US team develops self-healing 3D printed rubber

Los Angeles, California – Researchers at the University of Southern California (USC) Viterbi School of Engineering have developed a rubber material that can be 3D-printed into self-repairing products, USC reported 5 Feb.

The manufacturing process involves photopolymerisation reactions with thiol groups, which are also oxidised into disulfides groups that reform – or self-heal – when broken.

The research team was led by assistant professor Qiming Wang, working with Viterbi students Kunhao Yu, An Xin, and Haixu Du, and University of Connecticut assistant professor Ying Li.

Finding the right ratio between the two chemical groups was the key to unlocking the materials’ unique properties, according to the researchers.

“When we gradually increase the oxidant, the self-healing behaviour becomes stronger, but the photopolymerization behaviour becomes weaker,” explained Wang.

“Eventually we found the ratio that can enable both high self-healing and relatively rapid photopolymerisation,” the team leader added.

In five seconds, the materials can be printed into a 17.5-millimeter square, according to the USC report.

Whole objects, it added, can be completed in around 20 minutes, with parts able to repair themselves in just a few hours.

In a study, published in NPG Asia Materials, the new material was shown to self-heal on a shoe pad, a soft robot, a composite material and an electronic sensor.

After being cut in half, the rubber healed completely in just two hours at 60 degrees C - retaining strength and function.

“Under different temperatures – from 40 degrees C to 60 degrees C – the material can heal to almost 100%,” said Yu.

“By changing the temperature, we can manipulate the healing speed, even under room temperature the material can still self-heal,” the researcher said.

The team are now working to develop different self-healable polymers in a range of stiffnesses, from the current soft rubber to rigid materials.