3D-printed rubber material for self-repairing tires, shoes

Scientists have 3Dprinted rubber material that can repair itself if it becomes fractured or punctured, paving the way for self healing car tires or shoes.

The material, developed by researchers from University of Southern California in the US, could be game-changing for soft robotics and even electronics, decreasing manufacturing time while increasing product durability and longevity. It is manufactured using a 3D-printing method that uses photopolymerisation. This process uses light to solidify a liquid resin in a desired shape or geometry.

Photopolymerisation is achieved through a reaction with a certain chemical group called thiols. By adding an oxidiser to the equation, these transform into another group called disulphides. “When we gradually increase the oxidant, the self-healing behaviour becomes stronger, but the photopolymerisation behaviour becomes weaker,” said Qiming Wang, an assistant professor at University of Southern California in the US.

“There is competition between these two behaviours. And eventually we found the ratio that can enable both high self-healing and relatively rapid photopolymerisation,” Wang said. In just 5 seconds, they can print a 17.5-millimetre square, completing whole objects in around 20 minutes that can repair themselves in just a few hours. In the study they demonstrate their material’s ability on a range of products, including a shoe pad, a soft robot, a multiphase composite, and an electronic sensor.

“We actually show that under different temperatures — from 40 degrees Celsius to 60 degrees Celsius — the material can heal to almost 100 per cent,” said Kunhao Yu, a student at University of Southern California. “By changing the temperature, we can manipulate the healing speed, even under room temperature the material can still self-heal,” said Yu.