Retraction Behavior of Stretchable Hydrogels

Elastic biopolymers such as resilin exhibit exceptional stretchability and resilience, which many species exploit in nature for mechanical energy storage to facilitate their movement. Inspired by that, we synthesized highly stretchable hydrogels with low dissipation and high resilience. When released from a highly stretched state, these gels retract rapidly. Capturing the retraction velocity and acceleration allows us to investigate the mechanical energy storage and release behavior of these hydrogels. Two different gel systems have been considered: UV-cured polyacrylamide (PAAm) hydrogels with different volume fractions and free radical polymerized hydrogels composed of acrylic acid (AAc), alkyl-acrylamide, such as methacrylamide (MAM), and poly(propylene glycol diacrylate) (PPGDA). The PAAm hydrogels mostly consist of hydrophilic components, whereas moderately hydrophobic PPGDA leads to hydrophobic domains in the second gel system. The effect of different microstructures for these two hydrogels on the tensile properties, retraction velocity, and acceleration will be presented. Our study broadens the understanding of the structure-property relationships for hydrogels at large strain, essential for their applications in numerous areas.