Materials that can heal themselves, and even self-regenerate have been developed by a team of researchers at University of Illinois at Urbana-Champaign. Previous self-repairing materials were only able to bond tiny microscopic cracks, but these regenerating materials fill in large cracks and holes through the regrowth of material.
“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.
Self-repair abilities such as this would be of benefit for commercial products. One example is a cracked car windshield that repairs itself within minutes of an accident. Difficult to replace or repair parts and products would also benefit, like [easyazon_link asin=”0750691697″ locale=”US” new_window=”default” nofollow=”default” tag=”sharonfilms-20″ add_to_cart=”default” cloaking=”default” localization=”default” popups=”default”]carbon fiber composite[/easyazon_link] skins used in aerospace.
The regenerating properties are based on the team’s earlier work developing vascular materials. Employing specially designed fibers that disintegrate, the researchers can form 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 team member Nancy Sottos. “The vascular approach also enables multiple restorations if the material is damaged more than once.”
How large is a “large damage zone”? According to the study’s abstract:
“Through the control of reaction kinetics and vascular delivery rate, we filled impacted regions that exceed 35 mm in diameter within 20 min and restored mechanical function within 3 hours. After restoration of impact damage, 62% of the total absorbed energy was recovered in comparison with that in initial impact tests.”
In the regenerating materials, two adjoining, parallel capillaries are filled with regenerative chemicals that flow out when damage occurs. The two liquids mix to form a gel, which spans the gap caused by damage, filling in cracks and holes. Afterwards, 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 lead 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 re-growth process by pumping more fluid into the hole.”
Thermoplastics and Thermosets
Thermoplastics and thermosets, the two biggest classes of commercial plastics were the materials the team demonstrated their regeneration system on. They are able to 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 instance, 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.
Although the possibilities are exciting, to call these materials self-regenerating seems a bit of a stretch. They are closer to pre-generated, as the materials must always carry their repair materials with them. It is not clear if this technology would scale up to be commercial and large scale usage, either. Any use would have to take into consideration weight added by the vascular structure and fluid.
S. R. White, J. S. Moore, N. R. Sottos, B. P. Krull, W. A. Santa Cruz, R. C. R. Gergely.
Restoration of Large Damage Volumes in Polymers.
Science, 2014; 344 (6184): 620 DOI: 10.1126/science.1251135