The swelling properties of single component (gelatin) and electrostatically assembled (gelatin–gum tragacanth) edible composite films exposed to water and salt solution.

This article focuses on investigating the swelling behavior and material properties of edible films composed of gelatin (GL) and gum tragacanth (GT) biopolymers to advance four-dimensional (4D) printing applications in food. The study prepared film-forming solutions with varying concentrations of GT and GL, analyzed their physical, microstructural, and rheological characteristics, and evaluated swelling in distilled water and salt solutions. Results showed that films combining oppositely charged GT and GL formed more uniform, structurally intact networks with restricted water uptake compared to gelatin-only films, exhibiting shear-thinning behavior and yield stress consistent with the Herschel–Bulkley model. These findings highlight the importance of biopolymer compatibility and molecular interactions in designing edible films with controlled swelling properties, providing a foundation for future use in extrusion-based 4D food printing.