(405a) Highly Stretchable Hydrogels and Their Retraction Behavior

Biological elastomeric proteins such as resilin display high stretchability and resilience, and such properties lead to power amplified activities in biological species necessary for locomotion, feeding, and defense such as 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 acrylic acid, methacrylamide, and poly(propylene glycol) diacrylate [PPGDA]. Gels with elastic modulus as high as 100 kPa, and stretchability up to 800% have been obtained. These properties enable the synthesized gels to catapult projectiles with very little dissipation. Further, when released from a stretched state, these gels achieve a retraction velocity of 16 m s^-1 with an acceleration of 4×10³ m s^-2. These values are comparable to those observed in many biological species during the power amplification process (e.g., appendage strike by Mantis shrimp, frog jump). The gel stretcability and retraction velocity can be varied by changing overall monomers and PPGDA contents. By varying the monomer compostions and the environmental conditions, we are developing a fundamental structure-property relationship for synthesizing stretchable and resilient hydrogels from synthetic polymers. The potential applications of these materials will be in artificial muscles, and soft robotics.