(558d) Effects of Hydrophobic Components on the Stretchability and Retractability of a Multi-Component Hydrogel

Elastic biopolymers such as resilin display remarkable mechanical properties, including high stretchability and resilience, which are exploited in nature by many species for mechanical energy storage towards facilitating their movement. Such properties of resilin have been attributed to the balanced combination of hydrophilic and hydrophobic segments present. In this work, we investigated the effects of hydrophobic components present in a gel on its mechanical properties. We prepared three component hydrogels composed of acrylic acid (AAc), alkyl-acrylamide, for example, methacrylamide (MAM), N-Isopropyl acrylamide (NIPAM), butyl acrylamide (BAM), and poly(propylene glycol diacrylate) (PPGDA). The gels were synthesized by free-radical polymerization in a salt solution in the presence of a surfactant, sodium dodecyl sulfate, using KPS as an initiator. Gels with MAM and varying concentrations of PPGDA were considered, for which the elastic moduli increased with PPGDA concentration. When released from a stretched state, these gels retracted rapidly, and the retraction velocity and acceleration also increased with PPGDA concentration. PPGDA is slightly hydrophobic, but additional hydrophobic domains in the hydrogels considered here can be incorporated by increasing the chain length of alkyl-acrylamide. Hydrophobic NIPAM and BAM were considered here, and the effects of increased hydrophobicity on the tensile properties, retraction velocity, and acceleration compared to methacrylamide will be presented.