Mechanisms and applications of bioinspired underwater/wet adhesives

Abstract

In nature, many organisms can effectively fix to contact substrates and move and prey in complex living environments, such as underwater, seawater, and tidal environments, owing to special secreted chemical components and/or special micro/nanostructures on the adhesive surface of these organisms.Inspired by the adhesive performance of organisms, extensive research related to adhesive components and adhesive surfaces has been conducted recently.To better understand the underlying adhesive mechanisms and facilitate further continuous inspiration, a brief overview of recent wet/underwater adhesive materials is provided herein. First, the adhesive processes and underlying mechanisms of commonly researched organisms, such as mussels, octopuses, clingfish, and tree frogs, are discussed, and the corresponding bioinspired artificial adhesives are presented. Then, the applications of these bioinspired adhesives, such as intelligent robots (signal monitoring and sensing devices), wearable devices (including wet climbing and electronic skin), biomedicines (including wound dressings, bone adhesion, and rapid hemostasis), are presented and summarized. Finally, we offer our perspective on the future challenges and development of bioinspired artificial adhesives. K E Y W O R D S adhesive surfaces, applications, artificial components, natural organisms 1 | INTRODUCTION Recently, the development of wet/underwater adhesives inspired by natural organisms has attracted increasing attention and achieved significant progress based on various Chao Cai and Zhen Chen contributed equally to this work

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

“…However, using covalent bonds for underwater adhesion oen relies on specic adherend surfaces or requires surface modication. 48,49 The underwater adhesion of hydrogels to biological tissues is usually achieved by covalent bonds. [50][51][52] Biological tissue surfaces have nucleophiles, including amines, thiol, and hydroxyl groups, and catechol groups (including o-quinone groups) in hydrogels can form covalent bonds with nucleophiles on tissue surfaces, thereby adhering to biological tissue (Fig.…”

“…Water molecules can form a hydration layer on the hydrogel surface or penetrate into the internal network of the hydrogel, leading to the detachment of the adhesive layer and the hydrolysis of the hydrogel polymer network. 49 In the adhesion mechanism, we summarized in detail the methods for removing the hydration layer. Among them, at the molecular level, hydrophobic interactions are constructed by introducing hydrophobic monomers or solvents 1,34,104 to provide a basis for underwater adhesion (Section 2.1.1).…”

Paper‐Structure Inspired Multiresponsive Hydrogels with Solvent‐Induced Reversible Information Recording, Self‐Encryption, and Multidecryption

“…[16,17] Recently, stimulus-responsive hydrogels, that can undergo reversible volume or color changes upon triggering via external stimuli, such as pH, temperature, light, magnetic fields, and ionic concentrations, have attracted tremendous attention. [18][19][20][21][22] The adequate molecular and structural designs and directly responsive behaviors of these materials make them ideal candidates for generating multifunctional information-handling models. [23,24] For example, Chen et al [25] designed a fluorescent hydrogel via an ionoprinting technique by introducing Fe 3+ ions, inducing the fluorescence quenching of pyrene groups in the hydrogel matrix, and exhibiting the ability to record information under UV light.…”

Underwater luminescent labeling materials constructed from a supramolecular approach

“…Tough and long-lasting labeling in aqueous environments has two main requisites: (a) strong and long-term adhesion to surfaces in aqueous media; (b) remaining legible, readily identifiable, and easily distinguishable throughout the labeling period. [1][2][3][4][5] Hydrogel and coacervate adhesives have been used in underwater adhesion over the past decade. [6][7][8][9] Unfortunately, longterm adhesion is frequently accompanied by the swelling behavior of polymers, resulting in the deformation of the adhesion layers and/or weakened adhesion effects.…”