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

This study develops mussel-inspired PEG–DOPA hydrogels and flexible polymer films crosslinked through coordination between catechol moieties and vanadium dioxide (VO₂) nanoparticles. The authors first characterized VO₂ nanoparticles (100–200 nm) via SEM, PXRD, TGA, and DSC, confirming the monoclinic–rutile thermochromic phase transition near 70 °C (Fig. 2B). Mixing VO₂ nanoparticles with PEG–DOPA at neutral pH produced mechanically robust, self-healing hydrogels in which nanoparticle-mediated multivalent crosslinking yielded solid-like rheological behavior without modulus crossover in frequency sweeps (Fig. 3B). Stress-relaxation and step-strain experiments demonstrated slow viscoelastic relaxation and rapid recovery, reflecting reversible coordination bonds at the polymer–nanoparticle interface. Spin-coated films retained the thermochromic behavior of VO₂ and exhibited large extensibility (≈200–300% strain), plastic deformation, and toughness ≈10.5 MJ/m³ in dry conditions (Fig. 4A). Hydrated films became softer and elastomeric, sustaining reversible cyclic deformation below 40% strain (Fig. 4B). The combination of dynamic coordination chemistry, tunable mechanical response, and thermochromic switching establishes a scalable route to multifunctional VO₂–polymer composite materials.