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Breakthrough in 3D-printed self-healing soft materials

Breakthrough in 3D-printed self-healing soft materials
A team from the University of Southern California and University of Connecticut have developed a
new rubber material that can repair itself after breaking, fracturing or being punctured, and which
could lead to a new generation of self-healing products. The 3D-printed materials are able to be
manufactured quickly and offer improved product durability and longevity for a range of applications,
including tires, shoes, soft robotics and flexible electronics.
The material is made by a 3D printing method based on photopolymerization, a process that utilizes
light to solidify a liquid resin into a particular shape. Photopolymerization depends on the optimum
combination of two chemical groups, thiols and disulfides. When an oxidizer is added to a thiol, they
transform into disulfides, which can re-form when broken, offering the ability to self-heal. On slowly
increasing the oxidant, the self-healing behavior of the material becomes stronger while the
photopolymerization behavior becomes weaker. The team identified the ratio between the two that
enables both high self-healing and relatively rapid photopolymerization.
A 17.5-millimeter square of the material was shown to be printed in only five seconds, with whole
objects taking about 20 minutes, and they can repair themselves in just a few hours. This was
achieved with a variety of products, such as a soft robot, a shoe pad, a multiphase composite and an
electronic sensor. When cut in two, it took only two hours for the material to fully heal while retaining
its strength and function.
At temperatures between 40 degrees Celsius and 60 degrees Celsius, the material can heal to nearly
100%, and by changing the temperature they can alter the healing speed, with the material able to
self-heal even at room temperature. As team leader Qimin Wang told Materials Today, “The research
provides a new paradigm to rapidly 3D print structures that can be rapidly healed after damage”.
While existing 3D methods of shaping self-healing polymers involve molding and direct writing, this
could be the first stereolithography of self-healing polymers. As well as the obvious uses for rubber
products, the researchers hope to develop other 3D-printable and self-healable materials with
different stiffnesses, including rigid hard plastics that could be used in vehicle parts, composite
materials and body armor. The eventual aim is to produce a library of 3D-printable and self-healable
polymers for a range of engineering applications.
Breakthrough in 3D-printed self-healing soft materials