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April 7, 2013

Self Healing Plastic

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  Beckman Institute – Autonomous Materials Systems

University of Illinois - Autonomic Healing Research

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Even high tech machines like the space shuttle need the occasional repair. But what if materials like plastics could repair themselves? As this ScienCentral News video reports, scientists are doing just that by imitating how our bodies work to heal small wounds.

Stuff, Heal Thyself

Cuts and scrapes on our skin usually heal quickly. Skin has a remarkable ability to repair itself after injuries in a small amount of time. Materials researcher and doctoral student Kathleen Toohey is impressed not only by the speed, but also the reliability.

"With minor damage, if you cut the same spot again, the same thing will occur and it will heal that same damage over and over and over, due to the vascular system in the tissue," Toohey says.
That's what Toohey is trying to imitate in plastic, making it heal itself again and again.
Toohey is a member of a team of researchers at the University of Illinois' Beckman Institute working to develop these self-healing materials.

As she reported in the journal Nature Materials, her research team gave a plastic bar a kind of circulatory system. They did this by pouring a polymer, or liquid plastic, around a solid framework, letting the liquid polymer/plastic solidify, then removing the solid framework. They were left with a small plastic beam with a network of hollow tubes.

They injected a healing agent into the network system, so that it would be available to repair any damage. When they bent the bar and cracked its brittle surface, the healing agent in the system rushed into the crack. The agent mixed with a chemical catalyst spread throughout the brittle surface layer, and hardened. The crack was then healed over completely, good as new.

Previous kinds of self-healing materials have mastered this technique of repairing minor damage, but like skin, Toohey's variation also has the advantage of reliability."And the nice thing about this microvascular network is when you reload that beam and crack it again, that same crack will reopen and more fluid will flow from the network into the crack and the same crack can heal multiple times," she says.

Toohey's study showed that her microvascular network can sustain up to seven healing cycles, six more than in any previous experiments with self-healing materials. She says the only reason her lab was unable to get past the maximum of seven was that, similar to human skin, self-healing plastics develop scar tissue.

After a number of bouts of healing and cracking, it becomes more and more difficult for the liquid healing agent to reach the catalyst in the surface layer. Solid pieces of the healing agent left over from previous cycles eventually clog up the cracks and prevent further healing.
Toohey hopes to improve upon these results by altering her approach to bypass the problem of scarring.

She thinks that by using two separate microvascular networks, one filled with the healing agent, and one with the catalyst, the creation of scars won't be an issue.

"So there's no need to be concerned with this scar tissue that may build up in the previous system, because now both components are fluids, and so they can be continuously supplied repeatedly, " Toohey says.

Internal structure of "circulatory system"
Toohey is currently finishing up her research on this new and improved network, and says the results look promising. The researchers hope that self-healing materials will soon be used in a variety of industrial and commercial applications. After all, as Toohey points out, plastic products are everywhere in our daily lives.

"Anything from your cell phone to the outside of your TV, parts of your car are plastic, there are many different kinds and they all crack," she laughs.
Although the cost of using self-healing plastics in these everyday items is too high right now, she says there are some practical applications where the benefit of self-healing plastics outweigh the cost of using them, for example, in microelectronic systems.
Microchips are mostly plastic, and like all plastics, they can develop small cracks and injuries that seriously impact their functioning. In some environments, like on spacecraft, this can mean life or death for the people that rely upon their continued functioning.

Toohey and her fellow researchers say that by installing microelectronics systems that heal themselves in the next generation of spacecraft, we could be ensuring the prolonged usefulness and durability of those ships far beyond what was possible before. These self-healing chips might also cut down on the number of dangerous spacewalks and repair missions currently necessary to keep spacecraft in working order.

This research was published in the June 2007 issue of Nature Materials and was funded by the Air Force Office of Scientific Research.

       email to a friend by Christopher Bergendorff

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