Scientists have created materials that react chemically with carbon dioxide from the air to grow, strengthen, and even repair themselves.

Carbon is found everywhere on the planet, from the things we build, to the foods we eat, and even in our own bodies. Scientists have created materials can that access the abundant carbon in the air around us to grow and repair themselves. While these ‘self-healing’ materials currently only exist in laboratories, the day when they become commercially viable is fast approaching. Excess carbon dioxide could be a fantastic opportunity for materials science, not just a burden on economic growth.

What are ‘self-healing’ materials?
According to Michael Strano, professor of chemical engineering at MIT, self-healing materials can grow and repair themselves like plants and trees using the carbon in the air. In a recent interview with Popular Science, Strano observed that we already use petroleum to create “the plastic fibers and sheets that we see all around us”. Using carbon from the air is the next logical step towards creating materials that continuously renew themselves.

Self-healing materials only need “atmospheric CO2 and ambient light,” said Strano. No other external stimuli are required for such materials to function. At present, however, these materials don’t yet exist outside the lab.

How do ‘self-healing’ materials work?
Strano was part of a group of ten researchers from the University of California, Riverside and MIT who published a recent study in the journal Advanced Materials.

The study outlined how a polymer gel containing isolated chloroplasts taken from plants could react with sunlight and C02 to self-heal. As chloroplasts usually stop working as soon as they are removed from plants, Strano’s team developed ways to increase their lifespan for the purposes of the study. In the future, Strano plans to find synthetic alternatives that can stand in for organic chloroplasts.

How will self-healing materials be used?
When they become commercially available, self-healing materials will likely be used as “self-healing” coatings. The variety of potential applications is tremendous, from smartphone screens to car trims and even fabrics. Motorola has already patented a phone screen that can remove cracks when heated, but self-heating materials are different. They can easily fill in the gaps caused by scratches when exposed to air and sunlight, without any external source of heat. This offers a tremendous opportunity for builders and manufacturers. They can use this material to coat almost any surface of any finished product. This should dramatically increase the product’s lifespan while reducing maintenance costs.

Self-healing materials could have environmental benefits
The synthetic polymer developed by Strano’s laboratory is a gel that uses chloroplasts from spinach leaves to harness sunlight. This is the same biological component that plants use to reinforce themselves. The polymer continuously reinforces itself by converting C02 in the atmosphere into a carbon-based substance. As such, no other input – such as mechanical stress, heat, or ultraviolet light – is required.

Materials that use atmospheric carbon to self-heal have huge implications for the environment. The widespread use of such materials could help remove CO2 from the atmosphere and help to address the challenge of climate change. If the polymer developed by Strano’s lab could be mass produced and used to coat buildings and structures, significant amounts of C02 could be removed from the air without any additional action being required. As Strano pointed out, these materials aren’t just carbon neutral; “They are carbon negative,” he said.

What challenges do self-healing materials face?
Surprisingly, scientists already have the ability to produce self-healing polymer gel “by the ton,” Strano said. The gel is made from a polymer containing glucose and aminopropyl methacrylamide (APMA), coupled with the chloroplasts and an enzyme called glucose oxidase. We may have to wait a few years before we start to see coatings or crack fillers become more widely used, though. The main stumbling block is that additional advances in chemistry and materials science are necessary before such gel can be used in construction as it isn’t currently strong enough for use as a building material.

Conclusion
Although self-healing materials currently only exist in labs, Strano’s team are confident that barriers to commercial adoption can be overcome through further research and development. In particular, his team are focused on developing a synthetic substitute for the plant-derived chloroplasts. If all goes according to plan, self-healing smartphone screens could become a reality sooner than you think.
 

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