A Highly Stretchable, Tough, Fast Self-Healing Hydrogel Based on Peptide⁻Metal Ion Coordination.

Liang Zeng,Yi Cao,Mingming Song,Bin Xue,Jie Gu,Zhengyu Xu,Ying Li

doi:10.3390/biomimetics4020036

Abstract

Metal coordination bonds are widely used as the dynamic cross-linkers to construct self-healing hydrogels. However, it remains challenging to independently improve the toughness of metal coordinated hydrogels without affecting the stretchability and self-healing properties, as all these features are directly correlated with the dynamic properties of the same metal coordination bonds. In this work, using histidine–Zn2+ binding as an example, we show that the coordination number (the number of binding sites in each cross-linking ligand) is an important parameter for the mechanical strength of the hydrogels. By increasing the coordination number of the binding site, the mechanical strength of the hydrogels can be greatly improved without sacrificing the stretchability and self-healing properties. By adjusting the peptide and Zn2+ concentrations, the hydrogels can achieve a set of demanding mechanical features, including the Young’s modulus of 7–123 kPa, fracture strain of 434–781%, toughness of 630–1350 kJ m−3, and self-healing time of ~1 h. We anticipate the engineered hydrogels can find broad applications in a variety of biomedical fields. Moreover, the concept of improving the mechanical strength of metal coordinated hydrogels by tuning the coordination number may inspire the design of other dynamically cross-linked hydrogels with further improved mechanical performance.

Highlights

Self-healing hydrogels have received considerable attention in recent years due to their diverse biomedical applications, such as wound dressing, soft tissue medical adhesives, injectable drug carriers, and self-supporting 3D printing inks [1,2,3,4,5,6,7,8]
Here we report on the construction of highly stretchable, tough and fast self-healing hydrogels cross-linked by peptide–metal ion coordination sites with high coordination number
Metal coordination bonds have been extensively used as reversible dynamic for for engineering self-healing hydrogels, a major challenge is that the resulting hydrogels havebonds limited engineering self-healing hydrogels, a major challengeare is essential that the for resulting hydrogelsapplications, have limited mechanical strength

Summary

Introduction

Self-healing hydrogels have received considerable attention in recent years due to their diverse biomedical applications, such as wound dressing, soft tissue medical adhesives, injectable drug carriers, and self-supporting 3D printing inks [1,2,3,4,5,6,7,8]. Dynamic covalent cross-linkers include boronate ester bonds [9,10,11,12,13,14], imine bonds [15,16], acylhydrazone bonds [17,18], and oxime bonds [19], etc. These bonds are chemically labile under physiological conditions. Despite that the hydrogels cross-linked by dynamic covalent cross-linkers possess high mechanical stability, they self-heal slowly, as typical dynamic covalent bonds show very slow exchange dynamics. Physical cross-linkers, including hydrophobic effects [20,21,22,23], hydrogen bonding [24,25,26,27,28,29], host–guest

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Discussion

Conclusion