Damaged Material, Heal Thyself

The Science

Inspired by healing wounds in skin, a new approach protects and heals surfaces using a fluid secretion process. In response to damage, dispersed liquid-storage droplets are controllably secreted. The stored liquid replenishes the surface and completes the repair of the polymer in seconds to hours.

The Impact

The fluid secretion approach to repair the material has also been demonstrated in fibers and microbeads. This bioinspired approach could be extended to create highly desired adaptive, resilient materials with possible uses in heat transfer, humidity control, slippery surfaces, and fluid delivery.

Summary

A polymer that secretes stored liquid in response to damage has been designed and created to function as a self-healing material. While human-made material systems can trigger the release of stored contents, the ability to continuously self-adjust and monitor liquid supply in these compartments is a challenge. In contrast, biological systems manage complex protection and healing functions by having individual components work in concert to initiate and self-regulate a coordinated response. Inspired by biological wound-healing, this new process, developed by researchers at Harvard University, involves trapping and dispersing liquid-storage droplets within a reversibly crosslinked polymer gel network topped with a thin liquid overlayer. This novel approach allows storage of the liquid, yet is reconfigurable to induce finely controlled secretion in response to polymer damage. When the gel was damaged by slicing, the ruptured droplets in the immediate vicinity of the damage released oil and the gel network was squeezed. This squeezing allowed oil to be pushed out from neighboring droplets and the polymer network linkages to unzip and rezip rapidly, allowing just enough oil to flow to the damaged region. Healing occurred at ambient temperature within seconds to hours as fluid was secreted into the crack, severed polymer ends diffused across the gap, and new network linkages were created. Droplet-embedded polymers repaired faster or at lower temperatures than polymers without oil droplets. Also, the repaired droplet-embedded materials were much stronger than the repaired networks that did not contain the droplets. This dynamic liquid exchange to repair the material has also been demonstrated in other forms, showing the potential to extend this bioinspired approach for fabricating highly desired adaptive, resilient materials to a wide range of polymeric structures.

Funding

This work was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences (polymer synthesis and self-healing) and the Department of Defense, Office of Naval Research (wetting and anti-fouling properties).

Publications

J. Cui, D. Daniel, A. Grinthal, K. Lin, and J. Aizenberg, “Dynamic polymer systems with self-regulated secretion for the control of surface properties and material healing.” Nature Materials 14 790 (2015). [DOI: 10.1038/nmat4325]