Design Principles for Deployable Fibers Inspired by Hagfish Defense.

Hagfish produce extraordinary slime as a defense mechanism, releasing exudate from glands that rapidly form a fibrous, soft, ultra-dilute, water-capturing network upon contact with seawater (up to 10 000 times its original volume). The gland thread cell (GTC) produces high-strength protein threads (filament diameter df = 1-3 µm) meticulously coiled into skeins (coil diameter Do ∼ 150 µm) that rapidly unravel upon deployment to reveal their hidden length (Lf = 15 cm), forming a cohesive fibrous slime network through interaction with mucin vesicles and seawater. To date, no engineered material is able to replicate the fiber uncoiling mechanics observed in slime, which are responsible for the unique set of mechanical properties that slime exhibits. Focusing on fundamental physical mechanisms rather than specific biochemistry or biomaterials, it is demonstrated that how existing materials and manufacturing processes can be used to achieve comparable functional performance. To engineer rapidly deployable soft materials inspired by hagfish slime, this work establishes design principles for synthetic skeins used to create the first-ever deployable synthetic skeins. Four design principles are revealed for engineering synthetic skeins: (1) the mechanics of high-strain fiber coiling and uncoiling, (2) adhesives to maintain elastic energy in non-equilibrium deformed states, (3) fluid-mediated deployment of coiled fibers, and (4) the individual fiber stiffness and size needed to result in a soft, deformable fibrous network. As proof of concept, the first successful fabrication of synthetic skeins with tightly coiled threads arranged in controlled packing geometries is demonstrated. These synthetic structures undergo fluid-mediated unraveling under flow, replicating the deployment behavior of their biological counterparts and demonstrating the feasibility of engineered, deployable fibrous networks.