Effect of Amyloid Fibrillization on the Mechanical Properties of Protein-Based Bioplastic Films: a Comparison Between BSA, BSF and Sericin

Organic waste and byproducts from food and agricultural chains represent promising feedstocks for biopolymers. Among them, proteins stand out for their versatility, functional heterogeneity, and ability to self-assemble into ordered structures. In particular, protein self-assembly into amyloid fibrils has recently emerged as an effective strategy for engineering high-performance bio-based materials. This work investigates the influence of amyloid fibrillization on the tensile properties of protein-based bioplastic films derived from three structurally distinct protein sources: bovine serum albumin (BSA), Black Soldier Fly (Hermetia illucens, BSF) proteins, and silk sericin. Fibrillization protocols were tailored for each protein, including the conventional acidic thermal treatment (pH 2, T > 80 °C) widely employed as a universal approach, and an alkaline thermal treatment (0.1 M NaOH, 80 °C, 8 h) recently demonstrated effective for BSF proteins. Films were produced via controlled solubilization under modulated temperature and pH conditions to promote protein dissolution and eventual fibril formation. Glycerol was used as a green plasticizer to enhance flexibility, followed by solvent casting to obtain free-standing and detachable films. The cross-β fibrillar architecture of the nanostructures was confirmed through ATR-FTIR spectroscopy and transmission electron microscopy (TEM). Polymeric blending was further explored through incorporation of poly(vinyl alcohol) (PVOH). Quasi-static tensile tests were conducted on fibrillized and non-fibrillized films for each protein source, enabling direct evaluation of mechanical reinforcement induced by amyloid nanostructures. The study aims to elucidate protein-dependent fibrillization behavior and quantify the reinforcing role of amyloid fibrils within biodegradable polymer matrices.