Cooking‐Inspired Versatile Design of an Ultrastrong and Tough Polysaccharide Hydrogel through Programmed Supramolecular Interactions

Abstract

The prerequisites for hydrogels in loadingbearing applications are mechanical strength and toughness. In order to simultaneously achieve both properties, several approaches, including the combination of covalent and noncovalent systems, [1] the design of a synergistic effect triggered by attractive interaction between constituents [2] and the construction of an anisotropic structure through incorporating well-ordered nanomaterials [3] have been developed. As stated above, combining the advantages of two or multiphase, particularly for the typical double-network (DN) system, [4] is significantly effective in fabricating high-performance hydrogels, as has been recently attempted by many researchers. However, the mechanical enhancement of an individual hydrogel through optimizing its internal structure has been rarely focused, despite it being extremely meaningful, particularly for those physically crosslinking hydrogels with many inactive interaction sites. Based on the Lake-Thomas model, both the quantity of polymer chain per unit surface and linkage dissociation energy influence the fracture energy. [5] In natural tissues, such as ligaments, lower water content (60-70 wt%) compared to a synthetic polymer hydrogel (≈90 wt%) imparts strong tensile strength of ≈60 MPa due to the dense gel domain. [6] Inspired by this, hydrogels treated with phase separation [7] or water dehydration [8] methods exhibit exceptional fracture resistance and load-bearing capacity similar to that of biomaterials. Nevertheless, these methods serve as postprocessing treatments, where polymer chains approach limitedly in the presence of crosslinking points and the inactive interaction sites are only partially activated. Thus, according to the mechanism of energy-dissipating sacrificial bonds, if a suitable approach can realize free polymer aggregation accompanied with maximization of supramolecular interactions (e.g., metal-ligand coordination and hydrogen bonds (H-bonds)), the mechanical parameters will further approach their theoretical values. This is the interest of the current work.To justify our hypothesis, a water-soluble natural macromolecule-sodium alginate (SA)-crosslinked with Ca 2+ Simultaneously achieving strength and toughness in soft materials remains a challenge, especially for physically crosslinked hydrogels with many inactive interaction sites. In this work, inspired by the cooking of thick soup in China, a facile method that includes free water evaporation of the diluted pregel solution followed by crosslinking (WEC) is proposed to fabricate polysaccharide hydrogels. Herein, without the constraints of viscosity and crosslinking, polymer chains can homogenously approach as much as possible, thereby enabling the transformation of inactive supramolecular interaction (H-bonding and ionic coordination) sites into active sites until reaching the maximum level. Through facilely tuning the concentrating degree, programmed supramolecular interactions, serving as energy-dissipating sacrificial bonds, impart the hydrogels with ...

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