Temperature-responsive gating chitosan-based microcapsules for controlled release of urea fertilizers

Polysaccharides-based smart fertilizers are essential for promoting plant growth, yet significant challenges exist in achieving stable structures and synchronizing nutrient release and plant growth. This study developed a temperature-responsive gating chitosan-based microcapsule (CTSMC-g-PNIPAM) by grafting N-isopropyl acrylamide (NIPAM) onto chitosan microcapsules (CTSMC) via atom transfer radical polymerization (ATRP). The interfacial crosslinking of chitosan (CTS) and terephthalendehyde (TPA) formed the CTSMC matrix with a hollow chamber structure and ensured stability. CTSMC-g-PNIPAM exhibited reversible temperature-responsive gating properties and sustained release behavior, and the PNIPAM chains acted like gating switches. Below the low critical solution temperature (LCST) (25 °C), the PNIPAM chains stretched and the gating switch closed, slowing down the release rate. Above the LCST (40 °C), the PNIPAM chains contracted and the gating switch opened, accelerating the release rate. The release behaviors of CTSMC-g-PNIPAM in soil indicated that the gating microcapsule effectively prolonged the release of urea. Moreover, the cumulative release of CTSMC-g-PNIPAM at 40 °C was significantly higher than at 25 °C. The first-order kinetic and Korsmeyer-Peppas model indicate that the urea release involves concentration gradient diffusion and skeleton dissolution. Compared with pure urea, urea@(CTSMC-g-PNIPAM) increased the growth status of maize, suggesting a promising strategy for smart fertilizers.