Smart coating that’s hard like enamel but can self-heal was inspired by human skin

Smart coatings: they’re either too soft and wear down easily, or too hard and offer little room for flexibility. This is a dilemma that researchers from the Harbin Institute of Technology have tackled and attempted to overcome. To that end, the investigative team has come up with a smart coating that possesses both the durability of teeth enamel and the self-healing capabilities of skin.

According to, they came up with the smart coating by using layers of polyvinyl alcohol and tannic acid. Though instead of just stacking the materials one on top of the other, the researchers utilized molecular assembly to precisely weave the polymers and bonds together. The end product is a smart coating that, when cut, fills up the incision with polyvinyl alcohol and tannic acid molecules.

As for the enamel-like surface, that is due to the inclusion of graphene oxide. The coating’s uppermost layers contain graphene oxide that pull off the double job of trapping and protecting the polyvinyl alcohol and tannic acid molecules underneath. This has also resulted in the coating having a stiffness of 31.4 gigapascals (Gpa), which is about 4.5 million pounds (lbs) for every square inch.

“The multilayer structure is the key,” senior study author Ming Yang told “By placing a hard layer containing graphene oxide on top of a soft layer, we create a smart hybridization you can get the most out of.”

Yang added that this combination of hard and soft layers is what gave the coating its self-healing properties. On their own, none of the materials would have been able to do what the coating can. Moreover, the smart coating is antibacterial: tests conducted by Yang and his colleagues have shown that their smart coating is as protective as human skin.

Speaking of the results of their work, Yang stated: “It is exciting to see we can integrate demanding properties in two natural structures, namely self-healing property in skin and mechanical stiffness and hardness in tooth enamel, into an artificial smart coating. And this design principle is likely useful for any self-healing polymer system.” (Related: Flexible, eco-friendly AND less expensive: Researchers are one step closer to the smart screen of the future.)

In addition to protecting phones, the team believes that the smart coating could have a variety of other applications. One is to safeguard buildings from scratches, and the other is as a veneer for biomedical instruments. Another major advantage that their smart coating has over the others currently on the market is that it’s made up of environmentally friendly materials. This, according to Yang, gives their coating a leg up over the rest since it can make managing plastic waste that much easier.

Though before any of the team’s smart coating can become hard reality, Yang and his team first have to find a way to produce the coating in an efficient manner.

“The current research uses molecular assembly to achieve the desirable structure. In the future, we will need a more efficient way to accelerate the production line. Spray-assisted coating can be a good choice. We are also trying to apply similar design principles to other self-healing polymers especially those that are already commercially available,” Yang explained.

Regardless, the team is optimistic that a prototype of the smart coating will be available in one to two years’ time. It may take even longer for a mature version of the product to make its way onto the shelves of stores, but they believe that it can and will happen.

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