Instant, Tough, Noncovalent Adhesion

Abstract

Noncovalent adhesion has long been developed for numerous applications, including pressure-sensitive adhesives, wound closure, and drug delivery. Recent advances highlight an urgent need: a general principle to guide the development of instant, tough, noncovalent adhesion. Here, we show that noncovalent adhesion can be both instant and tough by separately selecting two types of noncovalent bonds for distinct functions: tougheners and interlinks. We demonstrate the principle using a hydrogel with a covalent polymer network and noncovalent tougheners, adhering another material through noncovalent interlinks. The adhesion is instant if the interlinks form fast. When an external force separates the adhesion, the covalent polymer network transmits the force through the bulk of the hydrogel to the front of the separation. The adhesion is tough if the interlinks are strong enough for many tougheners to unzip. Our best result achieves adhesion energy above 750 J/m2 within seconds. The adhesion detaches in response to a cue, such as a change in pH or temperature. We identify several topologies of noncovalent adhesion and demonstrate them in the form of tape, powder, brush, solution, and interpolymer complex. The abundant diversity of noncovalent bonds offers enormous design space to create instant, tough, noncovalent adhesion for engineering and medicine.

Hydrogel Adhesion: A Supramolecular Synergy of Chemistry, Topology, and Mechanics

“…Supramolecular adhesion through noncovalent bonds can be both strong and dynamic. [177] Covalent bonds are all alike; every noncovalent bond is noncovalent in its own way. This statement-like that of Tolstoy about families-is of course an exaggeration, but does point to an important fact: the diversity of noncovalent bonds, as well as the diversity of topologies, offers an enormous design space for the art of supramolecular adhesion.…”

“…An aggregate of noncovalent bonds, however, can be strong. [85,176,177] Polymer chains can interact strongly with each other through aggregates of noncovalent bonds, forming a polymer complex. [178,179] Polymer complexes have enabled hydrogels of high toughness and self-heal, [176,[180][181][182] as well as supramolecular assembly of intricate structures.…”

“…[219,220] Hydrogen-bonded complexes have been used to enable hydrogel adhesion. [177,221] Hydrogen bonds between nucleobases enable the molecular recognition in DNA and RNA, and the nucleobases have been copolymerized in polymer chains to enable hydrogel adhesion. [222]…”

“…Spray coat N/A Hydrophilic surface modification [245] Bulk modification with silanes [84] Surface modification with hydrophobic initiators [53] Bulk modification with interlink initiators [140] N/A Mussel-inspired adhesion [242,243,278] Mucoadhesion [23,279] Bulk modification with silanes [84] Surface modification with hydrophobic initiators [83] Polymer complex [177] Interfacial mineralization [70] Swellable microneedles [280] N/A N/A Nanoparticle solution [15,78] Cyanoacrylate [87,125] Bridging polymers [5] Topological adhesion [85,168] Nanoparticle solution [77] Cyanoacrylate [71] Topological adhesion and covalent interlink [86,168] Polymer complex [177] Cyanoacrylate [71] Topological adhesion and covalent interlink [86,168] a) N/A stands for Not Available.…”

Ultrafast self-gelling powder mediates robust wet adhesion to promote healing of gastrointestinal perforations

“…In addition, chemically cross-linked PAA gel powder can also adhere two PAAm hydrogels together by absorbing interfacial water and forming weak noncovalent bonds with the surface of the PAAm hydrogels. However, PAA gel powder cannot re-form a complete bulk gel upon hydration, and the resultant adhesion could be hampered by the weak matrix cohesion and limited mobility of the chemically cross-linked bulk PAA network ( 53 ).…”