Self-healing hydrogel forms strong bond in seconds

Bioengineers from the University of California (UC) San Diego have developed a self-healing hydrogel that binds in seconds and forms a bond strong enough to withstand repeated stretching.

The material has numerous potential applications, including medical sutures, targeted drug delivery, industrial sealants and self-healing plastics, a team of UC San Diego Jacobs School of Engineering researchers reported yesterday in the Proceedings of the National Academy of Sciences online.

According to the university, hydrogels are made of linked chains of polymer molecules that form a flexible material similar to soft tissues.

Until now, researchers have been unable to develop hydrogels that can rapidly repair themselves when a cut is introduced, limiting their potential applications.

The team, led by Shyni Varghese, overcame this challenge with the use of ‘dangling side chain’ molecules that extend like fingers from the primary structure of the hydrogel network and enable them to grasp one another.

‘Self healing is one of the most fundamental properties of living tissues that allows them to sustain repeated damage,’ said Varghese. ‘Being bioengineers, one question that repeatedly appeared before us was if one could mimic self healing in synthetic, tissue-like materials such as hydrogels. The benefits of creating such an aqueous self-healing material would be far reaching in medicine and engineering.’

To design the side chain molecules of the hydrogel that would enable rapid self healing, Varghese and her collaborators performed computer simulations of the hydrogel network.

The simulations revealed that the ability of the hydrogel to self heal depended critically on the length of the side chain molecules and that hydrogels having an optimal length of side chain molecules exhibited the strongest self healing.

When two cylindrical pieces of gels were placed together in an acidic solution, they stuck together instantly.

Varghese’s lab further found that, by simply adjusting the solution’s pH levels up or down, the pieces weld (low pH) and separate (high pH) easily. The process was successfully repeated numerous times without any reduction in the weld strength.

Ameya Phadke, a fourth-year PhD student in Varghese’s lab, said the hydrogel’s strength and flexibility in an acidic environment makes it ideal as an adhesive to heal stomach perforations or for controlled drug delivery to ulcers.

Such healing materials could also be useful in the field of energy conservation and recycling, where self-healing materials could help to reduce industrial and consumer waste, according to Varghese.