Pittsburgh Engineering Team Working on Regenerating Composites

When a chair leg breaks or a mobile phone shatters, you must either repair or replace, but what if these materials could be programmed to regenerate-themselves, replenishing the damaged or missing components, extending their lifetime and reducing the need for repairs?

According to researchers at the University of Pittsburgh Swanson School of Engineering this could be very much a possibility. The team have developed computational models to design a new polymer gel that would enable complex materials to regenerate themselves. The article, “Harnessing Interfacially-Active Nanorods to Regenerate Severed Polymer Gels”, was published November 19 in the American Chemical Society journal Nano Letters.

Principal investigator is Anna C. Balazs, PhD, the Swanson School’s Distinguished Robert v. d. Luft Professor of chemical and petroleum engineering, and co-authors are Xin Yong, PhD, postdoctoral associate, who is the article’s lead author; Olga Kuksenok, PhD, research associate professor; and Krzysztof Matyjaszewski, PhD, J.C. Warner University Professor of Natural Sciences, department of chemistry at Carnegie Mellon University.

Dr. Balazs commented;

This is one of the holy grails of materials science, while others have developed materials that can mend small defects, there is no published research regarding systems that can regenerate bulk sections of a severed material. This has a tremendous impact on sustainability because you could potentially extend the lifetime of a material by giving it the ability to regrow when damaged.

The research team was inspired by biological processes in species such as amphibians, which can regenerate severed limbs. This type of tissue regeneration is guided by three critical instruction sets – initiation, propagation, and termination – which Dr. Balazs describes as a “beautiful dynamic cascade” of biological events.

When the researchers looked at the biological processes behind tissue regeneration in amphibians, they considered how to replicate the dynamic cascade within a synthetic material, they needed to develop a system that first would sense the removal of material and initiate regrowth, then propagate that growth until the material reached the desired size and then, self-terminate the process.

The team developed a hybrid material of nanorods embedded in a polymer gel, which is surrounded by a solution containing monomers and cross-linkers (molecules that link one polymer chain to another) in order to replicate the dynamic cascade. When part of the gel is severed, the nanorods near the cut act as sensors and migrate to the new interface. The functionalised chains or “skirts” on one end of these nanorods keeps them localised at the interface and the sites (or “initiators”) along the rod’s surface trigger a polymerisation reaction with the monomer and cross-linkers in the outer solution. Drs. Yong and Kuksenok developed the computational models, and thereby established guidelines to control the process so that the new gel behaves and appears like the gel it replaced, and to terminate the reaction so that the material would not grow out of control.

In the future, the researchers plan to improve the process and strengthen the bonds between the old and newly formed gels, and for this they were inspired by another nature metaphor, the giant sequoia tree. “One sequoia tree will have a shallow root system, but when they grow in numbers, the root systems intertwine to provide support and contribute to their tremendous growth,” Dr. Balazs explains. Similarly, the skirts on the nanorods can provide additional strength to the regenerated material.

The next generation of research would further optimise the process to grow multiple layers, creating more complex materials with multiple functions.

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