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Natural proteins present a sustainable and biocompatible alternative to conventional fossil fuel-derived plastics, with versatile applications in fields ranging from medicine to food packaging. Extending our previous research on silk–corn zein composites, this study utilizes soy protein—another plant protein extensively employed within biomedical applications—in conjunction with silk fibroin proteins extracted from a variety of domestic (Mori and Thai) and wild (Muga, Tussah, and Eri) silkworm species. By combining these proteins in varying ratios (0%, 10%, 25%, 50%, 75%, 90%, and 100%), silk–soy films were successfully fabricated with high miscibility. The structural and thermal stability of these films was confirmed through various characterization techniques, including Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). Structural refinements were then achieved through post-water annealing treatments. After annealing, it was observed that when soy protein was introduced into both types of silk, the silks exhibited a greater amount of intermolecular and intramolecular β-sheet content. This phenomenon can be attributed to soy’s intrinsic ability to self-assemble into β-sheets through electrostatic and hydrophobic interactions, which also improved the overall thermal stability and morphology of the composite films. The unique self-assembling properties of soy and its ability to promote β-sheet formation facilitate the customization of the silk source and the soy-to-silk ratio. This adaptability establishes protein-based thin films as a versatile and sustainable option for diverse applications in fields such as medicine, tissue engineering, food packaging, and beyond. 

Biocompatible materials fabricated from natural protein polymers are an attractive alternative to conventional petroleum-based plastics. They offer a green, sustainable fabrication method while also opening new applications in biomedical sciences. Available from several sources in the wild and on domestic farms, silk is a widely used biopolymer and one of the strongest natural materials. This study aims to compare five different types of silk (Mori, Thai, Muga, Tussah, and Eri) fabricated into thin composite films in conjunction with plant-based proteins. To offer a wider range of morphologies, corn zein, another widely available protein material, was introduced into the silk protein networks to form blended polymers with various ratios of silk to zein. This resulted in the successful alloying of protein from an animal source with protein from a plant source. The material properties were confirmed through structural, morphological, and thermal analyses. FTIR analysis revealed the dominance of intramolecular beta-sheet structures in wild silks, while the domestic silks and zein favored random coil and alpha-helical structures, respectively. Post-treatments using water annealing further refined the structure and morphology of the films, resulting in stable composites with both inter- and intramolecular beta-sheet structures in wild silks. While in domestic silks, the random coils were converted into intermolecular beta-sheets with enhanced beta-sheet crystallinity. This improvement significantly enhanced the thermal and structural properties of the materials. By deciding on the source, ratio, and treatment of these biopolymers, it is possible to tailor protein blends for a wide range of applications in medicine, tissue engineering, food packaging, drug delivery, and bio-optics.