Highly Stretchable and Tough Hydrogels
Hydrogels are used as scaffolds for tissue engineering, vehicles for drug delivery, actuators for optics and fluidics, and model extracellular matrices for biological studies. The scope of hydrogel applications, however, is often severely limited by their mechanical behaviors. Most hydrogels are brittle, sensitive to notches, and do not exhibit high stretchability. We report the synthesis of hydrogels from polymers forming ionically and covalently crosslinked networks. Although such gels contain 90% water, they can be stretched beyond 20 times their initial length, and have fracture energies of ~9,000 Jm-2. Even for samples containing notches, a stretch of 17 is demonstrated. We attribute the gels’ toughness to the synergy of two mechanisms: crack bridging by the network of covalent crosslinks, and hysteresis by unzipping the network of ionic cross- links.