Dynamic Interfacial Adhesion through Cucurbit[n]uril Molecular Recognition

Abstract

Supramolecular building blocks, such as cucurbit[n]uril (CB[n])-based host-guest complexes, have been extensively studied at the nano- and microscale as adhesion promoters. Herein, we exploit a new class of CB[n]-threaded highly branched polyrotaxanes (HBP-CB[n]) as aqueous adhesives to macroscopically bond two wet surfaces, including biological tissue, through the formation of CB[8] heteroternary complexes. The dynamic nature of these complexes gives rise to adhesion with remarkable toughness, displaying recovery and reversible adhesion upon mechanical failure at the interface. Incorporation of functional guests, such as azobenzene moieties, allows for stimuli-activated on-demand adhesion/de-adhesion. Macroscopic interfacial adhesion through dynamic host-guest molecular recognition represents an innovative strategy for designing the next generation of functional interfaces, biomedical devices, tissue adhesives, and wound dressings.

Dynamic Hydrogels from Host–Guest Supramolecular Interactions

“…B) CB[8]‐rotaxane cross‐linking of polymeric materials (HBP‐CB[8]) enables reversible adhesives through ternary complex formation with polymers containing a second guest for CB[8] (Benz‐hydrogel). Adapted with permission . Copyright 2018, John Wiley & Sons, Inc.…”

“…As the “slow” step in ternary complex formation, the binding of the second guest typically dictates the mechanical properties of the gel as a higher energetic barrier of dissociation yields greater mechanical strength, and a lower energetic barrier of association for the second guest improves self‐healing . In another interesting approach to the generation of hydrogels, CB[8] can be threaded as a rotaxane on the first guest and used to cross‐link polymer network, which can then bind to a second guest pendant from a different polymer to enable additional cross‐linking for reversible interfacial adhesion (Figure B) . Hybrid hydrogels with altered mechanical properties can also be created from CB[8]‐based ternary complexes, such as by affixing the first guest to silica nanoparticles and the second guest to a polymer chain .…”

“…[95] In another interesting approach to the generation of hydrogels, CB [8] can be threaded as a rotaxane on the first guest and used to cross-link polymer network, which can then bind to a second guest pendant from a different polymer to enable additional cross-linking for reversible interfacial adhesion ( Figure 3B). [96] Hybrid hydrogels with altered mechanical properties can also be created from CB [8]-based ternary complexes, such as by affixing the first guest to silica nanoparticles and the second guest to a polymer chain. [97] Precursors that were first pre-organized by ternary complex formation and subsequently polymerized into a hydrogel have also been explored for applications such as wound dressings, with the gel being easily removed by addition of a competing adamantane-based guest for CB [8].…”

Metallopolymer Organohydrogels with Photo‐Controlled Coordination Crosslinks Work Properly Below 0 °C

“…Compared to other stimuli, light has high spatiotemporal resolution, enables remote control of hydrogels, and can be obtained from the sun. Therefore, light has been used to fabricate 3D extracellular matrices in hydrogels,1,3,4 induce cargo release from hydrogels,6,11 regulate adhesion,12 and control the motion of actuators 13,14…”

“…Compared to other stimuli, light has high spatiotemporal resolution, enables remote control of hydrogels, and can be obtained from the sun. Therefore, light has been used to fabricate 3D extracellular matrices in hydrogels, [1,3,4] induce cargo release from hydrogels, [6,11] regulate adhesion, [12] and control the motion of actuators. [13,14] Although photoresponsive hydrogels function normally at room temperature, they lose photoresponsiveness below the freezing temperature of water because the frozen matrix hinders photoreactions and structural changes in the hydrogels.…”