Healing via ‘entanglement’
The secret of the material lies not only in the organised arrangement of the nanosheets, but also in the polymers that are entangled between them – and a process that’s as simple as baking. Postdoctoral researcher Chen Liang mixed a powder of monomers with water that contains nanosheets. The mixture was then placed under a UV lamp – similar to that used to set gel nail polish. "The UV-radiation from the lamp causes the individual molecules to bind together so that everything becomes an elastic solid – a gel," Liang explains.
"Entanglement means that the thin polymer layers start to twist around each other like tiny wool yarns, but in a random order," adds Hang Zhang, from Aalto University. "When the polymers are fully entangled, they are indistinguishable from each other. They are very dynamic and mobile at the molecular level, and when you cut them, they start to intertwine again."
Want more breaking news?
Subscribe to Technology Networks’ daily newsletter, delivering breaking science news straight to your inbox every day.
Subscribe for FREE
Four hours after cutting it with a knife, the material is already 80 or 90 percent self-healed. After 24 hours, it is typically completely repaired. Furthermore, a one-millimetre-thick hydrogel contains 10,000 layers of nanosheets, which makes the material as stiff as human skin, and gives it a comparable degree of stretch and flexibility.
"Stiff, strong and self-healing hydrogels have long been a challenge. We have discovered a mechanism to strengthen the conventionally soft hydrogels. This could revolutionise the development of new materials with bio-inspired properties," says Zhang.
Gaining inspiration from nature
"This work is an exciting example of how biological materials inspire us to look for new combinations of properties for synthetic materials. Imagine robots with robust, self-healing skins or synthetic tissues that autonomously repair,” says Olli Ikkala, from Aalto University. And even though there may be some way to go before real-world application, the current results represent a pivotal leap. "It’s the kind of fundamental discovery that could renew the rules of material design."
"The key to achieving high strength is the addition of ultra-large and thin clay nanosheets that have extremely uniform swelling by water. To visualize the nanoscale phenomena, one can imagine separating a stack of printer paper to a uniform distance of 1 mm. The polymers are then squeezed inbetween the nanosheets," added Prof. Josef Breu.
The collaboration was led by Dr. Hang Zhang, Prof. Olli Ikkala and Prof. Josef Breu. The synthetic clay nanosheets were designed and manufactured by Prof. Josef Breu at the University of Bayreuth in Germany.
Reference: Liang C, Dudko V, Khoruzhenko O, et al. Stiff and self-healing hydrogels by polymer entanglements in co-planar nanoconfinement. Nat Mater. 2025:1-8. doi: 10.1038/s41563-025-02146-5
This article has been republished from the following materials. Note: material may have been edited for length and content. For further information, please contact the cited source. Our press release publishing policy can be accessedhere.