Tuning network rheology by controlling filament helicity

The rheological properties of a dense suspension depend on the microscopic structure of its constituent filaments. The exact nature of this relationship remains unclear; Yet, it is vital to creating elastic networks with tunable properties. Here, we study the effect of a filament with a set, tunable shape on network rheology. Bacterial flagella - a rigid, micron-sized biopolymer - assumes distinct shapes via point mutations of the constituent protein. We tune the helicity of a flagella, varying the shape from a stiff, straight rod to an easily deformable, highly-wound slinky-like coil. Dense suspensions of flagella form elastic networks due to entanglements between filaments. We quantify the relationship between flagella shape and the elasticity of their dense suspensions. Filaments with lower helicities form stiffer networks than would coil-like filaments. This contrasts with the microscopic diffusion of flagella in dense suspensions, in which the motion of coiled flagella is highly arrested. We propose that while entanglements are important for elastic network formation, it is the effective stiffness of the flagella shape that determines network stiffness.