Barnacle Cement Proteins‐Inspired Tough Hydrogels with Robust, Long‐Lasting, and Repeatable Underwater Adhesion

Abstract

The development of adhesives that can achieve robust and repeatable adhesion to various surfaces underwater is promising; however, this remains a major challenge primarily because the surface hydration layer weakens the interfacial molecular interactions. Herein, a strategy is proposed to develop tough hydrogels that are robust, reusable, and long‐lasting for underwater adhesion. Hydrogels from cationic and aromatic monomers with an aromatic‐rich composition inspired by the amino acid residuals in barnacle cement proteins are synthesized. The hydrogels are mechanically strong and tough (elastic modulus 0.35 MPa, fracture stress 1.0 MPa, and fracture strain 720%), owing to the interchain π–π and cation–π interactions. In water, the hydrogels firmly adhere to diverse surfaces through interfacial electrostatic and hydrophobic interactions (adhesion strength of 180 kPa), which allows for instant adhesion and reversibility (50 times). Moreover, the hydrogel shows long‐lasting adhesion in water for months (100 days). Novel adhesive hydrogels may be useful in many applications, including underwater transfer, water‐based devices, underwater repair, and underwater soft robots.

Facile tuning of hydrogel properties by manipulating cationic-aromatic monomer sequences

“…The monomer sequence also had a strong impact on the underwater adhesion of the hydrogels (Figure 9). The tack test shows that P(cation-adj-π) hydrogels exhibit strong adhesion to negatively charged glass in saltwater (0.7 M NaCl) because the aromatic groups can enhance the electrostatic interactions of their adjacent cationic residues with the counter surfaces in high ionic media [15,22]. In contrast, the P(cation-co-π) hydrogels, which lack adjacent cationic-aromatic sequences, exhibit weak adhesion on the glass substrate in saltwater.…”

Environmentally Compatible Wearable Electronics Based on Ionically Conductive Organohydrogels for Health Monitoring with Thermal Compatibility, Anti‐Dehydration, and Underwater Adhesion

“…Furthermore, in wet environment, the interfacial adhesion may be weakened by the occurrence of water at the device–skin interface, leading to potential device delamination and further inferior reliability of the acquired data. [ 13,14 ] Therefore, it is highly desirable to develop environmentally compatible hydrogel electronics owning thermal compatibility (capability at subzero and elevated temperatures) and hydration compatibility (capability at dehydrated and hydrated environments) for extended applications.…”

Contact Friction Regulation of the UV Laser Textured PVA Hydrogel and Titanium Alloy Interface

“…The strong adhesion and super-slip surface properties of hydrogels have attracted great interest of research. According to Hailong Fan et al [14], a novel hydrogel for instant adhesion and reversibility (50 times) with strong adhesion strength (180 kPa), hydrophobic, positively charged in water is designed and synthesized by cationic and aromatic monomers, which can firmly adhere to diverse surfaces through interfacial electrostatic and hydrophobic interactions.…”