Preparation and mechanical properties of strong and tough poly (vinyl alcohol)-polypeptide double-network hydrogels

Poly(vinyl alcohol) (PVA)-polypeptide double-network hydrogels with various ionic liquid (IL)-based polypeptides were prepared by a freezing/thawing method. Tensile tests revealed that the stiffness and toughness of the PVA hydrogels were significantly improved (e.g., 6.3 times the Young’s modulus and 5.8 times the work of extension) by incorporation of IL-based polypeptides. An optimized mechanical property was achieved by incorporation of α-helical imidazolium-based polypeptides at x = 0.03. Rheological tests revealed a thermally induced transition at 51.4–58.1 °C for the double network PVA/PPLG-ImBF4-x-67 (x = 0.01, 0.02, 0.03) hydrogels due to the rupture of the electrostatic interactions. Field emission scanning electron microscopy (FESEM) and wide-angle X-ray diffraction (WAXD) results suggested that the strong and tough double-network hydrogel was constructed by PVA crystallites and ionic bonds of IL-based polypeptide as the double physical cross-linkers.