In Seville, a team of scientists has developed a biodegradable hydrogel that can absorb and retain up to 60 times its own weight in water. Designed to address agricultural drought, the material could help crops withstand water scarcity.
The hydrogel is made from chitosan and alginate, two natural compounds sourced from shrimp shells and seaweed. Dry, it resembles a sponge; once hydrated, it forms a gel-like network that traps water and makes it available to plant roots over time. That property is especially valuable in regions where rainfall is unpredictable or insufficient. Hydrogels are networks of polymer chains that take up and retain water. Their swelling depends on factors including polymer composition, crosslinking density, pH and salts in the surrounding water.
Natural Alternative to Synthetic Hydrogels
Traditional agricultural hydrogels often come from petrochemicals and can persist in the environment long after they are no longer useful. The University of Seville’s approach replaces them with biodegradable, marine-based ingredients. Chitosan, extracted from crustacean shells, provides structural strength, while alginate from seaweed boosts water absorption. Together, they form a formulation tailored for agricultural use. Chitosan and alginate carry opposing electrical charges, so they can form a polyelectrolyte complex. The resulting material’s properties depend in part on the proportions used and how it is processed.
Calcium reinforces the gel’s structure, improving its stability and helping it retain its shape and water-holding capacity when fully hydrated. Calcium ions can coordinate with guluronic-acid regions in alginate to create an ionically crosslinked network. This gives the material the strength needed for real-world farming conditions.
Testing and Performance
To assess the gel’s effectiveness, researchers prepared three mixtures: one with chitosan, one with alginate, and one combining both in equal parts. They turned the mixtures into gels by adjusting the pH and adding calcium chloride to solidify the final structure.
The resulting material is moist and flexible, with a texture similar to gelatin. After freeze-drying, it develops a porous structure that rapidly swells when exposed to water, acting as a miniature reservoir in the soil. Laboratory analysis found that the chitosan-alginate blend offered the best balance of strength and absorption, retaining between 40 and 60 times its own weight in water. The gel also remained stable at temperatures up to 40°C, a critical threshold for many agricultural soils in southern Spain. That result concerns the material’s stability; crop response and water savings also depend on soil type, irrigation-water salinity and how the gel releases water as conditions change.
Next Steps: Integrating Nutrients and Field Trials
The study, published in the Journal of Environmental Chemical Engineering, addresses pressing agricultural problems, including declining soil fertility and water shortages, as well as the overuse of chemical additives. The hydrogel can absorb water from irrigation or rainfall and gradually release it as the soil dries, helping buffer crops against drought stress. Chitosan is also studied in agriculture as a carrier for slow-release fertilizers, with potential to limit nutrient losses through leaching. Its performance varies with molecular structure and molecular weight.
Researchers are exploring ways to load the gel with natural fertilizers or micronutrients for slow, controlled release into the soil. Before the material can be adopted on a large scale, the team plans to test its performance under real farming conditions, across different soil types and with irrigation water that varies in salinity and acidity. Replicated field tests can show whether laboratory swelling translates into measurable changes in soil moisture, irrigation needs and crop performance.
Environmental safety is also a priority. The team will thoroughly assess the gel’s biodegradability and potential ecotoxicity to ensure it poses no risk to ecosystems. These assessments can examine how quickly a material breaks down and its effects on soil organisms, plants and water quality. The project has received funding from the Junta de Andalucía, European funds, and Spain’s Ministry of Science, New idea and Universities through the State Research Agency.
As climate change intensifies drought cycles across southern Europe, this hydrogel could help sustain agricultural productivity while reducing reliance on synthetic chemicals. If field trials succeed, the technology may offer farmers a practical, eco-friendly option as conditions grow harsher.
