Fabrication of alginate-carboxymethyl chitosan hydrogel granules for achieving anti-photolysis and controlled release of spinosad

The development of long-acting and controlled-release systems is an effective way to improve the efficacy of pesticides, especially those that are highly effective but susceptible to photodegradation. Herein, hydrogel granules of sodium alginate and carboxymethyl chitosan were successfully prepared for the controlled release of biological insecticide spinosad. The obtained formulation displayed an excellent encapsulation efficiency of 91.5 % and a good loading content of 22.3 %. Instrument characterization (SEM, FT-IR, TGA, and DSC) demonstrated that the spinosad was encapsulated by hydrogel via physical adsorption and adhesion without chemical bonding. Compared with unformulated spinosad, the photodegradation rate of spinosad in the controlled-release granules was reduced by more than 50 %, indicating the excellent UV-shielding ability of the formulation. Moreover, the in vitro release profile and swelling behavior exhibited dual-sensitivity to pH and temperature, with the release dynamics following the Fickian diffusion mechanism of Ritger-Peppas model. Within the simulated intestinal environment of lepidopteran pests (pH 8.0 to 10.0), spinosad was observed to be released rapidly from the granules, which helps to improve its targeting efficacy. This work contributes to the development of insecticide controlled-release systems using natural polymers as carriers, with a good potential in sustainable pest control.