Dynamic interactions between nematic point defects in the spinning extrusion duct of spiders

Abstract

Spider silk fibers have remarkable mechanical properties as a result of an ultraoptimized spinning process. Silk fibers are spun from a lyotropic nematic liquid crystalline anisotropic fluid phase which undergoes significant structural changes throughout the spinning pathway. In the silk extrusion duct, those structural changes are expected to be driven by elastic-mediated interactions between point defects. In this work, the interaction between two point defects of opposite topological charges located on the axis of a cylindrical cavity is studied using a tensor order parameter formalism. Distinct regimes leading to defect annihilation and structural transitions are described in detail. The driving force setting the defects into motion is also examined. The different results suggest that the tensorial approach is primordial in describing the complicated physics of the problem. The phenomenon described is important to the understanding of the process-induced structuring of silk fibers and to defect physics in a more general context.

Liquid crystal models of biological materials and silk spinning

“…Verifiable and testable mesoscopic modelling based on liquid crystal thermodynamics, material science, and rheology provides an integrated approach to material characterization and material processing descriptions. 16,23,27,[97][98][99][100][101][102][103][104][105][106] Spider silk spinning relies on confinement, anchoring, and flow-induced structuring, in addition to chemical effects, which are shown to produce textural transitions in agreement with experimental reported measurements. The range of verified predictions shows that liquid crystal models will play a significant role in the understanding, characterization, and use of biological mesophases and in future biomimetic developments.…”

“…In addition, the figure shows that there is always a likelihood of remaining defects due to the fact under capillary confinement the interaction force is vanishingly small when the defect-defect distance is larger than the radius of the capillary. 89 This simulations indicate that collective modes and slight increases in defect separation distances slow or halt annihilation.…”

“…Thus the observed (see Figure 12) texture transition between the escaped and the optical texture as the silk dope travel trough the beginning of the duct is captured by nematostatics under capillary confinement, as shown by the arrow in Figure 12, the actual slope of the arrowed black line depends on the actual water loss. The E texture with neutral conditions (no torques) and under no flow conditions eventually decays due to the defect-defect interactions 16,89 and its stability in the spider and silk worm duct can be attributed to the flow effect.…”

“…Figure 17b shows that as the third defect moves closer to the upper pair (vertical arrow) the annihilation dynamics of the pair slows down (horizontal arrow) as well as the symmetry is broken, such that annihilation does not occur at the midpoint. 89 Figure 17c shows collective modes of many defect pairs, where large variability, sometimes by a factor of five, on annihilation times are observed. In addition, the figure shows that there is always a likelihood of remaining defects due to the fact under capillary confinement the interaction force is vanishingly small when the defect-defect distance is larger than the radius of the capillary.…”

Study on the pulsating flow of a worm-like micellar solution

“…In biorheology, examples are the flow of blood in veins which is forced by a periodic pressure gradient [4][5][6][7][8][9][10] and interesting manifestations of biological fluid flow such as the flow of spider silk [11][12][13]. From a practical point of view, pulsatile flow of complex liquids (worm-like micellar systems and lyotropic liquid crystals) has applications in enhanced oil recovery.…”