Solvent‐Free Mussel‐Inspired Adhesive with Rapid Underwater Curing Capability

Abstract

In the past two decades, mussels have inspired the design of novel adhesives that can be used underwater, since they secrete a super-strong mucus (mussel adhesion proteins, MAPs) that keeps them firmly attached to the surface of the reef beneath the sea, braving wind, and waves. [3] Structure-function relationship studies on MAPs have disclosed the sophisticated mechanisms for adhesion; nevertheless, the key factor is the catechol containing 3, 4-dihydroxyphenylalanine residue, and many biomimetic adhesives were designed based on this key structure. [4] This work can be traced back to Messersmith's first publication for reversible wet/ dry adhesives using catechol-containing poly(acrylamide-acrylate) coated nanofabricated polymer pillars. [5] After that, the design of mussel-inspired adhesives is under fast growth, and many polymers conjugated with catechol moieties have been reported. Most of them were focused on the bio-adhesives that can be used in dry and humid environments, and some of them even exceeded the adhesive properties of natural mussels. [6] In contrast, the studies on the mussel-inspired adhesives that can be directly used in underwater conditions are lagged behind, and only handful of cases have been reported. For instance, Joy et al. synthesized a mussel-inspired self-coacervating polyester, which showing rapidly adhere to substrates submerged underwater and exhibiting an adhesion strength of ≈100 kPa when cured under UV-A irradiation for 10 min under underwater conditions. [7] Zhou et al. synthesized poly(dopamine-alt-2,2-bis-(4-glycidyloxyphenyl) propane) via epoxy-amino click chemistry, which exhibited a bonding strength up to 1.1 MPa on glass substrates at an underseawater condition after curing in artificial seawater at room temperature for a week. [8] Liu et al. reported a hyperbranched polymer with a hydrophobic backbone and hydrophilic adhesive catechol side branches, which exhibited a bonding strength up to 0.4 MPa on iron sheets after curing in water for 12 h. [9] More recently, poly(catechol-styrene) developed by Wilker's group displayed underwater bonding up to 3.1 MPa when curd at room temperature for 24 h. [10] We also showed that when catechol was grafted onto polyvinylpyrrolidone, the resulting polymer showed an underwater bonding strength at 1.1 MPa at the same curing time. [11] These reported adhesives generally take a long time to reach the best underwater bonding strength but only exhibit relatively low bonding strength in a short curing time, How to realize fast and strong underwater adhesion has gained much attention recently. Although some mussel-inspired adhesives that can be cured underwater have been reported, reports on underwater adhesion with both high bonding strength and rapid curing capability are still rare. Furthermore, organic solvents are generally utilized in these adhesives, which are ecounfriendly. Here, by taking advantages of the strong underwater adhesion capability of catecholic groups in mussel adhesion proteins (MAPs) and the fast curing capability of...

Hydrogels for underwater adhesion: adhesion mechanism, design strategies and applications

“…In the eld of underwater adhesion of hydrogels, the hydration layer is considered as a water lm between the hydrogel and the adherend, which seriously hinders the adhesion of the hydrogel to the adherend. [29][30][31][32][33] Therefore, removing the hydration layer is the rst step in underwater adhesion. In this section, two hydration layer removal methods are introduced and a concise overview of the research progress of interfacial water removal is given.…”

“…Meanwhile, the bidentate hydrogen bond formed by the catechol group and pp interaction are stronger than those of water to achieve strong adhesion. 33,129 Due to the polyurethane group's ability to generate a strong hydrogen domain, the negative effect of improving the dispersion of water molecules is improved. 130 Jia et al brought in a polyurethane structure to help the adhesive eliminate interface water resistance and enhance adhesion.…”

“…Adhesives are widely used in modern society, but with the development of environmental engineering and industrial engineering, underwater adhesives have become indispensable and important materials. 86,136 Because water will affect the internal cross-linking of the gel during underwater adhesion, 33,137 and the hydration layer will destroy the interaction between the hydrogel and the substrate surface, inuence of adhesive adhesion. 32,[138][139][140] Due to the hydrophilicity of traditional adhesives, they only maintain weak adhesion underwater, and even lose adhesion.…”

“…Xia et al proposed a simple and powerful strategy for rapid curing of mussel underwater adhesives by exploiting the strong underwater adhesion of catechol groups in mussel adhesion proteins (MAPs) and the fast curing ability of polyurethane (PU) prepolymers. 33 They prepared a mussel PU prepolymer consisting of isocyanate-terminated polypropylene glycol (PPG) and isocyanate-terminated dopamine bis(hydroxymethyl)propane (DBHP). When it is applied for underwater bonding, the isocyanate group can react with water at the interface to form a polymer structure.…”

Hot Melt Super Glue: Multi‐Recyclable Polyphenol‐Based Supramolecular Adhesives

“…[ 10 ] Different polymers, including polyethylenimine, chitosan, poly(vinyl alcohol), and DNA have been used for the preparation of phenolic polymer hydrogels. [ 11 ] Covalent cross‐linking of polymers [ 12 ] and/or the addition of inorganic nanoparticles (e.g., TiO 2 and SiO 2 nanoparticles) can significantly increase the adhesion strength of hydrogels while it requires long curing time. [ 11c ] PEG, as one of the most common and biocompatible polymers applied in various fields (e.g., biomedical applications), has been widely used for biomedical applications.…”