Plastics capable of regeneration have been announced in Science. Although plastics capable of filling microscopic holes already exist, the new product restores holes a hundred times the size that has been achieved previously.. As demonstrated in this video holes the size of bullets, because the are caused by bullets, can be filled in as though they were never there.
"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," said Professor Jeffrey Moore of the University of Illinois.
The team report filling a 35mm hole in 20 minutes, with mechanical function restored in 3 hours, although the have restricted their claims of reliable performance to 9mm.
The plastic is the latest step in a series of advances from the same university. In 2011 they announced a synthetic vascular system modeled on that in animals and plants. These contain fibers that degrade after manufacturing leaving tunnels that can carry liquids to sites of damage. Earlier this year other researchers at the same lab published related work in Nature Communications. While this was designed to address much smaller cracks it has other advantages “This material is catalyst-free and low-temperature, and can be healed multiple times,” said Jianjun Cheng, one of the authors of the earlier paper.
Just as with home epoxy resins, the restoration process uses chemicals that bond to form a strong solid, delivered through parallel systems of arteries and capillaries. Any large hole will inevitably pierce both delivery systems releasing the chemicals to mix and fill the gap before hardening to something approaching the strength of the original material.
"We have to battle a lot of extrinsic factors for regeneration, including gravity," said study leader Professor Scott White. "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 speed of gel formation and hardening can be tuned to fit the most likely kind of damage a material might experience. It is important to slow the hardening process enough that materials can fill cracks or gaps before hardening.
"The vascular approach also enables multiple restorations if the material is damaged more than once,” said author Professor Nancy Sottos.
Useful as these technologies could be for extending the life of everyday materials, the prime benefit seems likely to come in cases where opportunities for repair are limited; not surprisingly the work has attracted support from the Air Force Office of Scientific Research.