Tuning mechanical properties of a stretchable hydrogel system

Hydrogels mimicking the mechanical responses of biomaterials can lead to new applications. Resilin is a bioelastomer found in the tissues of many species, allowing them to perform power amplified activities, including hopping of a froghopper and appendage strike of a mantis shrimp. Developing a synthetic material with resilin-like properties requires high stretchability to store elastic energy, low hysteresis for high energy conversion, and high retraction velocity when released from a stretched state for power amplification. Here, we present a hydrogel system capable of mimicking some of these properties. These gels are synthesized through a free-radical reaction of acrylic acid, methacrylamide, and poly(propylene glycol) diacrylate. The gel structures have similarities to resilin as the hydrophobic aggregates are connected through hydrophilic polymer chains. By varying the chemical composition, the low-strain modulus of these gels can be tuned from 15 to150 kPa, and the stretchability from 2 to 10 times the original length. These gels retract rapidly to their original length when released from a stretched state. The stability of these gels at high salinity aqueous solutions opens up their applications in developing undersea soft-robotics and engineered devices.