Cellulose nanofibrils-based emulgels: Impact on surface film formation and performance as slow-release fertilizers

Conventional slow-release fertilizers often suffer from poor structural control and inefficient nutrient release, leading to environmental pollution and resource waste. To address this challenge, we developed a biphasic emulgel system that combines chloroform (CHCl₃)/poly(lactic acid) (PLA) droplets stabilized by cellulose nanofibrils (CNF)/nanochitin (NCh) as the oil phase with a CNF/poly(acrylic acid) (PAA) gel matrix containing hydrophilic particles. During 3D printing through low-surface-energy nozzles, shear forces trigger spontaneous phase separation, driving PLA to form a continuous surface film that encapsulates the printed microstructure-a design that enables precise control over nutrient release. Unlike conventional systems, this surface film forms independently of the hydrophilic fillers in the gel phase, ensuring structural robustness. As a proof-of-concept, urea-loaded scaffolds exhibited sustained release, with only 69 % cumulative release after 31 days in soil column tests. Release kinetics followed the Korsmeyer-Peppas model (n > 0.5), indicating an anomalous transport mechanism governed by both diffusion and matrix relaxation. This platform not only overcomes the limitations of traditional fertilizers but also opens new avenues for designing hierarchically structured, programmable release systems for agriculture and beyond.