Plastic hit by bullet regrows after getting hit

Self-healing materials are a bit of a holy grail at the moment, and several have been developed that can fix small cuts and hairline fractures, but this latest development appears to advance the technology by a major leap. Researchers at the University of Illinois have invented a type of plastic that not only heals fractures, but can regenerate over large cracks and holes.

"We have demonstrated repair of a nonliving, synthetic materials system in a way that is reminiscent of repair-by-regrowth as seen in some living systems," explained chemistry professor Jeffry Moore, who worked on the research team under aerospace engineering professor Scott White.

This could be useful not just in day-to-day life -- think a self-healing car bumper -- but in areas where repairs are particularly difficult, like space.

The team used something called "vascular delivery", a technology it has been developing for some years that is based on veins. Liquid materials circulated within the material perform various tasks.

In this case, the liquid materials are two chemicals that flow into the gaps created by damage via parallel capillaries. These chemicals, inspired by the way blood coagulates in the open air, mix in the spaces to form a gel, which hardens into a strong polymer. This restores the plastic's structural integrity.

"We have to battle a lot of extrinsic factors for regeneration, including gravity," Professor White said. "The reactive liquids we use form a gel fairly quickly, so that as it's released it starts to harden immediately. If it didn't, the liquids would just pour out of the damaged area and you'd essentially bleed out. Because it forms a gel, it supports and retains the fluids. Since it's not a structural material yet, we can continue the regrowth process by pumping more fluid into the hole."

The technology has been tested on both thermoplastics and thermosets, and has been demonstrated to regenerate a hole created by a nine-millimetre bullet. In the experiments performed by the researchers, the chemicals were fed into the plastic, but the team envisions material pre-filled with the chemicals that can self-regenerate as needed.

"For the first time, we've shown that you can regenerate lost material in a structural polymer. That's the kicker here," Professor White said. "Prior to this work, if you cut off a piece of material, it's gone. Now we've shown that the material can actually regrow."

The full study, "Restoration of Large Damage Volumes in Polymers", can be read online in Science Magazine.