Self-Healing Material Builds Itself from Carbon Exposure

Diagrams illustrate the self-healing properties. At top, a crack is created in the material, which is composed of a hydrogel (dark green) with plant-derived chloroplasts (light green) embedded in it. At bottom, in the presence of light, the material reacts with carbon dioxide in the air to expand and fill the gap, repairing the damage. Images courtesy of MIT.

A research team comprised of chemical engineers from the Massachusetts Institute of Technology (MIT) (Cambridge, Massachusetts, USA) and the University of California, Riverside (UC Riverside) (Riverside, California, USA) has developed a polymer that reacts with carbon dioxide (CO2) in the air to regenerate itself.

The polymer, which might someday be used as construction or repair material or for protective coatings, continuously converts the greenhouse gas into a carbon-based material that reinforces itself, according to the researchers.

This “self-healing material,” designed to mimic the CO2 absorption properties of green plants, has potential applications in a variety of construction and protective coatings projects.

New Materials Science Concept

The current version of the material is a synthetic gel-like substance that performs a chemical process similar to the way plants incorporate CO2 from the air into their growing tissues, the researchers explain.

The material might, for example, be made into panels of a lightweight matrix that could be shipped to a construction site, where they would harden and solidify just from exposure to air and sunlight. In turn, this could produce savings on the energy and cost of transportation.

The research1 was organized by Michael Strano, an MIT chemical engineering professor; Seon-Yeong Kwak, an MIT post-doctoral student; and eight others at MIT and UC Riverside.

“This is a completely new concept in materials science,” Strano says. “What we call carbon-fixing materials don’t exist yet today” outside of the biological realm, he adds, describing materials that can transform CO2 in the ambient air into a solid, stable form, using only the power of sunlight, just as plants do.

Developing a synthetic material that not only avoids the use of fossil fuels for its creation, but actually consumes CO2 from the air, has other clear benefits for the environment and climate, the researchers note. “Imagine a synthetic material that could grow like trees, taking the carbon from the carbon dioxide and incorporating it into the material’s backbone,” Strano says.

Technical Details of the Material

The material the team used in its initial proof-of-concept experiments did make use of one biological component in the form of chloroplasts, described as light-harnessing components within plant cells. The researchers obtained these chloroplasts from spinach leaves.

While the chloroplasts are not alive, they do catalyze the reaction of CO2 to glucose. Isolated chloroplasts are quite unstable, the researchers say, since they tend to stop functioning after a few hours when removed from the plant. However, Strano and his research team demonstrate methods to significantly increase the catalytic lifetime of the extracted chloroplasts. In ongoing and future work, the chloroplast is being replaced by catalysts that are nonbiological in origin.

The current material is a gel matrix composed of a polymer from aminopropyl methacrylamide (APMA) and glucose, an enzyme called glucose oxidase, and the chloroplasts, and the material becomes stronger as it incorporates the carbon. It is not yet strong enough to be used as a building material, though it might function as a crack filling or coating material.

“It is exciting to watch it as it starts to grow and cluster,” Kwak says of the material, which starts out as a liquid but moves toward a solid form.

Future Research Steps

The team says it has worked out methods to produce materials of this type by the ton and is now focusing on optimizing the material’s properties. Commercial applications such as self-healing coatings and crack filling are possible in the near term, they say, whereas additional advances in backbone chemistry and materials science are needed before construction materials and composites can be developed.

One key advantage of such materials is they would be self-repairing upon exposure to sunlight or some indoor lighting, Strano explains. If the surface is scratched or cracked, the affected area grows to fill in the gaps and repair the damage, without requiring any external action.

While there has been widespread effort to develop self-healing materials that could mimic this ability of biological organisms, the researchers say, these have all previously required an active outside input to function. Heating, ultraviolet (UV) light, mechanical stress, or chemical treatment were needed to activate the process. By contrast, these materials need nothing but ambient light, and they incorporate mass from carbon in the atmosphere, which is ubiquitous.

“Materials science has never produced anything like this,” Strano says. “These materials mimic some aspects of something living, even though it’s not reproducing.”

“Our work shows that carbon dioxide need not be purely a burden and a cost,” Strano adds. “It is also an opportunity in this respect. There’s carbon everywhere. We build the world with carbon. Humans are made of carbon. Making a material that can access the abundant carbon all around us is a significant opportunity for materials science. In this way, our work is about making materials that are not just carbon neutral, but carbon negative.”

The research was supported by the U.S. Department of Energy (Washington, DC, USA), which is also sponsoring a new program directed by Strano to further develop this work.

Source: MIT News,


1 “Self-Healing Material Can Build Itself from Carbon in the Air,” MIT News, October 11, 2018, (November 20, 2018).

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