Utilizing the Metastability of Spidroins as a Strategy for Improving Mechanical Properties of Biomimetic Spider Silk Fibers

ABSTRACT Spider silk is appreciated for its outstanding properties and provides an attractive opportunity for sustainable and biocompatible high‐performance materials. For developing new materials, engineered spider silk proteins are produced recombinantly and spun into fibres. The spinning process is complex and dependent on pre‐processing, coagulation, and post‐drawing of the fibers. As an initial step, silk proteins undergo phase transitions forming dynamic liquid‐like droplets called condensates. We found that their phase behavior exhibits metastability, with the phases evolving toward different structures with time. Here, we studied a type of recombinant silk proteins called minispidroins and show that the metastability of the intermediate condensed phase can play a major role in their assembly. Three minispidroin variants were investigated, and they showed different kinetics in their metastability. They formed dynamically arrested states accompanied by protein secondary structure changes. Depending on how the system was allowed to evolve before spinning, some variants showed distinctly different final mechanical properties. Especially the yield strength and Young's modulus were affected by protein metastability. We show that dope metastability is a key parameter to consider in biomimetic silk fiber spinning processes. Control of metastability is suggested to be a way to tune and improve properties of engineered silk‐based materials.