Biomimetic Approach to the Formation of Protein Materials via Complex Coacervation of Engineered Polypeptides

Protein liquid-liquid phase separation underlies the formation of membraneless organelles in cells and plays a key role in the assembly process of natural materials such as the assembly of tropoelastin into elastic fibers. Here, we engineered a series of charged elastin-like polypeptides (ELPs) that form complex coacervates, providing a rapid method of concentrating proteins into a fluid state. Compared with coacervates formed via simple coacervation, complex coacervates exhibited greater fluidity, likely due to differences between electrostatic interactions and hydrophobic forces. We designed these ELPs to further contain cross-linking domains compatible with tyrosinase or transglutaminase and found that cross-linking was enhanced when proteins were in a condensed state compared to free in solution. Cross-linking the ELP complex coacervates led to the formation of gels with distinct properties dependent on the nature of the cross-linking. This work expands the design space of protein hydrogels, offering a novel strategy for forming cross-linked networks from complex coacervates and providing opportunity for future use in tissue engineering and biocompatible biomaterials applications.