Multistimuli responsive hydrogels with shape fix/memory capability fabricated from gold nanorod‐conjugated amino acid‐based vinyl polymer networks

Abstract

AbstractFabricating robust shape‐memory hydrogels that respond to multiple external stimuli is an important challenge in facilitating gel technology for versatile applications. In this study, we report a simple approach for constructing thermo‐, redox‐, and photo‐responsive hydrogels with high mechanical strength and shape fix/memory capability. Upper critical solution temperature (UCST)‐type amino acid‐based hydrogels were facilely prepared by radical copolymerization of N‐acryloyl glycinamide (NAGAm) with cystine‐derived divinyl acrylamides (ionic cystine [NAC] or nonionic cystine‐methyl ester [NACMe]) units at different monomer concentrations (1/2 M). These hydrogels were transparent and exhibited good mechanical strength (tensile strength of 0.3–0.4 MPa and breaking elongation of 400%–700%). All hydrogels showed UCST‐type swelling‐shrinking behaviors based on thermo‐driven reversible hydrogen bonds among the PNAGAm units, and thus could be fixed into variety of shapes and recovered to the original shape by temperature manipulation. The cystine‐based crosslinkers having SS bonds served as efficient redox‐sensitive and gold‐nanorod‐(AuNR)‐adsorbing moieties; thus, AuNR could be conjugated stably and evenly into the PNAGAm/NAC hydrogel. Moreover, upon light‐irradiation, the AuNR‐conjugated hybrid hydrogel exhibited shape‐memory behavior owing to the photothermal effect of the AuNRs. These multiresponsive/functional hydrogels composed of amino acid units have considerable potential for various applications in the fields of soft actuators and biomedicines.