Self-healing printed material 'could be game-changing for soft robotics'

A 3D printing technique that creates self-healing materials could be “game-changing” for soft robotics and lead to repairable vehicle parts, researchers have claimed.

“Instead of throwing away your broken boots… why not let them fix themselves,” the team from the University of Southern California Viterbi School of Engineering asked.

The team created a new material that can be manufactured quickly and can repair itself if fractured or punctured, using a 3D printing method involving photopolymerisation. The process uses light to solidify a liquid resin in a desired shape.

Photopolymerisation uses a reaction with a chemical group called thiols. The team added an oxidiser to transform the thiols into disulfides, which are able to reform when broken. Finding the right ratio between thiols and disulfides was the key to unlocking the materials' unique properties.

"When we gradually increase the oxidant, the self-healing behaviour becomes stronger, but the photopolymerisation behaviour becomes weaker," said assistant professor Qiming Wang. "There is competition between these two behaviours, and eventually we found the ratio that can enable both high self-healing and relatively rapid photopolymerisation."

The team reported manufacturing speeds of five seconds for a 17.5mm² square, completing objects in 20 minutes that could repair themselves after breaking over several hours. In the study, they demonstrated the material’s ability in a range of products, including a shoe pad, soft robot and an electronic sensor.

“This material could be game-changing for industries like shoes, tires, soft robotics, and even electronics, decreasing manufacturing time while increasing product durability and longevity,” a press release said.

The healing technique currently depends on high temperatures – two hours at 60ºC for the rubbery material, four hours when carbon was included for electricity transmission – but first author Kunhao Yu said the material still self heals at room temperature.

After working on soft materials, the team is now developing different self-healing materials with a range of stiffnesses. Self-healing hard plastics could be used for vehicle parts, composite materials and even body armour, they claimed.

The work was published in NPG Asia Materials.