Lotus leaf inspired sustainable and multifunctional Janus film for food packaging

Multifunctional and sustainable packaging materials applicable to changeable conditions are in high demand as alternatives to petroleum-based polymers. Soybean polysaccharides (SPS) with remarkable antioxidation and film-formation properties are great candidates for sustainable packaging materials. However, the poor water resistance and mechanical properties of SPS hinder their further application. Inspired by the Janus properties of lotus leaf, we developed asymmetric multifunctional packaging films by addressing the problems of SPS while keeping their merits. Specifically, SPS-stabilized silver nanoparticles were incorporated with gelatin and wax to enhance the mechanical properties and water tolerance of the resulting film. Moreover, hierarchical micro-/nano-structures consisting of carnauba wax were feasibly fabricated on one side of the film, resembling the natural front lotus leaf. This Janus film has outstanding water resistance, outperforming all other SPS-based materials reported to date. In addition, the excellent antibacterial activity (>95 % against Escherichia coli and Staphylococcus aureus), antioxidation properties (2-fold enhancements), and UV-blocking performance (∼100 % at 200–400 nm) were well retained. By virtue of these multifunctional properties, the resulting film has been successfully applied in food packaging, as evidenced by meat and fruit preservation experiments. This biomimetic strategy provides a reference for the fabrication of sustainable high-performance food packaging.