We have all had that favorite pair of shoes that broke and was lost forever. We have also all experienced the burden of a flat tire. But what if those experiences became a thing of the past? What if these items could self-repair?

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This is exactly what researchers at the University of Southern California Viterbi School of Engineering have been working on. And what they have achieved is nothing short of impressive.

3D-printed rubber that self-repairs

The scientists have developed a 3D-printed rubber material that can self-repair. Yes! , you heard right. The material simply repairs itself.

Better yet, the new material can be manufactured quickly and has countless applications in industries ranging from soft robotics to electronics. This is because it is based on a 3D printing method that uses photopolymerization.

Photopolymerization is a process that uses light, visible or ultraviolet, to solidify a liquid resin and it is achieved through a reaction with a chemical group called thiols. If you add an oxidizer to the equation, the thiols transform into disulfides, a chemical group that is able to self-repair.

What the researchers needed to do was establish the right ratio between these two groups to lead to effective self-healing capabilities.

"When we gradually increase the oxidant, the self-healing behavior becomes stronger, but the photopolymerization behavior becomes weaker," explained Assistant Professor Qiming Wang. "There is competition between these two behaviors. And eventually, we found the ratio that can enable both high self-healing and relatively rapid photopolymerization."

Fast printing

The speed of printing objects with this material is indeed very high. The researchers report that they can print a 17.5-millimeter square in just 5 seconds!

Printing whole objects takes about 20 minutes. But how about the time it takes them to repair themselves? That takes a few hours, but we would argue it is worth the wait.

"We actually show that under different temperatures - from 40 degreesCelsius to 60 degrees Celsius - the material can heal to almost 100percent," said Kunhao Yu, who was the first author of the study. "By changing the temperature, we can manipulate the healing speed, even under room temperature the material can still self-heal."

The researchers tested their theory on several products including a shoe pad, a soft robot, a multiphase composite, and an electronic sensor. Now, they are working on self-healing materials with different levels of stiffness in order to expand the materials' applications.

The study is published in NPG Asia Materials.