Date:12 May 2014
Imagine watching your car’s mangled bumper heal itself within minutes of an accident, then casually driving home knowing you needn’t hassle your insurance company for a costly repair. As unlikely as this scenario sounds, if researchers at the University of Illinois get their way, this present day science fiction could soon become science fact.
While self-repairing plastics have been around for some time, to date their drawback has been that they can only handle microscopic cracks. Anything bigger (think gashes or puncture holes), and there’s either not enough available resin to complete the job, or the resin just bleeds out without sealing the void.
What the University of Illinois’ multidisciplinary team, led by Prof Scott White, has achieved is truly remarkable – they’ve managed to demonstrate a new class of regenerative material that boasts the ability to fill large cracks and holes by regrowing material.
These regenerating capabilities build on the team’s previous work on developing artificial vascular materials. Using specially formulated fibres that disintegrate, they have discovered how to create materials with networks of capillaries inspired by biological circulatory systems.
Here’s how it works: Two adjoining, parallel capillaries are filled with regenerative chemicals that flow out when damage occurs. The two liquids then mix to form a gel, which spans the gap caused by the damage, filling in cracks and holes. After the damaged specimen has completely recovered, the gel undergoes another transition to a rigid, structural solid, completing the restoration process and returning the damaged material to its original function.
Says White: “We have to battle a lot of extrinsic factors for regeneration, including gravity. 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. And, since it’s not a structural material yet, we can continue the regrowth process by pumping more fluid into the hole.”
The team demonstrated their regenerating system on the two biggest classes of commercial plastics: thermoplastics and thermosets. The researchers can tune the chemical reactions to control the speed of the gel formation or the speed of hardening, depending on the kind of damage. For example, a bullet impact might cause a radiating series of cracks as well as a central hole, so the gel reaction could be slowed to allow the chemicals to seep into the cracks before hardening.
White and his colleagues envisage commercial plastics and polymers with vascular networks filled with regenerative agents ready to be deployed whenever damage occurs, much like biological healing. Their previous work established ease of manufacturing, so now they’re working on optimising the regenerative chemical systems for different types of materials.
“For the first time, we’ve shown we can regenerate lost material in a structural polymer. That’s the kicker here,” said White. “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.”
Source: University of Illinois