If you have an ACS member number, please enter it here so we can link this account to your membership. (optional)

ACS values your privacy. By submitting your information, you are gaining access to C&EN and subscribing to our weekly newsletter. We use the information you provide to make your reading experience better, and we will never sell your data to third party members.



Hydrogels reinforced with rings on strings

Reversible crystallization of polyethylene glycol chains makes material tougher

by Bethany Halford
June 3, 2021 | A version of this story appeared in Volume 99, Issue 21


Chains connected by rings slide but stay cross-linked when stretched.
Credit: Adapted from Science
Cyclodextrin rings (green) threaded onto polyethylene glycol chains (blue) covalently bind one another, which keeps the network intact when it is stretched. Stretching also crystallizes portions of the polymer chains (red, right).

Hydrogels have promise as tissue engineering scaffolds and in other biomedical applications. But these materials, which are made mostly of water held together by hydrophilic, cross-linked polymers, tend to be weak. To toughen up hydrogels, scientists have introduced sacrificial bonds: stretch the material, and these bonds break, dissipating energy so that rupturing the hydrogel is more difficult. These bonds can be slow to re-form, however, so the boost in strength doesn’t last.

Researchers at the University of Tokyo have come up with an alternative toughening strategy. A team led by Koichi Mayumi and Kohzo Ito created a hydrogel that contains polyethylene glycol chains threaded through pairs of covalently linked cyclodextrin rings to make a netlike structure (Science 2021, DOI: 10.1126/science.aaz6694).

When the hydrogel is stretched, the polymer chains slide through the rings, which maintain the cross-links between polymer strands. Stretch the polymer enough, and the polyethylene glycol crystallizes at points, increasing toughness. Studies show this slide-ring hydrogel is 10 times as tough as a hydrogel made from polyethylene glycol with conventional cross-links. The researchers say the slide-ring reinforcement strategy could be used with other gels made of semicrystalline polymers.


This article has been sent to the following recipient:

Chemistry matters. Join us to get the news you need.