(751c) Self-Assembly and Fibrillization of Waste Protein into High-Performance Films

Petroleum resources have greatly improved longevity and quality of life across the globe through innovative new polymers, but they have also contributed to the escalating crisis of global climate change and plastic waste in the environment. Therefore, there is an urgent need to develop alternatives that can enhance sustainability. While a great deal of work has focused on sugar-based materials, proteins offer a promising feedstock to mimic and replace polymers such as nylon and polyurethane. Polyurethanes are a particularly attractive target for replacement because of their additional chemical hazards and toxicity in the manufacturing process. However, proteins are usually either too brittle (neat materials) or too weak (plasticized materials) to serve as suitable substitutes. Our group has previously demonstrated that this limitation can be overcome by designing protein copolymers in which proteins act as ‘hard blocks’ and low-T_g acrylates as ‘soft blocks’. In order to achieve broader applications, however, there are other scientific challenges, for example, the reported range of mechanical properties does not yet match that of high-strength synthetic polyurethanes.

Since protein domains (‘hard blocks’) in current materials are largely amorphous, an increase in protein crystallinity (i.e., formation of ordered structures) is expected to improve mechanical performance. Amyloid fibrils prepared from protein monomers stand out because they are the strongest known proteinaceous materials, owing to their highly ordered and dense cross-b sheet structures. A large number of different proteins, including those derived from food and agricultural waste such as whey protein, have been shown to be readily converted into amyloid nanofibrils in vitro under designed conditions. Here, ‘hard block’ crystallization was improved by carefully controlling protein fibrillization, leading to the mechanical improvement of the resultant materials. We chose whey protein isolate-hydroxypropyl acrylate copolymers as an example and found that protein fibrillization can significantly improve the mechanical properties of the ensued materials. In particular, compared to the protein monomer system, protein fibrillization led to an 8, 3, and 2-fold increase in Young's modulus, tensile strength, and toughness of the final elastomer, respectively, with minimal reduction in strain at break. This result provides a scalable and sustainable strategy for improving the performance of protein materials and replacing polyurethanes-like materials.