Bioinspired Underwater Adhesives by Using the Supramolecular Toolbox

Abstract

several excellent reviews. [9][10][11][12] Recently, it was emphasized by Waite that catechol moieties alone are insufficient to ensure proper underwater adhesion and that the performance is a complex interplay between DOPA and its local environment. [13] Therefore, attention is shifted to include other (noncovalent) interactions used in these natural glues, and much progress has been made in understanding both their performance and delivery process. [14] In this review, we take the sandcastle worm and mussel as a basis for inspiration. We discuss (noncovalent) interactions found in these natural adhesive systems and extend our discussion to additional supramolecular moieties that can be used to control the adhesive and cohesive performance of synthetically designed adhesives. In Section 2, we examine the natural systems and identify the versatile supramolecular interactions used in such protein-based adhesives. These include electrostatic interactions, hydrogen bonding, hydrophobic forces, π-π interactions, metal coordination, cation-π complexation, and dynamic covalent linkages. The use of these interactions in synthetic adhesive systems is explored in the subsequent sections. Section 3 is devoted to the different interactions that catechols (the functional group of DOPA) display to bond to a submerged substrate or to provide cohesive properties to the adhesive. Despite the fact that catechols have already been the topic of many excellent reviews, [9,13,17] we believe that catechols play a pivotal role in both the sandcastle worm and the mussel adhesive systems and, therefore, should not be omitted from this review. In Section 4, we discuss the use of electrostatic interactions in protein-based and synthetic adhesive formulations for wet conditions. These interactions can be tailored to a wide distribution of bond strengths and thus can be tuned to change multi ple mechanical properties, which is essential for design of an adhesive. Besides the effect on the adhesive and cohesive properties, we highlight work where electrostatic interactions cause liquid-liquid phase separation in aqueous polymer solutions. The resulting (complex) coacervate is a concentrated, liquid, yet water-insoluble phase of the adhesive material, which can act as a powerful delivery tool for underwater adhesives. Hydrogen bonding in adhesives is explored in Section 5. The use of hydrogen bonding to adjust the viscoelastic properties of adhesives has been identified decades, ago, and hydrogen bonding moieties are commonly used in pressure sensitive adhesives (PSAs). However, besides simple, single hydrogen bonding motifs, many interesting alternative Nature has developed protein-based adhesives whose underwater performance has attracted much research attention over the last few decades. The adhesive proteins are rich in catechols combined with amphiphilic and ionic features. This combination of features constitutes a supramolecular toolbox, to provide stimuli-responsive processing of the adhesive, to secure strong adhesion to a variety of...

Dynamic Interfacial Adhesion through Cucurbit[n]uril Molecular Recognition

“…[7,9,14,[32][33][34] Covalent-bond-based adhesives,such as super glue (cyanoacrylate), fibrin glue (TISSEEL, Baxter) and PEG-based adhesives (DURASEAL, Confluent Surgical), have been clinically used for tissue repair and wound dressing. [7,9,14,[32][33][34] Covalent-bond-based adhesives,such as super glue (cyanoacrylate), fibrin glue (TISSEEL, Baxter) and PEG-based adhesives (DURASEAL, Confluent Surgical), have been clinically used for tissue repair and wound dressing.…”

Self‐Hydrophobization in a Dynamic Hydrogel for Creating Nonspecific Repeatable Underwater Adhesion

“…The hydration overlayer either prevents the formation of molecular bridges between the adhesive and applied surfaces, or induces swelling stress that leads to the failure of adhesion . To overcome these challenges, underwater adhesive hydrogels based on proteins, synthetic polymers, and biomolecules (i.e., catechol derivatives), have recently been developed recently. These materials can undergo in situ gelation/crosslinking reactions at the interfaces, or form specific interactions with some functional substrates, to generate strong underwater adhesion.…”

Mussel‐inspired catechol‐based chemistry for direct construction of super‐hydrophilic and waterproof coatings on intrinsic hydrophobic surfaces

“…Many interesting methods based on catechol have been developed to modify almost all types of surfaces, and it is a universal method . Most of the reported works are coated with DA only, followed by another reaction, such as alkali treatment . Covalently grafting catechol groups to the existing polymer will greatly enhance the design and application area of surface modification …”

“…Most of the reported works are coated with DA only, followed by another reaction, such as alkali treatment . Covalently grafting catechol groups to the existing polymer will greatly enhance the design and application area of surface modification …”

“…The water can potentially weaken the interactions between polymers and surfaces. Fortunately, catechol‐functionalized polymers can enhance the surface adhesion and enable a mechanically robust coating tightly on the surface of the intrinsic hydrophobic polymers . This is of particular interest for practical applications.…”