Strengthening protein-based materials through protein self-assembly and processing*

The development of sustainable polymeric materials with comparable performance to petroleum-derived ones is urgently needed, especially in light of the irreversible environmental and resource impacts associated with conventional plastics. While a great deal of work has focused on sugar-based materials, proteins offer a promising feedstock to mimic and replace petroleum-derived polymers such as nylon and polyurethane. 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’. There are other scientific challenges to achieve broader applications, for example, the reported range of mechanical properties does not yet match that of high-strength synthetic polyurethanes. Here, we found that the mechanical properties of subsequent materials can be greatly improved by controlling the unfolding-assembly process of proteins, i.e. the reordering of the "hard block". This is a result of the additional, dense intermolecular forces generated by the reassembly between protein molecules. Importantly, this toughening mechanism is generalized among the proteins examined, such as whey protein and bovine serum albumin. This result provides a scalable and sustainable strategy for improving the performance of protein materials and replacing polyurethanes-like materials.