A pilot takes his small plane in for a hard emergency landing, but in the process he hits his head and suffers a small cut. Within seconds, his body's skin begins the task of sending blood to the cut to begin the healing process. But what if the plane suffered a small crack during the landing? And what if the plane's body immediately began to heal the crack on its surface, much like the pilot's cut?
A University of Illinois multidisciplinary team, which includes an LAS chemistry professor, has taken another step closer to this remarkable possibility. They have devised the next-generation of self-healing material that can heal itself many times over.
"In the same manner that a cut in the skin triggers blood flow to promote healing, a crack in these new materials will trigger the flow of healing agent to repair the damage," says Nancy Sottos, professor of materials science and engineering. She co-invented the material with LAS chemistry professor Jeffrey Moore, aerospace engineer Scott White, and materials science professor Jennifer Lewis.
In their earlier approach, Moore explains, the self-healing materials contained a healing agent within microcapsules. When the materials cracked, the microcapsules would rupture and release the healing agent, which reacted with an embedded catalyst to repair the damage. The problem was that repeated damage in the same location would quickly exhaust the healing agent.
Therefore, the team has devised a microvascular network that acts much like the body's circulatory system. In this case, if a crack occurs in the coating, the crack will propagate through the coating until it encounters one of the fluid-filled "capillaries." Healing agent then moves from the capillary into the crack, where it interacts with catalyst particles and repairs the material.
If the crack reopens under additional stress, Moore says, the healing cycle is repeated.
In the new circulation-based approach, there is a continuous supply of healing agent, but only for so long. The healing process stops after seven healing cycles. However, they are investigating alternatives that could lead to unlimited healing capability. They also hope to improve the system to mend deeper cracks.
"Currently, the material can heal cracks in the epoxy coating—analogous to small cuts in skin," Sottos adds. "The next step is to extend the design to where the network can heal ‘lacerations' that extend into the material's substrate."
