Robust Electrostatically Interactive Hydrogel Coatings for Macroscopic Supramolecular Assembly via Rapid Wet Adhesion

Abstract

A macroscopic supramolecular assembly (MSA) refers to non-covalent interactions between building blocks over a micrometer scale, which provides insights into bio-/wet adhesion, self-healing, and so on and new fabrication strategies to heterogeneous structures and bio-scaffolds. The key to realize the MSA of rigid materials is pre-modifying a compliant coating known as a "flexible spacing coating" beneath the interactive moieties. However, available coatings are limited to polyelectrolyte multilayers with shortcomings of tedious fabrication, weak adhesion to substrates, susceptibility to external reagents, and so on. Here, we develop a facile method to induce a new "flexible spacing coating" of a poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogel with electrostatic interactions to achieve MSA of diverse rigid materials (quartz, metal, rubber, and plastics). Selective self-assembly of positive−negative charged surfaces is observed by the naked eye under 3 min of shaking in water, providing strategies to rapid wet adhesion. The interfacial binding force between positive−negative interacted surfaces is 1018.1 ± 299.2 N/m 2 , which is over two magnitudes larger than that of control groups, that is, positive−positive (24.4 ± 10.0 N/m 2 ) and negative−negative (67.5 ± 16.7 N/m 2 ) interacted surfaces. In situ force measurements and control experiments of identically charged building blocks have strongly supported the improved binding strength and chemical selectivity between interactive building blocks. The coating is advantageous with a simple fabrication, strong adhesion to materials, robust solvent tolerance to assembly solutions, and feasibility of photo-patterning. We envision that the above strategy would broaden the material choices of flexible spacing coatings for efficient MSA and new methods for rapid interfacial adhesion.

Reversible Assembly of Conductive Supragel Building Blocks by Metallo‐Complexes

“…Here, chemical crosslinking based on the formation of covalent bonds between two hydrogels [ 12–14 ] or physical crosslinking based on physical interactions, such as electrostatic interactions, [ 15 ] still remain the most common method of choice. Various strategies of inter‐crosslinking have been proposed, [ 11,16–30 ] they often require complex chemical modification of the precursors or gels, [ 20 ] lack stability, [ 21 ] have high costs of the reagents, [ 22,23 ] or significant modification time, [ 24 ] thereby restricting the supragels' broader applicability. As we believe that control over the information flow within supragels is crucial to unlock their full potential as smart materials, our goal is to apply an inter‐crosslinking method enabling efficient reversible inter‐crosslinking of hydrogel building blocks, that does not require complex chemical modifications of the initial components or the final hydrogel, and ensures high stability as well as the implementation of additional functionality, e.g., conductivity across building blocks.…”

A Microwave-Responsive Supramolecular Adhesive for Strong Adhesion of Thermolabile Substrates

“…Stimuli-responsive adhesives that can controllably debond and rebond have gained rapidly growing interest owing to their great potentials in biomedical engineering, microelectronics, and manufacturing industries. − Recently, various types of stimuli-responsive adhesives that respond to different stimuli, such as temperature, light, electricity, and chemicals, have been developed. − For example, hot melt adhesives can be easily debonded by heating substrates to their melting temperature, meaning that sufficient thermal conductivity and stability are required for substrates. − Besides, light and electrical stimulus can be applied to debond adhesives when substrates have good transparency and conductivity, respectively. − However, we notice that some kinds of substrates such as plastics are sensitive to high temperature and organic solvents and inert to stimuli like light and electricity, making them not applicable to conventional stimuli-responsive adhesives. Therefore, developing new types of stimuli-responsive adhesives that can stably adhere to thermolabile plastic substrates is of great significance.…”