How often has it happened to you that ride over a nail or other sharp object, and your tire goes flat? No matter if it’s about your bicycle or car tires, fixing the problem is a hassle that only makes car and bicycle repair people happy. However, punctured tires may soon be a thing of the past. Researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences have developed a new type of rubber that is as tough as natural rubber, but, in addition, can heal itself.

We have seen more self-healing materials, including asphalt, concrete and even cars, which just proves that we do not like fixing things if it can be done for us.

Rubber is a challenging material to make self-healing, according to the researchers, as it is made of polymers that are connected by permanent, covalent bonds, which are strong, but never reconnect once broken. Back in 2008, French researchers made an artificial rubber that was self-healing. According to the Harvard team, “Previous research used reversible hydrogen bonds to connect polymers to form a rubber, but reversible bonds are intrinsically weaker than covalent bonds.”

Mixing covalent and reversible bonds is not an option, as they reject each other like oil and water. Instead, the researchers developed a molecular rope of randomly branched polymers to tie these two types of bonds together and mix them homogeneously. This creates a transparent, tough, and self-healing rubber.

Typical rubber tends to crack when a certain force is applied. The self-healing rubber, on the other hand, develops so-called crazes, which are cracks that are connected by fibrous stands. The crazes redistribute the stress, so that there is no localised point if stress that could cause failure. When the stress is realised, the material snaps back to its original form and the crazes heal.

The material can be used for a variety of rubber products.

For more self-healing materials, click here.

Photos: Peter and Ryan Allen/Harvard SEAS / Wikimedia