Chitosan-Alginate Hybrid Hydrogels: Prospects for Sustainable Horticulture

New materials are needed to mitigate the eutrophication and soil degradation promoted by fertilizer overuse, highlighting biopolymer-based hydrogels due to their contribution to sustainable agriculture. In this regard, two notable biopolymers emerge: chitosan (CH) and sodium alginate (ALG). Chitosan possesses excellent mechanical properties and has been explored for controlled-release applications, while sodium alginate is known for its water-retention capacity, a critical factor in addressing drought under intensifying climate change. Thus, the objective of this article is the synthesis of hybrid hydrogels combining both biopolymers and characterizing their physicochemical, thermal, mechanical, morphological and functional properties. In this context, 3 distinct formulations were engineered, varying the polymer ratios (100-0, 50-50 and 0-100 CH-ALG). Hence, the synthesis process showed that gelation was enhanced in the case of chitosan due to ionic reinforcement promoted by calcium ions (an increase of 572% in the elastic modulus). The results indicate the formation of hard, stable gels with tan(δ) values below 0.2 and elastic moduli above 10 MPa in some formulations, in combination with thermal stability up to 40 °C (an extreme soil temperature). However, clear trends can be observed: the 50-50 CH-ALG hydrogels exhibited adequate water retention for horticultural applications (4000-6000%, depending on immersion time), highlighting enhanced water absorption compared to commercial formulations that incorporate gelatin. These findings underscore the potential of biopolymer-based hydrogels as a sustainable alternative to traditional fertilizers as well as a vital tool in restoring ecological balance and ensuring food sustainability. • Biopolymer-based hydrogels offer eco-friendly solutions for sustainable agriculture. • Hybrid chitosan-alginate hydrogels exhibit good strength and water retention. • Chitosan provides mechanical resistance; alginate ensures superabsorbent materials. • Hybrid systems remain stable after long immersion and multiple cycles.