Plastics: Pull Yourself Together, Man!
Erin Green posted on December 04, 2015 |
“Self-healing” polymer hydrogel duo pulls itself together to fix damaged circuits.

Flexible electronics have been all the rage this year. Whether you need it to bend just enough or roll right up for easy transportation, there’s something out there that can do it.

The one catch with this technology is that circuits aren’t really meant to bend. What happens when these circuits crack under the pressure?

So far, the answer has been the use of so-called “self-healing” polymer hydrogels. These gels can fix damage to circuits caused by wear and tear, but they generally require some sort of external stimulus – be it heat, light or something else.

This makes repairs difficult, especially if the circuit isn’t easily accessible. As a result, these plastics really need to be able to pull themselves back together.

A sample of the hydrogel being developed to heal itself autonomously. (Image courtesy of University of Texas Austin.)

A sample of the hydrogel being developed to heal itself autonomously. (Image courtesy of University of Texas Austin.)

Autonomous Healing in Circuitry

A new type of polymer hydrogel promises to solve this issue by healing itself without any stimulus so it can repair and connect electric circuits with complete autonomy. No fussing required.

The hydrogel, developed by a team of researchers at UT Austin’s Cockrell School of Engineering, is actually a combination of two separate gels.

  • A polymer hydrogel, in this case polypyrrole, conducts electricity through the circuit.
  • A metal-ligand gel, constructed into a disc-shaped liquid crystal molecule, acts as a structural glue to keep the gel stable and repair damage.

According to the team’s paper, this combination makes for a hydrogel that rivals the conductivity of regular metal circuit components, capable of reassembling itself when the going gets tough.

How Does the Gel Stay Together?

“In the last decade, the self-healing concept has been popularized by people working on different applications, but this is the first time it has been done without external stimuli,” said Guihua Yu, assistant professor of mechanical engineering and the developer of the gel.

This depiction from the team's paper demonstrates a bond between oxygen and nitrogen atoms. I suspect this is how the gel

This depiction from the team's paper demonstrates a bond between oxygen and nitrogen atoms. I suspect this is how the gel "heals" itself. (Image courtesy of Guihua Yu et al.)

The hydrogel appears to use many weak dipole-ion forces between the nitrogen in the polypyrrole and oxygen in the metal-ligand ion to hold itself together.

Presumably, a series of these bonds would pull themselves back together after breaking if enough of the others survived the break. It might remind you of a magnetic screen door.

A Flexible Option for Circuits

Existing circuits really aren’t built to be flexible or repair cracks and breaks caused by normal wear and tear. This is where the self-healing hydrogel comes in.

The structures used to keep it all together are some of the smallest possible, meaning that the hydrogel could theoretically be used effectively in circuits of any size.

Its apparent level of conductivity means that the hydrogel could plausibly replace metal components in circuits, but the team sees the hydrogel as more of a bandage solution to create soft joints between these components.

This could be applied to a wide range of fields, including flexible electronics. It could also be handy for medical machinery, which requires its circuits to be long-lasting and rugged.

If you’d like to bend your brain around more information on the hydrogel, check out the team’s paper.

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