Deciphering How the Viscoelastic Properties of Mussel-Inspired Metal-Coordinate Transiently Cross-Linked Gels Dictate Their Tack Behavior.

In recent years, researchers have incorporated mussel-inspired metal-coordinate cross-links into various types of gels to improve their mechanical properties, particularly toughness and self-healing. However, not much is understood about how the linear mechanical properties of these gels dictate their tack properties. In this study, we use shear rheology and tack tests to explore correlations between linear viscoelastic properties (i.e., plateau modulus, , and characteristic relaxation time, τ) and tack behavior (i.e., peak stress, σ, and energy dissipation per volume, EDV) of transiently cross-linked hydrogels comprised of histidine-functionalized 4-arm PEG coordinated with Ni. By using the Ni-histidine ratio and polymer wt % of the transient networks to control their viscoelastic properties, we demonstrate a strong dependence of σ on and τ. The observed correlation between network dynamics and mechanics under tensile load is in good quantitative agreement with a theoretical framework for σ, which includes the linear viscoelastic properties as parameters. EDV is also influenced by and τ, and the EDV after reaching σ is additionally dependent on the polymer wt %. These findings are consistent with previously proposed molecular mechanics of reversible HisNi cross-links and provide us with new insights into the correlations between bulk mechanics and adhesive dynamics of gels with transient metal-coordinate cross-links.