Most tough hydrogels are reinforced by introducing sacrificial structures that can dissipate input energy. However, because the sacrificial damage cannot rapidly recover, the toughness of these gels drops substantially during consecutive cyclic loadings. We propose a damageless reinforcement strategy for hydrogels using strain-induced crystallization. For slide-ring gels in which polyethylene glycol chains are highly oriented and mutually exposed under large deformation, crystallinity forms and melts with elongation and retraction, resulting both in almost 100% rapid recovery of extension energy and excellent toughness of 6.6 to 22 megajoules per square meter, which is one order of magnitude larger than the toughness of covalently cross-linked homogeneous gels of polyethylene glycol.

Retinal G-protein-coupled receptor (RGR) plays a crucial role in the visual system of vertebrates as a retinal photoisomerase, which isomerizes all-trans-retinal to 11-cis-retinal to maintain the photosensitivity of visual rhodopsins. Despite the previous characterization of bovine RGR, little is known about the spectral properties of RGR from other species. In addition, photoreactivity of the 11-cis-retinal-binding form remains unclear. In this study, we revealed that human and chicken RGRs form blue-absorbing pigments similar to bovine RGR. Furthermore, the spectroscopic and biochemical analyses revealed that bovine and chicken RGRs are bistable rhodopsins displaying a reversible photoreaction. These findings provide insight into the behavior of RGR as a retinal photoisomerase and aid in understanding its role in the visual system.