Predator-prey interactions mediate the formation of Janus droplets: The role of sodium alginate droplets

The asymmetric structure of Janus droplets endows them with unique functionalities, such as self-propulsion, compartmentalized reactions, and directional encapsulation, demonstrating broad application potential in the food industry. However, the fabrication of food-grade Janus droplets still faces the challenges of low efficiency and yield. Drawing inspiration from predator-prey relationships in nature, this study proposed a novel biomimetic strategy for constructing Janus droplets and regulating their yield through predator-prey interactions. The difference in the interfacial tension between zein and sodium alginate droplets conceptually rationalized the predator-prey interactions and the formation of Janus droplets in the mixed water-in-oil droplet system. The predator-prey interactions between the droplets were activated by external forces, driving the mixed droplet system toward the direction of free energy minimization. In this process, driven by the Marangoni effect arising from the interfacial tension gradient, zein droplets (the predator) captured sodium alginate droplets (the prey). Crucially, the yield of Janus droplets could be controlled by adjusting the physical parameters of sodium alginate droplets within the predator-prey framework. Specifically, regulating the number ratio and size ratio of sodium alginate to zein droplets, as well as the molecular weight of sodium alginate, led to an increase in Janus droplet proportion. This work provides a biomimetic approach for the efficient fabrication of food-grade Janus droplets, paving the way for their advanced applications in the food industry.