A study led by the Institute for Bioengineering of Catalonia (IBEC) demonstrates that chitosan—a natural polymer obtained from shrimp shells—can transform into a more robust material when wet. This finding reverses one of the major limitations of biomaterials, which tend to weaken with hydration, and offers a path to creating sustainable alternatives to conventional plastics.

The researchers incorporated nickel, a naturally occurring trace element, into the chitosan structure. After forming thin sheets, they found that the biomaterial increases its strength by up to 50% after immersion in water. The mechanism is based on a dynamic network of reversible bonds that reorganize thanks to the nickel ions and water molecules. This reconfiguration allows it to absorb mechanical stress, mimicking the behavior of certain biological tissues.

Biologically Pure

“The material remains biologically pure; it is essentially the same molecule found in the exoskeletons of insects and fungi,” explains Javier G. Fernández, a researcher at IBEC and leader of the study, published in Nature Communications. This purity facilitates its reintegration into natural cycles without generating persistent waste.

The discovery is inspired by the cuticle of arthropods and previous observations on the action of metals in natural structures. According to the authors, water becomes an active component of the system and ceases to be an enemy of the biopolymers. Fernández summarizes the principle as “a material in which being ‘soft’ at the molecular level makes it stronger.”

The manufacturing process also incorporates a closed nickel cycle: the metal that does not participate in the structure is recovered during the initial hydration and reused to produce new batches of material. The method thus achieves 100% nickel utilization, without generating waste and at reduced costs.

Scalability is one of the key arguments of the study. Chitin—from which chitosan is derived—is produced in nature on a large scale. “Every year, the world generates about one hundred billion tons of chitin, the equivalent of three centuries of plastic production,” says Akshayakumar Kompa, a postdoctoral researcher in Fernández's group and first author of the study. This abundance would allow for distributed manufacturing adapted to local resources, from shellfish remains to organic waste or fungal byproducts.

Applications in agriculture, fishing, and packaging

The first applications of this biomaterial could be in agriculture, fishing gear, and packaging, especially in water-related contexts, where biodegradable and resistant materials are needed. Furthermore, both nickel and chitosan already have FDA approval for certain medical uses, opening the possibility of developing waterproof coatings for medical devices.

The team has also demonstrated that the material can form watertight containers, such as cups or large sheets, reinforcing its potential as a substitute for single-use plastics. Researchers believe other metals could generate similar effects and expand the range of hydration-enhanced biomaterials.

“This is just the first study. Now that we know this effect exists, we can look for new combinations and new materials,” Fernández points out. For the authors, the finding marks a shift in thinking: instead of isolating materials from the environment, the focus is on designing them to work with it and become part of ecological cycles without leaving a trace.

NATURE