An ultra-stretchable glycerol-ionic hybrid hydrogel with reversible gelid adhesion

Functional hydrogels have attracted enormous interest as wet adhesives for biomedical research and engineering applications. However, reversible hydrogel adhesives that can be used for gelid conditions were rarely reported. In this work, we have developed a freezing-tolerant (freezing temperature similar to 50 degrees C), ultra-stretchable (stretch strain 30000% at 25 degrees C) glycerol-ionic hydrogel via the ultraviolet curing of acrylamide monomer and hyper-branched polyethylenimine polymer in CaCl2-water-glycerol solution. The fabricated hydrogel exhibited reversible gelid adhesion, rapid self-healing (recover in 3 s) and weight-retaining (>2 weeks) properties. The hydrogel allows two iron substrates to adhere together at similar to 40 degrees C with the lap-shear adhesion strength as high as similar to 1 MPa. Such strong adhesion measured was reversible, specifically achieving similar to 100% of initial adhesion strength at 25 degrees C and similar to 36% at similar to 40 degrees C. Additionally, decreasing the testing temperature significantly improved the tensile strength but decreased the fracture strain of the hydrogel. Interestingly, lap-shear adhesion tests suggested that the gelid adhesion strength was enhanced by 130 times as the testing temperature decreased from 25 degrees C to 40 degrees C, which was mainly attributed to the enhanced mechanical strength of the bulk hydrogel as well as the increased surface interaction at gel-substrate interfaces. More importantly, the adhesion failure gradually changed from cohesive failure to adhesive failure as the temperature decreased. This work provides new practical and fundamental insights into developing multifunctional freezing-tolerant hydrogel adhesive for gelid conditions. (C) 2020 Elsevier Inc. All rights reserved.

Automated summary

A freezing-tolerant, ultra-stretchable hydrogel adhesive was developed with reversible gelid adhesion, rapid self-healing, weight-retaining properties, suitable for applications in low-temperature environments.