Knitting Networks: Smooth Contractile Motion in Networks of Entangled Snapping Filaments

Biological systems are inherently built up of discrete components whose individual motions coordinate to generate large-scale ordered structures. To better understand the role of individual elements in building a smooth macroscopic motion, we create a contractile elastic network composed of bacterial flagella—a rigid biological helix. Flagella are polymorphic structures, capable of transforming between several discrete shapes in response to environmental conditions or stress. We utilize a transition from a native helical form into a tightly wound slinky-like structure when heated in a particular solvent. This dramatic transformation contracts the axial length of the flagella, reducing the pitch by >3 times. We bundle hundreds of flagella, coupling the response of individual filaments into a single snapping event for the entire collection of flagella. Entanglement between neighboring bundles allows these snapping events to percolate into a smoothly contracting elastic network. Furthermore, by shining patterned light, we introduce instabilities into the elastic network which result in macroscopic anisotropic deformations. These results showcase how motion and morphogenesis emerge from coupling microscopic polymorphic elements.