Structural and mechanical comparison of Eri and Mulberry silk fibroin nanofibers films through advanced mechanical treatments for sustainable applications.

Mulberry silk (Bombyx mori) and eri silk (Samia/Philosamia ricini) are widely used silks. Eri silk is a wild silk that contains an arginine-glycine-aspartic acid tripeptide sequence within its structure, making it a potential and sustainable biomaterial. However, its poor solubility using conventional methods has resulted in limited research compared with that of mulberry silk fibroin. This study investigated the differences between nanofibrillated fibroins from both silks to assess their biomedical potential, focusing on their structural, morphological, and mechanical properties, as well as their biodegradability. Both silks were degummed and processed into fibroin microfibers (FMF) and fibroin nanofibers (FNF) via high-pressure ultrasonication and grinding in an aqueous solution. Analyses were performed using fourier transform infrared spectroscopy (FT-IR), X-ray diffractometry (XRD), atomic force microscopy (AFM), scanning electron microscope (SEM), UV-visible spectrometry, and thermogravimetric analysis (TGA) techniques. The results showed that both silks were prepared by high-pressure ultrasonication and exhibited microfibers when treated with a grinder machine, which can produce fibroin nanofibers. In terms of the type of fibroin, when comparing the properties of both silks, it was found that they have similar chemical structures but differ in their physical properties. Moreover, eri fibroin films showed superior transparency, high thermal resistance, and high strength, but were more brittle than mulberry fibroin films, which was attributed to amino acid differences. Eri silk has unique features that are interesting for the development of new materials and can create new pathways for utilizing non-mulberry silk.