Effects of microstructure on the stretchability and retractability of a multicomponent hydrogel

Elastic biopolymers such as resilin display remarkable mechanical properties, including high stretchability and resilience, which many species exploit in nature for mechanical energy storage to facilitate their movement. Such properties of resilin have been attributed to its balanced combination of hydrophilic and hydrophobic segments. We have synthesized gels with both hydrophilic and hydrophobic components, and we will present the effect of gel microstructure, particularly that of hydrophobic components, on their mechanical properties. Hydrogels composed of acrylic acid (AAc), alkyl-acrylamide, for example, methacrylamide (MAM), butyl acrylamide (BAM), and poly(propylene glycol diacrylate) (PPGDA) were synthesized using a free radical polymerization. Gels with MAM and varying concentrations of PPGDA displayed increasing elastic moduli with PPGDA concentration. When released from a stretched state, these gels retracted rapidly, and the retraction velocity also increased with PPGDA concentration. PPGDA is slightly hydrophobic, but additional hydrophobic domains in the gels were incorporated by replacing MAM with hydrophobic BAM. The effects of increased hydrophobicity on the tensile properties, retraction velocity and acceleration will be presented.