Effect of helicity on wrapping and bundling of semi-flexible filaments twirled in a viscous fluid
Abstract
In many motile microorganisms, propulsion is achieved by rotating or twirling one or more long appendages called flagella. These semi-flexible filaments are also intrinsically helical. Recent studies have revealed that zero-Reynolds number propulsion in a viscous environment is possible even with simpler achiral filaments flexible enough to undergo a wrapping transition to twisted shapes when twirled at one end at high torques. We use simulations to show that intrinsic helicity eliminates the transition. This makes operating characteristics of more twisted filaments smoother over a wide range of applied torques, both in single filaments, as well as in a pair of filaments hydrodynamically bundling together when co-twirled in the same direction.