Trapping and Wiggling: Elastohydrodynamics of Driven Microfilaments

TL;DR

This paper develops a theoretical framework for understanding the elastohydrodynamics of driven semiflexible microfilaments, providing analytical solutions and experimental validation for measuring their bending properties.

Contribution

It introduces a general analytical approach to model driven microfilaments under viscous forces, enabling new methods to determine their elastic bending moduli.

Findings

Analytical solutions for shape dynamics of moving filaments are derived.

Experimental validation confirms the scaling law for actin filaments.

Re-analysis of microtubule experiments demonstrates the method's applicability.

Abstract

We present a general theoretical analysis of semiflexible filaments subject to viscous drag or point forcing. These are the relevant forces in dynamic experiments designed to measure biopolymer bending moduli. By analogy with the ``Stokes problems" in hydrodynamics (fluid motion induced by that of a wall bounding a viscous fluid), we consider the motion of a polymer one end of which is moved in an impulsive or oscillatory way. Analytical solutions for the time-dependent shapes of such moving polymers are obtained within an analysis applicable to small-amplitude deformations. In the case of oscillatory driving, particular attention is paid to a characteristic length determined by the frequency of oscillation, the polymer persistence length, and the viscous drag coefficient. Experiments on actin filaments manipulated with optical traps confirm the scaling law predicted by the analysis and provide a new technique for measuring the elastic bending modulus. A re-analysis of several published experiments on microtubules is also presented.