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The multiscale structure of spider silk is widely studied because of its superior mechanical properties. Its high tenacity allows the absorption of the kinetic energy of fast and large preys. The mechanism of sacrificial bonds enhances the stretchability and toughness of spider capture-silk. With this in mind, we fabricate microstructured fibers with sacrificial bonds using the dragged viscous thread instability. A thread of viscous liquid flowing towards a perpendicular moving platform buckles repetitively and creates different periodical patterns. A solution of 25% polylactid acid (PLA) dissolved in the dichloromethane (DCM) is extruded from a 30μm diameter needle onto a moving platform. By decreasing the speed ratio between the thread extrusion speed and the platform moving speed, we obtain different instability patterns: catenary, meandering, alternating (loop falling on alternate sides of the main thread), and coiling (all the loops falling on the same side). The spatial frequency of the periodical patterns linearly increases with the speed ratio until overlapping occurs. When the thread loops on itself, it welds and fuses with itself to form a bond which solidifies as the solvent evaporates and the thread dries. Different fiber patterns are tested in an electromechanical tensile machine and their performance are compared to a straight fiber. Sacrificial bonds require significant energy to break (i.e., ranging between 0 to 110% of the yield value of a straight fiber). Finally by controlling the instability parameters, we are able to tailor the mechanical properties of the resulting fibers such as its breaking strain, rigidity and toughness which could lead to different protective wear applications. |
