(83h) Designing a Resilin-like Retractable and Stretchable Hydrogel

Hydrogels mimicking the mechanical responses of biomaterials can lead to new applications of these materials. Resilin is a bioelastomer that can be found in many species' tissues, allowing them to perform power amplified activities, including hopping of a froghopper, projection of a chameleon tongue, 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 the synthesis and characterization of hydrogels capable of mimicking some of these properties. These gels are synthesized through a single-step free-radical reaction of hydrophilic acrylic acid, methacrylamide, and hydrophobic poly(propylene glycol) diacrylate [PPGDA]. Here, the gel structures have similarities to resilin as the hydrophobic aggregates are connected through hydrophilic polymer chains. We have investigated the effect of monomer concentration and PPGDA concentration on the mechanical responses of these gels. The low-strain modulus of these gels can be tuned from 15 to150 kPa, and the stretchability from 2 to 11 times the original length. Also, these gels retract rapidly to their original length when released from a stretched state. A higher monomer concentration increases the gel stiffness but results in a decrease in stretchability. Similarly, higher concentrations of PPGDA increase the ultimate failure stress but decrease the stretchability of the gel. With an increase in monomer and PPGDA concentrations, the resilience and retraction capability increase. These gels' stability at high salinity aqueous solutions opens up their applications in developing undersea soft-robotics, prosthetics, and engineered devices.