Gels are a common part of everyday life, with applications ranging from the sticky substances we use in our hair to the jelly-like components found in food. These materials share some characteristics with human skin, which also exhibits gel-like qualities, though skin is a far more complex material. Human skin uniquely combines high stiffness with flexibility, and it has remarkable self-healing abilities, often repairing itself within 24 hours of injury. Despite years of research, replicating these properties in synthetic gels has been challenging.
Historically, artificial gels have been able to achieve one of these traits, either mimicking skin’s high stiffness or its ability to self-heal, but not both simultaneously. However, a new breakthrough in material science from researchers at Aalto University and the University of Bayreuth has overcome this limitation. The team has developed an innovative hydrogel with a unique structure that combines both high stiffness and remarkable self-healing properties. This development opens up exciting possibilities for applications in areas such as drug delivery, wound healing, soft robotics sensors, and even artificial skin.
The research, published in Nature Materials, introduces an advanced hydrogel that incorporates large, ultra-thin nanosheets of clay into its structure. Hydrogels are typically soft and squishy, but by introducing these nanosheets, the researchers have created a highly ordered material that features densely entangled polymers between the nanosheets. This arrangement not only strengthens the mechanical properties of the hydrogel but also gives it the ability to repair itself after damage.
The breakthrough process relies on a clever technique that could be likened to baking. Postdoctoral researcher Chen Liang explains that the creation of this hydrogel begins with a powder of monomers mixed with water containing nanosheets. This mixture is then placed under a UV lamp, similar to the kind used to set gel nail polish. The UV radiation causes the individual molecules to bind together, forming a gel. This simple process sets the stage for the material’s remarkable properties.
The key to the hydrogel’s self-healing abilities lies in its molecular structure. Hang Zhang, from Aalto University, describes the process of “entanglement,” where the thin polymer layers twist around each other like tiny wool yarns in a random order. When the polymers become fully entangled, they become indistinguishable from one another, forming a dynamic and mobile network at the molecular level. This interwoven structure allows the material to repair itself when damaged. When the hydrogel is cut, the entangled polymers immediately begin to intertwine once more, restoring the material to its original state.
Remarkably, just four hours after the hydrogel is cut, it has already healed 80 to 90 percent of the damage. After 24 hours, the material is typically fully repaired. This self-healing process, combined with the stiffness and flexibility of the hydrogel, makes it comparable to human skin, which contains a complex network of fibers and cells that give it both durability and elasticity.
The strength and self-healing abilities of this hydrogel are groundbreaking. Traditionally, hydrogels have been relatively weak, with limited mechanical properties. This new approach has strengthened these traditionally soft materials by introducing nanosheets into the structure, leading to an innovative solution that replicates nature’s bio-inspired materials. This could potentially revolutionize the development of new materials with properties that mimic those found in living organisms.
The inspiration for this breakthrough came from studying natural biological materials. Olli Ikkala, from Aalto University, highlights how this work exemplifies how nature’s solutions can inspire new materials. He envisions a future where robots could be equipped with self-healing, robust skins or synthetic tissues that autonomously repair themselves—an idea that could have profound implications for fields ranging from robotics to medicine.
Although practical applications of this technology are still a few years away, this discovery marks a significant leap in material science. It could change the way engineers approach the design of synthetic materials, opening up new possibilities in a variety of fields. Prof. Ikkala refers to it as a fundamental discovery that could renew the rules of material design, laying the groundwork for innovations that were once thought impossible.
The research team behind this breakthrough includes Dr. Hang Zhang, Prof. Olli Ikkala, and Prof. Josef Breu, who led the project. Prof. Breu, based at the University of Bayreuth in Germany, was responsible for designing and manufacturing the synthetic clay nanosheets that played a crucial role in the success of the project.
This hydrogel’s combination of high stiffness, flexibility, and self-healing properties is a monumental achievement. With further research and development, it may become an essential material for a wide range of applications, from medical treatments like wound healing and drug delivery to cutting-edge technologies like soft robotics and artificial skin. As researchers continue to explore the potential of this new material, it is clear that this is just the beginning of what could be a transformative era in materials science.
More information: ‘Stiff and self-healing hydrogels by polymer entanglements in co-planar nanoconfinement, Nature Materials (2025). DOI: 10.1038/s41563-025-02146-5