Glassy Hydrogels: From New State to High Performances of Gel Materials

The rapid development of tough hydrogels has greatly expanded the application scope of gel materials. The strength and toughness of some synthetic hydrogels have surpassed those of soft biotissues, however, the elastic modulus of gels is usually less than 1 MPa, much lower than that of connective tissues such as tendons. One major reason is the water molecules have strong hydration and plasticizing effects on hydrophilic polymer network, resulting in the gels in the elastic or viscoelastic state. In recent years, we have developed high-performance (high strength, high stiffness, high toughness) hydrogels through molecular design to form dense and robust associative interactions within the matrix that effectively reduce the dynamics of the network to afford the gel in a glassy state at room temperature. The glassy state is one new state of gel materials, which opens a new avenue to develop high-performance hydrogels and broadens the tuning range of mechanical and viscoelastic behaviors as well as the application potentials. This account summarizes and reviews the synthesis and structure-property relationship of glassy hydrogels, including the general characters, molecular mechanism, design principles, and unique functions. Finally, we introduce some applications of glassy hydrogels in the fields of biomedicine, engineering, etc., and give prospects to the challenges and future directions in this area. [GRAPHICS] .