old shoe

The Advent of the 3D Printed Material That Repairs Itself

Self-Healing Materials: The Correct Mix

Out of the University of Southern California (USC) researchers have developed a 3D printed rubber material that has the ability to repair itself. The rubber material, an elastomer, is able to potentially decrease manufacturing time and increase longevity for shoes, tires, soft robotics and electronics. The self-healable materials were 3D printed using a customized photopolymerization process. Photopoly- merization is a technique that uses light (visible or ultraviolet; UV) to initiate and propagate a polymerization reaction. It is a practical approach to produce micrometer sized 3D structures. In this process laser light excitation hardens an appropriate photopolymer.

The researchers say that self-healing and polymerization are two different behaviors. There is actually a competition between the two, but the researchers were eventually able to find the ratio that can enable both high self-healing and relatively rapid photopolymerization.

This research focuses on the photopolymerization reaction of the alcohol-analogous thiol chemical group present in the rubber materials. An oxidizer was added to the process which transformed the thiols into a different group of chemicals called disulfides. The new chemicals have the ability to reform when broken, enabling self-healing. However, when they gradually increase the oxidant, the self-healing behavior becomes stronger, but the photopolymerization behavior becomes weaker.

Healing Time & Temperature

Part of the research is a study where the material’s ability to heal on a range of rubber products. The different items were cut in half, and after 2 hours, at 60 degrees Celsius, the products were able to heal completely. The repair time is variable depending on the temperature. Under different temperatures – from 40 degrees Celsius to 60 degrees Celsius – the material can heal to almost 100 percent.

There have been studies on self-healing materials that are 3D-printable. There’s the conductive self-healing hydrogel developed at the University of Manitoba; it came from chitosan, which is found in the shells of crabs, shrimp and other crustaceans. At the University of Melbourne, a team found that synthetic benzaldehyde, typically obtained by extraction from cinnamon oil, was a key ingredient to developing a 3D printable healing gel. From the University of South Carolina a study was published titled Additive Manufacturing of Self-healing Elastomers about self-healing materials.

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