Left to right: Before...after, with damaged red welt...and after, with no welt.
It sounds like something out of a Grade Z sci-fi flick, but a new genre of plastics that mimic the human skin’s ability to heal scratches and cuts might just allow for self-repairing surfaces on some of the world’s most commonly damaged consumer goods.
Developed by researchers at the University of Southern Mississippi, and presented at an annual meeting of the American Chemical Society in March, in San Diego, Calif., the plastic is made from water-based copolymers, and turns red when damaged and can self-heal with little more than exposure to light.
“Mother Nature has endowed all kinds of biological systems with the ability to repair themselves,” said lead researcher and professor Marek W. Urban, who reported on the research. “Some we can see, like the skin healing and new bark forming in cuts on a tree trunk. Some are invisible, but help keep us alive and healthy, like the self-repair system that DNA uses to fix genetic damage to genes. Our new plastic tries to mimic nature, issuing a red signal when damaged and then renewing itself when exposed to visible light, temperature or pH changes.”
Urban foresees a wide range of potential applications for plastic with warn-and-self-repair capabilities. Scratches in cell phones, laptops, and automobile fenders, for instance, might be repaired by simply exposing the plastic to intense light. Critical structural parts in aircraft might warn of damage by turning red along cracks so that engineers could decide whether to shine the light and heal the damage or undertake a complete replacement of the component. And there could be a range of applications in battlefield weapons systems.
Designed to address the longstanding issue of what to do with scratched or cracked plastic products, there have been two main approaches to developing self-healing polymers. The first involves seeding plastics with capsules that break open when cracked or scratched and release repairing compounds that heal scratches or cuts; the second is to make plastics that respond to an outside stimulus — like light, heat or a chemical agent — by repairing themselves.
With a foot in both camps, Urban’s group developed plastics with small molecular links or “bridges” that span the length of the material. When the item is scratched or cracked, these links break and change shape, forming a red splotch around the “injury.” In the presence of ordinary sunlight or visible light from a light bulb, pH changes or temperature, the bridges reform, healing the damage and erasing the red mark.
And unlike self-healing plastics that rely on embedded healing compounds that can self-repair only once, this plastic can heal itself over and over again, Urban said. The material is also more environmentally friendly than many other plastics because it’s water-based, rather than relying on potentially toxic ingredients.
The next step? Urban and his team are now working on incorporating the technology into plastics that can withstand high temperatures.