Conventional design wisdom prevents both bulk and interfacial toughness to be presented in the same hydrogel, because the bulk properties of hydrogels are usually different from the interfacial properties of the same hydrogels on solid surfaces. Here, we design and synthesize a fully physically-linked Agar (the 1 st network)/poly(N-hydroxyethyl acrylamide) (pHEAA, the 2 nd network) where both networks are physically crosslinked via hydrogen bonds. Bulk Agar/pHEAA hydrogels exhibit high mechanical properties (~2.6 MPa tensile stress, 8.0 tensile strain, ~8000 J/m 2 tearing energy, ~1.62 MJ/m 3 energy dissipation), high self-recovery without any external stimuli (~62%/30% toughness/stiffness recovery), and self-healing property. More impressively, without any surface modification, Agar/pHEAA hydrogels can be easily and physically anchored onto different non-porous solid substrates of glass, titanium, aluminum, and ceramics to produce super adhesive hydrogel-solid interfaces (i.e. high interfacial toughness of ~2000-7000 J/m 2 ). Comparison of as-prepared and swollen gels in water and hydrogen-bond-breaking solvents reveals that strong bulk toughness provides a structural basis for strong interfacial toughness, and both high toughness mainly stem from cooperative hydrogen bonds between and within two networks and between two networks and solid substrates. This work demonstrates a new gel system to achieve super high bulk and interfacial toughness on non-porous solid surfaces.

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Zwitterionic materials as a new class of emerging materials have recently been developed and applied to a broad range of biomedical and engineering applications. Zwitterionic materials possess a unique molecular structure combining both cationic and anionic groups with overall charge neutrality and high hydrophilicity. In this review, we first provide the structure-property relationship of the zwitterionic materials at molecular level, from a molecular simulation viewpoint. Then, we discuss the recent experimental developments in the preparation, properties, and applications of zwitterionic materials, with a particular focus on their antifouling properties on coating surfaces and with additional functionality and applications. Finally, we offer our personal viewpoint of current challenges and future directions in this emerging area. Our goal is to introduce the current status of this type of new zwitterionic materials to researchers from different areas and motivate them to explore all the potentials.

Development of highly stretchable and sensitive soft strain sensors is of great importance for broad applications in artificial intelligence, wearable devices, and soft robotics, but it proved to be profound...