Rapid self-healing hydrogels

Abstract

Synthetic materials that are capable of autonomous healing upon damage are being developed at a rapid pace because of their many potential applications. Despite these advancements, achieving selfhealing in permanently cross-linked hydrogels has remained elusive because of the presence of water and irreversible cross-links. Here, we demonstrate that permanently cross-linked hydrogels can be engineered to exhibit self-healing in an aqueous environment. We achieve this feature by arming the hydrogel network with flexible-pendant side chains carrying an optimal balance of hydrophilic and hydrophobic moieties that allows the side chains to mediate hydrogen bonds across the hydrogel interfaces with minimal steric hindrance and hydrophobic collapse. The self-healing reported here is rapid, occurring within seconds of the insertion of a crack into the hydrogel or juxtaposition of two separate hydrogel pieces. The healing is reversible and can be switched on and off via changes in pH, allowing external control over the healing process. Moreover, the hydrogels can sustain multiple cycles of healing and separation without compromising their mechanical properties and healing kinetics. Beyond revealing how secondary interactions could be harnessed to introduce new functions to chemically crosslinked polymeric systems, we also demonstrate various potential applications of such easy-to-synthesize, smart, self-healing hydrogels.biomimetic materials | hydrophobicity | smart materials | molecular dynamics | adhesives R ecent years have witnessed an increasing interest in the development of "smart" materials that can sense changes in their environment and can accordingly adapt their properties and function, similar to living systems. Over the last decade, we have discovered and demonstrated a class of smart hydrogels that exhibit unique biomimicking functions: thermoresponsive volume phase transitions similar to sea cucumbers (1), self-organization into core-shell hollow structures similar to coconuts (2), shape memory as exhibited by living organisms (2), and metal ion-mediated cementing similar to marine mussels (3). A common thread connecting these smart hydrogels is their possession of a unique balance of hydrophilic and hydrophobic interactions that endows the hydrogels with the biomimicking properties described above. In this study, we demonstrate how this concept of balancing hydrophilic and hydrophobic forces could be exploited to design chemically cross-linked hydrogels with self-healing abilities.Indeed, materials capable of autonomous healing upon damage have numerous potential applications (4-6). So far, self-healing has been demonstrated in linear polymers (7), supramolecular networks (8, 9), dendrimer-clay systems (10), metal ion-polymer systems (11,12), and multicomponent systems (13-17). Whereas multicomponent thermosetting systems harness the ability of embedded chemical agents to repair cracks, supramolecular networks and noncovalent hydrogels employ secondary interactions such as hydrogen bonding, ionic interact...

Self-Healing and Damage Resilience for Soft Robotics: A Review

“…This diffusion-limited process has been used repeatedly in soft robots as a potential actuation method (Gerlach and Arndt, 2009;Richter, 2009;Kim et al, 2013). Self-healing hydrogels are their own field of research for materials scientists, as can be seen in recent reviews (Phadke et al, 2012;Taylor and Marc in het Panhuis, 2016). Yet, despite this field of research, hydrogel self-healing has yet to enter the soft robotics community, so this section is mostly forward-looking based on presently developed systems.…”

Smart and green interfaces: From single bubbles/drops to industrial environmental and biomedical applications

“…Over the last decades, a class of smart hydrogels exhibiting unique biomimicking functions was discovered and demonstrated by the authors of [94] -thermoresponsible volume phase transitions similar to sea cucumbers, self-organization into core-shell hollow structures similar to coconuts, shape memory as exhibited by living organisms, and metal ion-mediated cementing similar to marine mussels. It was demonstrated how the concept of balancing hydrophilic and hydrophobic forces could be exploited for designing chemically cross-linked hydrogels with self-healing properties.…”

Supramolecular Nested Microbeads as Building Blocks for Macroscopic Self‐Healing Scaffolds

“…The construction of self‐healing materials has been driven by developments in materials science and biotechnology with a view to environmental sustainability 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11. To develop maintenance‐free self‐healing structures, the ideal materials should be liquid‐like before processing and then be converted into a free‐standing solid‐like network 12, 13, 14, 15.…”