Engineering tough, energy-dissipating soft materials via sacrificial chemical bonds

Impact-resistant materials such as Kevlar provide impact protection but lack flexibility and processability due to their highly crystalline, rigid structures. In contrast, the natural world is replete with examples of soft materials that can resist applied load. For example, sea cucumbers and other echinoderms modulate the stiffness of their outer skin in response to predators. This dynamic change in mechanical properties is regulated by transient, non-covalent interactions between the collagenic protein fibers that comprise the dermis. Upon the application of force, these transient interactions break, thereby acting as sacrificial bonds and providing a means of energy dissipation without damaging the protein fibers. This mechanism has been mimicked in synthetic materials, typically based on covalent polymers augmented with non-covalent bonding motifs. In this review, we survey the current state-of-the-art in the field of energy-dissipating soft materials. Specifically, we present recent (post-2017) highlights from the primary literature, organized by the chemical nature of the weak sacrificial bonds to outline the chemical toolkit available for programming material properties. We conclude by highlighting some opportunities to advance the development of soft yet tough energy-dissipating materials that harness the sacrificial bond.