Exceptional Mechanical Properties of Phase-Separation-Free Mo₃Se₃^–‑Chain-Reinforced Hydrogel Prepared by Polymer Wrapping Process

As Mo₃Se₃^– chain nanowires have dimensions comparable to those of natural hydrogel chains (molecular-level diameters of ∼0.6 nm and lengths of several micrometers) and excellent mechanical strength and flexibility, they have large potential to reinforce hydrogels and improve their mechanical properties. When a Mo₃Se₃^–-chain-nanowire-gelatin composite hydrogel is prepared simply by mixing Mo₃Se₃^– nanowires with gelatin, phase separation of the Mo₃Se₃^– nanowires from the gelatin matrix occurs in the micronetwork, providing only small improvements in their mechanical properties. In contrast, when the surface of the Mo₃Se₃^– nanowire is wrapped with the gelatin polymer, the chemical compatibility of the Mo₃Se₃^– nanowire with the gelatin matrix is significantly improved, which enables the fabrication of a phase-separation-free Mo₃Se₃^–-reinforced gelatin hydrogel. The composite gelatin hydrogel exhibits significantly improved mechanical properties, including a tensile strength of 27.6 kPa, fracture toughness of 26.9 kJ/m³, and elastic modulus of 54.8 kPa, which are 367%, 868%, and 378% higher than those of the pure gelatin hydrogel, respectively. Furthermore, the amount of Mo₃Se₃^– nanowires added in the composite hydrogel is as low as 0.01 wt %. The improvements in the mechanical properties are significantly larger than those for other reported composite hydrogels reinforced with one-dimensional materials.