Preparation of smart antibacterial sodium alginate hydrogel based on cinnamaldehyde Pickering emulsion

Pure sodium alginate (SA) hydrogels face limited capacity for loading hydrophobic actives due to inherent hydrophilicity. Incorporating oil-in-water (O/W) Pickering emulsions into hydrogels enables the introduction of hydrophobic functional components, facilitating smart controlled release and modulating mechanical properties. In this study, we developed a smart antibacterial hydrogel by incorporating cinnamaldehyde-loaded O/W Pickering emulsions into an SA/cellulose nanofibril (CNF) matrix. A stable emulsion was first prepared using ZnO nanoparticles (1.8 wt%) with 30 % oil phase. The emulsion and CaCl₂ were then incorporated into SA/CNF, forming a Pickering emulsion hydrogel (PEH) through ionic crosslinking (Zn²⁺/Ca²⁺-SA) and hydrogen bonding (SA-CNF). The emulsion droplets acted as active fillers, enhancing the mechanical properties of the hydrogel and dispersing evenly. The compressive strength of PEH was 128.2 ± 2.1 kPa, and the hardness was 51.3 ± 0.5 N at 50 wt% emulsion content. PEH responded to alkaline conditions to release cinnamaldehyde and realize smart antibacterial. The cumulative release of cinnamaldehyde reached 79.3 % and the inhibition rate against E. coli was 98.4 % at pH 8.0. This strategy successfully encapsulates hydrophobic actives while offering pH-responsive antimicrobial functionality, highlighting PEH's potential for food preservation packaging.