Abstract
Biology offers a valuable inspiration toward the development of self-healing engineering composites and polymers. In particular, chemical level design principles extracted from proteinaceous biopolymers, especially the mussel byssus, provide inspiration for design of autonomous and intrinsic healing in synthetic polymers. The mussel byssus is an acellular tissue comprised of extremely tough protein-based fibers, produced by mussels to secure attachment on rocky surfaces. Threads exhibit self-healing response following an apparent plastic yield event, recovering initial material properties in a time-dependent fashion. Recent biochemical analysis of the structure–function relationships defining this response reveal a key role of sacrificial cross-links based on metal coordination bonds between Zn2+ ions and histidine amino acid residues. Inspired by this example, many research groups have developed self-healing polymeric materials based on histidine (imidazole)–metal chemistry. In this review, we provide a detailed overview of the current understanding of the self-healing mechanism in byssal threads, and an overview of the current state of the art in histidine- and imidazole-based synthetic polymers.
Highlights
The Role of Histidine–Metal Coordination in Self-Healing Behaviors of Biopolymeric Materials1.1
The most prominent example of bioinspired self-healing from an acellular biopolymeric source is the use of metal coordination cross-linking as a dynamic and reversible sacrificial bond, which breaks and reforms on time scales relevant to the material function [4,11]
Several prominent examples, including the mussel byssus, harness metal coordination cross‐links as strong, yet reversible sacrificial bonds that can contribute to material toughness and a capacity for self‐healing [4,11]
Summary
The functional lifetime and efficacy of materials is limited by the onset of damage, whether they are composites comprising aircraft and automobiles, concretes comprising bridges and buildings or polymeric materials comprising device components. Self-healing describes the capacity of a material to actively repair damage, and it is becoming a critical design feature with the potential for extending the functional lifetime of polymers, composites, metals and concretes and for allowing materials to function near their theoretical optimum since they no longer need to be overdesigned [1,2,3]. Material damage ranges from fatigue microcracking, plastic yield, and outright fracture, which all require different sorts of healing response [1]. It is challenging to achieve this inherent dynamicity and maintain material performance relevant for real-world applications In light of these challenges, researchers have looked to nature for material design inspiration based on the capacity of living organisms and natural materials to heal damage
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