Highly Stretchable, Compressible, Resilient, and Equilibrium Swelling Hydrogels with Elastic Nano Junctions

In this work, a flexible and polymerizable polyurethane-urea (PUU) nanoparticle is used for the first time to prepare hydrogels showing highly stretchable, compressible, and resilient properties in their equilibrium swelling state. The PUU nanoparticles are prepared by reported interfacial polycondensation of O/W nanoemulsions followed by surface modification with acrylate groups. The hydrogels are prepared by simple free-radical copolymerization of acrylamide and the polymerizable PUU nanoparticles. These PUU nanoparticles are expected to act as polyfunctional nanocrosslinkers and elastic junctions of the hydrogel's network. The obtained hydrogels show high water containing character (94-97 wt%) in their equilibrium swelling state. The equilibrium swelling hydrogels can still be stretched and compressed up to 430-1170% and 95%, respectively, without fracture. Furthermore, cyclic tensile tests with a maximum strain of 500% or 700% show that the resilience of these equilibrium swelling hydrogels is as high as 95-97%. This work provides a new strategy and some new insights into the fabrication of fully swelling hydrogels with both extraordinary ductility and resilience, which is of critical importance for many of their practical applications.