reagents. It is also demonstrated that the hydrogels can directly adhere to biological tissues in the presence of under sweat, blood, or body fluid exposure, and that the adhesion is compatible with in vivo dynamic movements. This study provides a novel strategy for fabricating underwater adhesive hydrogels for many applications, such as soft robots, wearable devices, tissue adhesives, and wound dressings.

2019, Prieto-López, L.O., Xu, J., Cui, J.

The handling of droplets in a controlled manner is essential to numerous technological and scientific applications. In this work, we present a new open-surface platform for droplet manipulation based on an array of bendable nozzles that are dynamically controlled by a magnetic field. The actuation of these nozzles is possible thanks to the magnetically responsive elastomeric composite which forms the tips of the nozzles; this is fabricated with Fe3O4 microparticles embedded in a polydimethylsiloxane matrix. The transport, mixing, and splitting of droplets can be controlled by bringing together and separating the tips of these nozzles under the action of a magnet. Additionally, the characteristic configuration for droplet mixing in this platform harnesses the kinetic energy from the feeding streams; this provided a remarkable reduction of 80% in the mixing time between drops of liquids about eight times more viscous than water, i.e., 6.5 mPa/s, when compared against the mixing between sessile drops of the same fluids. © 2019 by the authors.

2020, Mredha, M.T.I., Le, H.H., Cui, J., Jeon, I.

In recent years, various hydrogels with a wide range of functionalities have been developed. However, owing to the two major drawbacks of hydrogels—air-drying and water-swelling—hydrogels developed thus far have yet to achieve most of their potential applications. Herein, a bioinspired, facile, and versatile method for fabricating hydrogels with high stability in both air and water is reported. This method includes the creation of a bioinspired homogeneous fusion layer of a hydrophobic polymer and oil in the outermost surface layer of the hydrogel via a double-hydrophobic-coating produced through quenching. As a proof-of-concept, this method is applied to a polyacrylamide hydrogel without compromising its mechanical properties. The coated hydrogel exhibits strong resistance to both drying in air and swelling in multiple aqueous environments. Furthermore, the versatility of this method is demonstrated using different types of hydrogels and oils. Because this method is easy to apply and is not dependent on hydrogel surface chemistry, it can significantly broaden the scope of next-generation hydrogels for real-world applications in both wet and dry environments.

2020, Zhao, H., Sun, Q., Zhou, J., Deng, X., Cui, J.

Space cooling and heating currently result in huge amounts of energy consumption and various environmental problems. Herein, a switching strategy is described for efficient energy-saving cooling and heating based on the dynamic cavitation of silicone coatings that can be reversibly and continuously tuned from a highly porous state to a transparent solid. In the porous state, the coatings can achieve efficient solar reflection (93%) and long-wave infrared emission (94%) to induce a subambient temperature drop of about 5 °C in hot weather (≈35 °C). In the transparent solid state, the coatings allow active sunlight permeation (95%) to induce solar heating to raise the ambient temperature from 10 to 28 °C in cold weather. The coatings are made from commercially available, cheap materials via a facile, environmentally friendly method, and are durable, reversible, and patternable. They can be applied immediately to various existed objects including rigid substrates.