Topological defects produce kinks in biopolymer filament bundles

Abstract

SignificanceA common structural motif for stress-bearing intracellular structures and tissues is a network of filament bundles. When observed in optical microscopy, these bundles often show localized bends—kinks—in their contour even though the stress-free state of their constituent filaments is straight. Using a combination of analytical mechanics and large-scale, finite-element Brownian dynamics simulations, we show that the optically observable kinks are related to topological defects in the interior, nanoscale structure of the bundle. Moreover, the kinks are more compliant to bending than the rest of the bundle. As a result, defected bundle networks must contain a random distribution of soft hinges, which, being the most compliant elastic elements, control the low-energy excitations of these bundle networks.