Blending recombinant amyloid silk proteins generates composite fibers with tunable mechanical properties

Recent efforts in microbial production of recombinant silk and silk-inspired proteins have yielded fibers with excellent mechanical performances on par with or even superior to their natural counterparts. However, most previous recombinant fibers comprise a single protein. Studies exploring composite fibers of recombinant proteins with varied sequences and properties have been limited. Here, we explored the impact of blending different amyloid-silk proteins on the mechanical properties of the resulting composite fibers. Amyloid-silk hybrid proteins contain repetitive sequences of an amyloid zipper-forming peptide flanked by flexible glycine-rich peptides from a spider silk protein. We pursued three blending strategies, by mixing amyloid-silk proteins of different molecular weights, opposite protein charges, and distinct mechanical behaviors. Our findings revealed that the ultimate strength of composite fibers consistently fell within the range of the pure protein fibers across all three blending strategies. However, composite fibers comprising oppositely charged proteins displayed toughness higher than both pure protein fibers. Additionally, mixing amyloid-silk proteins of different molecular weights or mechanical properties allowed us to fine-tune the mechanical properties of composite fibers by controlling the protein ratios. The findings highlight the potential of composite protein fibers as a versatile platform for achieving diverse yet precisely tunable mechanical properties. The trends in fiber properties and blending strategies observed in this study open up exciting prospects for future engineering of protein materials tailored to specific characteristics.