New materials that not only self-repair but also regenerate like living tissue have been created by researchers in the USA.
Until now self-repairing materials could only bond tiny microscopic cracks, but the new materials developed by scientists at the University of Illinois can fill in large cracks and holes by re-growing material.
Such self-repair capabilities could be used in a host of commercial goods – for instance car bumpers that can repair themselves within minutes of an accident – but also for parts and products that are difficult to replace or repair, such as those used in aerospace applications.
“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 chemistry professor Jeffry S. Moore who was part of the research team.
The regenerating capabilities, reported in a paper in today’s issue of journal Science, build on the team’s previous work in developing vascular materials with networks of capillaries inspired by biological circulatory systems.
“Vascular delivery lets us deliver a large volume of healing agents – which, in turn, enables restoration of large damage zones,” said Nancy Sottos, a professor of materials science and engineering. “The vascular approach also enables multiple restorations if the material is damaged more than once.”
For regenerating materials, two adjoining, parallel capillaries are filled with regenerative chemicals that flow out when damage occurs. These two liquids mix to form a gel, which spans the gap caused by damage, filling in cracks and holes before the gel hardens into a strong polymer, restoring the plastic’s mechanical strength.
“We have to battle a lot of extrinsic factors for regeneration, including gravity,” said study leader Scott White, a professor of aerospace engineering. “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 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 the 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.
The researchers envision 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 are working to optimize the regenerative chemical systems for different types of materials.
“For the first time, we’ve shown that you can regenerate lost material in a structural polymer. That’s the kicker here,” 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.”