Multifunctional Mussel-Inspired Hydrogels and Films Formed via Catechol-VO₂ Nanoparticle Coordination

Marine mussels utilize DOPA-V metal coordination bonds as dynamic cross-links to fabricate tough and self-healing coatings and glues. Inspired by mussels, researchers have harnessed DOPA-metal coordination to create dynamic and mechanically responsive polymeric materials. Here, we harness the robust DOPA-V interactions observed in mussels combined with the temperature-responsive properties of vanadium dioxide (VO₂) to develop a room-temperature process to produce thermochromic VO₂ hydrogels and films. 4-arm polyethylene glycol (PEG) polymers functionalized with DOPA-catechol moieties were mixed with VO₂ nanoparticles in solution. Raising pH led to formation of hydrogels, while spin coating enabled processing into thin films. Hydrogels possessed mechanically tunable viscoelasticity and self-healing response. Furthermore, dried free-standing films were highly flexible and exhibited plastic deformation with extensibilities of 200% and beyond, while still retaining the thermochromic properties of the nanoparticles. The facile fabrication method and the resulting versatile mechanical response combined with thermochromic properties are promising for future development VO₂-polymer composite materials.