Reviewed by Lexie CornerMar 10 2025
Researchers from Aalto University and the University of Bayreuth have developed a hydrogel that combines high stiffness with self-healing properties, overcoming previous limitations. This development could facilitate progress in drug delivery, wound healing, soft robotics sensors, and artificial skin. The study was published in Nature Materials.
Artistic representation of hydrogels in a mobius-ring formed through self-healing. Image Credit: Margot Lepetit / Aalto University
Gels are commonly encountered in daily life, from hair styling products to jelly-like components in various foods. While human skin shares some gel-like properties, its unique combination of high stiffness, flexibility, and remarkable self-healing capabilities, often recovering within 24 hours after injury, is difficult to replicate.
In this study, the researchers combined hydrogels, typically soft and flexible, with large, ultra-thin clay nanosheets. The result is a highly ordered structure with densely entangled polymers between nanosheets, which improves the hydrogel's mechanical properties and enables self-healing.
Healing via “Entanglement”
The polymers that are entangled between the nanosheets and their well-organized arrangement—achieved through a simple process—are key to the material’s performance. Chen Liang, a Postdoctoral Researcher, combined a monomer powder with water containing nanosheets. A UV lamp, similar to those used to set gel nail polish, was then applied to the mixture.
The UV-radiation from the lamp causes the individual molecules to bind together so that everything becomes an elastic solid—a gel.
Chen Liang, Postdoctoral Researcher, Aalto University
“Entanglement means that the thin polymer layers start to twist around each other like tiny wool yarns, but in a random order. 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,” said Hang Zhang of Aalto University.
Around 80 to 90 % of the material has already self-healed four hours after being cut with a knife. Usually, it is fully restored after a day. Additionally, 10,000 layers of nanosheets form a hydrogel that is 1 mm thick, giving it similar stretch and flexibility to human skin while maintaining the necessary stiffness.
Stiff, strong, and self-healing hydrogels have long been a challenge. We have discovered a mechanism to strengthen the conventionally soft hydrogels. This could revolutionize the development of new materials with bio-inspired properties.
Dr. Hang Zhang, Aalto University
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.
Olli Ikkala, Professor, Aalto University
And even though there may be some way to go before real-world application, the current results represent a significant step. “It’s the kind of fundamental discovery that could renew the rules of material design.”
Dr. Hang Zhang, Prof. Olli Ikkala, and Prof. Josef Breu led the collaboration. Prof. Josef Breu of the University of Bayreuth in Germany was responsible for creating and producing the artificial clay nanosheets.
Journal Reference:
Liang, C., et al. (2025) Stiff and self-healing hydrogels by polymer entanglements in co-planar nanoconfinement. Nature Materials. doi.org/10.1038/s41563-025-02146-5