Dynamic Supramolecular Hydrogels: Regulating Hydrogel Properties through Self-Complementary Quadruple Hydrogen Bonds and Thermo-Switch

We report here a supramolecular hydrogel displaying a wide array of dynamic desirable properties. The key is using an ABA triblock copolymer containing a central poly(ethylene oxide) block and terminal poly(N-isopropylacrylamide) (PNI-PAm) block with ureido pyrimidinone (UPy) moieties randomly incorporated. Rapid hydrogelation is triggered upon increasing temperature above the lower critical solution temperature (LCST) of the supramolecular copolymer, where PNIPAm segments dehydrate and assemble into micelles, which subsequently provide hydrophobic microenvironments promoting UPy dimerization to grab polymer chains, thus forming hydrogen-bonded cross-linking points. The supramolecular hydrogels demonstrate fascinating shear-thinning, self-healable, thermo-reversible, and injectable properties, which allow withstanding repeated deformations and 3D construction of complex objects. Mesenchymal stem cells mixed with the hydrogel and injected through needles remain highly viable (>90%) during the encapsulation and delivery process. With these attractive dynamic physical properties, the supramolecular hydrogel holds great promise to support cell or drug therapies.